Adding upstream version 1.1.0+debian.upstream/1.1.0+debian

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

41 files changed, 7747 insertions, 0 deletions

diff --git a/src/output/dnscli.c b/src/output/dnscli.c
new file mode 100644
index 0000000..f7c5b5e
--- /dev/null
+++ b/src/output/dnscli.c
@@ -0,0 +1,888 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/dnscli.h"
+#include "core/assert.h"
+#include "core/object/dns.h"
+#include "core/object/payload.h"
+#include "core/object/udp.h"
+#include "core/object/tcp.h"
+
+#include <netdb.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#ifdef HAVE_ENDIAN_H
+#include <endian.h>
+#else
+#ifdef HAVE_SYS_ENDIAN_H
+#include <sys/endian.h>
+#else
+#ifdef HAVE_MACHINE_ENDIAN_H
+#include <machine/endian.h>
+#endif
+#endif
+#endif
+#ifdef HAVE_BYTESWAP_H
+#include <byteswap.h>
+#endif
+#ifndef bswap_16
+#ifndef bswap16
+#define bswap_16(x) swap16(x)
+#define bswap_32(x) swap32(x)
+#define bswap_64(x) swap64(x)
+#else
+#define bswap_16(x) bswap16(x)
+#define bswap_32(x) bswap32(x)
+#define bswap_64(x) bswap64(x)
+#endif
+#endif
+
+static inline uint16_t _need16(const void* ptr)
+{
+    uint16_t v;
+    memcpy(&v, ptr, sizeof(v));
+    return be16toh(v);
+}
+
+static core_log_t      _log      = LOG_T_INIT("output.dnscli");
+static output_dnscli_t _defaults = {
+    LOG_T_INIT_OBJ("output.dnscli"),
+    OUTPUT_DNSCLI_MODE_NONE,
+    0, 0, 0, -1, 0, 0,
+    { 0, 0, 0 }, 0,
+    { 0 }, 0,
+    { 0 }, CORE_OBJECT_PAYLOAD_INIT(0), 0, 0, 0, 0, 0,
+    { 0, 0 },
+    0, 0
+};
+
+core_log_t* output_dnscli_log()
+{
+    return &_log;
+}
+
+void output_dnscli_init(output_dnscli_t* self, output_dnscli_mode_t mode)
+{
+    mlassert_self();
+
+    *self             = _defaults;
+    self->mode        = mode;
+    self->pkt.payload = self->recvbuf;
+
+    switch (mode & OUTPUT_DNSCLI_MODE_MODES) {
+    case OUTPUT_DNSCLI_MODE_UDP:
+    case OUTPUT_DNSCLI_MODE_TCP:
+        break;
+    case OUTPUT_DNSCLI_MODE_TLS: {
+        int err;
+        if ((err = gnutls_certificate_allocate_credentials(&self->cred)) != GNUTLS_E_SUCCESS) {
+            lfatal("gnutls_certificate_allocate_credentials() error: %s", gnutls_strerror(err));
+        } else if ((err = gnutls_init(&self->session, GNUTLS_CLIENT | ((mode & OUTPUT_DNSCLI_MODE_NONBLOCKING) ? GNUTLS_NONBLOCK : 0))) != GNUTLS_E_SUCCESS) {
+            lfatal("gnutls_init() error: %s", gnutls_strerror(err));
+        } else if ((err = gnutls_set_default_priority(self->session)) != GNUTLS_E_SUCCESS) {
+            lfatal("gnutls_set_default_priority() error: %s", gnutls_strerror(err));
+        } else if ((err = gnutls_credentials_set(self->session, GNUTLS_CRD_CERTIFICATE, self->cred)) != GNUTLS_E_SUCCESS) {
+            lfatal("gnutls_credentials_set() error: %s", gnutls_strerror(err));
+        }
+
+        gnutls_handshake_set_timeout(self->session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);
+        break;
+    }
+    default:
+        lfatal("Invalid mode %x", mode);
+    }
+}
+
+void output_dnscli_destroy(output_dnscli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd > -1) {
+        switch (self->mode & OUTPUT_DNSCLI_MODE_MODES) {
+        case OUTPUT_DNSCLI_MODE_UDP:
+        case OUTPUT_DNSCLI_MODE_TCP:
+            shutdown(self->fd, SHUT_RDWR);
+            close(self->fd);
+            break;
+        case OUTPUT_DNSCLI_MODE_TLS:
+            if (self->session) {
+                gnutls_bye(self->session, GNUTLS_SHUT_RDWR);
+                gnutls_deinit(self->session);
+            }
+            shutdown(self->fd, SHUT_RDWR);
+            close(self->fd);
+            if (self->cred) {
+                gnutls_certificate_free_credentials(self->cred);
+            }
+            break;
+        default:
+            break;
+        }
+    }
+}
+
+int output_dnscli_connect(output_dnscli_t* self, const char* host, const char* port)
+{
+    struct addrinfo* addr;
+    int              err;
+    mlassert_self();
+    lassert(host, "host is nil");
+    lassert(port, "port is nil");
+
+    if (self->fd > -1) {
+        lfatal("already connected");
+    }
+
+    if ((err = getaddrinfo(host, port, 0, &addr))) {
+        lcritical("getaddrinfo(%s, %s) error %s", host, port, gai_strerror(err));
+        return -1;
+    }
+    if (!addr) {
+        lcritical("getaddrinfo failed, no address returned");
+        return -1;
+    }
+
+    switch (self->mode & OUTPUT_DNSCLI_MODE_MODES) {
+    case OUTPUT_DNSCLI_MODE_UDP:
+        memcpy(&self->addr, addr->ai_addr, addr->ai_addrlen);
+        self->addr_len = addr->ai_addrlen;
+        freeaddrinfo(addr);
+
+        if ((self->fd = socket(((struct sockaddr*)&self->addr)->sa_family, SOCK_DGRAM, 0)) < 0) {
+            lcritical("socket() error %s", core_log_errstr(errno));
+            return -2;
+        }
+        break;
+    case OUTPUT_DNSCLI_MODE_TCP:
+    case OUTPUT_DNSCLI_MODE_TLS:
+        if ((self->fd = socket(addr->ai_addr->sa_family, SOCK_STREAM, 0)) < 0) {
+            lcritical("socket() error %s", core_log_errstr(errno));
+            freeaddrinfo(addr);
+            return -2;
+        }
+
+        if (connect(self->fd, addr->ai_addr, addr->ai_addrlen)) {
+            lcritical("connect() error %s", core_log_errstr(errno));
+            freeaddrinfo(addr);
+            return -2;
+        }
+
+        freeaddrinfo(addr);
+        break;
+    default:
+        break;
+    }
+
+    switch (self->mode & OUTPUT_DNSCLI_MODE_MODES) {
+    case OUTPUT_DNSCLI_MODE_UDP:
+    case OUTPUT_DNSCLI_MODE_TCP:
+        if (self->mode & OUTPUT_DNSCLI_MODE_NONBLOCKING) {
+            int flags;
+
+            if ((flags = fcntl(self->fd, F_GETFL)) == -1) {
+                lcritical("fcntl(FL_GETFL) error %s", core_log_errstr(errno));
+                return -3;
+            }
+
+            if (fcntl(self->fd, F_SETFL, flags | O_NONBLOCK)) {
+                lcritical("fcntl(FL_SETFL, %x) error %s", flags, core_log_errstr(errno));
+                return -3;
+            }
+            self->nonblocking = 1;
+        }
+        if (self->timeout.sec > 0 || self->timeout.nsec > 0) {
+            self->poll.fd      = self->fd;
+            self->poll_timeout = (self->timeout.sec * 1e3) + (self->timeout.nsec / 1e6); //NOSONAR
+            if (!self->poll_timeout) {
+                self->poll_timeout = 1;
+            }
+        }
+        break;
+    case OUTPUT_DNSCLI_MODE_TLS: {
+        unsigned int ms;
+        gnutls_transport_set_int(self->session, self->fd);
+        ms = (self->timeout.sec * 1000) + (self->timeout.nsec / 1000000);
+        if (!ms && self->timeout.nsec) {
+            ms = 1;
+        }
+        gnutls_record_set_timeout(self->session, ms);
+
+        /* Establish TLS */
+        do {
+            err = gnutls_handshake(self->session);
+        } while (err < 0 && gnutls_error_is_fatal(err) == 0);
+        if (err == GNUTLS_E_PREMATURE_TERMINATION) {
+            lcritical("gnutls_handshake() error: %s", gnutls_strerror(err));
+            return -3;
+        } else if (err < 0) {
+            lcritical("gnutls_handshake() failed: %s (%d)\n", gnutls_strerror(err), err);
+            return -3;
+        }
+        break;
+    }
+    default:
+        break;
+    }
+
+    self->conn_ok = 1;
+    return 0;
+}
+
+inline ssize_t _send_udp(output_dnscli_t* self, const uint8_t* payload, size_t len, size_t sent)
+{
+    ssize_t n;
+
+    if (self->poll_timeout) {
+        self->poll.events = POLLOUT;
+        n                 = poll(&self->poll, 1, self->poll_timeout);
+        if (n != 1 || !(self->poll.revents & POLLOUT)) {
+            if (!n) {
+                self->timeouts++;
+                return -1;
+            }
+            self->errs++;
+            return -2;
+        }
+    }
+    n = sendto(self->fd, payload + sent, len - sent, 0, (struct sockaddr*)&self->addr, self->addr_len);
+    if (n > -1) {
+        return n;
+    }
+    switch (errno) {
+    case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+    case EWOULDBLOCK:
+#endif
+    case EINTR:
+        return -1;
+    default:
+        break;
+    }
+    return -2;
+}
+
+static void _receive_udp(output_dnscli_t* self, const core_object_t* obj)
+{
+    const uint8_t* payload;
+    size_t         len, sent = 0;
+    ssize_t        n;
+    mlassert_self();
+
+    switch (obj->obj_type) {
+    case CORE_OBJECT_DNS:
+        payload = ((core_object_dns_t*)obj)->payload;
+        len     = ((core_object_dns_t*)obj)->len;
+
+        if (((core_object_dns_t*)obj)->includes_dnslen) {
+            if (len < 2) {
+                return;
+            }
+            payload += 2;
+            len -= 2;
+        }
+        break;
+    case CORE_OBJECT_PAYLOAD:
+        payload = ((core_object_payload_t*)obj)->payload;
+        len     = ((core_object_payload_t*)obj)->len;
+        break;
+    default:
+        return;
+    }
+
+    for (;;) {
+        n = _send_udp(self, payload, len, sent);
+        if (n > -1) {
+            sent += n;
+            if (sent < len) {
+                continue;
+            }
+            self->pkts++;
+            return;
+        }
+        if (n == -1) {
+            if (self->nonblocking) {
+                // TODO: warn?
+                return;
+            }
+            continue;
+        }
+        break;
+    }
+    self->errs++;
+}
+
+inline ssize_t _send_tcp(output_dnscli_t* self, const uint8_t* payload, size_t len, size_t sent)
+{
+    ssize_t n;
+
+    if (self->poll_timeout) {
+        self->poll.events = POLLOUT;
+        n                 = poll(&self->poll, 1, self->poll_timeout);
+        if (n != 1 || !(self->poll.revents & POLLOUT)) {
+            if (!n) {
+                self->timeouts++;
+                return -1;
+            }
+            self->errs++;
+            return -2;
+        }
+    }
+    n = sendto(self->fd, payload + sent, len - sent, 0, 0, 0);
+    if (n > -1) {
+        return n;
+    }
+    switch (errno) {
+    case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+    case EWOULDBLOCK:
+#endif
+    case EINTR:
+        return -1;
+    default:
+        break;
+    }
+    return -2;
+}
+
+static void _receive_tcp(output_dnscli_t* self, const core_object_t* obj)
+{
+    const uint8_t* payload;
+    size_t         len, sent = 0;
+    ssize_t        n;
+    mlassert_self();
+
+    switch (obj->obj_type) {
+    case CORE_OBJECT_DNS:
+        if (!((core_object_dns_t*)obj)->includes_dnslen) {
+            uint16_t dnslen = htons(((core_object_dns_t*)obj)->len);
+            payload         = (const uint8_t*)&dnslen;
+            len             = sizeof(dnslen);
+
+            for (;;) {
+                n = _send_tcp(self, payload, len, sent);
+                if (n > -1) {
+                    sent += n;
+                    if (sent < len) {
+                        continue;
+                    }
+                    break;
+                }
+                if (n == -1) {
+                    if (self->nonblocking) {
+                        // TODO: warn?
+                        return;
+                    }
+                    continue;
+                }
+                self->errs++;
+                return;
+            }
+            sent = 0;
+        }
+        payload = ((core_object_dns_t*)obj)->payload;
+        len     = ((core_object_dns_t*)obj)->len;
+        break;
+    case CORE_OBJECT_PAYLOAD:
+        payload = ((core_object_payload_t*)obj)->payload;
+        len     = ((core_object_payload_t*)obj)->len;
+        break;
+    default:
+        return;
+    }
+
+    for (;;) {
+        n = _send_tcp(self, payload, len, sent);
+        if (n > -1) {
+            sent += n;
+            if (sent < len) {
+                continue;
+            }
+            self->pkts++;
+            return;
+        }
+        if (n == -1) {
+            if (self->nonblocking) {
+                // TODO: warn?
+                return;
+            }
+            continue;
+        }
+        break;
+    }
+    self->errs++;
+}
+
+inline ssize_t _send_tls(output_dnscli_t* self, const uint8_t* payload, size_t len, size_t sent)
+{
+    ssize_t n;
+
+    n = gnutls_record_send(self->session, payload + sent, len - sent);
+    if (n > -1) {
+        return n;
+    }
+    switch (n) {
+    case GNUTLS_E_AGAIN:
+    case GNUTLS_E_TIMEDOUT:
+    case GNUTLS_E_INTERRUPTED:
+        return -1;
+    default:
+        break;
+    }
+    return -2;
+}
+
+static void _receive_tls(output_dnscli_t* self, const core_object_t* obj)
+{
+    const uint8_t* payload;
+    size_t         len, sent = 0;
+    ssize_t        n;
+    mlassert_self();
+
+    switch (obj->obj_type) {
+    case CORE_OBJECT_DNS:
+        if (!((core_object_dns_t*)obj)->includes_dnslen) {
+            uint16_t dnslen = htons(((core_object_dns_t*)obj)->len);
+            payload         = (const uint8_t*)&dnslen;
+            len             = sizeof(dnslen);
+
+            for (;;) {
+                n = _send_tls(self, payload, len, sent);
+                if (n > -1) {
+                    sent += n;
+                    if (sent < len) {
+                        continue;
+                    }
+                    break;
+                }
+                if (n == -1) {
+                    if (self->nonblocking) {
+                        // TODO: warn?
+                        return;
+                    }
+                    continue;
+                }
+                self->errs++;
+                return;
+            }
+            sent = 0;
+        }
+        payload = ((core_object_dns_t*)obj)->payload;
+        len     = ((core_object_dns_t*)obj)->len;
+        break;
+    case CORE_OBJECT_PAYLOAD:
+        payload = ((core_object_payload_t*)obj)->payload;
+        len     = ((core_object_payload_t*)obj)->len;
+        break;
+    default:
+        return;
+    }
+
+    for (;;) {
+        n = _send_tls(self, payload, len, sent);
+        if (n > -1) {
+            sent += n;
+            if (sent < len) {
+                continue;
+            }
+            self->pkts++;
+            return;
+        }
+        if (n == -1) {
+            if (self->nonblocking) {
+                // TODO: warn?
+                return;
+            }
+            continue;
+        }
+        break;
+    }
+    self->errs++;
+}
+
+luajit_ssize_t output_dnscli_send(output_dnscli_t* self, const core_object_t* obj, size_t sent)
+{
+    const uint8_t* payload;
+    size_t         len;
+    uint16_t       dnslen;
+    mlassert_self();
+
+    switch (self->mode & OUTPUT_DNSCLI_MODE_MODES) {
+    case OUTPUT_DNSCLI_MODE_UDP:
+        switch (obj->obj_type) {
+        case CORE_OBJECT_DNS:
+            payload = ((core_object_dns_t*)obj)->payload;
+            len     = ((core_object_dns_t*)obj)->len;
+
+            if (((core_object_dns_t*)obj)->includes_dnslen) {
+                if (len < 2) {
+                    return -2;
+                }
+                payload += 2;
+                len -= 2;
+            }
+            break;
+        case CORE_OBJECT_PAYLOAD:
+            payload = ((core_object_payload_t*)obj)->payload;
+            len     = ((core_object_payload_t*)obj)->len;
+            break;
+        default:
+            return -2;
+        }
+
+        return _send_udp(self, payload, len, sent);
+
+    case OUTPUT_DNSCLI_MODE_TCP:
+        switch (obj->obj_type) {
+        case CORE_OBJECT_DNS:
+            if (!((core_object_dns_t*)obj)->includes_dnslen) {
+                if (sent < sizeof(dnslen)) {
+                    dnslen  = htons(((core_object_dns_t*)obj)->len);
+                    payload = (const uint8_t*)&dnslen;
+                    len     = sizeof(dnslen);
+
+                    return _send_tcp(self, payload, len, sent);
+                }
+                sent -= sizeof(dnslen);
+            }
+            payload = ((core_object_dns_t*)obj)->payload;
+            len     = ((core_object_dns_t*)obj)->len;
+            break;
+        case CORE_OBJECT_PAYLOAD:
+            payload = ((core_object_payload_t*)obj)->payload;
+            len     = ((core_object_payload_t*)obj)->len;
+            break;
+        default:
+            return -2;
+        }
+
+        return _send_tcp(self, payload, len, sent);
+
+    case OUTPUT_DNSCLI_MODE_TLS:
+        switch (obj->obj_type) {
+        case CORE_OBJECT_DNS:
+            if (!((core_object_dns_t*)obj)->includes_dnslen) {
+                if (sent < sizeof(dnslen)) {
+                    dnslen  = htons(((core_object_dns_t*)obj)->len);
+                    payload = (const uint8_t*)&dnslen;
+                    len     = sizeof(dnslen);
+
+                    return _send_tls(self, payload, len, sent);
+                }
+                sent -= sizeof(dnslen);
+            }
+            payload = ((core_object_dns_t*)obj)->payload;
+            len     = ((core_object_dns_t*)obj)->len;
+            break;
+        case CORE_OBJECT_PAYLOAD:
+            payload = ((core_object_payload_t*)obj)->payload;
+            len     = ((core_object_payload_t*)obj)->len;
+            break;
+        default:
+            return -2;
+        }
+
+        return _send_tls(self, payload, len, sent);
+
+    default:
+        break;
+    }
+
+    return -2;
+}
+
+core_receiver_t output_dnscli_receiver(output_dnscli_t* self)
+{
+    mlassert_self();
+
+    if (!self->conn_ok) {
+        lfatal("not connected");
+    }
+
+    switch (self->mode & OUTPUT_DNSCLI_MODE_MODES) {
+    case OUTPUT_DNSCLI_MODE_UDP:
+        return (core_receiver_t)_receive_udp;
+    case OUTPUT_DNSCLI_MODE_TCP:
+        return (core_receiver_t)_receive_tcp;
+    case OUTPUT_DNSCLI_MODE_TLS:
+        return (core_receiver_t)_receive_tls;
+    default:
+        break;
+    }
+
+    lfatal("internal error");
+    return 0;
+}
+
+static const core_object_t* _produce_udp(output_dnscli_t* self)
+{
+    ssize_t n;
+    mlassert_self();
+
+    for (;;) {
+        if (self->poll_timeout) {
+            self->poll.events = POLLIN;
+            n                 = poll(&self->poll, 1, self->poll_timeout);
+            if (n != 1 || !(self->poll.revents & POLLIN)) {
+                if (!n) {
+                    self->timeouts++;
+                    self->pkt.len = 0;
+                    return (core_object_t*)&self->pkt;
+                } else {
+                    self->errs++;
+                }
+                return 0;
+            }
+        }
+        n = recvfrom(self->fd, self->recvbuf, sizeof(self->recvbuf), 0, 0, 0);
+        if (n > -1) {
+            break;
+        }
+        switch (errno) {
+        case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+        case EWOULDBLOCK:
+#endif
+        case EINTR:
+            if (self->nonblocking) {
+                self->pkt.len = 0;
+                return (core_object_t*)&self->pkt;
+            }
+            continue;
+        default:
+            break;
+        }
+        self->errs++;
+        break;
+    }
+
+    if (n < 1) {
+        return 0;
+    }
+
+    self->pkts_recv++;
+    self->pkt.len = n;
+    return (core_object_t*)&self->pkt;
+}
+
+static const core_object_t* _produce_tcp(output_dnscli_t* self)
+{
+    ssize_t n;
+    mlassert_self();
+
+    if (self->have_pkt) {
+        if (self->recv > self->dnslen + sizeof(self->dnslen)) {
+            self->recv -= self->dnslen + sizeof(self->dnslen);
+            memmove(self->recvbuf, self->recvbuf + self->dnslen + sizeof(self->dnslen), self->recv);
+        } else {
+            self->recv = 0;
+        }
+        self->have_pkt    = 0;
+        self->have_dnslen = 0;
+    }
+
+    if (!self->have_dnslen && self->recv >= sizeof(self->dnslen)) {
+        self->dnslen      = _need16(self->recvbuf);
+        self->have_dnslen = 1;
+    }
+    if (self->have_dnslen && self->recv >= self->dnslen + sizeof(self->dnslen)) {
+        self->pkts_recv++;
+        self->pkt.len  = self->dnslen + sizeof(self->dnslen);
+        self->have_pkt = 1;
+        return (core_object_t*)&self->pkt;
+    }
+
+    for (;;) {
+        if (self->poll_timeout) {
+            self->poll.events = POLLIN;
+            n                 = poll(&self->poll, 1, self->poll_timeout);
+            if (n != 1 || !(self->poll.revents & POLLIN)) {
+                if (!n) {
+                    self->timeouts++;
+                    self->pkt.len = 0;
+                    return (core_object_t*)&self->pkt;
+                } else {
+                    self->errs++;
+                }
+                return 0;
+            }
+        }
+        n = recvfrom(self->fd, self->recvbuf + self->recv, sizeof(self->recvbuf) - self->recv, 0, 0, 0);
+        if (n > 0) {
+            self->recv += n;
+
+            if (!self->have_dnslen && self->recv >= sizeof(self->dnslen)) {
+                self->dnslen      = _need16(self->recvbuf);
+                self->have_dnslen = 1;
+            }
+            if (self->have_dnslen && self->recv >= self->dnslen + sizeof(self->dnslen)) {
+                self->pkts_recv++;
+                self->pkt.len  = self->dnslen + sizeof(self->dnslen);
+                self->have_pkt = 1;
+                return (core_object_t*)&self->pkt;
+            }
+
+            if (self->nonblocking) {
+                break;
+            }
+            continue;
+        }
+        if (!n) {
+            break;
+        }
+        switch (errno) {
+        case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+        case EWOULDBLOCK:
+#endif
+        case EINTR:
+            if (self->nonblocking) {
+                self->pkt.len = 0;
+                return (core_object_t*)&self->pkt;
+            }
+            continue;
+        default:
+            break;
+        }
+        self->errs++;
+        break;
+    }
+
+    if (n < 1) {
+        return 0;
+    }
+
+    self->pkt.len = 0;
+    return (core_object_t*)&self->pkt;
+}
+
+static const core_object_t* _produce_tls(output_dnscli_t* self)
+{
+    ssize_t n;
+    mlassert_self();
+
+    if (self->have_pkt) {
+        if (self->recv > self->dnslen + sizeof(self->dnslen)) {
+            self->recv -= self->dnslen + sizeof(self->dnslen);
+            memmove(self->recvbuf, self->recvbuf + self->dnslen + sizeof(self->dnslen), self->recv);
+        } else {
+            self->recv = 0;
+        }
+        self->have_pkt    = 0;
+        self->have_dnslen = 0;
+    }
+
+    if (!self->have_dnslen && self->recv >= sizeof(self->dnslen)) {
+        self->dnslen      = _need16(self->recvbuf);
+        self->have_dnslen = 1;
+    }
+    if (self->have_dnslen && self->recv >= self->dnslen + sizeof(self->dnslen)) {
+        self->pkts_recv++;
+        self->pkt.len  = self->dnslen + sizeof(self->dnslen);
+        self->have_pkt = 1;
+        return (core_object_t*)&self->pkt;
+    }
+
+    for (;;) {
+        if (!gnutls_record_check_pending(self->session) && self->poll_timeout) {
+            self->poll.events = POLLIN;
+            n                 = poll(&self->poll, 1, self->poll_timeout);
+            if (n != 1 || !(self->poll.revents & POLLIN)) {
+                if (!n) {
+                    self->timeouts++;
+                    self->pkt.len = 0;
+                    return (core_object_t*)&self->pkt;
+                } else {
+                    self->errs++;
+                }
+                return 0;
+            }
+        }
+        n = gnutls_record_recv(self->session, self->recvbuf + self->recv, sizeof(self->recvbuf) - self->recv);
+        if (n > 0) {
+            self->recv += n;
+
+            if (!self->have_dnslen && self->recv >= sizeof(self->dnslen)) {
+                self->dnslen      = _need16(self->recvbuf);
+                self->have_dnslen = 1;
+            }
+            if (self->have_dnslen && self->recv >= self->dnslen + sizeof(self->dnslen)) {
+                self->pkts_recv++;
+                self->pkt.len  = self->dnslen + sizeof(self->dnslen);
+                self->have_pkt = 1;
+                return (core_object_t*)&self->pkt;
+            }
+
+            if (self->nonblocking) {
+                break;
+            }
+            continue;
+        }
+        if (!n) {
+            break;
+        }
+        switch (n) {
+        case GNUTLS_E_AGAIN:
+        case GNUTLS_E_TIMEDOUT:
+        case GNUTLS_E_INTERRUPTED:
+            if (self->nonblocking) {
+                self->pkt.len = 0;
+                return (core_object_t*)&self->pkt;
+            }
+            continue;
+        default:
+            break;
+        }
+        self->errs++;
+        break;
+    }
+
+    if (n < 1) {
+        return 0;
+    }
+
+    self->pkt.len = 0;
+    return (core_object_t*)&self->pkt;
+}
+
+core_producer_t output_dnscli_producer(output_dnscli_t* self)
+{
+    mlassert_self();
+
+    if (!self->conn_ok) {
+        lfatal("not connected");
+    }
+
+    switch (self->mode & OUTPUT_DNSCLI_MODE_MODES) {
+    case OUTPUT_DNSCLI_MODE_UDP:
+        return (core_producer_t)_produce_udp;
+    case OUTPUT_DNSCLI_MODE_TCP:
+        return (core_producer_t)_produce_tcp;
+    case OUTPUT_DNSCLI_MODE_TLS:
+        return (core_producer_t)_produce_tls;
+    default:
+        break;
+    }
+
+    lfatal("internal error");
+    return 0;
+}
diff --git a/src/output/dnscli.h b/src/output/dnscli.h
new file mode 100644
index 0000000..27f2207
--- /dev/null
+++ b/src/output/dnscli.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "core/log.h"
+#include "core/receiver.h"
+#include "core/producer.h"
+#include "core/object/payload.h"
+#include "core/timespec.h"
+#include "core/compat.h"
+
+#ifndef __dnsjit_output_dnscli_h
+#define __dnsjit_output_dnscli_h
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <gnutls/gnutls.h>
+#include <poll.h>
+
+#include "output/dnscli.hh"
+
+#endif
diff --git a/src/output/dnscli.hh b/src/output/dnscli.hh
new file mode 100644
index 0000000..4126423
--- /dev/null
+++ b/src/output/dnscli.hh
@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+//lua:require("dnsjit.core.compat_h")
+//lua:require("dnsjit.core.log")
+//lua:require("dnsjit.core.receiver_h")
+//lua:require("dnsjit.core.producer_h")
+//lua:require("dnsjit.core.object.payload_h")
+//lua:require("dnsjit.core.timespec_h")
+
+typedef enum output_dnscli_mode {
+    OUTPUT_DNSCLI_MODE_NONE        = 0,
+    OUTPUT_DNSCLI_MODE_OPTIONS     = 0xf,
+    OUTPUT_DNSCLI_MODE_NONBLOCKING = 0x1,
+    OUTPUT_DNSCLI_MODE_MODES       = 0xf0,
+    OUTPUT_DNSCLI_MODE_UDP         = 0x10,
+    OUTPUT_DNSCLI_MODE_TCP         = 0x20,
+    OUTPUT_DNSCLI_MODE_TLS         = 0x30,
+} output_dnscli_mode_t;
+
+typedef struct output_dnscli {
+    core_log_t _log;
+
+    output_dnscli_mode_t mode;
+
+    size_t pkts, errs, timeouts;
+    int    fd, nonblocking, conn_ok;
+
+    struct pollfd poll;
+    int           poll_timeout;
+
+    struct sockaddr_storage addr;
+    size_t                  addr_len;
+
+    uint8_t               recvbuf[(64 * 1024) + 2];
+    core_object_payload_t pkt;
+    uint16_t              dnslen;
+    uint8_t               have_dnslen, have_pkt;
+    size_t                recv, pkts_recv;
+
+    core_timespec_t timeout;
+
+    gnutls_session_t                 session;
+    gnutls_certificate_credentials_t cred;
+} output_dnscli_t;
+
+core_log_t* output_dnscli_log();
+
+void           output_dnscli_init(output_dnscli_t* self, output_dnscli_mode_t mode);
+void           output_dnscli_destroy(output_dnscli_t* self);
+int            output_dnscli_connect(output_dnscli_t* self, const char* host, const char* port);
+luajit_ssize_t output_dnscli_send(output_dnscli_t* self, const core_object_t* obj, size_t sent);
+
+core_receiver_t output_dnscli_receiver(output_dnscli_t* self);
+core_producer_t output_dnscli_producer(output_dnscli_t* self);
diff --git a/src/output/dnscli.lua b/src/output/dnscli.lua
new file mode 100644
index 0000000..bfdaf36
--- /dev/null
+++ b/src/output/dnscli.lua
@@ -0,0 +1,187 @@
+-- Copyright (c) 2018-2021, OARC, Inc.
+-- All rights reserved.
+--
+-- This file is part of dnsjit.
+--
+-- dnsjit is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation, either version 3 of the License, or
+-- (at your option) any later version.
+--
+-- dnsjit is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License
+-- along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+
+-- dnsjit.output.dnscli
+-- DNS aware UDP/TCP/TLS client
+--   local dnscli = require("dnsjit.output.dnscli")
+-- .SS UDP Receiver Chain
+--   local output = dnscli.new(dnscli.UDP)
+--   output:connect("127.0.0.1", "53")
+--   input:receiver(output)
+-- .SS TCP Nonblocking
+--   local output = dnscli.new(dnscli.TCP + dnscli.NONBLOCKING)
+--   output:send(object)
+--
+-- The DNS client can a
+-- .I core.object.dns
+-- or a
+-- .I core.object.payload
+-- object via the receiver interface or using
+-- .I send()
+-- and send it as DNS query after which it can receive the response by using
+-- the producer interface.
+-- If the object being sent is a
+-- .I core.object.dns
+-- then it will look at
+-- .I includes_dnslen
+-- attribute and depending on the protocol it will disregard, include or send
+-- the DNS length as an extra packet.
+-- If the object being sent is a
+-- .I core.object.payload
+-- then no special handling will be done and it will be sent as is.
+-- When receiving responses the producer interface will generate
+-- .I core.object.payload
+-- objects which may include the DNS length depending on the protocol used and
+-- must be handled by the caller.
+-- .SS MODES
+-- These transport modes and options are available when creating a new Dnscli
+-- output.
+-- .TP
+-- UDP
+-- Create an output using UDP.
+-- .TP
+-- TCP
+-- Create an output using TCP.
+-- .TP
+-- TLS
+-- Create an output using TCP and encrypt it with TLS.
+-- .TP
+-- NONBLOCKING
+-- Make the client nonblocking, see
+-- .I send()
+-- and
+-- .IR produce() .
+module(...,package.seeall)
+
+require("dnsjit.output.dnscli_h")
+local ffi = require("ffi")
+local C = ffi.C
+
+local t_name = "output_dnscli_t"
+local output_dnscli_t = ffi.typeof(t_name)
+local Dnscli = {
+    NONBLOCKING = 0x1,
+    UDP = 0x10,
+    TCP = 0x20,
+    TLS = 0x30,
+}
+
+-- Create a new Dnscli output.
+function Dnscli.new(mode)
+    local self = {
+        obj = output_dnscli_t(),
+    }
+    C.output_dnscli_init(self.obj, mode)
+    ffi.gc(self.obj, C.output_dnscli_destroy)
+    return setmetatable(self, { __index = Dnscli })
+end
+
+-- Set or return the timeout used for sending and reciving, must be used before
+-- .IR connect() .
+function Dnscli:timeout(seconds, nanoseconds)
+    if seconds == nil and nanoseconds == nil then
+        return self.obj.timeout
+    end
+    if nanoseconds == nil then
+        nanoseconds = 0
+    end
+    self.obj.timeout.sec = seconds
+    self.obj.timeout.nsec = nanoseconds
+end
+
+-- Connect to the
+-- .I host
+-- and
+-- .I port
+-- and return 0 if successful.
+function Dnscli:connect(host, port)
+    return C.output_dnscli_connect(self.obj, host, port)
+end
+
+-- Return if nonblocking mode is on (true) or off (false).
+function Dnscli:nonblocking()
+    if self.obj.nonblocking == 1 then
+        return true
+    end
+    return false
+end
+
+-- Send an object and optionally continue sending after
+-- .I sent
+-- bytes.
+-- Unlike the receive interface this function lets you know if the sending was
+-- successful or not which might be needed on nonblocking connections.
+-- Returns -2 on error, -1 if interrupted, timed out or unable to send due to
+-- nonblocking, or the number of bytes sent.
+-- .B Note
+-- the counters for sent, received, errors and timeouts are not affected by
+-- this function.
+function Dnscli:send(object, sent)
+    if sent == nil then
+        sent = 0
+    end
+    return C.output_dnscli_send(self.obj, object, sent)
+end
+
+-- Return the C functions and context for receiving objects, these objects
+-- will be sent.
+function Dnscli:receive()
+    return C.output_dnscli_receiver(self.obj), self.obj
+end
+
+-- Return the C functions and context for producing objects, these objects
+-- are received.
+-- If nonblocking mode is enabled the producer will return a payload object
+-- with length zero if there was nothing to receive.
+-- If nonblocking mode is disabled the producer will wait for data and if
+-- timed out (see
+-- .IR timeout )
+-- it will return a payload object with length zero.
+-- The producer returns nil on error.
+function Dnscli:produce()
+    return C.output_dnscli_producer(self.obj), self.obj
+end
+
+-- Return the number of "packets" sent, actually the number of completely sent
+-- payloads.
+function Dnscli:packets()
+    return tonumber(self.obj.pkts)
+end
+
+-- Return the number of "packets" received, actually the number of successful
+-- calls to
+-- .IR recvfrom (2)
+-- that returned data.
+function Dnscli:received()
+    return tonumber(self.obj.pkts_recv)
+end
+
+-- Return the number of errors when sending or receiving.
+function Dnscli:errors()
+    return tonumber(self.obj.errs)
+end
+
+-- Return the number of timeouts when sending or receiving.
+function Dnscli:timeouts()
+    return tonumber(self.obj.timeouts)
+end
+
+-- core.object.dns (3),
+-- core.object.payload (3),
+-- core.timespec (3)
+return Dnscli
diff --git a/src/output/dnssim.c b/src/output/dnssim.c
new file mode 100644
index 0000000..acd0a05
--- /dev/null
+++ b/src/output/dnssim.c
@@ -0,0 +1,502 @@
+/*
+ * Copyright (c) 2019-2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/dnssim.h"
+#include "output/dnssim/internal.h"
+#include "output/dnssim/ll.h"
+#include "core/assert.h"
+#include "core/object/ip.h"
+#include "core/object/ip6.h"
+
+#include <gnutls/gnutls.h>
+#include <string.h>
+
+static core_log_t      _log      = LOG_T_INIT("output.dnssim");
+static output_dnssim_t _defaults = { LOG_T_INIT_OBJ("output.dnssim") };
+
+static uint64_t _now_ms()
+{
+#if HAVE_CLOCK_NANOSLEEP
+    struct timespec ts;
+    uint64_t        now_ms;
+    if (clock_gettime(CLOCK_REALTIME, &ts)) {
+        mlfatal("clock_gettime()");
+    }
+    now_ms = ts.tv_sec * 1000;
+    now_ms += ts.tv_nsec / 1000000;
+    return now_ms;
+#else
+    mlfatal("clock_gettime() not available");
+    return 0;
+#endif
+}
+
+core_log_t* output_dnssim_log()
+{
+    return &_log;
+}
+
+output_dnssim_t* output_dnssim_new(size_t max_clients)
+{
+    output_dnssim_t* self;
+    int              ret, i;
+
+    mlfatal_oom(self = calloc(1, sizeof(_output_dnssim_t)));
+    *self                      = _defaults;
+    self->handshake_timeout_ms = 5000;
+    self->idle_timeout_ms      = 10000;
+    output_dnssim_timeout_ms(self, 2000);
+
+    _self->source            = NULL;
+    _self->transport         = OUTPUT_DNSSIM_TRANSPORT_UDP_ONLY;
+    _self->h2_zero_out_msgid = false;
+
+    self->max_clients = max_clients;
+    lfatal_oom(_self->client_arr = calloc(max_clients, sizeof(_output_dnssim_client_t)));
+
+    for (i = 0; i < max_clients; ++i) {
+        _self->client_arr[i].dnssim = self;
+    }
+
+    ret = gnutls_certificate_allocate_credentials(&_self->tls_cred);
+    if (ret < 0)
+        lfatal("failed to allocated TLS credentials (%s)", gnutls_strerror(ret));
+
+    ret = uv_loop_init(&_self->loop);
+    if (ret < 0)
+        lfatal("failed to initialize uv_loop (%s)", uv_strerror(ret));
+    ldebug("initialized uv_loop");
+
+    return self;
+}
+
+void output_dnssim_free(output_dnssim_t* self)
+{
+    mlassert_self();
+    int                      ret, i;
+    _output_dnssim_source_t* source;
+    _output_dnssim_source_t* first = _self->source;
+    output_dnssim_stats_t*   stats_prev;
+
+    free(self->stats_sum->latency);
+    free(self->stats_sum);
+    do {
+        stats_prev = self->stats_current->prev;
+        free(self->stats_current->latency);
+        free(self->stats_current);
+        self->stats_current = stats_prev;
+    } while (self->stats_current != NULL);
+
+    if (_self->source != NULL) {
+        // free cilcular linked list
+        do {
+            source = _self->source->next;
+            free(_self->source);
+            _self->source = source;
+        } while (_self->source != first);
+    }
+
+    for (i = 0; i < self->max_clients; ++i) {
+        if (_self->client_arr[i].tls_ticket.size != 0) {
+            gnutls_free(_self->client_arr[i].tls_ticket.data);
+        }
+    }
+    free(_self->client_arr);
+
+    ret = uv_loop_close(&_self->loop);
+    if (ret < 0) {
+        lcritical("failed to close uv_loop (%s)", uv_strerror(ret));
+    } else {
+        ldebug("closed uv_loop");
+    }
+
+    gnutls_certificate_free_credentials(_self->tls_cred);
+    if (_self->tls_priority != NULL) {
+        gnutls_priority_deinit(*_self->tls_priority);
+        free(_self->tls_priority);
+    }
+
+    free(self);
+}
+
+void output_dnssim_log_name(output_dnssim_t* self, const char* name)
+{
+    mlassert_self();
+    lassert(name, "name is nil");
+
+    strncpy(self->_log.name, name, sizeof(self->_log.name) - 1);
+    self->_log.name[sizeof(self->_log.name) - 1] = 0;
+    self->_log.is_obj                            = false;
+}
+
+static uint32_t _extract_client(const core_object_t* obj)
+{
+    uint32_t client;
+    uint8_t* ip;
+
+    switch (obj->obj_type) {
+    case CORE_OBJECT_IP:
+        ip = ((core_object_ip_t*)obj)->dst;
+        break;
+    case CORE_OBJECT_IP6:
+        ip = ((core_object_ip6_t*)obj)->dst;
+        break;
+    default:
+        return -1;
+    }
+
+    memcpy(&client, ip, sizeof(client));
+    return client;
+}
+
+static void _receive(output_dnssim_t* self, const core_object_t* obj)
+{
+    mlassert_self();
+    core_object_t*         current = (core_object_t*)obj;
+    core_object_payload_t* payload;
+    uint32_t               client;
+
+    self->processed++;
+
+    /* get payload from packet */
+    for (;;) {
+        if (current->obj_type == CORE_OBJECT_PAYLOAD) {
+            payload = (core_object_payload_t*)current;
+            break;
+        }
+        if (current->obj_prev == NULL) {
+            self->discarded++;
+            lwarning("packet discarded (missing payload object)");
+            return;
+        }
+        current = (core_object_t*)current->obj_prev;
+    }
+
+    /* extract client information from IP/IP6 layer */
+    for (;;) {
+        if (current->obj_type == CORE_OBJECT_IP || current->obj_type == CORE_OBJECT_IP6) {
+            client = _extract_client(current);
+            break;
+        }
+        if (current->obj_prev == NULL) {
+            self->discarded++;
+            lwarning("packet discarded (missing ip/ip6 object)");
+            return;
+        }
+        current = (core_object_t*)current->obj_prev;
+    }
+
+    if (self->free_after_use) {
+        /* free all objects except payload */
+        current               = (core_object_t*)obj;
+        core_object_t* parent = current;
+        while (current != NULL) {
+            parent  = current;
+            current = (core_object_t*)current->obj_prev;
+            if (parent->obj_type != CORE_OBJECT_PAYLOAD) {
+                core_object_free(parent);
+            }
+        }
+    }
+
+    if (_self->h2_zero_out_msgid) {
+        lassert(_self->transport == OUTPUT_DNSSIM_TRANSPORT_HTTPS2, "must use HTTP/2 to zero-out msgid");
+        if (payload->len < 2) {
+            self->discarded++;
+            lwarning("packet discarded (payload len < 2)");
+            return;
+        }
+        uint8_t* data = (uint8_t*)payload->payload;
+        data[0]       = 0x00;
+        data[1]       = 0x00;
+    }
+
+    if (client >= self->max_clients) {
+        self->discarded++;
+        lwarning("packet discarded (client exceeded max_clients)");
+        return;
+    }
+
+    ldebug("client(c): %d", client);
+    _output_dnssim_create_request(self, &_self->client_arr[client], payload);
+}
+
+core_receiver_t output_dnssim_receiver()
+{
+    return (core_receiver_t)_receive;
+}
+
+void output_dnssim_set_transport(output_dnssim_t* self, output_dnssim_transport_t tr)
+{
+    mlassert_self();
+
+    switch (tr) {
+    case OUTPUT_DNSSIM_TRANSPORT_UDP_ONLY:
+        lnotice("transport set to UDP (no TCP fallback)");
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_TCP:
+        lnotice("transport set to TCP");
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_TLS:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        lnotice("transport set to TLS");
+#else
+        lfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_HTTPS2:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        lnotice("transport set to HTTP/2 over TLS");
+        if (&_self->h2_uri_authority[0])
+            lnotice("set uri authority to: %s", _self->h2_uri_authority);
+#else
+        lfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_UDP:
+        lfatal("UDP transport with TCP fallback is not supported yet.");
+        break;
+    default:
+        lfatal("unknown or unsupported transport");
+        break;
+    }
+
+    _self->transport = tr;
+}
+
+int output_dnssim_target(output_dnssim_t* self, const char* ip, uint16_t port)
+{
+    int ret;
+    mlassert_self();
+    lassert(ip, "ip is nil");
+    lassert(port, "port is nil");
+
+    ret = uv_ip6_addr(ip, port, (struct sockaddr_in6*)&_self->target);
+    if (ret != 0) {
+        ret = uv_ip4_addr(ip, port, (struct sockaddr_in*)&_self->target);
+        if (ret != 0) {
+            lfatal("failed to parse IPv4 or IPv6 from \"%s\"", ip);
+        } else {
+            ret = snprintf(_self->h2_uri_authority, _MAX_URI_LEN, "%s:%d", ip, port);
+        }
+    } else {
+        ret = snprintf(_self->h2_uri_authority, _MAX_URI_LEN, "[%s]:%d", ip, port);
+    }
+
+    if (ret > 0) {
+        if (_self->transport == OUTPUT_DNSSIM_TRANSPORT_HTTPS2)
+            lnotice("set uri authority to: %s", _self->h2_uri_authority);
+    } else {
+        _self->h2_uri_authority[0] = '\0';
+        if (_self->transport == OUTPUT_DNSSIM_TRANSPORT_HTTPS2)
+            lfatal("failed to set authority");
+    }
+
+    lnotice("set target to %s port %d", ip, port);
+    return 0;
+}
+
+int output_dnssim_bind(output_dnssim_t* self, const char* ip)
+{
+    int ret;
+    mlassert_self();
+    lassert(ip, "ip is nil");
+
+    _output_dnssim_source_t* source;
+    lfatal_oom(source = malloc(sizeof(_output_dnssim_source_t)));
+
+    ret = uv_ip6_addr(ip, 0, (struct sockaddr_in6*)&source->addr);
+    if (ret != 0) {
+        ret = uv_ip4_addr(ip, 0, (struct sockaddr_in*)&source->addr);
+        if (ret != 0) {
+            lfatal("failed to parse IPv4 or IPv6 from \"%s\"", ip);
+        }
+    }
+
+    if (_self->source == NULL) {
+        source->next  = source;
+        _self->source = source;
+    } else {
+        source->next        = _self->source->next;
+        _self->source->next = source;
+    }
+
+    lnotice("bind to source address %s", ip);
+    return 0;
+}
+
+int output_dnssim_tls_priority(output_dnssim_t* self, const char* priority)
+{
+    mlassert_self();
+    lassert(priority, "priority is nil");
+
+    if (_self->tls_priority != NULL) {
+        gnutls_priority_deinit(*_self->tls_priority);
+        free(_self->tls_priority);
+    }
+    lfatal_oom(_self->tls_priority = malloc(sizeof(gnutls_priority_t)));
+
+    int ret = gnutls_priority_init(_self->tls_priority, priority, NULL);
+    if (ret < 0) {
+        lfatal("failed to initialize TLS priority cache: %s", gnutls_strerror(ret));
+    } else {
+        lnotice("GnuTLS priority set: %s", priority);
+    }
+
+    return 0;
+}
+
+int output_dnssim_run_nowait(output_dnssim_t* self)
+{
+    mlassert_self();
+
+    return uv_run(&_self->loop, UV_RUN_NOWAIT);
+}
+
+void output_dnssim_timeout_ms(output_dnssim_t* self, uint64_t timeout_ms)
+{
+    mlassert_self();
+    lassert(timeout_ms > 0, "timeout must be greater than 0");
+
+    if (self->stats_sum != NULL) {
+        free(self->stats_sum->latency);
+        free(self->stats_sum);
+        self->stats_sum = 0;
+    }
+    if (self->stats_current != NULL) {
+        output_dnssim_stats_t* stats_prev;
+        do {
+            stats_prev = self->stats_current->prev;
+            free(self->stats_current->latency);
+            free(self->stats_current);
+            self->stats_current = stats_prev;
+        } while (self->stats_current != NULL);
+    }
+
+    self->timeout_ms = timeout_ms;
+
+    lfatal_oom(self->stats_sum = calloc(1, sizeof(output_dnssim_stats_t)));
+    lfatal_oom(self->stats_sum->latency = calloc(self->timeout_ms + 1, sizeof(uint64_t)));
+
+    lfatal_oom(self->stats_current = calloc(1, sizeof(output_dnssim_stats_t)));
+    lfatal_oom(self->stats_current->latency = calloc(self->timeout_ms + 1, sizeof(uint64_t)));
+
+    self->stats_first = self->stats_current;
+}
+
+void output_dnssim_h2_uri_path(output_dnssim_t* self, const char* uri_path)
+{
+    mlassert_self();
+    lassert(uri_path, "uri_path is nil");
+    lassert(strlen(uri_path) < _MAX_URI_LEN, "uri_path too long");
+
+    strncpy(_self->h2_uri_path, uri_path, _MAX_URI_LEN - 1);
+    _self->h2_uri_path[_MAX_URI_LEN - 1] = 0;
+    lnotice("http2: set uri path to: %s", _self->h2_uri_path);
+}
+
+void output_dnssim_h2_method(output_dnssim_t* self, const char* method)
+{
+    mlassert_self();
+    lassert(method, "method is nil");
+
+    if (strcmp("GET", method) == 0) {
+        _self->h2_method = OUTPUT_DNSSIM_H2_GET;
+    } else if (strcmp("POST", method) == 0) {
+        _self->h2_method = OUTPUT_DNSSIM_H2_POST;
+    } else {
+        lfatal("http2: unsupported method: \"%s\"", method);
+    }
+
+    lnotice("http2: set method to %s", method);
+}
+
+void output_dnssim_h2_zero_out_msgid(output_dnssim_t* self, bool zero_out_msgid)
+{
+    mlassert_self();
+
+    if (zero_out_msgid) {
+        lassert(_self->transport == OUTPUT_DNSSIM_TRANSPORT_HTTPS2, "transport must be set to HTTP/2 to set zero_out_msgid");
+        _self->h2_zero_out_msgid = zero_out_msgid;
+    }
+}
+
+static void _on_stats_timer_tick(uv_timer_t* handle)
+{
+    uint64_t         now_ms = _now_ms();
+    output_dnssim_t* self;
+    mlassert(handle, "handle is nil");
+    self = (output_dnssim_t*)handle->data;
+    mlassert_self();
+    lassert(self->stats_sum, "stats_sum is nil");
+    lassert(self->stats_current, "stats_current is nil");
+
+    lnotice("total processed:%10ld; answers:%10ld; discarded:%10ld; ongoing:%10ld",
+        self->processed, self->stats_sum->answers, self->discarded, self->ongoing);
+
+    output_dnssim_stats_t* stats_next;
+    lfatal_oom(stats_next = calloc(1, sizeof(output_dnssim_stats_t)));
+    lfatal_oom(stats_next->latency = calloc(self->timeout_ms + 1, sizeof(uint64_t)));
+
+    self->stats_current->until_ms = now_ms;
+    stats_next->since_ms          = now_ms;
+    stats_next->conn_active       = self->stats_current->conn_active;
+
+    stats_next->ongoing       = self->ongoing;
+    stats_next->prev          = self->stats_current;
+    self->stats_current->next = stats_next;
+    self->stats_current       = stats_next;
+}
+
+void output_dnssim_stats_collect(output_dnssim_t* self, uint64_t interval_ms)
+{
+    uint64_t now_ms = _now_ms();
+    mlassert_self();
+    lassert(self->stats_sum, "stats_sum is nil");
+    lassert(self->stats_current, "stats_current is nil");
+
+    if (self->stats_interval_ms != 0) {
+        lfatal("statistics collection has already started!");
+    }
+    self->stats_interval_ms = interval_ms;
+
+    self->stats_sum->since_ms     = now_ms;
+    self->stats_current->since_ms = now_ms;
+
+    _self->stats_timer.data = (void*)self;
+    uv_timer_init(&_self->loop, &_self->stats_timer);
+    uv_timer_start(&_self->stats_timer, _on_stats_timer_tick, interval_ms, interval_ms);
+}
+
+void output_dnssim_stats_finish(output_dnssim_t* self)
+{
+    uint64_t now_ms = _now_ms();
+    mlassert_self();
+    lassert(self->stats_sum, "stats_sum is nil");
+    lassert(self->stats_current, "stats_current is nil");
+
+    self->stats_sum->until_ms     = now_ms;
+    self->stats_current->until_ms = now_ms;
+
+    uv_timer_stop(&_self->stats_timer);
+    uv_close((uv_handle_t*)&_self->stats_timer, NULL);
+}
diff --git a/src/output/dnssim.h b/src/output/dnssim.h
new file mode 100644
index 0000000..f843000
--- /dev/null
+++ b/src/output/dnssim.h
@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2019, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "core/log.h"
+#include "core/receiver.h"
+
+#ifndef __dnsjit_output_dnssim_h
+#define __dnsjit_output_dnssim_h
+
+#include <stdbool.h>
+
+#include "output/dnssim.hh"
+
+#endif
diff --git a/src/output/dnssim.hh b/src/output/dnssim.hh
new file mode 100644
index 0000000..a17125d
--- /dev/null
+++ b/src/output/dnssim.hh
@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2018-2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+//lua:require("dnsjit.core.log")
+//lua:require("dnsjit.core.receiver_h")
+
+typedef enum output_dnssim_transport {
+    OUTPUT_DNSSIM_TRANSPORT_UDP_ONLY,
+    OUTPUT_DNSSIM_TRANSPORT_UDP,
+    OUTPUT_DNSSIM_TRANSPORT_TCP,
+    OUTPUT_DNSSIM_TRANSPORT_TLS,
+    OUTPUT_DNSSIM_TRANSPORT_HTTPS2
+} output_dnssim_transport_t;
+
+typedef enum output_dnssim_h2_method {
+    OUTPUT_DNSSIM_H2_GET,
+    OUTPUT_DNSSIM_H2_POST
+} output_dnssim_h2_method_t;
+
+typedef struct output_dnssim_stats output_dnssim_stats_t;
+struct output_dnssim_stats {
+    output_dnssim_stats_t* prev;
+    output_dnssim_stats_t* next;
+
+    uint64_t* latency;
+
+    uint64_t since_ms;
+    uint64_t until_ms;
+
+    uint64_t requests;
+    uint64_t ongoing;
+    uint64_t answers;
+
+    /* Number of connections that are open at the end of the stats interval. */
+    uint64_t conn_active;
+
+    /* Number of connection handshake attempts during the stats interval. */
+    uint64_t conn_handshakes;
+
+    /* Number of connection that have been resumed with TLS session resumption. */
+    uint64_t conn_resumed;
+
+    /* Number of timed out connection handshakes during the stats interval. */
+    uint64_t conn_handshakes_failed;
+
+    uint64_t rcode_noerror;
+    uint64_t rcode_formerr;
+    uint64_t rcode_servfail;
+    uint64_t rcode_nxdomain;
+    uint64_t rcode_notimp;
+    uint64_t rcode_refused;
+    uint64_t rcode_yxdomain;
+    uint64_t rcode_yxrrset;
+    uint64_t rcode_nxrrset;
+    uint64_t rcode_notauth;
+    uint64_t rcode_notzone;
+    uint64_t rcode_badvers;
+    uint64_t rcode_badkey;
+    uint64_t rcode_badtime;
+    uint64_t rcode_badmode;
+    uint64_t rcode_badname;
+    uint64_t rcode_badalg;
+    uint64_t rcode_badtrunc;
+    uint64_t rcode_badcookie;
+    uint64_t rcode_other;
+};
+
+typedef struct output_dnssim {
+    core_log_t _log;
+
+    uint64_t processed;
+    uint64_t discarded;
+    uint64_t ongoing;
+
+    output_dnssim_stats_t* stats_sum;
+    output_dnssim_stats_t* stats_current;
+    output_dnssim_stats_t* stats_first;
+
+    size_t max_clients;
+    bool   free_after_use;
+
+    uint64_t timeout_ms;
+    uint64_t idle_timeout_ms;
+    uint64_t handshake_timeout_ms;
+    uint64_t stats_interval_ms;
+} output_dnssim_t;
+
+core_log_t* output_dnssim_log();
+
+output_dnssim_t* output_dnssim_new(size_t max_clients);
+void             output_dnssim_free(output_dnssim_t* self);
+
+void output_dnssim_log_name(output_dnssim_t* self, const char* name);
+void output_dnssim_set_transport(output_dnssim_t* self, output_dnssim_transport_t tr);
+int  output_dnssim_target(output_dnssim_t* self, const char* ip, uint16_t port);
+int  output_dnssim_bind(output_dnssim_t* self, const char* ip);
+int  output_dnssim_tls_priority(output_dnssim_t* self, const char* priority);
+int  output_dnssim_run_nowait(output_dnssim_t* self);
+void output_dnssim_timeout_ms(output_dnssim_t* self, uint64_t timeout_ms);
+void output_dnssim_h2_uri_path(output_dnssim_t* self, const char* uri_path);
+void output_dnssim_h2_method(output_dnssim_t* self, const char* method);
+void output_dnssim_h2_zero_out_msgid(output_dnssim_t* self, bool zero_out_msgid);
+void output_dnssim_stats_collect(output_dnssim_t* self, uint64_t interval_ms);
+void output_dnssim_stats_finish(output_dnssim_t* self);
+
+core_receiver_t output_dnssim_receiver();
diff --git a/src/output/dnssim.lua b/src/output/dnssim.lua
new file mode 100644
index 0000000..25193c4
--- /dev/null
+++ b/src/output/dnssim.lua
@@ -0,0 +1,433 @@
+-- Copyright (c) 2018-2021, CZ.NIC, z.s.p.o.
+-- All rights reserved.
+--
+-- This file is part of dnsjit.
+--
+-- dnsjit is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation, either version 3 of the License, or
+-- (at your option) any later version.
+--
+-- dnsjit is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License
+-- along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+
+-- dnsjit.output.dnssim
+-- Simulate independent DNS clients over various transports
+--   output = require("dnsjit.output.dnssim").new()
+-- .SS Usage
+--   output:udp()
+--   output:target("::1", 53)
+--   recv, rctx = output:receive()
+--   -- pass in objects using recv(rctx, obj)
+--   -- repeatedly call output:run_nowait() until it returns 0
+-- .SS DNS-over-TLS example configuration
+--   output:tls("NORMAL:-VERS-ALL:+VERS-TLS1.3")  -- enforce TLS 1.3
+-- .SS DNS-over-HTTPS/2 example configuration
+--   output:https2({ method = "POST", uri_path = "/doh" })
+--
+-- Output module for simulating traffic from huge number of independent,
+-- individual DNS clients.
+-- Uses libuv for asynchronous communication.
+-- There may only be a single DnsSim in a thread.
+-- Use
+-- .I dnsjit.core.thread
+-- to have multiple DnsSim instances.
+-- .P
+-- With proper use of this component, it is possible to simulate hundreds of
+-- thousands of clients when using a high-performance server.
+-- This also applies for state-full transports.
+-- The complete set-up is quite complex and requires other components.
+-- See DNS Shotgun
+-- .RI ( https://gitlab.nic.cz/knot/shotgun )
+-- for dnsjit scripts ready for use for high-performance
+-- benchmarking.
+module(...,package.seeall)
+
+require("dnsjit.output.dnssim_h")
+local bit = require("bit")
+local object = require("dnsjit.core.objects")
+local ffi = require("ffi")
+local C = ffi.C
+
+local DnsSim = {}
+
+local _DNSSIM_VERSION = 20210129
+local _DNSSIM_JSON_VERSION = 20200527
+
+-- Create a new DnsSim output for up to max_clients.
+function DnsSim.new(max_clients)
+    local self = {
+        obj = C.output_dnssim_new(max_clients),
+        max_clients = max_clients,
+    }
+    ffi.gc(self.obj, C.output_dnssim_free)
+    return setmetatable(self, { __index = DnsSim })
+end
+
+local function _check_version(version, req_version)
+    if req_version == nil then
+        return version
+    end
+    local min_version = tonumber(req_version)
+    if min_version == nil then
+        C.output_dnssim_log():fatal("invalid version number: "..req_version)
+        return nil
+    end
+    if version >= min_version then
+        return version
+    end
+    return nil
+end
+
+-- Check that version of dnssim is at minimum the one passed as
+-- .B req_version
+-- and return the actual version number.
+-- Return nil if the condition is not met.
+--
+-- If no
+-- .B req_version
+-- is specified no check is done and only the version number is returned.
+function DnsSim.check_version(req_version)
+    return _check_version(_DNSSIM_VERSION, req_version)
+end
+
+-- Check that version of dnssim's JSON data format is at minimum the one passed as
+-- .B req_version
+-- and return the actual version number.
+-- Return nil if the condition is not met.
+--
+-- If no
+-- .B req_version
+-- is specified no check is done and only the version number is returned.
+function DnsSim.check_json_version(req_version)
+    return _check_version(_DNSSIM_JSON_VERSION, req_version)
+end
+
+-- Return the Log object to control logging of this instance or module.
+-- Optionally, set the instance's log name.
+-- Unique name should be used for each instance.
+function DnsSim:log(name)
+    if self == nil then
+        return C.output_dnssim_log()
+    end
+    if name ~= nil then
+        C.output_dnssim_log_name(self.obj, name)
+    end
+    return self.obj._log
+end
+
+-- Set the target IPv4/IPv6 address where queries will be sent to.
+function DnsSim:target(ip, port)
+    local nport = tonumber(port)
+    if nport == nil then
+        self.obj._log:fatal("invalid port: "..port)
+        return -1
+    end
+    if nport <= 0 or nport > 65535 then
+        self.obj._log:fatal("invalid port number: "..nport)
+        return -1
+    end
+    return C.output_dnssim_target(self.obj, ip, nport)
+end
+
+-- Specify source IPv4/IPv6 address for sending queries.
+-- Can be set multiple times.
+-- Addresses are selected round-robin when sending.
+function DnsSim:bind(ip)
+    return C.output_dnssim_bind(self.obj, ip)
+end
+
+-- Set the preferred transport to UDP.
+--
+-- When the optional argument
+-- .B tcp_fallback
+-- is set to true, individual queries are re-tried over TCP when TC bit is set in the answer.
+-- Defaults to
+-- .B false
+-- (aka only UDP is used).
+function DnsSim:udp(tcp_fallback)
+    if tcp_fallback == true then
+        C.output_dnssim_set_transport(self.obj, C.OUTPUT_DNSSIM_TRANSPORT_UDP)
+    else
+        C.output_dnssim_set_transport(self.obj, C.OUTPUT_DNSSIM_TRANSPORT_UDP_ONLY)
+    end
+end
+
+-- Set the transport to TCP.
+function DnsSim:tcp()
+    C.output_dnssim_set_transport(self.obj, C.OUTPUT_DNSSIM_TRANSPORT_TCP)
+end
+
+-- Set the transport to TLS.
+--
+-- The optional argument
+-- .B tls_priority
+-- is a GnuTLS priority string, which can be used to select TLS versions, cipher suites etc.
+-- For example:
+--
+-- .RB "- """ NORMAL:%NO_TICKETS """"
+-- will use defaults without TLS session resumption.
+--
+-- .RB "- """ SECURE128:-VERS-ALL:+VERS-TLS1.3 """"
+-- will use only TLS 1.3 with 128-bit secure ciphers.
+--
+-- Refer to:
+-- .I https://gnutls.org/manual/html_node/Priority-Strings.html
+function DnsSim:tls(tls_priority)
+    if tls_priority ~= nil then
+        C.output_dnssim_tls_priority(self.obj, tls_priority)
+    end
+    C.output_dnssim_set_transport(self.obj, C.OUTPUT_DNSSIM_TRANSPORT_TLS)
+end
+
+-- Set the transport to HTTP/2 over TLS.
+--
+-- .B http2_options
+-- is a lua table which supports the following keys:
+--
+-- .B method:
+-- .B GET
+-- (default)
+-- or
+-- .B POST
+--
+-- .B uri_path:
+-- where queries will be sent.
+-- Defaults to
+-- .B /dns-query
+--
+-- .B zero_out_msgid:
+-- when
+-- .B true
+-- (default), query ID is always set to 0
+--
+-- See tls() method for
+-- .B tls_priority
+-- documentation.
+function DnsSim:https2(http2_options, tls_priority)
+    if tls_priority ~= nil then
+        C.output_dnssim_tls_priority(self.obj, tls_priority)
+    end
+
+    uri_path = "/dns-query"
+    zero_out_msgid = true
+    method = "GET"
+
+    if http2_options ~= nil then
+        if type(http2_options) ~= "table" then
+            self.obj._log:fatal("http2_options must be a table")
+        else
+            if http2_options["uri_path"] ~= nil then
+                uri_path = http2_options["uri_path"]
+            end
+            if http2_options["zero_out_msgid"] ~= nil and http2_options["zero_out_msgid"] ~= true then
+                zero_out_msgid = false
+            end
+            if http2_options["method"] ~= nil then
+                method = http2_options["method"]
+            end
+        end
+    end
+
+    C.output_dnssim_set_transport(self.obj, C.OUTPUT_DNSSIM_TRANSPORT_HTTPS2)
+    C.output_dnssim_h2_uri_path(self.obj, uri_path)
+    C.output_dnssim_h2_method(self.obj, method)
+    C.output_dnssim_h2_zero_out_msgid(self.obj, zero_out_msgid)
+end
+
+-- Set timeout for the individual requests in seconds (default 2s).
+--
+-- .BR Beware :
+-- increasing this value while the target resolver isn't very responsive
+-- (cold cache, heavy load) may degrade DnsSim's performance and skew
+-- the results.
+function DnsSim:timeout(seconds)
+    if seconds == nil then
+        seconds = 2
+    end
+    timeout_ms = math.floor(seconds * 1000)
+    C.output_dnssim_timeout_ms(self.obj, timeout_ms)
+end
+
+-- Set TCP connection idle timeout for connection reuse according to RFC7766,
+-- Section 6.2.3 (defaults to 10s).
+-- When set to zero, connections are closed immediately after there are no
+-- more pending queries.
+function DnsSim:idle_timeout(seconds)
+    if seconds == nil then
+        seconds = 10
+    end
+    self.obj.idle_timeout_ms = math.floor(seconds * 1000)
+end
+
+-- Set TCP connection handshake timeout (defaults to 5s).
+-- During heavy load, the server may no longer accept new connections.
+-- This parameter ensures such connection attempts are aborted after the
+-- timeout expires.
+function DnsSim:handshake_timeout(seconds)
+    if seconds == nil then
+        seconds = 5
+    end
+    self.obj.handshake_timeout_ms = math.floor(seconds * 1000)
+end
+
+-- Run the libuv loop once without blocking when there is no I/O.
+-- This should be called repeatedly until 0 is returned and no more data
+-- is expected to be received by DnsSim.
+function DnsSim:run_nowait()
+    return C.output_dnssim_run_nowait(self.obj)
+end
+
+-- Set this to true if DnsSim should free the memory of passed-in objects
+-- (useful when using
+-- .I dnsjit.filter.copy
+-- to pass objects from different thread).
+function DnsSim:free_after_use(free_after_use)
+    self.obj.free_after_use = free_after_use
+end
+
+-- Number of input packets discarded due to various reasons.
+-- To investigate causes, run with increased logging level.
+function DnsSim:discarded()
+    return tonumber(self.obj.discarded)
+end
+
+-- Number of valid requests (input packets) processed.
+function DnsSim:requests()
+    return tonumber(self.obj.stats_sum.requests)
+end
+
+-- Number of requests that received an answer
+function DnsSim:answers()
+    return tonumber(self.obj.stats_sum.answers)
+end
+
+-- Number of requests that received a NOERROR response
+function DnsSim:noerror()
+    return tonumber(self.obj.stats_sum.rcode_noerror)
+end
+
+-- Configure statistics to be collected every N seconds.
+function DnsSim:stats_collect(seconds)
+    if seconds == nil then
+        self.obj._log:fatal("number of seconds must be set for stats_collect()")
+    end
+    interval_ms = math.floor(seconds * 1000)
+    C.output_dnssim_stats_collect(self.obj, interval_ms)
+end
+
+-- Stop the collection of statistics.
+function DnsSim:stats_finish()
+    C.output_dnssim_stats_finish(self.obj)
+end
+
+-- Export the results to a JSON file.
+function DnsSim:export(filename)
+    local file = io.open(filename, "w")
+    if file == nil then
+        self.obj._log:fatal("export failed: no filename")
+        return
+    end
+
+    local function write_stats(file, stats)
+        file:write(
+            "{ ",
+                '"since_ms":', tonumber(stats.since_ms), ',',
+                '"until_ms":', tonumber(stats.until_ms), ',',
+                '"requests":', tonumber(stats.requests), ',',
+                '"ongoing":', tonumber(stats.ongoing), ',',
+                '"answers":', tonumber(stats.answers), ',',
+                '"conn_active":', tonumber(stats.conn_active), ',',
+                '"conn_handshakes":', tonumber(stats.conn_handshakes), ',',
+                '"conn_resumed":', tonumber(stats.conn_resumed), ',',
+                '"conn_handshakes_failed":', tonumber(stats.conn_handshakes_failed), ',',
+                '"rcode_noerror":', tonumber(stats.rcode_noerror), ',',
+                '"rcode_formerr":', tonumber(stats.rcode_formerr), ',',
+                '"rcode_servfail":', tonumber(stats.rcode_servfail), ',',
+                '"rcode_nxdomain":', tonumber(stats.rcode_nxdomain), ',',
+                '"rcode_notimp":', tonumber(stats.rcode_notimp), ',',
+                '"rcode_refused":', tonumber(stats.rcode_refused), ',',
+                '"rcode_yxdomain":', tonumber(stats.rcode_yxdomain), ',',
+                '"rcode_yxrrset":', tonumber(stats.rcode_yxrrset), ',',
+                '"rcode_nxrrset":', tonumber(stats.rcode_nxrrset), ',',
+                '"rcode_notauth":', tonumber(stats.rcode_notauth), ',',
+                '"rcode_notzone":', tonumber(stats.rcode_notzone), ',',
+                '"rcode_badvers":', tonumber(stats.rcode_badvers), ',',
+                '"rcode_badkey":', tonumber(stats.rcode_badkey), ',',
+                '"rcode_badtime":', tonumber(stats.rcode_badtime), ',',
+                '"rcode_badmode":', tonumber(stats.rcode_badmode), ',',
+                '"rcode_badname":', tonumber(stats.rcode_badname), ',',
+                '"rcode_badalg":', tonumber(stats.rcode_badalg), ',',
+                '"rcode_badtrunc":', tonumber(stats.rcode_badtrunc), ',',
+                '"rcode_badcookie":', tonumber(stats.rcode_badcookie), ',',
+                '"rcode_other":', tonumber(stats.rcode_other), ',',
+                '"latency":[')
+        file:write(tonumber(stats.latency[0]))
+        for i=1,tonumber(self.obj.timeout_ms) do
+            file:write(',', tonumber(stats.latency[i]))
+        end
+        file:write("]}")
+    end
+
+    file:write(
+        "{ ",
+            '"version":', _DNSSIM_JSON_VERSION, ',',
+            '"merged":false,',
+            '"stats_interval_ms":', tonumber(self.obj.stats_interval_ms), ',',
+            '"timeout_ms":', tonumber(self.obj.timeout_ms), ',',
+            '"idle_timeout_ms":', tonumber(self.obj.idle_timeout_ms), ',',
+            '"handshake_timeout_ms":', tonumber(self.obj.handshake_timeout_ms), ',',
+            '"discarded":', self:discarded(), ',',
+            '"stats_sum":')
+    write_stats(file, self.obj.stats_sum)
+    file:write(
+            ',',
+            '"stats_periodic":[')
+
+    local stats = self.obj.stats_first
+    write_stats(file, stats)
+
+    while (stats.next ~= nil) do
+        stats = stats.next
+        file:write(',')
+        write_stats(file, stats)
+    end
+
+    file:write(']}')
+    file:close()
+    self.obj._log:notice("results exported to "..filename)
+end
+
+-- Return the C function and context for receiving objects.
+-- Only
+-- .I dnsjit.filter.core.object.ip
+-- or
+-- .I dnsjit.filter.core.object.ip6
+-- objects are supported.
+-- The component expects a 32bit integer (in host order) ranging from 0
+-- to max_clients written to first 4 bytes of destination IP.
+-- See
+-- .IR dnsjit.filter.ipsplit .
+function DnsSim:receive()
+    local receive = C.output_dnssim_receiver()
+    return receive, self.obj
+end
+
+-- Deprecated: use udp() instead.
+--
+-- Set the transport to UDP (without any TCP fallback).
+function DnsSim:udp_only()
+    C.output_dnssim_set_transport(self.obj, C.OUTPUT_DNSSIM_TRANSPORT_UDP_ONLY)
+end
+
+-- dnsjit.filter.copy (3),
+-- dnsjit.filter.ipsplit (3),
+-- dnsjit.filter.core.object.ip (3),
+-- dnsjit.filter.core.object.ip6 (3),
+-- https://gitlab.nic.cz/knot/shotgun
+return DnsSim
diff --git a/src/output/dnssim/CHANGELOG.md b/src/output/dnssim/CHANGELOG.md
new file mode 100644
index 0000000..9cbfa55
--- /dev/null
+++ b/src/output/dnssim/CHANGELOG.md
@@ -0,0 +1,16 @@
+dnssim v20210129
+================
+
+- Added DNS-over-HTTPS support with https2()
+- Added IPv4 support
+- Abort operation on insufficient file descriptors
+- Match QUESTION section of received responses
+- Improvements in connection state handling
+- Deprecate udp_only() in favor of udp()
+- Allow setting logger name with log(name)
+- Added check_version() and check_json_version()
+
+dnssim v20200723
+================
+
+- First released dnssim version with UDP, TCP and DoT support
diff --git a/src/output/dnssim/common.c b/src/output/dnssim/common.c
new file mode 100644
index 0000000..e170aec
--- /dev/null
+++ b/src/output/dnssim/common.c
@@ -0,0 +1,384 @@
+/*
+ * Copyright (c) 2019-2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/dnssim.h"
+#include "output/dnssim/internal.h"
+#include "output/dnssim/ll.h"
+#include "core/assert.h"
+
+#include <string.h>
+
+#define MAX_LABELS 127
+
+static core_log_t _log = LOG_T_INIT("output.dnssim");
+
+static void _close_request(_output_dnssim_request_t* req);
+
+static void _on_request_timeout(uv_timer_t* handle)
+{
+    _close_request((_output_dnssim_request_t*)handle->data);
+}
+
+static ssize_t parse_qsection(core_object_dns_t* dns)
+{
+    core_object_dns_q_t            q;
+    static core_object_dns_label_t labels[MAX_LABELS];
+    const uint8_t*                 start;
+    int                            i;
+    int                            ret;
+
+    if (!dns || !dns->have_qdcount)
+        return -1;
+
+    start = dns->at;
+
+    for (i = 0; i < dns->qdcount; i++) {
+        ret = core_object_dns_parse_q(dns, &q, labels, MAX_LABELS);
+        if (ret < 0)
+            return -1;
+    }
+
+    return (dns->at - start);
+}
+
+int _output_dnssim_answers_request(_output_dnssim_request_t* req, core_object_dns_t* response)
+{
+    const uint8_t* question;
+    ssize_t        len;
+
+    if (!response->have_id || !response->have_qdcount)
+        return _ERR_MALFORMED;
+
+    if (req->dns_q->id != response->id)
+        return _ERR_MSGID;
+
+    if (req->dns_q->qdcount != response->qdcount)
+        return _ERR_QUESTION;
+
+    question = response->at;
+    len      = parse_qsection(response);
+
+    if (req->question_len != len)
+        return _ERR_QUESTION;
+
+    if (memcmp(req->question, question, len) != 0)
+        return _ERR_QUESTION;
+
+    return 0;
+}
+
+void _output_dnssim_create_request(output_dnssim_t* self, _output_dnssim_client_t* client, core_object_payload_t* payload)
+{
+    int                       ret;
+    _output_dnssim_request_t* req;
+    mlassert_self();
+    lassert(client, "client is nil");
+    lassert(payload, "payload is nil");
+
+    lfatal_oom(req = calloc(1, sizeof(_output_dnssim_request_t)));
+    req->dnssim          = self;
+    req->client          = client;
+    req->payload         = payload;
+    req->dns_q           = core_object_dns_new();
+    req->dns_q->obj_prev = (core_object_t*)req->payload;
+    req->dnssim->ongoing++;
+    req->state = _OUTPUT_DNSSIM_REQ_ONGOING;
+    req->stats = self->stats_current;
+
+    ret = core_object_dns_parse_header(req->dns_q);
+    if (ret != 0) {
+        ldebug("discarded malformed dns query: couldn't parse header");
+        goto failure;
+    }
+
+    req->question     = req->dns_q->at;
+    req->question_len = parse_qsection(req->dns_q);
+    if (req->question_len < 0) {
+        ldebug("discarded malformed dns query: invalid question");
+        goto failure;
+    }
+
+    req->dnssim->stats_sum->requests++;
+    req->stats->requests++;
+
+    switch (_self->transport) {
+    case OUTPUT_DNSSIM_TRANSPORT_UDP_ONLY:
+    case OUTPUT_DNSSIM_TRANSPORT_UDP:
+        ret = _output_dnssim_create_query_udp(self, req);
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_TCP:
+        ret = _output_dnssim_create_query_tcp(self, req);
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_TLS:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        ret = _output_dnssim_create_query_tls(self, req);
+#else
+        lfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_HTTPS2:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        ret = _output_dnssim_create_query_https2(self, req);
+#else
+        lfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    default:
+        lfatal("unsupported dnssim transport");
+        break;
+    }
+    if (ret < 0) {
+        goto failure;
+    }
+
+    req->created_at = uv_now(&_self->loop);
+    req->ended_at   = req->created_at + self->timeout_ms;
+    lfatal_oom(req->timer = malloc(sizeof(uv_timer_t)));
+    uv_timer_init(&_self->loop, req->timer);
+    req->timer->data = req;
+    uv_timer_start(req->timer, _on_request_timeout, self->timeout_ms, 0);
+
+    return;
+failure:
+    self->discarded++;
+    _close_request(req);
+    return;
+}
+
+/* Bind before connect to be able to send from different source IPs. */
+int _output_dnssim_bind_before_connect(output_dnssim_t* self, uv_handle_t* handle)
+{
+    mlassert_self();
+    lassert(handle, "handle is nil");
+
+    if (_self->source != NULL) {
+        struct sockaddr* addr = (struct sockaddr*)&_self->source->addr;
+        struct sockaddr* dest = (struct sockaddr*)&_self->target;
+        int              ret  = -1;
+        if (addr->sa_family != dest->sa_family) {
+            lfatal("failed to bind: source/desitnation address family mismatch");
+        }
+        switch (handle->type) {
+        case UV_UDP:
+            ret = uv_udp_bind((uv_udp_t*)handle, addr, 0);
+            break;
+        case UV_TCP:
+            ret = uv_tcp_bind((uv_tcp_t*)handle, addr, 0);
+            break;
+        default:
+            lfatal("failed to bind: unsupported handle type");
+            break;
+        }
+        if (ret < 0) {
+            /* This typically happens when we run out of file descriptors.
+             * Quit to prevent skewed results or unexpected behaviour. */
+            lfatal("failed to bind: %s", uv_strerror(ret));
+            return ret;
+        }
+        _self->source = _self->source->next;
+    }
+    return 0;
+}
+
+void _output_dnssim_maybe_free_request(_output_dnssim_request_t* req)
+{
+    mlassert(req, "req is nil");
+
+    if (req->qry == NULL && req->timer == NULL) {
+        if (req->dnssim->free_after_use) {
+            core_object_payload_free(req->payload);
+        }
+        core_object_dns_free(req->dns_q);
+        free(req);
+    }
+}
+
+static void _close_query(_output_dnssim_query_t* qry)
+{
+    mlassert(qry, "qry is nil");
+
+    switch (qry->transport) {
+    case OUTPUT_DNSSIM_TRANSPORT_UDP:
+        _output_dnssim_close_query_udp((_output_dnssim_query_udp_t*)qry);
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_TCP:
+        _output_dnssim_close_query_tcp((_output_dnssim_query_tcp_t*)qry);
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_TLS:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        _output_dnssim_close_query_tls((_output_dnssim_query_tcp_t*)qry);
+#else
+        mlfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_HTTPS2:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        _output_dnssim_close_query_https2((_output_dnssim_query_tcp_t*)qry);
+#else
+        mlfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    default:
+        mlfatal("invalid query transport");
+        break;
+    }
+}
+
+static void _on_request_timer_closed(uv_handle_t* handle)
+{
+    _output_dnssim_request_t* req = (_output_dnssim_request_t*)handle->data;
+    mlassert(req, "req is nil");
+    free(handle);
+    req->timer = NULL;
+    _output_dnssim_maybe_free_request(req);
+}
+
+static void _close_request(_output_dnssim_request_t* req)
+{
+    if (req == NULL || req->state == _OUTPUT_DNSSIM_REQ_CLOSING)
+        return;
+    mlassert(req->state == _OUTPUT_DNSSIM_REQ_ONGOING, "request to be closed must be ongoing");
+    req->state = _OUTPUT_DNSSIM_REQ_CLOSING;
+    req->dnssim->ongoing--;
+
+    /* Calculate latency. */
+    uint64_t latency;
+    req->ended_at = uv_now(&((_output_dnssim_t*)req->dnssim)->loop);
+    latency       = req->ended_at - req->created_at;
+    if (latency > req->dnssim->timeout_ms) {
+        req->ended_at = req->created_at + req->dnssim->timeout_ms;
+        latency       = req->dnssim->timeout_ms;
+    }
+    req->stats->latency[latency]++;
+    req->dnssim->stats_sum->latency[latency]++;
+
+    if (req->timer != NULL) {
+        uv_timer_stop(req->timer);
+        uv_close((uv_handle_t*)req->timer, _on_request_timer_closed);
+    }
+
+    /* Finish any queries in flight. */
+    _output_dnssim_query_t* qry = req->qry;
+    if (qry != NULL)
+        _close_query(qry);
+
+    _output_dnssim_maybe_free_request(req);
+}
+
+void _output_dnssim_request_answered(_output_dnssim_request_t* req, core_object_dns_t* msg)
+{
+    mlassert(req, "req is nil");
+    mlassert(msg, "msg is nil");
+
+    req->dnssim->stats_sum->answers++;
+    req->stats->answers++;
+
+    switch (msg->rcode) {
+    case CORE_OBJECT_DNS_RCODE_NOERROR:
+        req->dnssim->stats_sum->rcode_noerror++;
+        req->stats->rcode_noerror++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_FORMERR:
+        req->dnssim->stats_sum->rcode_formerr++;
+        req->stats->rcode_formerr++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_SERVFAIL:
+        req->dnssim->stats_sum->rcode_servfail++;
+        req->stats->rcode_servfail++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_NXDOMAIN:
+        req->dnssim->stats_sum->rcode_nxdomain++;
+        req->stats->rcode_nxdomain++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_NOTIMP:
+        req->dnssim->stats_sum->rcode_notimp++;
+        req->stats->rcode_notimp++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_REFUSED:
+        req->dnssim->stats_sum->rcode_refused++;
+        req->stats->rcode_refused++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_YXDOMAIN:
+        req->dnssim->stats_sum->rcode_yxdomain++;
+        req->stats->rcode_yxdomain++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_YXRRSET:
+        req->dnssim->stats_sum->rcode_yxrrset++;
+        req->stats->rcode_yxrrset++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_NXRRSET:
+        req->dnssim->stats_sum->rcode_nxrrset++;
+        req->stats->rcode_nxrrset++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_NOTAUTH:
+        req->dnssim->stats_sum->rcode_notauth++;
+        req->stats->rcode_notauth++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_NOTZONE:
+        req->dnssim->stats_sum->rcode_notzone++;
+        req->stats->rcode_notzone++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_BADVERS:
+        req->dnssim->stats_sum->rcode_badvers++;
+        req->stats->rcode_badvers++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_BADKEY:
+        req->dnssim->stats_sum->rcode_badkey++;
+        req->stats->rcode_badkey++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_BADTIME:
+        req->dnssim->stats_sum->rcode_badtime++;
+        req->stats->rcode_badtime++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_BADMODE:
+        req->dnssim->stats_sum->rcode_badmode++;
+        req->stats->rcode_badmode++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_BADNAME:
+        req->dnssim->stats_sum->rcode_badname++;
+        req->stats->rcode_badname++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_BADALG:
+        req->dnssim->stats_sum->rcode_badalg++;
+        req->stats->rcode_badalg++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_BADTRUNC:
+        req->dnssim->stats_sum->rcode_badtrunc++;
+        req->stats->rcode_badtrunc++;
+        break;
+    case CORE_OBJECT_DNS_RCODE_BADCOOKIE:
+        req->dnssim->stats_sum->rcode_badcookie++;
+        req->stats->rcode_badcookie++;
+        break;
+    default:
+        req->dnssim->stats_sum->rcode_other++;
+        req->stats->rcode_other++;
+    }
+
+    _close_request(req);
+}
+
+void _output_dnssim_on_uv_alloc(uv_handle_t* handle, size_t suggested_size, uv_buf_t* buf)
+{
+    mlfatal_oom(buf->base = malloc(suggested_size));
+    buf->len = suggested_size;
+}
diff --git a/src/output/dnssim/connection.c b/src/output/dnssim/connection.c
new file mode 100644
index 0000000..eeb1ce8
--- /dev/null
+++ b/src/output/dnssim/connection.c
@@ -0,0 +1,471 @@
+/*
+ * Copyright (c) 2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/dnssim.h"
+#include "output/dnssim/internal.h"
+#include "output/dnssim/ll.h"
+#include "core/assert.h"
+
+#include <string.h>
+
+static core_log_t _log = LOG_T_INIT("output.dnssim");
+
+static bool _conn_is_connecting(_output_dnssim_connection_t* conn)
+{
+    return (conn->state >= _OUTPUT_DNSSIM_CONN_TCP_HANDSHAKE && conn->state <= _OUTPUT_DNSSIM_CONN_ACTIVE);
+}
+
+void _output_dnssim_conn_maybe_free(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be nil");
+    mlassert(conn->client, "conn must belong to a client");
+    if (conn->handle == NULL && conn->handshake_timer == NULL && conn->idle_timer == NULL) {
+        _ll_try_remove(conn->client->conn, conn);
+        if (conn->tls != NULL) {
+            free(conn->tls);
+            conn->tls = NULL;
+        }
+        if (conn->http2 != NULL) {
+            free(conn->http2);
+            conn->http2 = NULL;
+        }
+        free(conn);
+    }
+}
+
+static void _on_handshake_timer_closed(uv_handle_t* handle)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)handle->data;
+    mlassert(conn, "conn is nil");
+    mlassert(conn->handshake_timer, "conn must have handshake timer when closing it");
+    free(conn->handshake_timer);
+    conn->handshake_timer = NULL;
+    _output_dnssim_conn_maybe_free(conn);
+}
+
+static void _on_idle_timer_closed(uv_handle_t* handle)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)handle->data;
+    mlassert(conn, "conn is nil");
+    mlassert(conn->idle_timer, "conn must have idle timer when closing it");
+    free(conn->idle_timer);
+    conn->is_idle    = false;
+    conn->idle_timer = NULL;
+    _output_dnssim_conn_maybe_free(conn);
+}
+
+void _output_dnssim_conn_close(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be nil");
+    mlassert(conn->stats, "conn must have stats");
+    mlassert(conn->client, "conn must have client");
+    mlassert(conn->client->dnssim, "client must have dnssim");
+
+    output_dnssim_t* self = conn->client->dnssim;
+
+    switch (conn->state) {
+    case _OUTPUT_DNSSIM_CONN_CLOSING:
+    case _OUTPUT_DNSSIM_CONN_CLOSED:
+        return;
+    case _OUTPUT_DNSSIM_CONN_TCP_HANDSHAKE:
+    case _OUTPUT_DNSSIM_CONN_TLS_HANDSHAKE:
+        conn->stats->conn_handshakes_failed++;
+        self->stats_sum->conn_handshakes_failed++;
+        break;
+    case _OUTPUT_DNSSIM_CONN_ACTIVE:
+    case _OUTPUT_DNSSIM_CONN_CONGESTED:
+        self->stats_current->conn_active--;
+        break;
+    case _OUTPUT_DNSSIM_CONN_INITIALIZED:
+    case _OUTPUT_DNSSIM_CONN_CLOSE_REQUESTED:
+        break;
+    default:
+        lfatal("unknown conn state: %d", conn->state);
+    }
+    if (conn->prevent_close) {
+        lassert(conn->state <= _OUTPUT_DNSSIM_CONN_CLOSE_REQUESTED, "conn already closing");
+        conn->state = _OUTPUT_DNSSIM_CONN_CLOSE_REQUESTED;
+        return;
+    }
+    conn->state = _OUTPUT_DNSSIM_CONN_CLOSING;
+
+    if (conn->handshake_timer != NULL) {
+        uv_timer_stop(conn->handshake_timer);
+        uv_close((uv_handle_t*)conn->handshake_timer, _on_handshake_timer_closed);
+    }
+    if (conn->idle_timer != NULL) {
+        conn->is_idle = false;
+        uv_timer_stop(conn->idle_timer);
+        uv_close((uv_handle_t*)conn->idle_timer, _on_idle_timer_closed);
+    }
+
+    switch (_self->transport) {
+    case OUTPUT_DNSSIM_TRANSPORT_TCP:
+        _output_dnssim_tcp_close(conn);
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_TLS:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        _output_dnssim_tls_close(conn);
+#else
+        lfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_HTTPS2:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        _output_dnssim_https2_close(conn);
+#else
+        lfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    default:
+        lfatal("unsupported transport");
+        break;
+    }
+}
+
+/* Close connection or run idle timer when there are no more outstanding queries. */
+void _output_dnssim_conn_idle(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be nil");
+
+    if (conn->queued == NULL && conn->sent == NULL) {
+        if (conn->idle_timer == NULL)
+            _output_dnssim_conn_close(conn);
+        else if (!conn->is_idle) {
+            conn->is_idle = true;
+            uv_timer_again(conn->idle_timer);
+        }
+    }
+}
+
+static void _send_pending_queries(_output_dnssim_connection_t* conn)
+{
+    _output_dnssim_query_tcp_t* qry;
+    mlassert(conn, "conn is nil");
+    mlassert(conn->client, "conn->client is nil");
+    qry = (_output_dnssim_query_tcp_t*)conn->client->pending;
+
+    while (qry != NULL && conn->state == _OUTPUT_DNSSIM_CONN_ACTIVE) {
+        _output_dnssim_query_tcp_t* next = (_output_dnssim_query_tcp_t*)qry->qry.next;
+        if (qry->qry.state == _OUTPUT_DNSSIM_QUERY_PENDING_WRITE) {
+            switch (qry->qry.transport) {
+            case OUTPUT_DNSSIM_TRANSPORT_TCP:
+                _output_dnssim_tcp_write_query(conn, qry);
+                break;
+            case OUTPUT_DNSSIM_TRANSPORT_TLS:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+                _output_dnssim_tls_write_query(conn, qry);
+#else
+                mlfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+                break;
+            case OUTPUT_DNSSIM_TRANSPORT_HTTPS2:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+                _output_dnssim_https2_write_query(conn, qry);
+#else
+                mlfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+                break;
+            default:
+                mlfatal("unsupported protocol");
+                break;
+            }
+        }
+        qry = next;
+    }
+}
+
+int _output_dnssim_handle_pending_queries(_output_dnssim_client_t* client)
+{
+    int ret = 0;
+    mlassert(client, "client is nil");
+
+    if (client->pending == NULL)
+        return ret;
+
+    output_dnssim_t* self = client->dnssim;
+    mlassert(self, "client must belong to dnssim");
+
+    /* Get active connection or find out whether new connection has to be opened. */
+    bool                         is_connecting = false;
+    _output_dnssim_connection_t* conn          = client->conn;
+    while (conn != NULL) {
+        if (conn->state == _OUTPUT_DNSSIM_CONN_ACTIVE)
+            break;
+        else if (_conn_is_connecting(conn))
+            is_connecting = true;
+        conn = conn->next;
+    }
+
+    if (conn != NULL) { /* Send data right away over active connection. */
+        _send_pending_queries(conn);
+    } else if (!is_connecting) { /* No active or connecting connection -> open a new one. */
+        lfatal_oom(conn = calloc(1, sizeof(_output_dnssim_connection_t)));
+        conn->state  = _OUTPUT_DNSSIM_CONN_INITIALIZED;
+        conn->client = client;
+        conn->stats  = self->stats_current;
+        if (_self->transport == OUTPUT_DNSSIM_TRANSPORT_TLS) {
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+            ret = _output_dnssim_tls_init(conn);
+            if (ret < 0) {
+                free(conn);
+                return ret;
+            }
+#else
+            lfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        } else if (_self->transport == OUTPUT_DNSSIM_TRANSPORT_HTTPS2) {
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+            ret = _output_dnssim_https2_init(conn);
+            if (ret < 0) {
+                free(conn);
+                return ret;
+            }
+#else
+            lfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        }
+        ret = _output_dnssim_tcp_connect(self, conn);
+        if (ret < 0)
+            return ret;
+        _ll_append(client->conn, conn);
+    } /* Otherwise, pending queries wil be sent after connected callback. */
+
+    return ret;
+}
+
+void _output_dnssim_conn_activate(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(conn->client, "conn must be associated with a client");
+    mlassert(conn->client->dnssim, "client must be associated with dnssim");
+
+    uv_timer_stop(conn->handshake_timer);
+
+    conn->state = _OUTPUT_DNSSIM_CONN_ACTIVE;
+    conn->client->dnssim->stats_current->conn_active++;
+    conn->read_state            = _OUTPUT_DNSSIM_READ_STATE_DNSLEN;
+    conn->dnsbuf_len            = 2;
+    conn->dnsbuf_pos            = 0;
+    conn->dnsbuf_free_after_use = false;
+
+    _send_pending_queries(conn);
+    _output_dnssim_conn_idle(conn);
+}
+
+int _process_dnsmsg(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be nil");
+    mlassert(conn->client, "conn must have client");
+    mlassert(conn->client->dnssim, "client must have dnssim");
+
+    output_dnssim_t* self = conn->client->dnssim;
+
+    core_object_payload_t payload = CORE_OBJECT_PAYLOAD_INIT(NULL);
+    core_object_dns_t     dns_a   = CORE_OBJECT_DNS_INIT(&payload);
+
+    payload.payload = (uint8_t*)conn->dnsbuf_data;
+    payload.len     = conn->dnsbuf_len;
+
+    dns_a.obj_prev = (core_object_t*)&payload;
+    int ret        = core_object_dns_parse_header(&dns_a);
+    if (ret != 0) {
+        lwarning("tcp response malformed");
+        return _ERR_MALFORMED;
+    }
+    ldebug("tcp recv dnsmsg id: %04x", dns_a.id);
+
+    _output_dnssim_query_t* qry;
+
+    if (_self->transport == OUTPUT_DNSSIM_TRANSPORT_HTTPS2) {
+        lassert(conn->http2, "conn must have http2 ctx");
+        lassert(conn->http2->current_qry, "http2 has no current_qry");
+        lassert(conn->http2->current_qry->qry.req, "current_qry has no req");
+        lassert(conn->http2->current_qry->qry.req->dns_q, "req has no dns_q");
+
+        ret = _output_dnssim_answers_request(conn->http2->current_qry->qry.req, &dns_a);
+        switch (ret) {
+        case 0:
+            _output_dnssim_request_answered(conn->http2->current_qry->qry.req, &dns_a);
+            break;
+        case _ERR_MSGID:
+            lwarning("https2 QID mismatch: request=0x%04x, response=0x%04x",
+                conn->http2->current_qry->qry.req->dns_q->id, dns_a.id);
+            break;
+        case _ERR_QUESTION:
+        default:
+            lwarning("https2 response question mismatch");
+            break;
+        }
+    } else {
+        qry = conn->sent;
+        while (qry != NULL) {
+            if (qry->req->dns_q->id == dns_a.id) {
+                ret = _output_dnssim_answers_request(qry->req, &dns_a);
+                if (ret != 0) {
+                    lwarning("response question mismatch");
+                } else {
+                    _output_dnssim_request_answered(qry->req, &dns_a);
+                }
+                break;
+            }
+            qry = qry->next;
+        }
+    }
+
+    return 0;
+}
+
+static int _parse_dnsbuf_data(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be nil");
+    mlassert(conn->dnsbuf_pos == conn->dnsbuf_len, "attempt to parse incomplete dnsbuf_data");
+    int ret = 0;
+
+    switch (conn->read_state) {
+    case _OUTPUT_DNSSIM_READ_STATE_DNSLEN: {
+        uint16_t* p_dnslen = (uint16_t*)conn->dnsbuf_data;
+        conn->dnsbuf_len   = ntohs(*p_dnslen);
+        if (conn->dnsbuf_len == 0) {
+            mlwarning("invalid dnslen received: 0");
+            conn->dnsbuf_len = 2;
+            conn->read_state = _OUTPUT_DNSSIM_READ_STATE_DNSLEN;
+        } else if (conn->dnsbuf_len < 12) {
+            mldebug("invalid dnslen received: %d", conn->dnsbuf_len);
+            ret = -1;
+        } else {
+            mldebug("dnslen: %d", conn->dnsbuf_len);
+            conn->read_state = _OUTPUT_DNSSIM_READ_STATE_DNSMSG;
+        }
+        break;
+    }
+    case _OUTPUT_DNSSIM_READ_STATE_DNSMSG:
+        ret = _process_dnsmsg(conn);
+        if (ret) {
+            conn->read_state = _OUTPUT_DNSSIM_READ_STATE_INVALID;
+        } else {
+            conn->dnsbuf_len = 2;
+            conn->read_state = _OUTPUT_DNSSIM_READ_STATE_DNSLEN;
+        }
+        break;
+    default:
+        mlfatal("tcp invalid connection read_state");
+        break;
+    }
+
+    conn->dnsbuf_pos = 0;
+    if (conn->dnsbuf_free_after_use) {
+        conn->dnsbuf_free_after_use = false;
+        free(conn->dnsbuf_data);
+    }
+    conn->dnsbuf_data = NULL;
+
+    return ret;
+}
+
+static unsigned int _read_dns_stream_chunk(_output_dnssim_connection_t* conn, size_t len, const char* data)
+{
+    mlassert(conn, "conn can't be nil");
+    mlassert(data, "data can't be nil");
+    mlassert(len > 0, "no data to read");
+    mlassert((conn->read_state == _OUTPUT_DNSSIM_READ_STATE_DNSLEN || conn->read_state == _OUTPUT_DNSSIM_READ_STATE_DNSMSG),
+        "connection has invalid read_state");
+
+    int          ret = 0;
+    unsigned int nread;
+    size_t       expected = conn->dnsbuf_len - conn->dnsbuf_pos;
+    mlassert(expected > 0, "no data expected");
+
+    if (conn->dnsbuf_free_after_use == false && expected > len) {
+        /* Start of partial read. */
+        mlassert(conn->dnsbuf_pos == 0, "conn->dnsbuf_pos must be 0 at start of partial read");
+        mlassert(conn->dnsbuf_len > 0, "conn->dnsbuf_len must be set at start of partial read");
+        mlfatal_oom(conn->dnsbuf_data = malloc(conn->dnsbuf_len * sizeof(char)));
+        conn->dnsbuf_free_after_use = true;
+    }
+
+    if (conn->dnsbuf_free_after_use) { /* Partial read is in progress. */
+        char* dest = conn->dnsbuf_data + conn->dnsbuf_pos;
+        if (expected < len)
+            len = expected;
+        memcpy(dest, data, len);
+        conn->dnsbuf_pos += len;
+        nread = len;
+    } else { /* Complete and clean read. */
+        mlassert(expected <= len, "not enough data to perform complete read");
+        conn->dnsbuf_data = (char*)data;
+        conn->dnsbuf_pos  = conn->dnsbuf_len;
+        nread             = expected;
+    }
+
+    /* If entire dnslen/dnsmsg was read, attempt to parse it. */
+    if (conn->dnsbuf_len == conn->dnsbuf_pos) {
+        ret = _parse_dnsbuf_data(conn);
+        if (ret < 0)
+            return ret;
+    }
+
+    return nread;
+}
+
+void _output_dnssim_read_dns_stream(_output_dnssim_connection_t* conn, size_t len, const char* data)
+{
+    int pos   = 0;
+    int chunk = 0;
+    while (pos < len) {
+        chunk = _read_dns_stream_chunk(conn, len - pos, data + pos);
+        if (chunk < 0) {
+            mlwarning("lost orientation in DNS stream, closing");
+            _output_dnssim_conn_close(conn);
+            break;
+        } else {
+            pos += chunk;
+        }
+    }
+    mlassert((pos == len) || (chunk < 0), "dns stream read invalid, pos != len");
+}
+
+void _output_dnssim_read_dnsmsg(_output_dnssim_connection_t* conn, size_t len, const char* data)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(len > 0, "len is zero");
+    mlassert(data, "no data");
+    mlassert(conn->dnsbuf_pos == 0, "dnsbuf not empty");
+    mlassert(conn->dnsbuf_free_after_use == false, "dnsbuf read in progress");
+
+    /* Read dnsmsg of given length from input data. */
+    conn->dnsbuf_len = len;
+    conn->read_state = _OUTPUT_DNSSIM_READ_STATE_DNSMSG;
+    int nread        = _read_dns_stream_chunk(conn, len, data);
+
+    if (nread != len) {
+        mlwarning("failed to read received dnsmsg");
+        if (conn->dnsbuf_free_after_use)
+            free(conn->dnsbuf_data);
+    }
+
+    /* Clean state afterwards. */
+    conn->read_state            = _OUTPUT_DNSSIM_READ_STATE_DNSLEN;
+    conn->dnsbuf_len            = 2;
+    conn->dnsbuf_pos            = 0;
+    conn->dnsbuf_free_after_use = false;
+}
diff --git a/src/output/dnssim/https2.c b/src/output/dnssim/https2.c
new file mode 100644
index 0000000..72fcdaf
--- /dev/null
+++ b/src/output/dnssim/https2.c
@@ -0,0 +1,592 @@
+/*
+ * Copyright (c) 2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/dnssim.h"
+#include "output/dnssim/internal.h"
+#include "output/dnssim/ll.h"
+#include "core/assert.h"
+#include "lib/base64url.h"
+
+#include <gnutls/gnutls.h>
+#include <string.h>
+
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+
+#define OUTPUT_DNSSIM_MAKE_NV(NAME, VALUE, VALUELEN)                 \
+    {                                                                \
+        (uint8_t*)NAME, (uint8_t*)VALUE, sizeof(NAME) - 1, VALUELEN, \
+            NGHTTP2_NV_FLAG_NONE                                     \
+    }
+
+#define OUTPUT_DNSSIM_MAKE_NV2(NAME, VALUE)                                   \
+    {                                                                         \
+        (uint8_t*)NAME, (uint8_t*)VALUE, sizeof(NAME) - 1, sizeof(VALUE) - 1, \
+            NGHTTP2_NV_FLAG_NONE                                              \
+    }
+
+#define OUTPUT_DNSSIM_HTTP_GET_TEMPLATE "?dns="
+#define OUTPUT_DNSSIM_HTTP_GET_TEMPLATE_LEN (sizeof(OUTPUT_DNSSIM_HTTP_GET_TEMPLATE) - 1)
+#define OUTPUT_DNSSIM_HTTP2_INITIAL_MAX_CONCURRENT_STREAMS 100
+#define OUTPUT_DNSSIM_HTTP2_DEFAULT_MAX_CONCURRENT_STREAMS 0xffffffffu
+
+static core_log_t _log = LOG_T_INIT("output.dnssim");
+
+static ssize_t _http2_send(nghttp2_session* session, const uint8_t* data, size_t length, int flags, void* user_data)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)user_data;
+    mlassert(conn, "conn can't be null");
+    mlassert(conn->tls, "conn must have tls ctx");
+    mlassert(conn->tls->session, "conn must have tls session");
+
+    mldebug("http2 (%p): sending data, len=%ld", session, length);
+
+    ssize_t len = 0;
+    if ((len = gnutls_record_send(conn->tls->session, data, length)) < 0) {
+        mlwarning("gnutls_record_send failed: %s", gnutls_strerror(len));
+        len = NGHTTP2_ERR_CALLBACK_FAILURE;
+    }
+
+    return len;
+}
+
+static ssize_t _http2_on_data_provider_read(nghttp2_session* session, int32_t stream_id, uint8_t* buf, size_t length, uint32_t* data_flags, nghttp2_data_source* source, void* user_data)
+{
+    _output_dnssim_https2_data_provider_t* buffer = source->ptr;
+    mlassert(buffer, "no data provider");
+    mlassert(buffer->len <= MAX_DNSMSG_SIZE, "invalid dnsmsg size: %zu B", buffer->len);
+
+    ssize_t sent = (length < buffer->len) ? length : buffer->len;
+    mlassert(sent >= 0, "negative length of bytes to send");
+
+    memcpy(buf, buffer->buf, sent);
+    buffer->buf += sent;
+    buffer->len -= sent;
+    if (buffer->len == 0)
+        *data_flags |= NGHTTP2_DATA_FLAG_EOF;
+
+    return sent;
+}
+
+static _output_dnssim_query_tcp_t* _http2_get_stream_qry(_output_dnssim_connection_t* conn, int32_t stream_id)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(stream_id >= 0, "invalid stream_id");
+
+    _output_dnssim_query_tcp_t* qry = (_output_dnssim_query_tcp_t*)conn->sent;
+    while (qry != NULL && qry->stream_id != stream_id) {
+        qry = (_output_dnssim_query_tcp_t*)qry->qry.next;
+    }
+
+    return qry;
+}
+
+static int _http2_on_header(nghttp2_session* session, const nghttp2_frame* frame, const uint8_t* name, size_t namelen, const uint8_t* value, size_t valuelen, uint8_t flags, void* user_data)
+{
+    if (frame->hd.type == NGHTTP2_HEADERS && frame->headers.cat == NGHTTP2_HCAT_RESPONSE) {
+        if (namelen == 7 && strncmp((char*)name, ":status", 7) == 0) {
+            if (valuelen != 3 || (value[0] != '1' && value[0] != '2')) {
+                /* When reponse code isn't 1xx or 2xx, close the query.
+                 * This will result in request timeout, which currently seems
+                 * slightly better than mocking SERVFAIL for statistics. */
+                _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)user_data;
+                mlassert(conn, "conn is nil");
+                _output_dnssim_query_tcp_t* qry = _http2_get_stream_qry(conn, frame->hd.stream_id);
+
+                if (qry != NULL) {
+                    _output_dnssim_close_query_https2(qry);
+                    mlinfo("http response %s, closing query", value);
+                }
+            }
+        }
+    }
+    return 0;
+}
+
+static int _http2_on_data_recv(nghttp2_session* session, uint8_t flags, int32_t stream_id, const uint8_t* data, size_t len, void* user_data)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)user_data;
+    mlassert(conn, "conn is nil");
+
+    _output_dnssim_query_tcp_t* qry = _http2_get_stream_qry(conn, stream_id);
+
+    mldebug("http2: data chunk recv, session=%p, len=%d", session, len);
+
+    if (qry) {
+        if (qry->recv_buf_len == 0) {
+            if (len > MAX_DNSMSG_SIZE) {
+                mlwarning("http response exceeded maximum size of dns message");
+                return -1;
+            }
+            mlfatal_oom(qry->recv_buf = malloc(len));
+            memcpy(qry->recv_buf, data, len);
+            qry->recv_buf_len = len;
+        } else {
+            size_t total_len = qry->recv_buf_len + len;
+            if (total_len > MAX_DNSMSG_SIZE) {
+                mlwarning("http response exceeded maximum size of dns message");
+                return -1;
+            }
+            mlfatal_oom(qry->recv_buf = realloc(qry->recv_buf, total_len));
+            memcpy(qry->recv_buf + qry->recv_buf_len, data, len);
+            qry->recv_buf_len = total_len;
+        }
+    } else {
+        mldebug("no query associated with this stream id, ignoring");
+    }
+
+    return 0;
+}
+
+static void _http2_check_max_streams(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be null");
+    mlassert(conn->http2, "conn must have http2 ctx");
+
+    switch (conn->state) {
+    case _OUTPUT_DNSSIM_CONN_ACTIVE:
+        if (conn->http2->open_streams >= conn->http2->max_concurrent_streams) {
+            mlinfo("http2 (%p): reached maximum number of concurrent streams (%ld)",
+                conn->http2->session, conn->http2->max_concurrent_streams);
+            conn->state = _OUTPUT_DNSSIM_CONN_CONGESTED;
+        }
+        break;
+    case _OUTPUT_DNSSIM_CONN_CONGESTED:
+        if (conn->http2->open_streams < conn->http2->max_concurrent_streams)
+            conn->state = _OUTPUT_DNSSIM_CONN_ACTIVE;
+        break;
+    default:
+        break;
+    }
+}
+
+static int _http2_on_stream_close(nghttp2_session* session, int32_t stream_id, uint32_t error_code, void* user_data)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)user_data;
+    mlassert(conn, "conn can't be null");
+    mlassert(conn->http2, "conn must have http2 ctx");
+    mlassert(conn->http2->open_streams > 0, "conn has no open streams");
+
+    conn->http2->open_streams--;
+    _http2_check_max_streams(conn);
+    return 0;
+}
+
+static int _http2_on_frame_recv(nghttp2_session* session, const nghttp2_frame* frame, void* user_data)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)user_data;
+    mlassert(conn, "conn can't be null");
+    mlassert(conn->tls, "conn must have tls ctx");
+    mlassert(conn->tls->session, "conn must have tls session");
+    mlassert(conn->http2, "conn must have http2 ctx");
+
+    switch (frame->hd.type) {
+    case NGHTTP2_DATA:
+        if (frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
+            mldebug("http2 (%p): final DATA frame recv", session);
+            _output_dnssim_query_tcp_t* qry = _http2_get_stream_qry(conn, frame->hd.stream_id);
+
+            if (qry != NULL) {
+                conn->http2->current_qry = qry;
+                _output_dnssim_read_dnsmsg(conn, qry->recv_buf_len, (char*)qry->recv_buf);
+            }
+        }
+        break;
+    case NGHTTP2_SETTINGS:
+        if (!conn->http2->remote_settings_received) {
+            /* On the first SETTINGS frame, set concurrent streams to unlimited, same as nghttp2. */
+            conn->http2->remote_settings_received = true;
+            conn->http2->max_concurrent_streams   = OUTPUT_DNSSIM_HTTP2_DEFAULT_MAX_CONCURRENT_STREAMS;
+            _http2_check_max_streams(conn);
+        }
+        nghttp2_settings* settings = (nghttp2_settings*)frame;
+        int               i;
+        for (i = 0; i < settings->niv; i++) {
+            switch (settings->iv[i].settings_id) {
+            case NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS:
+                conn->http2->max_concurrent_streams = settings->iv[i].value;
+                _http2_check_max_streams(conn);
+                break;
+            default:
+                break;
+            }
+        }
+        break;
+    default:
+        break;
+    }
+    return 0;
+}
+
+int _output_dnssim_https2_init(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(conn->tls == NULL, "conn already has tls context");
+    mlassert(conn->http2 == NULL, "conn already has http2 context");
+    mlassert(conn->client, "conn must be associated with a client");
+    mlassert(conn->client->dnssim, "client must have dnssim");
+
+    int                        ret = -1;
+    nghttp2_session_callbacks* callbacks;
+    nghttp2_option*            option;
+    output_dnssim_t*           self = conn->client->dnssim;
+
+    /* Initialize TLS session. */
+    ret = _output_dnssim_tls_init(conn);
+    if (ret < 0)
+        return ret;
+
+    /* Configure ALPN to negotiate HTTP/2. */
+    const gnutls_datum_t protos[] = {
+        { (unsigned char*)"h2", 2 }
+    };
+    ret = gnutls_alpn_set_protocols(conn->tls->session, protos, 1, 0);
+    if (ret < 0) {
+        lwarning("failed to set ALPN protocol: %s", gnutls_strerror(ret));
+        return ret;
+    }
+
+    lfatal_oom(conn->http2 = calloc(1, sizeof(_output_dnssim_http2_ctx_t)));
+    conn->http2->max_concurrent_streams = OUTPUT_DNSSIM_HTTP2_INITIAL_MAX_CONCURRENT_STREAMS;
+
+    /* Set up HTTP/2 callbacks and client. */
+    lassert(nghttp2_session_callbacks_new(&callbacks) == 0, "out of memory");
+    nghttp2_session_callbacks_set_send_callback(callbacks, _http2_send);
+    nghttp2_session_callbacks_set_on_header_callback(callbacks, _http2_on_header);
+    nghttp2_session_callbacks_set_on_data_chunk_recv_callback(callbacks, _http2_on_data_recv);
+    nghttp2_session_callbacks_set_on_frame_recv_callback(callbacks, _http2_on_frame_recv);
+    nghttp2_session_callbacks_set_on_stream_close_callback(callbacks, _http2_on_stream_close);
+
+    lassert(nghttp2_option_new(&option) == 0, "out of memory");
+    nghttp2_option_set_peer_max_concurrent_streams(option, conn->http2->max_concurrent_streams);
+
+    ret = nghttp2_session_client_new2(&conn->http2->session, callbacks, conn, option);
+
+    nghttp2_session_callbacks_del(callbacks);
+    nghttp2_option_del(option);
+
+    if (ret < 0) {
+        free(conn->http2);
+        conn->http2 = NULL;
+    }
+
+    return ret;
+}
+
+int _output_dnssim_https2_setup(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(conn->tls, "conn must have tls ctx");
+    mlassert(conn->tls->session, "conn must have tls session");
+    mlassert(conn->http2, "conn must have http2 ctx");
+    mlassert(conn->http2->session, "conn must have http2 session");
+
+    int ret = -1;
+
+    /* Check "h2" protocol was negotiated with ALPN. */
+    gnutls_datum_t proto;
+    ret = gnutls_alpn_get_selected_protocol(conn->tls->session, &proto);
+    if (ret < 0) {
+        mlwarning("http2: failed to get negotiated protocol: %s", gnutls_strerror(ret));
+        return ret;
+    }
+    if (proto.size != 2 || memcmp("h2", proto.data, 2) != 0) {
+        mlwarning("http2: protocol is not negotiated");
+        return ret;
+    }
+
+    /* Submit SETTIGNS frame. */
+    static const nghttp2_settings_entry iv[] = {
+        { NGHTTP2_SETTINGS_MAX_FRAME_SIZE, MAX_DNSMSG_SIZE },
+        { NGHTTP2_SETTINGS_ENABLE_PUSH, 0 }, /* Only we can initiate streams. */
+    };
+    ret = nghttp2_submit_settings(conn->http2->session, NGHTTP2_FLAG_NONE, iv, sizeof(iv) / sizeof(*iv));
+    if (ret < 0) {
+        mlwarning("http2: failed to submit SETTINGS: %s", nghttp2_strerror(ret));
+        return ret;
+    }
+
+    ret = 0;
+    return ret;
+}
+
+void _output_dnssim_https2_process_input_data(_output_dnssim_connection_t* conn, size_t len, const char* data)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(conn->http2, "conn must have http2 ctx");
+    mlassert(conn->http2->session, "conn must have http2 session");
+
+    /* Process incoming frames. */
+    ssize_t ret         = 0;
+    conn->prevent_close = true;
+    ret                 = nghttp2_session_mem_recv(conn->http2->session, (uint8_t*)data, len);
+    conn->prevent_close = false;
+    if (ret < 0) {
+        mlwarning("failed nghttp2_session_mem_recv: %s", nghttp2_strerror(ret));
+        _output_dnssim_conn_close(conn);
+        return;
+    } else if (conn->state == _OUTPUT_DNSSIM_CONN_CLOSE_REQUESTED) {
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+    mlassert(ret == len, "nghttp2_session_mem_recv didn't process all data");
+
+    /* Send any frames the read might have triggered. */
+    ret = nghttp2_session_send(conn->http2->session);
+    if (ret < 0) {
+        mlwarning("failed nghttp2_session_send: %s", nghttp2_strerror(ret));
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+}
+
+int _output_dnssim_create_query_https2(output_dnssim_t* self, _output_dnssim_request_t* req)
+{
+    mlassert_self();
+    lassert(req, "req is nil");
+    lassert(req->client, "request must have a client associated with it");
+
+    _output_dnssim_query_tcp_t* qry;
+
+    lfatal_oom(qry = calloc(1, sizeof(_output_dnssim_query_tcp_t)));
+
+    qry->qry.transport = OUTPUT_DNSSIM_TRANSPORT_HTTPS2;
+    qry->qry.req       = req;
+    qry->qry.state     = _OUTPUT_DNSSIM_QUERY_PENDING_WRITE;
+    qry->stream_id     = -1;
+    req->qry           = &qry->qry; // TODO change when adding support for multiple Qs for req
+    _ll_append(req->client->pending, &qry->qry);
+
+    return _output_dnssim_handle_pending_queries(req->client);
+}
+
+void _output_dnssim_close_query_https2(_output_dnssim_query_tcp_t* qry)
+{
+    mlassert(qry, "qry can't be null");
+    mlassert(qry->qry.req, "query must be part of a request");
+    _output_dnssim_request_t* req = qry->qry.req;
+    mlassert(req->client, "request must belong to a client");
+
+    _ll_try_remove(req->client->pending, &qry->qry);
+    if (qry->conn) {
+        _output_dnssim_connection_t* conn = qry->conn;
+        _ll_try_remove(conn->sent, &qry->qry);
+        qry->conn = NULL;
+        _output_dnssim_conn_idle(conn);
+    }
+
+    if (qry->recv_buf != NULL)
+        free(qry->recv_buf);
+
+    _ll_remove(req->qry, &qry->qry);
+    free(qry);
+}
+
+void _output_dnssim_https2_close(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be nil");
+    mlassert(conn->http2, "conn must have http2 ctx");
+
+    nghttp2_session_del(conn->http2->session);
+    _output_dnssim_tls_close(conn);
+}
+
+static int _http2_send_query_get(_output_dnssim_connection_t* conn, _output_dnssim_query_tcp_t* qry)
+{
+    mlassert(conn, "conn can't be null");
+    mlassert(qry, "qry can't be null");
+    mlassert(qry->qry.req, "req can't be null");
+    mlassert(qry->qry.req->payload, "payload can't be null");
+    mlassert(qry->qry.req->payload->len <= MAX_DNSMSG_SIZE, "payload too big");
+    mlassert(conn->client, "conn must be associated with client");
+    mlassert(conn->client->dnssim, "client must have dnssim");
+
+    output_dnssim_t*       self    = conn->client->dnssim;
+    core_object_payload_t* content = qry->qry.req->payload;
+
+    const size_t uri_path_len = strlen(_self->h2_uri_path);
+    const size_t path_len     = uri_path_len
+                            + OUTPUT_DNSSIM_HTTP_GET_TEMPLATE_LEN
+                            + (content->len * 4) / 3 + 3  /* upper limit of base64 encoding */
+                            + 1;  /* terminating null byte */
+    if (path_len >= _MAX_URI_LEN) {
+        self->discarded++;
+        linfo("http2: uri path with query too long, query discarded");
+        return 0;
+    }
+    char path[path_len];
+    memcpy(path, _self->h2_uri_path, uri_path_len);
+    memcpy(&path[uri_path_len], OUTPUT_DNSSIM_HTTP_GET_TEMPLATE, OUTPUT_DNSSIM_HTTP_GET_TEMPLATE_LEN);
+
+    int32_t ret = base64url_encode(content->payload, content->len,
+        (uint8_t*)&path[uri_path_len + OUTPUT_DNSSIM_HTTP_GET_TEMPLATE_LEN],
+        sizeof(path) - uri_path_len - OUTPUT_DNSSIM_HTTP_GET_TEMPLATE_LEN - 1);
+    if (ret < 0) {
+        self->discarded++;
+        linfo("http2: base64url encode of query failed, query discarded");
+        return 0;
+    }
+
+    nghttp2_nv hdrs[] = {
+        OUTPUT_DNSSIM_MAKE_NV2(":method", "GET"),
+        OUTPUT_DNSSIM_MAKE_NV2(":scheme", "https"),
+        OUTPUT_DNSSIM_MAKE_NV(":authority", _self->h2_uri_authority, strlen(_self->h2_uri_authority)),
+        OUTPUT_DNSSIM_MAKE_NV(":path", path, uri_path_len + sizeof(OUTPUT_DNSSIM_HTTP_GET_TEMPLATE) - 1 + ret),
+        OUTPUT_DNSSIM_MAKE_NV2("accept", "application/dns-message"),
+    };
+
+    qry->stream_id = nghttp2_submit_request(conn->http2->session, NULL, hdrs, sizeof(hdrs) / sizeof(nghttp2_nv), NULL, NULL);
+
+    if (qry->stream_id < 0) {
+        mldebug("http2 (%p): failed to submit request: %s", conn->http2->session, nghttp2_strerror(qry->stream_id));
+        return -1;
+    }
+    mldebug("http2 (%p): GET %s", conn->http2->session, path);
+    conn->http2->open_streams++;
+    _http2_check_max_streams(conn);
+
+    ret = nghttp2_session_send(conn->http2->session);
+    if (ret < 0) {
+        mldebug("http2 (%p): failed session send: %s", conn->http2->session, nghttp2_strerror(ret));
+        return -1;
+    }
+
+    return 0;
+}
+
+static int _http2_send_query_post(_output_dnssim_connection_t* conn, _output_dnssim_query_tcp_t* qry)
+{
+    mlassert(conn, "conn can't be null");
+    mlassert(qry, "qry can't be null");
+    mlassert(qry->qry.req, "req can't be null");
+    mlassert(qry->qry.req->payload, "payload can't be null");
+    mlassert(qry->qry.req->payload->len <= MAX_DNSMSG_SIZE, "payload too big");
+    mlassert(conn->client, "conn must be associated with client");
+    mlassert(conn->client->dnssim, "client must have dnssim");
+
+    output_dnssim_t* self = conn->client->dnssim;
+
+    core_object_payload_t* content = qry->qry.req->payload;
+
+    int window_size = nghttp2_session_get_remote_window_size(conn->http2->session);
+    if (content->len > window_size) {
+        mldebug("http2 (%p): insufficient remote window size, deferring", conn->http2->session);
+        return 0;
+    }
+
+    char content_length[6]; /* max dnslen "65535" */
+    int  content_length_len = snprintf(content_length, 6, "%zd", content->len);
+
+    nghttp2_nv hdrs[] = {
+        OUTPUT_DNSSIM_MAKE_NV2(":method", "POST"),
+        OUTPUT_DNSSIM_MAKE_NV2(":scheme", "https"),
+        OUTPUT_DNSSIM_MAKE_NV(":authority", _self->h2_uri_authority, strlen(_self->h2_uri_authority)),
+        OUTPUT_DNSSIM_MAKE_NV(":path", _self->h2_uri_path, strlen(_self->h2_uri_path)),
+        OUTPUT_DNSSIM_MAKE_NV2("accept", "application/dns-message"),
+        OUTPUT_DNSSIM_MAKE_NV2("content-type", "application/dns-message"),
+        OUTPUT_DNSSIM_MAKE_NV("content-length", content_length, content_length_len)
+    };
+
+    _output_dnssim_https2_data_provider_t data = {
+        .buf = content->payload,
+        .len = content->len
+    };
+
+    nghttp2_data_provider data_provider = {
+        .source.ptr    = &data,
+        .read_callback = _http2_on_data_provider_read
+    };
+
+    qry->stream_id = nghttp2_submit_request(conn->http2->session, NULL, hdrs, sizeof(hdrs) / sizeof(nghttp2_nv), &data_provider, NULL);
+
+    if (qry->stream_id < 0) {
+        mldebug("http2 (%p): failed to submit request: %s", conn->http2->session, nghttp2_strerror(qry->stream_id));
+        return -1;
+    }
+    mldebug("http2 (%p): POST payload len=%ld", conn->http2->session, content->len);
+    conn->http2->open_streams++;
+    _http2_check_max_streams(conn);
+
+    window_size = nghttp2_session_get_stream_remote_window_size(conn->http2->session, qry->stream_id);
+    mlassert(content->len <= window_size,
+        "unsupported: http2 stream window size (%ld B) is smaller than dns payload (%ld B)",
+        window_size, content->len);
+
+    int ret = nghttp2_session_send(conn->http2->session);
+    if (ret < 0) {
+        mldebug("http2 (%p): failed session send: %s", conn->http2->session, nghttp2_strerror(ret));
+        return -1;
+    }
+
+    return 0;
+}
+
+void _output_dnssim_https2_write_query(_output_dnssim_connection_t* conn, _output_dnssim_query_tcp_t* qry)
+{
+    mlassert(qry, "qry can't be null");
+    mlassert(qry->qry.state == _OUTPUT_DNSSIM_QUERY_PENDING_WRITE, "qry must be pending write");
+    mlassert(conn, "conn can't be null");
+    mlassert(conn->state == _OUTPUT_DNSSIM_CONN_ACTIVE, "connection state != ACTIVE");
+    mlassert(conn->http2, "conn must have http2 ctx");
+    mlassert(conn->http2->session, "conn must have http2 session");
+    mlassert(conn->client, "conn must be associated with client");
+    mlassert(conn->client->pending, "conn has no pending queries");
+    mlassert(conn->client->dnssim, "client must have dnssim");
+
+    int              ret  = 0;
+    output_dnssim_t* self = conn->client->dnssim;
+
+    if (!nghttp2_session_check_request_allowed(conn->http2->session)) {
+        mldebug("http2 (%p): request not allowed", conn->http2->session);
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+
+    switch (_self->h2_method) {
+    case OUTPUT_DNSSIM_H2_POST:
+        ret = _http2_send_query_post(conn, qry);
+        break;
+    case OUTPUT_DNSSIM_H2_GET:
+        ret = _http2_send_query_get(conn, qry);
+        break;
+    default:
+        lfatal("http2: unsupported method");
+    }
+
+    if (ret < 0) {
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+
+    qry->conn = conn;
+    _ll_remove(conn->client->pending, &qry->qry);
+    _ll_append(conn->sent, &qry->qry);
+
+    /* Stop idle timer, since there are queries to answer now. */
+    if (conn->idle_timer != NULL) {
+        conn->is_idle = false;
+        uv_timer_stop(conn->idle_timer);
+    }
+
+    qry->qry.state = _OUTPUT_DNSSIM_QUERY_SENT;
+}
+
+#endif
diff --git a/src/output/dnssim/internal.h b/src/output/dnssim/internal.h
new file mode 100644
index 0000000..b9feddf
--- /dev/null
+++ b/src/output/dnssim/internal.h
@@ -0,0 +1,343 @@
+/*
+ * Copyright (c) 2019-2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __dnsjit_output_dnssim_internal_h
+#define __dnsjit_output_dnssim_internal_h
+
+#include <gnutls/gnutls.h>
+#include <nghttp2/nghttp2.h>
+#include <uv.h>
+#include "core/object/dns.h"
+#include "core/object/payload.h"
+
+#define DNSSIM_MIN_GNUTLS_VERSION 0x030603
+#define DNSSIM_MIN_GNUTLS_ERRORMSG "dnssim tls/https2 transport requires GnuTLS >= 3.6.3"
+
+#define _self ((_output_dnssim_t*)self)
+#define _ERR_MALFORMED -2
+#define _ERR_MSGID -3
+#define _ERR_TC -4
+#define _ERR_QUESTION -5
+
+#define _MAX_URI_LEN 65536
+#define MAX_DNSMSG_SIZE 65535
+#define WIRE_BUF_SIZE (MAX_DNSMSG_SIZE + 2 + 16384) /** max tcplen + 2b tcplen + 16kb tls record */
+
+typedef struct _output_dnssim_request    _output_dnssim_request_t;
+typedef struct _output_dnssim_connection _output_dnssim_connection_t;
+typedef struct _output_dnssim_client     _output_dnssim_client_t;
+
+/*
+ * Query-related structures.
+ */
+
+typedef struct _output_dnssim_query _output_dnssim_query_t;
+struct _output_dnssim_query {
+    /*
+     * Next query in the list.
+     *
+     * Currently, next is used for TCP clients/connection, which makes it
+     * impossible to use for tracking multiple queries of a single request.
+     *
+     * TODO: refactor the linked lists to allow query to be part of multiple lists
+     */
+    _output_dnssim_query_t* next;
+
+    output_dnssim_transport_t transport;
+    _output_dnssim_request_t* req;
+
+    /* Query state, currently used only for TCP. */
+    enum {
+        _OUTPUT_DNSSIM_QUERY_PENDING_WRITE,
+        _OUTPUT_DNSSIM_QUERY_PENDING_WRITE_CB,
+        _OUTPUT_DNSSIM_QUERY_PENDING_CLOSE,
+        _OUTPUT_DNSSIM_QUERY_WRITE_FAILED,
+        _OUTPUT_DNSSIM_QUERY_SENT,
+        _OUTPUT_DNSSIM_QUERY_ORPHANED
+    } state;
+};
+
+typedef struct _output_dnssim_query_udp _output_dnssim_query_udp_t;
+struct _output_dnssim_query_udp {
+    _output_dnssim_query_t qry;
+
+    uv_udp_t* handle;
+    uv_buf_t  buf;
+};
+
+typedef struct _output_dnssim_query_tcp _output_dnssim_query_tcp_t;
+struct _output_dnssim_query_tcp {
+    _output_dnssim_query_t qry;
+
+    /* Connection this query is assigned to. */
+    _output_dnssim_connection_t* conn;
+
+    uv_write_t write_req;
+
+    /* Send buffers for libuv; 0 is for dnslen, 1 is for dnsmsg. */
+    uv_buf_t bufs[2];
+
+    /* HTTP/2 stream id that was used to send this query. */
+    int32_t stream_id;
+
+    /* HTTP/2 expected content length. */
+    int32_t content_len;
+
+    /* Receive buffer (currently used only by HTTP/2). */
+    uint8_t* recv_buf;
+    ssize_t  recv_buf_len;
+};
+
+struct _output_dnssim_request {
+    /* List of queries associated with this request. */
+    _output_dnssim_query_t* qry;
+
+    /* Client this request belongs to. */
+    _output_dnssim_client_t* client;
+
+    /* The DNS question to be resolved. */
+    core_object_payload_t* payload;
+    core_object_dns_t*     dns_q;
+    const uint8_t*         question;
+    ssize_t                question_len;
+
+    /* Timestamps for latency calculation. */
+    uint64_t created_at;
+    uint64_t ended_at;
+
+    /* Timer for tracking timeout of the request. */
+    uv_timer_t* timer;
+
+    /* The output component of this request. */
+    output_dnssim_t* dnssim;
+
+    /* State of the request. */
+    enum {
+        _OUTPUT_DNSSIM_REQ_ONGOING,
+        _OUTPUT_DNSSIM_REQ_CLOSING
+    } state;
+
+    /* Statistics interval in which this request is tracked. */
+    output_dnssim_stats_t* stats;
+};
+
+/*
+ * Connection-related structures.
+ */
+
+/* Read-state of connection's data stream. */
+typedef enum _output_dnssim_read_state {
+    _OUTPUT_DNSSIM_READ_STATE_CLEAN,
+    _OUTPUT_DNSSIM_READ_STATE_DNSLEN, /* Expecting bytes of dnslen. */
+    _OUTPUT_DNSSIM_READ_STATE_DNSMSG, /* Expecting bytes of dnsmsg. */
+    _OUTPUT_DNSSIM_READ_STATE_INVALID
+} _output_dnssim_read_state_t;
+
+/* TLS-related data for a single connection. */
+typedef struct _output_dnssim_tls_ctx {
+    gnutls_session_t session;
+    uint8_t*         buf;
+    ssize_t          buf_len;
+    ssize_t          buf_pos;
+    size_t           write_queue_size;
+} _output_dnssim_tls_ctx_t;
+
+/* HTTP2 context for a single connection. */
+typedef struct _output_dnssim_http2_ctx {
+    nghttp2_session* session;
+
+    /* Query to which the dnsbuf currently being processed belongs to. */
+    _output_dnssim_query_tcp_t* current_qry;
+
+    /* Maximum number of concurrent and currently open streams. */
+    uint32_t max_concurrent_streams;
+    uint32_t open_streams;
+
+    /* Flag indicating whether we received the peer's initial SETTINGS frame. */
+    bool remote_settings_received;
+} _output_dnssim_http2_ctx_t;
+
+struct _output_dnssim_connection {
+    _output_dnssim_connection_t* next;
+
+    uv_tcp_t* handle;
+
+    /* Timeout timer for establishing the connection. */
+    uv_timer_t* handshake_timer;
+
+    /* Idle timer for connection reuse. rfc7766#section-6.2.3 */
+    uv_timer_t* idle_timer;
+    bool        is_idle;
+
+    /* List of queries that have been queued (pending write callback). */
+    _output_dnssim_query_t* queued;
+
+    /* List of queries that have been sent over this connection. */
+    _output_dnssim_query_t* sent;
+
+    /* Client this connection belongs to. */
+    _output_dnssim_client_t* client;
+
+    /* State of the connection.
+     * Numeric ordering of constants is significant and follows the typical connection lifecycle.
+     * Ensure new states are added to a proper place. */
+    enum {
+        _OUTPUT_DNSSIM_CONN_INITIALIZED     = 0,
+        _OUTPUT_DNSSIM_CONN_TCP_HANDSHAKE   = 10,
+        _OUTPUT_DNSSIM_CONN_TLS_HANDSHAKE   = 20,
+        _OUTPUT_DNSSIM_CONN_ACTIVE          = 30,
+        _OUTPUT_DNSSIM_CONN_CONGESTED       = 35,
+        _OUTPUT_DNSSIM_CONN_CLOSE_REQUESTED = 38,
+        _OUTPUT_DNSSIM_CONN_CLOSING         = 40,
+        _OUTPUT_DNSSIM_CONN_CLOSED          = 50
+    } state;
+
+    /* State of the data stream read. */
+    _output_dnssim_read_state_t read_state;
+
+    /* Total length of the expected dns data (either 2 for dnslen, or dnslen itself). */
+    size_t dnsbuf_len;
+
+    /* Current position in the receive dns buffer. */
+    size_t dnsbuf_pos;
+
+    /* Receive buffer used for incomplete messages or dnslen. */
+    char* dnsbuf_data;
+    bool  dnsbuf_free_after_use;
+
+    /* Statistics interval in which the handshake is tracked. */
+    output_dnssim_stats_t* stats;
+
+    /* TLS-related data. */
+    _output_dnssim_tls_ctx_t* tls;
+
+    /* HTTP/2-related data. */
+    _output_dnssim_http2_ctx_t* http2;
+
+    /* Prevents immediate closure of connection. Instead, connection is moved
+     * to CLOSE_REQUESTED state and setter of this flag is responsible for
+     * closing the connection when clearing this flag. */
+    bool prevent_close;
+};
+
+/*
+ * Client structure.
+ */
+
+struct _output_dnssim_client {
+    /* Dnssim component this client belongs to. */
+    output_dnssim_t* dnssim;
+
+    /* List of connections.
+     * Multiple connections may be used (e.g. some are already closed for writing).
+     */
+    _output_dnssim_connection_t* conn;
+
+    /* List of queries that are pending to be sent over any available connection. */
+    _output_dnssim_query_t* pending;
+
+    /* TLS-ticket for session resumption. */
+    gnutls_datum_t tls_ticket;
+};
+
+/*
+ * DnsSim-related structures.
+ */
+
+typedef struct _output_dnssim_source _output_dnssim_source_t;
+struct _output_dnssim_source {
+    _output_dnssim_source_t* next;
+    struct sockaddr_storage  addr;
+};
+
+typedef struct _output_dnssim _output_dnssim_t;
+struct _output_dnssim {
+    output_dnssim_t pub;
+
+    uv_loop_t  loop;
+    uv_timer_t stats_timer;
+
+    struct sockaddr_storage   target;
+    _output_dnssim_source_t*  source;
+    output_dnssim_transport_t transport;
+
+    char                      h2_uri_authority[_MAX_URI_LEN];
+    char                      h2_uri_path[_MAX_URI_LEN];
+    bool                      h2_zero_out_msgid;
+    output_dnssim_h2_method_t h2_method;
+
+    /* Array of clients, mapped by client ID (ranges from 0 to max_clients). */
+    _output_dnssim_client_t* client_arr;
+
+    gnutls_priority_t*               tls_priority;
+    gnutls_certificate_credentials_t tls_cred;
+    char                             wire_buf[WIRE_BUF_SIZE]; /* thread-local buffer for processing tls input */
+};
+
+/* Provides data for HTTP/2 data frames. */
+typedef struct {
+    const uint8_t* buf;
+    size_t         len;
+} _output_dnssim_https2_data_provider_t;
+
+/*
+ * Forward function declarations.
+ */
+
+int  _output_dnssim_bind_before_connect(output_dnssim_t* self, uv_handle_t* handle);
+int  _output_dnssim_create_query_udp(output_dnssim_t* self, _output_dnssim_request_t* req);
+int  _output_dnssim_create_query_tcp(output_dnssim_t* self, _output_dnssim_request_t* req);
+void _output_dnssim_close_query_udp(_output_dnssim_query_udp_t* qry);
+void _output_dnssim_close_query_tcp(_output_dnssim_query_tcp_t* qry);
+int  _output_dnssim_answers_request(_output_dnssim_request_t* req, core_object_dns_t* response);
+void _output_dnssim_request_answered(_output_dnssim_request_t* req, core_object_dns_t* msg);
+void _output_dnssim_maybe_free_request(_output_dnssim_request_t* req);
+void _output_dnssim_on_uv_alloc(uv_handle_t* handle, size_t suggested_size, uv_buf_t* buf);
+void _output_dnssim_create_request(output_dnssim_t* self, _output_dnssim_client_t* client, core_object_payload_t* payload);
+int  _output_dnssim_handle_pending_queries(_output_dnssim_client_t* client);
+int  _output_dnssim_tcp_connect(output_dnssim_t* self, _output_dnssim_connection_t* conn);
+void _output_dnssim_tcp_close(_output_dnssim_connection_t* conn);
+void _output_dnssim_tcp_write_query(_output_dnssim_connection_t* conn, _output_dnssim_query_tcp_t* qry);
+void _output_dnssim_conn_close(_output_dnssim_connection_t* conn);
+void _output_dnssim_conn_idle(_output_dnssim_connection_t* conn);
+int  _output_dnssim_handle_pending_queries(_output_dnssim_client_t* client);
+void _output_dnssim_conn_activate(_output_dnssim_connection_t* conn);
+void _output_dnssim_conn_maybe_free(_output_dnssim_connection_t* conn);
+void _output_dnssim_read_dns_stream(_output_dnssim_connection_t* conn, size_t len, const char* data);
+void _output_dnssim_read_dnsmsg(_output_dnssim_connection_t* conn, size_t len, const char* data);
+
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+int  _output_dnssim_create_query_tls(output_dnssim_t* self, _output_dnssim_request_t* req);
+void _output_dnssim_close_query_tls(_output_dnssim_query_tcp_t* qry);
+int  _output_dnssim_tls_init(_output_dnssim_connection_t* conn);
+void _output_dnssim_tls_process_input_data(_output_dnssim_connection_t* conn);
+void _output_dnssim_tls_close(_output_dnssim_connection_t* conn);
+void _output_dnssim_tls_write_query(_output_dnssim_connection_t* conn, _output_dnssim_query_tcp_t* qry);
+
+int  _output_dnssim_create_query_https2(output_dnssim_t* self, _output_dnssim_request_t* req);
+void _output_dnssim_close_query_https2(_output_dnssim_query_tcp_t* qry);
+int  _output_dnssim_https2_init(_output_dnssim_connection_t* conn);
+int  _output_dnssim_https2_setup(_output_dnssim_connection_t* conn);
+void _output_dnssim_https2_process_input_data(_output_dnssim_connection_t* conn, size_t len, const char* data);
+void _output_dnssim_https2_close(_output_dnssim_connection_t* conn);
+void _output_dnssim_https2_write_query(_output_dnssim_connection_t* conn, _output_dnssim_query_tcp_t* qry);
+#endif
+
+#endif
diff --git a/src/output/dnssim/ll.h b/src/output/dnssim/ll.h
new file mode 100644
index 0000000..8e0b07a
--- /dev/null
+++ b/src/output/dnssim/ll.h
@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2019-2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __dnsjit_output_dnssim_ll_h
+#define __dnsjit_output_dnssim_ll_h
+
+#include "core/assert.h"
+
+/* Utility macros for linked list structures.
+ *
+ * - "list" is the pointer to the first node of the linked list
+ * - "list" can be NULL if there are no nodes
+ * - every node has "next", which points to the next node (can be NULL)
+ */
+
+/* Append a node to the list.
+ *
+ * Only a single node can be appended - node->next must be NULL.
+ */
+#define _ll_append(list, node)                                                    \
+    {                                                                             \
+        glassert((node)->next == NULL, "node->next must be null when appending"); \
+        if ((list) == NULL)                                                       \
+            (list) = (node);                                                      \
+        else if ((node) != NULL) {                                                \
+            typeof(list) _current = (list);                                       \
+            while (_current->next != NULL)                                        \
+                _current = _current->next;                                        \
+            _current->next = node;                                                \
+        }                                                                         \
+    }
+
+/* Remove a node from the list.
+ *
+ * In strict mode, the node must be present in the list.
+ */
+#define _ll_remove_template(list, node, strict)                                                    \
+    {                                                                                              \
+        if (strict)                                                                                \
+            glassert((list), "list can't be null when removing nodes");                            \
+        if ((list) != NULL && (node) != NULL) {                                                    \
+            if ((list) == (node)) {                                                                \
+                (list)       = (node)->next;                                                       \
+                (node)->next = NULL;                                                               \
+            } else {                                                                               \
+                typeof(list) _current = (list);                                                    \
+                while (_current != NULL && _current->next != (node)) {                             \
+                    if (strict)                                                                    \
+                        glassert((_current->next), "list doesn't contain the node to be removed"); \
+                    _current = _current->next;                                                     \
+                }                                                                                  \
+                if (_current != NULL) {                                                            \
+                    _current->next = (node)->next;                                                 \
+                    (node)->next   = NULL;                                                         \
+                }                                                                                  \
+            }                                                                                      \
+        }                                                                                          \
+    }
+
+/* Remove a node from the list. */
+#define _ll_remove(list, node) _ll_remove_template((list), (node), true)
+
+/* Remove a node from the list if it's present. */
+#define _ll_try_remove(list, node) _ll_remove_template((list), (node), false)
+
+#endif
diff --git a/src/output/dnssim/tcp.c b/src/output/dnssim/tcp.c
new file mode 100644
index 0000000..1f2b619
--- /dev/null
+++ b/src/output/dnssim/tcp.c
@@ -0,0 +1,356 @@
+/*
+ * Copyright (c) 2019-2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/dnssim.h"
+#include "output/dnssim/internal.h"
+#include "output/dnssim/ll.h"
+#include "core/assert.h"
+
+#include <string.h>
+
+static core_log_t _log = LOG_T_INIT("output.dnssim");
+
+static void _move_queries_to_pending(_output_dnssim_query_tcp_t* qry)
+{
+    _output_dnssim_query_tcp_t* qry_tmp;
+    while (qry != NULL) {
+        mlassert(qry->conn, "query must be associated with conn");
+        mlassert(qry->conn->state == _OUTPUT_DNSSIM_CONN_CLOSED, "conn must be closed");
+        mlassert(qry->conn->client, "conn must be associated with client");
+        qry_tmp       = (_output_dnssim_query_tcp_t*)qry->qry.next;
+        qry->qry.next = NULL;
+        _ll_append(qry->conn->client->pending, &qry->qry);
+        qry->conn         = NULL;
+        qry->qry.state    = _OUTPUT_DNSSIM_QUERY_ORPHANED;
+        qry->stream_id    = -1;
+        qry->recv_buf_len = 0;
+        if (qry->recv_buf != NULL) {
+            free(qry->recv_buf);
+            qry->recv_buf = NULL;
+        }
+        qry = qry_tmp;
+    }
+}
+
+static void _on_tcp_closed(uv_handle_t* handle)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)handle->data;
+    mlassert(conn, "conn is nil");
+    conn->state = _OUTPUT_DNSSIM_CONN_CLOSED;
+
+    /* Orphan any queries that are still unresolved. */
+    _move_queries_to_pending((_output_dnssim_query_tcp_t*)conn->queued);
+    conn->queued = NULL;
+    _move_queries_to_pending((_output_dnssim_query_tcp_t*)conn->sent);
+    conn->sent = NULL;
+
+    /* TODO Improve client re-connect behavior in case the connection fails to
+     * establish. Currently, queries are orphaned and attempted to be re-sent
+     * along with the next query that triggers a new connection.
+     *
+     * Attempting to establish new connection immediately leads to performance
+     * issues if the number of these attempts doesn't have upper limit. */
+    ///* Ensure orhpaned queries are re-sent over a different connection. */
+    //if (_output_dnssim_handle_pending_queries(conn->client) != 0)
+    //    mlinfo("tcp: orphaned queries failed to be re-sent");
+
+    mlassert(conn->handle, "conn must have tcp handle when closing it");
+    free(conn->handle);
+    conn->handle = NULL;
+    _output_dnssim_conn_maybe_free(conn);
+}
+
+static void _on_tcp_query_written(uv_write_t* wr_req, int status)
+{
+    _output_dnssim_query_tcp_t* qry = (_output_dnssim_query_tcp_t*)wr_req->data;
+    mlassert(qry, "qry/wr_req->data is nil");
+    mlassert(qry->conn, "query must be associated with connection");
+    _output_dnssim_connection_t* conn = qry->conn;
+
+    free(((_output_dnssim_query_tcp_t*)qry)->bufs[0].base);
+
+    if (qry->qry.state == _OUTPUT_DNSSIM_QUERY_PENDING_CLOSE) {
+        qry->qry.state                = status < 0 ? _OUTPUT_DNSSIM_QUERY_WRITE_FAILED : _OUTPUT_DNSSIM_QUERY_SENT;
+        _output_dnssim_request_t* req = qry->qry.req;
+        _output_dnssim_close_query_tcp(qry);
+        _output_dnssim_maybe_free_request(req);
+        qry = NULL;
+    }
+
+    if (status < 0) {
+        if (status != UV_ECANCELED)
+            mlinfo("tcp write failed: %s", uv_strerror(status));
+        if (qry != NULL)
+            qry->qry.state = _OUTPUT_DNSSIM_QUERY_WRITE_FAILED;
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+
+    if (qry == NULL)
+        return;
+
+    /* Mark query as sent and assign it to connection. */
+    mlassert(qry->qry.state == _OUTPUT_DNSSIM_QUERY_PENDING_WRITE_CB, "invalid query state");
+    qry->qry.state = _OUTPUT_DNSSIM_QUERY_SENT;
+    if (qry->conn->state == _OUTPUT_DNSSIM_CONN_ACTIVE) {
+        mlassert(qry->conn->queued, "conn has no queued queries");
+        _ll_remove(qry->conn->queued, &qry->qry);
+        _ll_append(qry->conn->sent, &qry->qry);
+    }
+}
+
+void _output_dnssim_tcp_write_query(_output_dnssim_connection_t* conn, _output_dnssim_query_tcp_t* qry)
+{
+    mlassert(qry, "qry can't be null");
+    mlassert(qry->qry.state == _OUTPUT_DNSSIM_QUERY_PENDING_WRITE, "qry must be pending write");
+    mlassert(qry->qry.req, "req can't be null");
+    mlassert(qry->qry.req->dns_q, "dns_q can't be null");
+    mlassert(qry->qry.req->dns_q->obj_prev, "payload can't be null");
+    mlassert(conn, "conn can't be null");
+    mlassert(conn->state == _OUTPUT_DNSSIM_CONN_ACTIVE, "connection state != ACTIVE");
+    mlassert(conn->client, "conn must be associated with client");
+    mlassert(conn->client->pending, "conn has no pending queries");
+
+    mldebug("tcp write dnsmsg id: %04x", qry->qry.req->dns_q->id);
+
+    core_object_payload_t* payload = (core_object_payload_t*)qry->qry.req->dns_q->obj_prev;
+    uint16_t*              len;
+    mlfatal_oom(len = malloc(sizeof(uint16_t)));
+    *len         = htons(payload->len);
+    qry->bufs[0] = uv_buf_init((char*)len, 2);
+    qry->bufs[1] = uv_buf_init((char*)payload->payload, payload->len);
+
+    qry->conn = conn;
+    _ll_remove(conn->client->pending, &qry->qry);
+    _ll_append(conn->queued, &qry->qry);
+
+    /* Stop idle timer, since there are queries to answer now. */
+    if (conn->idle_timer != NULL) {
+        conn->is_idle = false;
+        uv_timer_stop(conn->idle_timer);
+    }
+
+    qry->write_req.data = (void*)qry;
+    uv_write(&qry->write_req, (uv_stream_t*)conn->handle, qry->bufs, 2, _on_tcp_query_written);
+    qry->qry.state = _OUTPUT_DNSSIM_QUERY_PENDING_WRITE_CB;
+}
+
+static void _on_tcp_read(uv_stream_t* handle, ssize_t nread, const uv_buf_t* buf)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)handle->data;
+    output_dnssim_t*             self = conn->client->dnssim;
+
+    if (nread > 0) {
+        mldebug("tcp nread: %d", nread);
+        switch (_self->transport) {
+        case OUTPUT_DNSSIM_TRANSPORT_TCP:
+            _output_dnssim_read_dns_stream(conn, nread, buf->base);
+            break;
+        case OUTPUT_DNSSIM_TRANSPORT_TLS:
+        case OUTPUT_DNSSIM_TRANSPORT_HTTPS2:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+            mlassert(conn->tls, "con must have tls ctx");
+            conn->tls->buf     = (uint8_t*)buf->base;
+            conn->tls->buf_pos = 0;
+            conn->tls->buf_len = nread;
+            _output_dnssim_tls_process_input_data(conn);
+#else
+            mlfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+            break;
+        default:
+            mlfatal("unsupported transport");
+            break;
+        }
+    } else if (nread < 0) {
+        if (nread != UV_EOF)
+            mlinfo("tcp conn unexpected close: %s", uv_strerror(nread));
+        _output_dnssim_conn_close(conn);
+    }
+
+    if (buf->base != NULL)
+        free(buf->base);
+}
+
+static void _on_tcp_connected(uv_connect_t* conn_req, int status)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)conn_req->handle->data;
+    mlassert(conn, "conn is nil");
+
+    free(conn_req);
+
+    if (status < 0) {
+        mldebug("tcp connect failed: %s", uv_strerror(status));
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+
+    mlassert(conn->state == _OUTPUT_DNSSIM_CONN_TCP_HANDSHAKE, "connection state != TCP_HANDSHAKE");
+    int ret = uv_read_start((uv_stream_t*)conn->handle, _output_dnssim_on_uv_alloc, _on_tcp_read);
+    if (ret < 0) {
+        mlwarning("tcp uv_read_start() failed: %s", uv_strerror(ret));
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+
+    mldebug("tcp connected");
+    mlassert(conn->client, "conn must be associated with a client");
+    mlassert(conn->client->dnssim, "client must be associated with dnssim");
+    output_dnssim_t* self = conn->client->dnssim;
+    switch (_self->transport) {
+    case OUTPUT_DNSSIM_TRANSPORT_TCP:
+        _output_dnssim_conn_activate(conn);
+        break;
+    case OUTPUT_DNSSIM_TRANSPORT_TLS:
+    case OUTPUT_DNSSIM_TRANSPORT_HTTPS2:
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+        mldebug("init tls handshake");
+        _output_dnssim_tls_process_input_data(conn); /* Initiate TLS handshake. */
+#else
+        mlfatal(DNSSIM_MIN_GNUTLS_ERRORMSG);
+#endif
+        break;
+    default:
+        lfatal("unsupported transport protocol");
+        break;
+    }
+}
+
+static void _on_connection_timeout(uv_timer_t* handle)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)handle->data;
+    _output_dnssim_conn_close(conn);
+}
+
+int _output_dnssim_tcp_connect(output_dnssim_t* self, _output_dnssim_connection_t* conn)
+{
+    mlassert_self();
+    lassert(conn, "connection can't be null");
+    lassert(conn->handle == NULL, "connection already has a handle");
+    lassert(conn->handshake_timer == NULL, "connection already has a handshake timer");
+    lassert(conn->idle_timer == NULL, "connection already has idle timer");
+    lassert(conn->state == _OUTPUT_DNSSIM_CONN_INITIALIZED, "connection state != INITIALIZED");
+
+    lfatal_oom(conn->handle = malloc(sizeof(uv_tcp_t)));
+    conn->handle->data = (void*)conn;
+    int ret            = uv_tcp_init(&_self->loop, conn->handle);
+    if (ret < 0) {
+        lwarning("failed to init uv_tcp_t");
+        goto failure;
+    }
+
+    ret = _output_dnssim_bind_before_connect(self, (uv_handle_t*)conn->handle);
+    if (ret < 0)
+        goto failure;
+
+    /* Set connection parameters. */
+    ret = uv_tcp_nodelay(conn->handle, 1);
+    if (ret < 0)
+        lwarning("tcp: failed to set TCP_NODELAY: %s", uv_strerror(ret));
+
+    /* Set connection handshake timeout. */
+    lfatal_oom(conn->handshake_timer = malloc(sizeof(uv_timer_t)));
+    uv_timer_init(&_self->loop, conn->handshake_timer);
+    conn->handshake_timer->data = (void*)conn;
+    uv_timer_start(conn->handshake_timer, _on_connection_timeout, self->handshake_timeout_ms, 0);
+
+    /* Set idle connection timer. */
+    if (self->idle_timeout_ms > 0) {
+        lfatal_oom(conn->idle_timer = malloc(sizeof(uv_timer_t)));
+        uv_timer_init(&_self->loop, conn->idle_timer);
+        conn->idle_timer->data = (void*)conn;
+
+        /* Start and stop the timer to set the repeat value without running the timer. */
+        uv_timer_start(conn->idle_timer, _on_connection_timeout, self->idle_timeout_ms, self->idle_timeout_ms);
+        uv_timer_stop(conn->idle_timer);
+    }
+
+    mldebug("tcp connecting");
+    uv_connect_t* conn_req;
+    lfatal_oom(conn_req = malloc(sizeof(uv_connect_t)));
+    ret = uv_tcp_connect(conn_req, conn->handle, (struct sockaddr*)&_self->target, _on_tcp_connected);
+    if (ret < 0)
+        goto failure;
+
+    conn->stats->conn_handshakes++;
+    conn->client->dnssim->stats_sum->conn_handshakes++;
+    conn->state = _OUTPUT_DNSSIM_CONN_TCP_HANDSHAKE;
+    return 0;
+failure:
+    _output_dnssim_conn_close(conn);
+    return ret;
+}
+
+void _output_dnssim_tcp_close(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be nil");
+
+    if (conn->handle != NULL) {
+        uv_read_stop((uv_stream_t*)conn->handle);
+        uv_close((uv_handle_t*)conn->handle, _on_tcp_closed);
+    }
+}
+
+int _output_dnssim_create_query_tcp(output_dnssim_t* self, _output_dnssim_request_t* req)
+{
+    mlassert_self();
+    lassert(req, "req is nil");
+    lassert(req->client, "request must have a client associated with it");
+
+    _output_dnssim_query_tcp_t* qry;
+
+    lfatal_oom(qry = calloc(1, sizeof(_output_dnssim_query_tcp_t)));
+
+    qry->qry.transport = OUTPUT_DNSSIM_TRANSPORT_TCP;
+    qry->qry.req       = req;
+    qry->qry.state     = _OUTPUT_DNSSIM_QUERY_PENDING_WRITE;
+    req->qry           = &qry->qry; // TODO change when adding support for multiple Qs for req
+    _ll_append(req->client->pending, &qry->qry);
+
+    return _output_dnssim_handle_pending_queries(req->client);
+}
+
+void _output_dnssim_close_query_tcp(_output_dnssim_query_tcp_t* qry)
+{
+    mlassert(qry, "qry can't be null");
+    mlassert(qry->qry.req, "query must be part of a request");
+    _output_dnssim_request_t* req = qry->qry.req;
+    mlassert(req->client, "request must belong to a client");
+
+    if ((qry->qry.state == _OUTPUT_DNSSIM_QUERY_PENDING_WRITE_CB || qry->qry.state == _OUTPUT_DNSSIM_QUERY_PENDING_CLOSE)) {
+        /* Query can't be freed until uv callback is called. */
+        qry->qry.state = _OUTPUT_DNSSIM_QUERY_PENDING_CLOSE;
+        return;
+    }
+
+    _ll_try_remove(req->client->pending, &qry->qry);
+    if (qry->conn) {
+        _output_dnssim_connection_t* conn = qry->conn;
+        _ll_try_remove(conn->queued, &qry->qry); /* edge-case of cancelled queries */
+        _ll_try_remove(conn->sent, &qry->qry);
+        qry->conn = NULL;
+        _output_dnssim_conn_idle(conn);
+    }
+
+    _ll_remove(req->qry, &qry->qry);
+    free(qry);
+}
diff --git a/src/output/dnssim/tls.c b/src/output/dnssim/tls.c
new file mode 100644
index 0000000..e87ca47
--- /dev/null
+++ b/src/output/dnssim/tls.c
@@ -0,0 +1,475 @@
+/*
+ * Copyright (c) 2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/dnssim.h"
+#include "output/dnssim/internal.h"
+#include "output/dnssim/ll.h"
+#include "core/assert.h"
+
+#include <gnutls/gnutls.h>
+#include <string.h>
+
+#if GNUTLS_VERSION_NUMBER >= DNSSIM_MIN_GNUTLS_VERSION
+
+#ifndef MIN
+#define MIN(a, b) (((a) < (b)) ? (a) : (b)) /** Minimum of two numbers **/
+#endif
+
+static core_log_t _log = LOG_T_INIT("output.dnssim");
+
+struct async_write_ctx {
+    uv_write_t                   write_req;
+    _output_dnssim_connection_t* conn;
+    char                         buf[];
+};
+
+static int _tls_handshake(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(conn->tls, "conn must have tls context");
+    mlassert(conn->client, "conn must belong to a client");
+    mlassert(conn->state <= _OUTPUT_DNSSIM_CONN_TLS_HANDSHAKE, "conn in invalid state");
+
+    /* Set TLS session resumption ticket if available. */
+    if (conn->state < _OUTPUT_DNSSIM_CONN_TLS_HANDSHAKE && conn->client->tls_ticket.size != 0) {
+        gnutls_datum_t* ticket = &conn->client->tls_ticket;
+        gnutls_session_set_data(conn->tls->session, ticket->data, ticket->size);
+    }
+    conn->state = _OUTPUT_DNSSIM_CONN_TLS_HANDSHAKE;
+
+    return gnutls_handshake(conn->tls->session);
+}
+
+void _output_dnssim_tls_process_input_data(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(conn->client, "conn must have client");
+    mlassert(conn->client->dnssim, "client must have dnssim");
+    mlassert(conn->tls, "conn must have tls ctx");
+
+    if (conn->state >= _OUTPUT_DNSSIM_CONN_CLOSING)
+        return;
+
+    output_dnssim_t* self = conn->client->dnssim;
+
+    /* Ensure TLS handshake is performed before receiving data.
+     * See https://www.gnutls.org/manual/html_node/TLS-handshake.html */
+    while (conn->state <= _OUTPUT_DNSSIM_CONN_TLS_HANDSHAKE) {
+        int err = _tls_handshake(conn);
+        mldebug("tls handshake returned: %s", gnutls_strerror(err));
+        if (err == GNUTLS_E_SUCCESS) {
+            if (gnutls_session_is_resumed(conn->tls->session))
+                conn->stats->conn_resumed++;
+            if (_self->transport == OUTPUT_DNSSIM_TRANSPORT_HTTPS2) {
+                if (_output_dnssim_https2_setup(conn) < 0) {
+                    _output_dnssim_conn_close(conn);
+                    return;
+                }
+            }
+            _output_dnssim_conn_activate(conn);
+            break;
+        } else if (err == GNUTLS_E_AGAIN) {
+            return; /* Wait for more data */
+        } else if (err == GNUTLS_E_FATAL_ALERT_RECEIVED) {
+            gnutls_alert_description_t alert = gnutls_alert_get(conn->tls->session);
+            mlwarning("gnutls_handshake failed: %s", gnutls_alert_get_name(alert));
+            _output_dnssim_conn_close(conn);
+            return;
+        } else if (gnutls_error_is_fatal(err)) {
+            mlwarning("gnutls_handshake failed: %s", gnutls_strerror_name(err));
+            _output_dnssim_conn_close(conn);
+            return;
+        }
+    }
+
+    /* See https://gnutls.org/manual/html_node/Data-transfer-and-termination.html#Data-transfer-and-termination */
+    while (true) {
+        /* Connection might have been closed due to an error, don't try to use it. */
+        if (conn->state < _OUTPUT_DNSSIM_CONN_ACTIVE || conn->state >= _OUTPUT_DNSSIM_CONN_CLOSING)
+            return;
+
+        ssize_t count = gnutls_record_recv(conn->tls->session, _self->wire_buf, WIRE_BUF_SIZE);
+        if (count > 0) {
+            switch (_self->transport) {
+            case OUTPUT_DNSSIM_TRANSPORT_TLS:
+                _output_dnssim_read_dns_stream(conn, count, _self->wire_buf);
+                break;
+            case OUTPUT_DNSSIM_TRANSPORT_HTTPS2:
+                _output_dnssim_https2_process_input_data(conn, count, _self->wire_buf);
+                break;
+            default:
+                lfatal("unsupported transport layer");
+                break;
+            }
+        } else if (count == GNUTLS_E_AGAIN) {
+            if (conn->tls->buf_pos == conn->tls->buf_len) {
+                /* See https://www.gnutls.org/manual/html_node/Asynchronous-operation.html */
+                break; /* No more data available in this libuv buffer */
+            }
+            continue;
+        } else if (count == GNUTLS_E_INTERRUPTED) {
+            continue;
+        } else if (count == GNUTLS_E_REHANDSHAKE) {
+            continue; /* Ignore rehandshake request. */
+        } else if (count < 0) {
+            mlwarning("gnutls_record_recv failed: %s", gnutls_strerror_name(count));
+            _output_dnssim_conn_close(conn);
+            return;
+        } else if (count == 0) {
+            break;
+        }
+    }
+    mlassert(conn->tls->buf_len == conn->tls->buf_pos, "tls didn't read the entire buffer");
+}
+
+static ssize_t _tls_pull(gnutls_transport_ptr_t ptr, void* buf, size_t len)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)ptr;
+    mlassert(conn != NULL, "conn is null");
+    mlassert(conn->tls != NULL, "conn must have tls ctx");
+
+    ssize_t avail = conn->tls->buf_len - conn->tls->buf_pos;
+    if (avail <= 0) {
+        mldebug("tls pull: no more data");
+        errno = EAGAIN;
+        return -1;
+    }
+
+    ssize_t transfer = MIN(avail, len);
+    memcpy(buf, conn->tls->buf + conn->tls->buf_pos, transfer);
+    conn->tls->buf_pos += transfer;
+    return transfer;
+}
+
+static void _tls_on_write_complete(uv_write_t* req, int status)
+{
+    mlassert(req->data != NULL, "uv_write req has no data pointer");
+    struct async_write_ctx*      async_ctx = (struct async_write_ctx*)req->data;
+    _output_dnssim_connection_t* conn      = async_ctx->conn;
+    mlassert(conn, "conn is nil");
+    mlassert(conn->tls, "conn must have tls ctx");
+    mlassert(conn->tls->write_queue_size > 0, "invalid write_queue_size: %d", conn->tls->write_queue_size);
+    conn->tls->write_queue_size -= 1;
+    free(req->data);
+
+    if (status < 0)
+        _output_dnssim_conn_close(conn);
+}
+
+static ssize_t _tls_vec_push(gnutls_transport_ptr_t ptr, const giovec_t* iov, int iovcnt)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)ptr;
+    mlassert(conn != NULL, "conn is null");
+    mlassert(conn->tls != NULL, "conn must have tls ctx");
+
+    if (iovcnt == 0)
+        return 0;
+
+    /*
+     * This is a little bit complicated. There are two different writes:
+     * 1. Immediate, these don't need to own the buffered data and return immediately
+     * 2. Asynchronous, these need to own the buffers until the write completes
+     * In order to avoid copying the buffer, an immediate write is tried first if possible.
+     * If it isn't possible to write the data without queueing, an asynchronous write
+     * is created (with copied buffered data).
+     */
+
+    size_t   total_len = 0;
+    uv_buf_t uv_buf[iovcnt];
+    int      i;
+    for (i = 0; i < iovcnt; ++i) {
+        uv_buf[i].base = iov[i].iov_base;
+        uv_buf[i].len  = iov[i].iov_len;
+        total_len += iov[i].iov_len;
+    }
+
+    /* Try to perform the immediate write first to avoid copy */
+    int ret = 0;
+    if (conn->tls->write_queue_size == 0) {
+        ret = uv_try_write((uv_stream_t*)conn->handle, uv_buf, iovcnt);
+        /* from libuv documentation -
+           uv_try_write will return either:
+           > 0: number of bytes written (can be less than the supplied buffer size).
+           < 0: negative error code (UV_EAGAIN is returned if no data can be sent immediately).
+           */
+        if (ret == total_len) {
+            /* All the data were buffered by libuv.
+             * Return. */
+            return ret;
+        }
+
+        if (ret < 0 && ret != UV_EAGAIN) {
+            /* uv_try_write() has returned error code other then UV_EAGAIN.
+             * Return. */
+            errno = EIO;
+            return -1;
+        }
+        /* Since we are here expression below is true
+         * (ret != total_len) && (ret >= 0 || ret == UV_EAGAIN)
+         * or the same
+         * (ret != total_len && ret >= 0) || (ret != total_len && ret == UV_EAGAIN)
+         * i.e. either occurs partial write or UV_EAGAIN.
+         * Proceed and copy data amount to owned memory and perform async write.
+         */
+        if (ret == UV_EAGAIN) {
+            /* No data were buffered, so we must buffer all the data. */
+            ret = 0;
+        }
+    }
+
+    /* Fallback when the queue is full, and it's not possible to do an immediate write */
+    char* p = malloc(sizeof(struct async_write_ctx) + total_len - ret);
+    if (p != NULL) {
+        struct async_write_ctx* async_ctx = (struct async_write_ctx*)p;
+        async_ctx->conn                   = conn;
+        char* buf                         = async_ctx->buf;
+        /* Skip data written in the partial write */
+        size_t to_skip = ret;
+        /* Copy the buffer into owned memory */
+        size_t off = 0;
+        int    i;
+        for (i = 0; i < iovcnt; ++i) {
+            if (to_skip > 0) {
+                /* Ignore current buffer if it's all skipped */
+                if (to_skip >= uv_buf[i].len) {
+                    to_skip -= uv_buf[i].len;
+                    continue;
+                }
+                /* Skip only part of the buffer */
+                uv_buf[i].base += to_skip;
+                uv_buf[i].len -= to_skip;
+                to_skip = 0;
+            }
+            memcpy(buf + off, uv_buf[i].base, uv_buf[i].len);
+            off += uv_buf[i].len;
+        }
+        uv_buf[0].base = buf;
+        uv_buf[0].len  = off;
+
+        /* Create an asynchronous write request */
+        uv_write_t* write_req = &async_ctx->write_req;
+        memset(write_req, 0, sizeof(uv_write_t));
+        write_req->data = p;
+
+        /* Perform an asynchronous write with a callback */
+        if (uv_write(write_req, (uv_stream_t*)conn->handle, uv_buf, 1, _tls_on_write_complete) == 0) {
+            ret = total_len;
+            conn->tls->write_queue_size += 1;
+        } else {
+            free(p);
+            errno = EIO;
+            ret   = -1;
+        }
+    } else {
+        errno = ENOMEM;
+        ret   = -1;
+    }
+
+    return ret;
+}
+
+int _tls_pull_timeout(gnutls_transport_ptr_t ptr, unsigned int ms)
+{
+    _output_dnssim_connection_t* conn = (_output_dnssim_connection_t*)ptr;
+    mlassert(conn != NULL, "conn is null");
+    mlassert(conn->tls != NULL, "conn must have tls ctx");
+
+    ssize_t avail = conn->tls->buf_len - conn->tls->buf_pos;
+    if (avail <= 0) {
+        errno = EAGAIN;
+        return -1;
+    }
+    return avail;
+}
+
+int _output_dnssim_tls_init(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn is nil");
+    mlassert(conn->tls == NULL, "conn already has tls context");
+
+    int ret;
+    mlfatal_oom(conn->tls = malloc(sizeof(_output_dnssim_tls_ctx_t)));
+    conn->tls->buf              = NULL;
+    conn->tls->buf_len          = 0;
+    conn->tls->buf_pos          = 0;
+    conn->tls->write_queue_size = 0;
+
+    ret = gnutls_init(&conn->tls->session, GNUTLS_CLIENT | GNUTLS_NONBLOCK);
+    if (ret < 0) {
+        mldebug("failed gnutls_init() (%s)", gnutls_strerror(ret));
+        free(conn->tls);
+        conn->tls = 0;
+        return ret;
+    }
+
+    output_dnssim_t* self = conn->client->dnssim;
+    if (_self->tls_priority == NULL) {
+        ret = gnutls_set_default_priority(conn->tls->session);
+        if (ret < 0) {
+            mldebug("failed gnutls_set_default_priority() (%s)", gnutls_strerror(ret));
+            gnutls_deinit(conn->tls->session);
+            free(conn->tls);
+            conn->tls = 0;
+            return ret;
+        }
+    } else {
+        ret = gnutls_priority_set(conn->tls->session, *_self->tls_priority);
+        if (ret < 0) {
+            mldebug("failed gnutls_priority_set() (%s)", gnutls_strerror(ret));
+            gnutls_deinit(conn->tls->session);
+            free(conn->tls);
+            conn->tls = 0;
+            return ret;
+        }
+    }
+
+    ret = gnutls_credentials_set(conn->tls->session, GNUTLS_CRD_CERTIFICATE, _self->tls_cred);
+    if (ret < 0) {
+        mldebug("failed gnutls_credentials_set() (%s)", gnutls_strerror(ret));
+        gnutls_deinit(conn->tls->session);
+        free(conn->tls);
+        conn->tls = 0;
+        return ret;
+    }
+
+    gnutls_transport_set_pull_function(conn->tls->session, _tls_pull);
+    gnutls_transport_set_pull_timeout_function(conn->tls->session, _tls_pull_timeout);
+    gnutls_transport_set_vec_push_function(conn->tls->session, _tls_vec_push);
+    gnutls_transport_set_ptr(conn->tls->session, conn);
+
+    return 0;
+}
+
+int _output_dnssim_create_query_tls(output_dnssim_t* self, _output_dnssim_request_t* req)
+{
+    mlassert_self();
+    lassert(req, "req is nil");
+    lassert(req->client, "request must have a client associated with it");
+
+    _output_dnssim_query_tcp_t* qry;
+
+    lfatal_oom(qry = calloc(1, sizeof(_output_dnssim_query_tcp_t)));
+
+    qry->qry.transport = OUTPUT_DNSSIM_TRANSPORT_TLS;
+    qry->qry.req       = req;
+    qry->qry.state     = _OUTPUT_DNSSIM_QUERY_PENDING_WRITE;
+    req->qry           = &qry->qry; // TODO change when adding support for multiple Qs for req
+    _ll_append(req->client->pending, &qry->qry);
+
+    return _output_dnssim_handle_pending_queries(req->client);
+}
+
+void _output_dnssim_close_query_tls(_output_dnssim_query_tcp_t* qry)
+{
+    mlassert(qry, "qry can't be null");
+    mlassert(qry->qry.req, "query must be part of a request");
+    _output_dnssim_request_t* req = qry->qry.req;
+    mlassert(req->client, "request must belong to a client");
+
+    _ll_try_remove(req->client->pending, &qry->qry);
+    if (qry->conn) {
+        _output_dnssim_connection_t* conn = qry->conn;
+        _ll_try_remove(conn->sent, &qry->qry);
+        qry->conn = NULL;
+        _output_dnssim_conn_idle(conn);
+    }
+
+    _ll_remove(req->qry, &qry->qry);
+    free(qry);
+}
+
+void _output_dnssim_tls_close(_output_dnssim_connection_t* conn)
+{
+    mlassert(conn, "conn can't be nil");
+    mlassert(conn->tls, "conn must have tls ctx");
+    mlassert(conn->client, "conn must belong to a client");
+
+    /* Try and get a TLS session ticket for potential resumption. */
+    int ret;
+    if (gnutls_session_get_flags(conn->tls->session) & GNUTLS_SFLAGS_SESSION_TICKET) {
+        if (conn->client->tls_ticket.size != 0) {
+            gnutls_free(conn->client->tls_ticket.data);
+        }
+        ret = gnutls_session_get_data2(conn->tls->session, &conn->client->tls_ticket);
+        if (ret < 0) {
+            mldebug("gnutls_session_get_data2 failed: %s", gnutls_strerror(ret));
+            conn->client->tls_ticket.size = 0;
+        }
+    }
+
+    gnutls_deinit(conn->tls->session);
+    _output_dnssim_tcp_close(conn);
+}
+
+void _output_dnssim_tls_write_query(_output_dnssim_connection_t* conn, _output_dnssim_query_tcp_t* qry)
+{
+    mlassert(qry, "qry can't be null");
+    mlassert(qry->qry.state == _OUTPUT_DNSSIM_QUERY_PENDING_WRITE, "qry must be pending write");
+    mlassert(qry->qry.req, "req can't be null");
+    mlassert(qry->qry.req->dns_q, "dns_q can't be null");
+    mlassert(qry->qry.req->dns_q->obj_prev, "payload can't be null");
+    mlassert(conn, "conn can't be null");
+    mlassert(conn->state == _OUTPUT_DNSSIM_CONN_ACTIVE, "connection state != ACTIVE");
+    mlassert(conn->tls, "conn must have tls ctx");
+    mlassert(conn->client, "conn must be associated with client");
+    mlassert(conn->client->pending, "conn has no pending queries");
+
+    core_object_payload_t* payload = (core_object_payload_t*)qry->qry.req->dns_q->obj_prev;
+    uint16_t               len     = htons(payload->len);
+
+    gnutls_record_cork(conn->tls->session);
+    ssize_t count = 0;
+    if ((count = gnutls_record_send(conn->tls->session, &len, sizeof(len)) < 0) || (count = gnutls_record_send(conn->tls->session, payload->payload, payload->len) < 0)) {
+        mlwarning("gnutls_record_send failed: %s", gnutls_strerror_name(count));
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+
+    const ssize_t submitted = sizeof(len) + payload->len;
+
+    int ret = gnutls_record_uncork(conn->tls->session, GNUTLS_RECORD_WAIT);
+    if (gnutls_error_is_fatal(ret)) {
+        mlinfo("gnutls_record_uncorck failed: %s", gnutls_strerror_name(ret));
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+
+    if (ret != submitted) {
+        mlwarning("gnutls_record_uncork didn't send all data");
+        _output_dnssim_conn_close(conn);
+        return;
+    }
+
+    qry->conn = conn;
+    _ll_remove(conn->client->pending, &qry->qry);
+    _ll_append(conn->sent, &qry->qry);
+
+    /* Stop idle timer, since there are queries to answer now. */
+    if (conn->idle_timer != NULL) {
+        conn->is_idle = false;
+        uv_timer_stop(conn->idle_timer);
+    }
+
+    qry->qry.state = _OUTPUT_DNSSIM_QUERY_SENT;
+}
+
+#endif
diff --git a/src/output/dnssim/udp.c b/src/output/dnssim/udp.c
new file mode 100644
index 0000000..74f8569
--- /dev/null
+++ b/src/output/dnssim/udp.c
@@ -0,0 +1,156 @@
+/*
+ * Copyright (c) 2019-2020, CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/dnssim.h"
+#include "output/dnssim/internal.h"
+#include "output/dnssim/ll.h"
+#include "core/assert.h"
+
+static core_log_t _log = LOG_T_INIT("output.dnssim");
+
+static int _process_udp_response(uv_udp_t* handle, ssize_t nread, const uv_buf_t* buf)
+{
+    _output_dnssim_query_udp_t* qry = (_output_dnssim_query_udp_t*)handle->data;
+    _output_dnssim_request_t*   req;
+    core_object_payload_t       payload = CORE_OBJECT_PAYLOAD_INIT(NULL);
+    core_object_dns_t           dns_a   = CORE_OBJECT_DNS_INIT(&payload);
+    mlassert(qry, "qry is nil");
+    mlassert(qry->qry.req, "query must be part of a request");
+    req = qry->qry.req;
+
+    payload.payload = (uint8_t*)buf->base;
+    payload.len     = nread;
+
+    dns_a.obj_prev = (core_object_t*)&payload;
+    int ret        = core_object_dns_parse_header(&dns_a);
+    if (ret != 0) {
+        mldebug("udp response malformed");
+        return _ERR_MALFORMED;
+    }
+    if (dns_a.id != req->dns_q->id) {
+        mldebug("udp response msgid mismatch %x(q) != %x(a)", req->dns_q->id, dns_a.id);
+        return _ERR_MSGID;
+    }
+    if (dns_a.tc == 1) {
+        mldebug("udp response has TC=1");
+        return _ERR_TC;
+    }
+    ret = _output_dnssim_answers_request(req, &dns_a);
+    if (ret != 0) {
+        mlwarning("udp reponse question mismatch");
+        return _ERR_QUESTION;
+    }
+
+    _output_dnssim_request_answered(req, &dns_a);
+    return 0;
+}
+
+static void _on_udp_query_recv(uv_udp_t* handle, ssize_t nread, const uv_buf_t* buf, const struct sockaddr* addr, unsigned flags)
+{
+    if (nread > 0) {
+        mldebug("udp recv: %d", nread);
+
+        // TODO handle TC=1
+        _process_udp_response(handle, nread, buf);
+    }
+
+    if (buf->base != NULL) {
+        free(buf->base);
+    }
+}
+
+static void _on_query_udp_closed(uv_handle_t* handle)
+{
+    _output_dnssim_query_udp_t* qry = (_output_dnssim_query_udp_t*)handle->data;
+    _output_dnssim_request_t*   req;
+    mlassert(qry, "qry is nil");
+    mlassert(qry->qry.req, "query must be part of a request");
+    req = qry->qry.req;
+
+    free(qry->handle);
+
+    _ll_remove(req->qry, &qry->qry);
+    free(qry);
+
+    if (req->qry == NULL)
+        _output_dnssim_maybe_free_request(req);
+}
+
+void _output_dnssim_close_query_udp(_output_dnssim_query_udp_t* qry)
+{
+    int ret;
+    mlassert(qry, "qry is nil");
+
+    ret = uv_udp_recv_stop(qry->handle);
+    if (ret < 0) {
+        mldebug("failed uv_udp_recv_stop(): %s", uv_strerror(ret));
+    }
+
+    uv_close((uv_handle_t*)qry->handle, _on_query_udp_closed);
+}
+
+int _output_dnssim_create_query_udp(output_dnssim_t* self, _output_dnssim_request_t* req)
+{
+    int                         ret;
+    _output_dnssim_query_udp_t* qry;
+    core_object_payload_t*      payload;
+    mlassert_self();
+    lassert(req, "req is nil");
+    payload = (core_object_payload_t*)req->dns_q->obj_prev;
+
+    lfatal_oom(qry = calloc(1, sizeof(_output_dnssim_query_udp_t)));
+    lfatal_oom(qry->handle = malloc(sizeof(uv_udp_t)));
+
+    qry->qry.transport = OUTPUT_DNSSIM_TRANSPORT_UDP;
+    qry->qry.req       = req;
+    qry->buf           = uv_buf_init((char*)payload->payload, payload->len);
+    qry->handle->data  = (void*)qry;
+    ret                = uv_udp_init(&_self->loop, qry->handle);
+    if (ret < 0) {
+        lwarning("failed to init uv_udp_t");
+        goto failure;
+    }
+    _ll_append(req->qry, &qry->qry);
+
+    ret = _output_dnssim_bind_before_connect(self, (uv_handle_t*)qry->handle);
+    if (ret < 0)
+        return ret;
+
+    ret = uv_udp_try_send(qry->handle, &qry->buf, 1, (struct sockaddr*)&_self->target);
+    if (ret < 0) {
+        lwarning("failed to send udp packet: %s", uv_strerror(ret));
+        return ret;
+    }
+
+    // listen for reply
+    ret = uv_udp_recv_start(qry->handle, _output_dnssim_on_uv_alloc, _on_udp_query_recv);
+    if (ret < 0) {
+        lwarning("failed uv_udp_recv_start(): %s", uv_strerror(ret));
+        return ret;
+    }
+
+    return 0;
+failure:
+    free(qry->handle);
+    free(qry);
+    return ret;
+}
diff --git a/src/output/null.c b/src/output/null.c
new file mode 100644
index 0000000..9360afd
--- /dev/null
+++ b/src/output/null.c
@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/null.h"
+#include "core/assert.h"
+#include "core/object/pcap.h"
+
+static core_log_t    _log      = LOG_T_INIT("output.null");
+static output_null_t _defaults = {
+    LOG_T_INIT_OBJ("output.null"),
+    0, 0, 0
+};
+
+core_log_t* output_null_log()
+{
+    return &_log;
+}
+
+void output_null_init(output_null_t* self)
+{
+    mlassert_self();
+
+    *self = _defaults;
+}
+
+void output_null_destroy(output_null_t* self)
+{
+    mlassert_self();
+}
+
+static void _receive(output_null_t* self, const core_object_t* obj)
+{
+    mlassert_self();
+
+    self->pkts++;
+}
+
+core_receiver_t output_null_receiver()
+{
+    return (core_receiver_t)_receive;
+}
+
+void output_null_run(output_null_t* self, int64_t num)
+{
+    mlassert_self();
+
+    if (!self->prod) {
+        lfatal("no producer set");
+    }
+
+    if (num > 0) {
+        while (num--) {
+            const core_object_t* obj = self->prod(self->ctx);
+            if (!obj)
+                break;
+
+            self->pkts++;
+        }
+    } else {
+        for (;;) {
+            const core_object_t* obj = self->prod(self->ctx);
+            if (!obj)
+                break;
+
+            self->pkts++;
+        }
+    }
+}
diff --git a/src/output/null.h b/src/output/null.h
new file mode 100644
index 0000000..b8ccf70
--- /dev/null
+++ b/src/output/null.h
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "core/log.h"
+#include "core/receiver.h"
+#include "core/producer.h"
+
+#ifndef __dnsjit_output_null_h
+#define __dnsjit_output_null_h
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "output/null.hh"
+
+#endif
diff --git a/src/output/null.hh b/src/output/null.hh
new file mode 100644
index 0000000..3f5cd33
--- /dev/null
+++ b/src/output/null.hh
@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+//lua:require("dnsjit.core.log")
+//lua:require("dnsjit.core.receiver_h")
+//lua:require("dnsjit.core.producer_h")
+
+typedef struct output_null {
+    core_log_t      _log;
+    core_producer_t prod;
+    void*           ctx;
+    size_t          pkts;
+} output_null_t;
+
+core_log_t* output_null_log();
+void        output_null_init(output_null_t* self);
+void        output_null_destroy(output_null_t* self);
+void        output_null_run(output_null_t* self, int64_t num);
+
+core_receiver_t output_null_receiver();
diff --git a/src/output/null.lua b/src/output/null.lua
new file mode 100644
index 0000000..b634c56
--- /dev/null
+++ b/src/output/null.lua
@@ -0,0 +1,80 @@
+-- Copyright (c) 2018-2021, OARC, Inc.
+-- All rights reserved.
+--
+-- This file is part of dnsjit.
+--
+-- dnsjit is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation, either version 3 of the License, or
+-- (at your option) any later version.
+--
+-- dnsjit is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License
+-- along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+
+-- dnsjit.output.null
+-- Output to nothing (/dev/null)
+--   local output = require("dnsjit.output.null").new()
+--
+-- Output module for those that doesn't really like packets.
+module(...,package.seeall)
+
+require("dnsjit.output.null_h")
+local ffi = require("ffi")
+local C = ffi.C
+
+local t_name = "output_null_t"
+local output_null_t = ffi.typeof(t_name)
+local Null = {}
+
+-- Create a new Null output.
+function Null.new()
+    local self = {
+        _producer = nil,
+        obj = output_null_t(),
+    }
+    C.output_null_init(self.obj)
+    ffi.gc(self.obj, C.output_null_destroy)
+    return setmetatable(self, { __index = Null })
+end
+
+-- Return the Log object to control logging of this instance or module.
+function Null:log()
+    if self == nil then
+        return C.output_null_log()
+    end
+    return self.obj._log
+end
+
+-- Return the C functions and context for receiving objects.
+function Null:receive()
+    return C.output_null_receiver(), self.obj
+end
+
+-- Set the producer to get objects from.
+function Null:producer(o)
+    self.obj.prod, self.obj.ctx = o:produce()
+    self._producer = o
+end
+
+-- Retrieve all objects from the producer, if the optional
+-- .I num
+-- is a positive number then stop after that amount of objects have been
+-- retrieved.
+function Null:run(num)
+    if num == nil then
+        num = -1
+    end
+    C.output_null_run(self.obj, num)
+end
+
+-- Return the number of packets we sent into the void.
+function Null:packets()
+    return tonumber(self.obj.pkts)
+end
+
+return Null
diff --git a/src/output/pcap.c b/src/output/pcap.c
new file mode 100644
index 0000000..2b2aaa8
--- /dev/null
+++ b/src/output/pcap.c
@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/pcap.h"
+#include "core/assert.h"
+#include "core/object/pcap.h"
+
+static core_log_t    _log      = LOG_T_INIT("output.pcap");
+static output_pcap_t _defaults = {
+    LOG_T_INIT_OBJ("output.pcap"),
+    0, 0
+};
+
+core_log_t* output_pcap_log()
+{
+    return &_log;
+}
+
+void output_pcap_init(output_pcap_t* self)
+{
+    mlassert_self();
+
+    *self = _defaults;
+}
+
+void output_pcap_destroy(output_pcap_t* self)
+{
+    mlassert_self();
+}
+
+int output_pcap_open(output_pcap_t* self, const char* file, int linktype, int snaplen)
+{
+    mlassert_self();
+    if (self->dumper) {
+        lfatal("PCAP already opened");
+    }
+
+    if (!(self->pcap = pcap_open_dead(linktype, snaplen))) {
+        lcritical("pcap_open_dead() failed");
+        return -1;
+    }
+
+    if (!(self->dumper = pcap_dump_open(self->pcap, file))) {
+        lcritical("pcap_dump_open() error: %s", pcap_geterr(self->pcap));
+        pcap_close(self->pcap);
+        self->pcap = 0;
+        return -1;
+    }
+
+    return 0;
+}
+
+void output_pcap_close(output_pcap_t* self)
+{
+    mlassert_self();
+    if (self->dumper) {
+        pcap_dump_close(self->dumper);
+        self->dumper = 0;
+    }
+    if (self->pcap) {
+        pcap_close(self->pcap);
+        self->pcap = 0;
+    }
+}
+
+static void _receive(output_pcap_t* self, const core_object_t* obj)
+{
+    struct pcap_pkthdr hdr;
+    mlassert_self();
+
+    while (obj) {
+        if (obj->obj_type == CORE_OBJECT_PCAP) {
+            hdr.ts.tv_sec  = ((const core_object_pcap_t*)obj)->ts.sec;
+            hdr.ts.tv_usec = ((const core_object_pcap_t*)obj)->ts.nsec / 1000;
+            hdr.caplen     = ((const core_object_pcap_t*)obj)->caplen;
+            hdr.len        = ((const core_object_pcap_t*)obj)->len;
+
+            pcap_dump((void*)self->dumper, &hdr, ((const core_object_pcap_t*)obj)->bytes);
+            return;
+        }
+        obj = obj->obj_prev;
+    }
+}
+
+core_receiver_t output_pcap_receiver(output_pcap_t* self)
+{
+    if (!self->dumper) {
+        lfatal("PCAP not opened");
+    }
+
+    return (core_receiver_t)_receive;
+}
diff --git a/src/output/pcap.h b/src/output/pcap.h
new file mode 100644
index 0000000..fccf58d
--- /dev/null
+++ b/src/output/pcap.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "core/log.h"
+#include "core/receiver.h"
+#include "core/producer.h"
+
+#ifndef __dnsjit_output_pcap_h
+#define __dnsjit_output_pcap_h
+
+#include <pcap/pcap.h>
+
+#include "output/pcap.hh"
+
+#endif
diff --git a/src/output/pcap.hh b/src/output/pcap.hh
new file mode 100644
index 0000000..45f5150
--- /dev/null
+++ b/src/output/pcap.hh
@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#if 0
+typedef struct pcap_dumper {} pcap_dumper_t;
+#endif
+
+//lua:require("dnsjit.core.log")
+//lua:require("dnsjit.core.receiver_h")
+//lua:require("dnsjit.input.pcap_h")
+
+typedef struct output_pcap {
+    core_log_t     _log;
+    pcap_t*        pcap;
+    pcap_dumper_t* dumper;
+} output_pcap_t;
+
+core_log_t* output_pcap_log();
+void        output_pcap_init(output_pcap_t* self);
+void        output_pcap_destroy(output_pcap_t* self);
+int         output_pcap_open(output_pcap_t* self, const char* file, int linktype, int snaplen);
+void        output_pcap_close(output_pcap_t* self);
+
+core_receiver_t output_pcap_receiver(output_pcap_t* self);
diff --git a/src/output/pcap.lua b/src/output/pcap.lua
new file mode 100644
index 0000000..13f0c29
--- /dev/null
+++ b/src/output/pcap.lua
@@ -0,0 +1,79 @@
+-- Copyright (c) 2018-2021, OARC, Inc.
+-- All rights reserved.
+--
+-- This file is part of dnsjit.
+--
+-- dnsjit is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation, either version 3 of the License, or
+-- (at your option) any later version.
+--
+-- dnsjit is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License
+-- along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+
+-- dnsjit.output.pcap
+-- Output to a PCAP using libpcap
+--   local output = require("dnsjit.output.pcap").new()
+--   output:open("file.pcap")
+--   ...
+--   output:close()
+--
+-- Output module for writing
+-- .I dnsjit.core.object.pcap
+-- objects to a PCAP,
+module(...,package.seeall)
+
+require("dnsjit.output.pcap_h")
+local ffi = require("ffi")
+local C = ffi.C
+
+local t_name = "output_pcap_t"
+local output_pcap_t = ffi.typeof(t_name)
+local Pcap = {}
+
+-- Create a new Pcap output.
+function Pcap.new()
+    local self = {
+        obj = output_pcap_t(),
+    }
+    C.output_pcap_init(self.obj)
+    ffi.gc(self.obj, C.output_pcap_destroy)
+    return setmetatable(self, { __index = Pcap })
+end
+
+-- Return the Log object to control logging of this instance or module.
+function Pcap:log()
+    if self == nil then
+        return C.output_pcap_log()
+    end
+    return self.obj._log
+end
+
+-- Open the PCAP
+-- .I file
+-- to write to using the
+-- .I linktype
+-- and
+-- .IR snaplen .
+-- Returns 0 on success.
+function Pcap:open(file, linktype, snaplen)
+    return C.output_pcap_open(self.obj, file, linktype, snaplen)
+end
+
+-- Close the PCAP.
+function Pcap:close()
+    C.output_pcap_close(self.obj)
+end
+
+-- Return the C functions and context for receiving objects.
+function Pcap:receive()
+    return C.output_pcap_receiver(self.obj), self.obj
+end
+
+-- dnsjit.input.pcap (3)
+return Pcap
diff --git a/src/output/respdiff.c b/src/output/respdiff.c
new file mode 100644
index 0000000..834a264
--- /dev/null
+++ b/src/output/respdiff.c
@@ -0,0 +1,298 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/respdiff.h"
+#include "core/assert.h"
+#include "core/object/payload.h"
+
+#ifdef HAVE_LMDB_H
+#include <lmdb.h>
+#endif
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <string.h>
+
+static core_log_t        _log      = LOG_T_INIT("output.respdiff");
+static output_respdiff_t _defaults = {
+    LOG_T_INIT_OBJ("output.respdiff"),
+    0, 0, 0, 0, 0, 0
+};
+
+core_log_t* output_respdiff_log()
+{
+    return &_log;
+}
+
+void output_respdiff_init(output_respdiff_t* self, const char* path, size_t mapsize)
+{
+    mlassert_self();
+
+    if (!path) {
+        lfatal("path is nil");
+    }
+
+    *self = _defaults;
+
+#ifdef HAVE_LMDB_H
+    if (mkdir(path, 0775) && errno != EEXIST) {
+        lfatal("mkdir(%s) error %s", path, core_log_errstr(errno));
+    }
+    if (mdb_env_create((MDB_env**)&self->env)) {
+        lfatal("mdb_env_create failed");
+    }
+    if (mdb_env_set_mapsize((MDB_env*)self->env, mapsize)) {
+        lfatal("mdb_env_set_mapsize(%lu) failed", mapsize);
+    }
+    if (mdb_env_set_maxdbs((MDB_env*)self->env, 3)) {
+        lfatal("mdb_env_set_maxdbs failed");
+    }
+    if (mdb_env_open((MDB_env*)self->env, path, 0, 0664)) {
+        lfatal("mdb_env_open(%s) failed", path);
+    }
+    if (mdb_txn_begin((MDB_env*)self->env, 0, 0, (MDB_txn**)&self->txn)) {
+        lfatal("mdb_txn_begin failed for queries");
+    }
+    lfatal_oom(self->qdb = calloc(1, sizeof(MDB_dbi)));
+    if (mdb_dbi_open((MDB_txn*)self->txn, "queries", MDB_CREATE, (MDB_dbi*)self->qdb)) {
+        lfatal("mdb_dbi_open failed for queries");
+    }
+    lfatal_oom(self->rdb = calloc(1, sizeof(MDB_dbi)));
+    if (mdb_dbi_open((MDB_txn*)self->txn, "answers", MDB_CREATE, (MDB_dbi*)self->rdb)) {
+        lfatal("mdb_dbi_open failed for responses");
+    }
+    lfatal_oom(self->meta = calloc(1, sizeof(MDB_dbi)));
+    if (mdb_dbi_open((MDB_txn*)self->txn, "meta", MDB_CREATE, (MDB_dbi*)self->meta)) {
+        lfatal("mdb_dbi_open failed for meta");
+    }
+#endif
+}
+
+void output_respdiff_destroy(output_respdiff_t* self)
+{
+    mlassert_self();
+
+#ifdef HAVE_LMDB_H
+    if (self->env) {
+        mdb_env_close((MDB_env*)self->env);
+    }
+    free(self->qdb);
+    free(self->rdb);
+    free(self->meta);
+#endif
+}
+
+#ifdef HAVE_LMDB_H
+static const char* _meta_version     = "version";
+static const char* _meta_version_val = "2018-05-21";
+static const char* _meta_servers     = "servers";
+static const char* _meta_name0       = "name0";
+static const char* _meta_name1       = "name1";
+static const char* _meta_start_time  = "start_time";
+static const char* _meta_end_time    = "end_time";
+#endif
+
+void output_respdiff_commit(output_respdiff_t* self, const char* origname, const char* recvname, uint64_t start_time, uint64_t end_time)
+{
+#ifdef HAVE_LMDB_H
+    MDB_val  k, v;
+    uint32_t i;
+    int      err;
+    mlassert_self();
+    lassert(origname, "origname is nil");
+    lassert(recvname, "recvname is nil");
+
+    k.mv_size = strlen(_meta_version);
+    k.mv_data = (void*)_meta_version;
+    v.mv_size = strlen(_meta_version_val);
+    v.mv_data = (void*)_meta_version_val;
+    if ((err = mdb_put((MDB_txn*)self->txn, (MDB_dbi) * ((MDB_dbi*)self->meta), &k, &v, 0))) {
+        if (err == MDB_MAP_FULL) {
+            lfatal("mdb_put meta.version failed, database is full");
+        } else {
+            lfatal("mdb_put meta.version failed (%d)", err);
+        }
+    }
+
+    k.mv_size = strlen(_meta_servers);
+    k.mv_data = (void*)_meta_servers;
+    i         = 2;
+    v.mv_size = 4;
+    v.mv_data = (void*)&i;
+    if ((err = mdb_put((MDB_txn*)self->txn, (MDB_dbi) * ((MDB_dbi*)self->meta), &k, &v, 0))) {
+        if (err == MDB_MAP_FULL) {
+            lfatal("mdb_put meta.servers failed, database is full");
+        } else {
+            lfatal("mdb_put meta.servers failed (%d)", err);
+        }
+    }
+
+    k.mv_size = strlen(_meta_name0);
+    k.mv_data = (void*)_meta_name0;
+    v.mv_size = strlen(origname);
+    v.mv_data = (void*)origname;
+    if ((err = mdb_put((MDB_txn*)self->txn, (MDB_dbi) * ((MDB_dbi*)self->meta), &k, &v, 0))) {
+        if (err == MDB_MAP_FULL) {
+            lfatal("mdb_put meta.name0 failed, database is full");
+        } else {
+            lfatal("mdb_put meta.name0 failed (%d)", err);
+        }
+    }
+
+    k.mv_size = strlen(_meta_name1);
+    k.mv_data = (void*)_meta_name1;
+    v.mv_size = strlen(recvname);
+    v.mv_data = (void*)recvname;
+    if ((err = mdb_put((MDB_txn*)self->txn, (MDB_dbi) * ((MDB_dbi*)self->meta), &k, &v, 0))) {
+        if (err == MDB_MAP_FULL) {
+            lfatal("mdb_put meta.name1 failed, database is full");
+        } else {
+            lfatal("mdb_put meta.name1 failed (%d)", err);
+        }
+    }
+
+    k.mv_size = strlen(_meta_start_time);
+    k.mv_data = (void*)_meta_start_time;
+    i         = start_time;
+    v.mv_size = 4;
+    v.mv_data = (void*)&i;
+    if ((err = mdb_put((MDB_txn*)self->txn, (MDB_dbi) * ((MDB_dbi*)self->meta), &k, &v, 0))) {
+        if (err == MDB_MAP_FULL) {
+            lfatal("mdb_put meta.start_time failed, database is full");
+        } else {
+            lfatal("mdb_put meta.start_time failed (%d)", err);
+        }
+    }
+
+    k.mv_size = strlen(_meta_end_time);
+    k.mv_data = (void*)_meta_end_time;
+    i         = end_time;
+    v.mv_size = 4;
+    v.mv_data = (void*)&i;
+    if ((err = mdb_put((MDB_txn*)self->txn, (MDB_dbi) * ((MDB_dbi*)self->meta), &k, &v, 0))) {
+        if (err == MDB_MAP_FULL) {
+            lfatal("mdb_put meta.end_time failed, database is full");
+        } else {
+            lfatal("mdb_put meta.end_time failed (%d)", err);
+        }
+    }
+
+    if (self->txn) {
+        if (mdb_txn_commit((MDB_txn*)self->txn)) {
+            lfatal("mdb_txn_commit failed");
+        }
+        self->txn = 0;
+    }
+#endif
+}
+
+#ifdef HAVE_LMDB_H
+static void _receive(output_respdiff_t* self, const core_object_t* obj)
+{
+    const core_object_payload_t *query, *original, *response;
+    MDB_val                      k, v;
+    uint8_t                      responses[132096];
+    uint32_t                     msec;
+    uint16_t                     dnslen;
+    int                          err;
+    mlassert_self();
+
+    if (!obj || obj->obj_type != CORE_OBJECT_PAYLOAD) {
+        lfatal("invalid first object");
+    }
+    query = (core_object_payload_t*)obj;
+
+    if (!query->obj_prev || query->obj_prev->obj_type != CORE_OBJECT_PAYLOAD) {
+        lfatal("invalid second object");
+    }
+    original = (core_object_payload_t*)query->obj_prev;
+
+    response = (core_object_payload_t*)original->obj_prev;
+    if (response && response->obj_type != CORE_OBJECT_PAYLOAD) {
+        lfatal("invalid third object");
+    }
+
+    if (12 + original->len + (response ? response->len : 0) > sizeof(responses)) {
+        lfatal("not enough buffer space for responses");
+    }
+
+    self->count++;
+
+    k.mv_size = sizeof(self->id);
+    k.mv_data = (void*)&self->id;
+    v.mv_size = query->len;
+    v.mv_data = (void*)query->payload;
+    if ((err = mdb_put((MDB_txn*)self->txn, (MDB_dbi) * ((MDB_dbi*)self->qdb), &k, &v, 0))) {
+        if (err == MDB_MAP_FULL) {
+            lfatal("mdb_put query failed, database is full");
+        } else {
+            lfatal("mdb_put query failed (%d)", err);
+        }
+    }
+
+    msec = 1; // TODO
+    memcpy(responses, &msec, 4);
+    dnslen = original->len;
+    memcpy(&responses[4], &dnslen, 2);
+    memcpy(&responses[6], original->payload, original->len);
+    if (response) {
+        memcpy(&responses[6 + original->len], &msec, 4);
+        dnslen = response->len;
+        memcpy(&responses[10 + original->len], &dnslen, 2);
+        memcpy(&responses[12 + original->len], response->payload, response->len);
+    } else {
+        msec = 0xffffffff;
+        memcpy(&responses[6 + original->len], &msec, 4);
+        dnslen = 0;
+        memcpy(&responses[10 + original->len], &dnslen, 2);
+    }
+
+    v.mv_size = 12 + original->len + (response ? response->len : 0);
+    v.mv_data = (void*)responses;
+    if ((err = mdb_put((MDB_txn*)self->txn, (MDB_dbi) * ((MDB_dbi*)self->rdb), &k, &v, 0))) {
+        if (err == MDB_MAP_FULL) {
+            lfatal("mdb_put answers failed, database is full");
+        } else {
+            lfatal("mdb_put answers failed (%d)", err);
+        }
+    }
+
+    self->id++;
+}
+
+core_receiver_t output_respdiff_receiver(output_respdiff_t* self)
+{
+    mlassert_self();
+
+    if (!self->txn) {
+        lfatal("no LMDB opened");
+    }
+
+    return (core_receiver_t)_receive;
+}
+#else
+core_receiver_t output_respdiff_receiver(output_respdiff_t* self)
+{
+    mlassert_self();
+    lfatal("no LMDB support");
+    return 0;
+}
+#endif
diff --git a/src/output/respdiff.h b/src/output/respdiff.h
new file mode 100644
index 0000000..f375006
--- /dev/null
+++ b/src/output/respdiff.h
@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "core/log.h"
+#include "core/receiver.h"
+
+#ifndef __dnsjit_output_respdiff_h
+#define __dnsjit_output_respdiff_h
+
+#include <stdint.h>
+
+#include "output/respdiff.hh"
+
+#endif
diff --git a/src/output/respdiff.hh b/src/output/respdiff.hh
new file mode 100644
index 0000000..44f597e
--- /dev/null
+++ b/src/output/respdiff.hh
@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+//lua:require("dnsjit.core.log")
+//lua:require("dnsjit.core.receiver_h")
+
+typedef struct output_respdiff {
+    core_log_t _log;
+    void *     env, *txn, *qdb, *rdb, *meta;
+    uint32_t   id;
+    size_t     count;
+} output_respdiff_t;
+
+core_log_t* output_respdiff_log();
+void        output_respdiff_init(output_respdiff_t* self, const char* path, size_t mapsize);
+void        output_respdiff_destroy(output_respdiff_t* self);
+void        output_respdiff_commit(output_respdiff_t* self, const char* origname, const char* recvname, uint64_t start_time, uint64_t end_time);
+
+core_receiver_t output_respdiff_receiver(output_respdiff_t* self);
diff --git a/src/output/respdiff.lua b/src/output/respdiff.lua
new file mode 100644
index 0000000..7d17b4a
--- /dev/null
+++ b/src/output/respdiff.lua
@@ -0,0 +1,94 @@
+-- Copyright (c) 2018-2021, OARC, Inc.
+-- All rights reserved.
+--
+-- This file is part of dnsjit.
+--
+-- dnsjit is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation, either version 3 of the License, or
+-- (at your option) any later version.
+--
+-- dnsjit is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License
+-- along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+
+-- dnsjit.output.respdiff
+-- Output to respdiff LMDB
+--   local output = require("dnsjit.output.respdiff").new("/path/to/lmdb")
+--
+-- Output to an LMDB database (format 2018-05-21) that can be used by respdiff
+-- to compare the responses found in the input data with the responses
+-- received.
+-- The receive function expects to get a chain of 2 or 3
+-- .IR core.object.payload .
+-- For a completed query; The top of the chain is the query, after it the
+-- original response and then the received response.
+-- For a timed out query; The top of the chain is the query, after it the
+-- original response.
+module(...,package.seeall)
+
+require("dnsjit.output.respdiff_h")
+local ffi = require("ffi")
+local C = ffi.C
+
+local t_name = "output_respdiff_t"
+local output_respdiff_t = ffi.typeof(t_name)
+local Respdiff = {}
+
+-- Create a new Respdiff output and created the LMDB database in the directory
+-- .IR path .
+-- The
+-- .I origname
+-- and
+-- .I recvname
+-- are used to populate the meta table, these names should be the same as
+-- what is configured in
+-- .IR respdiff.cfg .
+-- Optional
+-- .I mapsize
+-- can be given to increase the database size beyond the default size of 10MB.
+function Respdiff.new(path, origname, recvname, mapsize)
+    if mapsize == nil then
+        mapsize = 10485760
+    end
+    local self = {
+        obj = output_respdiff_t(),
+        path = path,
+        origname = origname,
+        recvname = recvname,
+    }
+    C.output_respdiff_init(self.obj, path, mapsize)
+    ffi.gc(self.obj, C.output_respdiff_destroy)
+    return setmetatable(self, { __index = Respdiff })
+end
+
+-- Return the Log object to control logging of this instance or module.
+function Respdiff:log()
+    if self == nil then
+        return C.output_respdiff_log()
+    end
+    return self.obj._log
+end
+
+-- Return the C functions and context for receiving objects.
+function Respdiff:receive()
+    return C.output_respdiff_receiver(self.obj), self.obj
+end
+
+-- Commit the LMDB transactions, can not store any more objects after this
+-- call.
+-- The given
+-- .I start_time
+-- and
+-- .I end_time
+-- are used to fill the meta table.
+function Respdiff:commit(start_time, end_time)
+    C.output_respdiff_commit(self.obj, self.origname, self.recvname, start_time, end_time)
+end
+
+-- respdiff " https://gitlab.nic.cz/knot/respdiff"
+return Respdiff
diff --git a/src/output/tcpcli.c b/src/output/tcpcli.c
new file mode 100644
index 0000000..f2b218b
--- /dev/null
+++ b/src/output/tcpcli.c
@@ -0,0 +1,381 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/tcpcli.h"
+#include "core/assert.h"
+#include "core/object/dns.h"
+#include "core/object/payload.h"
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <poll.h>
+
+static core_log_t      _log      = LOG_T_INIT("output.tcpcli");
+static output_tcpcli_t _defaults = {
+    LOG_T_INIT_OBJ("output.tcpcli"),
+    0, 0, -1,
+    { 0 }, CORE_OBJECT_PAYLOAD_INIT(0),
+    0, 0, 0, 0,
+    { 5, 0 }, 1
+};
+
+core_log_t* output_tcpcli_log()
+{
+    return &_log;
+}
+
+void output_tcpcli_init(output_tcpcli_t* self)
+{
+    mlassert_self();
+
+    *self             = _defaults;
+    self->pkt.payload = self->recvbuf;
+}
+
+void output_tcpcli_destroy(output_tcpcli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd > -1) {
+        shutdown(self->fd, SHUT_RDWR);
+        close(self->fd);
+    }
+}
+
+int output_tcpcli_connect(output_tcpcli_t* self, const char* host, const char* port)
+{
+    struct addrinfo* addr;
+    int              err;
+    mlassert_self();
+    lassert(host, "host is nil");
+    lassert(port, "port is nil");
+
+    if (self->fd > -1) {
+        lfatal("already connected");
+    }
+
+    if ((err = getaddrinfo(host, port, 0, &addr))) {
+        lcritical("getaddrinfo(%s, %s) error %s", host, port, gai_strerror(err));
+        return -1;
+    }
+    if (!addr) {
+        lcritical("getaddrinfo failed, no address returned");
+        return -1;
+    }
+
+    if ((self->fd = socket(addr->ai_addr->sa_family, SOCK_STREAM, 0)) < 0) {
+        lcritical("socket() error %s", core_log_errstr(errno));
+        freeaddrinfo(addr);
+        return -2;
+    }
+
+    if (connect(self->fd, addr->ai_addr, addr->ai_addrlen)) {
+        lcritical("connect() error %s", core_log_errstr(errno));
+        freeaddrinfo(addr);
+        return -2;
+    }
+
+    freeaddrinfo(addr);
+    return 0;
+}
+
+int output_tcpcli_nonblocking(output_tcpcli_t* self)
+{
+    int flags;
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+
+    flags = fcntl(self->fd, F_GETFL);
+    if (flags != -1) {
+        flags = flags & O_NONBLOCK ? 1 : 0;
+    }
+
+    return flags;
+}
+
+int output_tcpcli_set_nonblocking(output_tcpcli_t* self, int nonblocking)
+{
+    int flags;
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+
+    if ((flags = fcntl(self->fd, F_GETFL)) == -1) {
+        lcritical("fcntl(FL_GETFL) error %s", core_log_errstr(errno));
+        return -1;
+    }
+
+    if (nonblocking) {
+        flags |= O_NONBLOCK;
+        self->blocking = 0;
+    } else {
+        flags &= ~O_NONBLOCK;
+        self->blocking = 1;
+    }
+
+    if (fcntl(self->fd, F_SETFL, flags | O_NONBLOCK)) {
+        lcritical("fcntl(FL_SETFL, %x) error %s", flags, core_log_errstr(errno));
+        return -1;
+    }
+
+    return 0;
+}
+
+static void _receive(output_tcpcli_t* self, const core_object_t* obj)
+{
+    const uint8_t* payload;
+    size_t         len, sent;
+    uint16_t       dnslen;
+    mlassert_self();
+
+    for (; obj;) {
+        switch (obj->obj_type) {
+        case CORE_OBJECT_DNS:
+            obj = obj->obj_prev;
+            continue;
+        case CORE_OBJECT_PAYLOAD:
+            payload = ((core_object_payload_t*)obj)->payload;
+            len     = ((core_object_payload_t*)obj)->len;
+            break;
+        default:
+            return;
+        }
+
+        sent   = 0;
+        dnslen = htons(len);
+
+        for (;;) {
+            ssize_t ret = sendto(self->fd, ((uint8_t*)&dnslen) + sent, sizeof(dnslen) - sent, 0, 0, 0);
+            if (ret > -1) {
+                sent += ret;
+                if (sent < sizeof(dnslen))
+                    continue;
+
+                sent = 0;
+                for (;;) {
+                    ssize_t ret = sendto(self->fd, payload + sent, len - sent, 0, 0, 0);
+                    if (ret > -1) {
+                        sent += ret;
+                        if (sent < len)
+                            continue;
+                        self->pkts++;
+                        return;
+                    }
+                    switch (errno) {
+                    case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+                    case EWOULDBLOCK:
+#endif
+                        continue;
+                    default:
+                        break;
+                    }
+                    break;
+                }
+                self->errs++;
+                return;
+            }
+            switch (errno) {
+            case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+            case EWOULDBLOCK:
+#endif
+                continue;
+            default:
+                break;
+            }
+            break;
+        }
+        self->errs++;
+        break;
+    }
+}
+
+core_receiver_t output_tcpcli_receiver(output_tcpcli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+
+    return (core_receiver_t)_receive;
+}
+
+static const core_object_t* _produce(output_tcpcli_t* self)
+{
+    ssize_t       n, recv = 0;
+    uint16_t      dnslen;
+    struct pollfd p;
+    int           to = 0;
+    mlassert_self();
+
+    // Check if last recvfrom() got more then we needed
+    if (!self->have_dnslen && self->recv > self->dnslen) {
+        recv = self->recv - self->dnslen;
+        if (recv < sizeof(dnslen)) {
+            memcpy(((uint8_t*)&dnslen), self->recvbuf + self->dnslen, recv);
+        } else {
+            memcpy(((uint8_t*)&dnslen), self->recvbuf + self->dnslen, sizeof(dnslen));
+
+            if (recv > sizeof(dnslen)) {
+                self->recv = recv - sizeof(dnslen);
+                memmove(self->recvbuf, self->recvbuf + self->dnslen + sizeof(dnslen), self->recv);
+            } else {
+                self->recv = 0;
+            }
+
+            self->dnslen      = ntohs(dnslen);
+            self->have_dnslen = 1;
+
+            if (self->recv > self->dnslen) {
+                self->pkts_recv++;
+                self->pkt.len     = self->dnslen;
+                self->have_dnslen = 0;
+                return (core_object_t*)&self->pkt;
+            }
+        }
+    }
+
+    if (self->blocking) {
+        p.fd      = self->fd;
+        p.events  = POLLIN;
+        p.revents = 0;
+        to        = (self->timeout.sec * 1e3) + (self->timeout.nsec / 1e6); //NOSONAR
+        if (!to) {
+            to = 1;
+        }
+    }
+
+    if (!self->have_dnslen) {
+        for (;;) {
+            n = poll(&p, 1, to);
+            if (n < 0 || (p.revents & (POLLERR | POLLHUP | POLLNVAL))) {
+                self->errs++;
+                return 0;
+            }
+            if (!n || !(p.revents & POLLIN)) {
+                if (recv) {
+                    self->errs++;
+                    return 0;
+                }
+                self->pkt.len = 0;
+                return (core_object_t*)&self->pkt;
+            }
+
+            n = recvfrom(self->fd, ((uint8_t*)&dnslen) + recv, sizeof(dnslen) - recv, 0, 0, 0);
+            if (n > 0) {
+                recv += n;
+                if (recv < sizeof(dnslen))
+                    continue;
+                break;
+            }
+            if (!n) {
+                break;
+            }
+            switch (errno) {
+            case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+            case EWOULDBLOCK:
+#endif
+                continue;
+            default:
+                break;
+            }
+            self->errs++;
+            break;
+        }
+
+        if (n < 1) {
+            return 0;
+        }
+
+        self->dnslen      = ntohs(dnslen);
+        self->have_dnslen = 1;
+        self->recv        = 0;
+    }
+
+    for (;;) {
+        n = poll(&p, 1, to);
+        if (n < 0 || (p.revents & (POLLERR | POLLHUP | POLLNVAL))) {
+            self->errs++;
+            return 0;
+        }
+        if (!n || !(p.revents & POLLIN)) {
+            self->pkt.len = 0;
+            return (core_object_t*)&self->pkt;
+        }
+
+        n = recvfrom(self->fd, self->recvbuf + self->recv, sizeof(self->recvbuf) - self->recv, 0, 0, 0);
+        if (n > 0) {
+            self->recv += n;
+            if (self->recv < self->dnslen)
+                continue;
+            break;
+        }
+        if (!n) {
+            break;
+        }
+        switch (errno) {
+        case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+        case EWOULDBLOCK:
+#endif
+            self->pkt.len = 0;
+            return (core_object_t*)&self->pkt;
+        default:
+            break;
+        }
+        self->errs++;
+        break;
+    }
+
+    if (n < 1) {
+        return 0;
+    }
+
+    self->pkts_recv++;
+    self->pkt.len     = self->dnslen;
+    self->have_dnslen = 0;
+    return (core_object_t*)&self->pkt;
+}
+
+core_producer_t output_tcpcli_producer(output_tcpcli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+
+    return (core_producer_t)_produce;
+}
diff --git a/src/output/tcpcli.h b/src/output/tcpcli.h
new file mode 100644
index 0000000..6eb80f3
--- /dev/null
+++ b/src/output/tcpcli.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "core/log.h"
+#include "core/receiver.h"
+#include "core/producer.h"
+#include "core/object/payload.h"
+#include "core/timespec.h"
+
+#ifndef __dnsjit_output_tcpcli_h
+#define __dnsjit_output_tcpcli_h
+
+#include "output/tcpcli.hh"
+
+#endif
diff --git a/src/output/tcpcli.hh b/src/output/tcpcli.hh
new file mode 100644
index 0000000..277b0dd
--- /dev/null
+++ b/src/output/tcpcli.hh
@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+//lua:require("dnsjit.core.log")
+//lua:require("dnsjit.core.receiver_h")
+//lua:require("dnsjit.core.producer_h")
+//lua:require("dnsjit.core.object.payload_h")
+//lua:require("dnsjit.core.timespec_h")
+
+typedef struct output_tcpcli {
+    core_log_t _log;
+    size_t     pkts, errs;
+    int        fd;
+
+    uint8_t               recvbuf[64 * 1024];
+    core_object_payload_t pkt;
+    uint16_t              dnslen;
+    uint8_t               have_dnslen;
+    size_t                recv, pkts_recv;
+
+    core_timespec_t timeout;
+    int8_t          blocking;
+} output_tcpcli_t;
+
+core_log_t* output_tcpcli_log();
+
+void output_tcpcli_init(output_tcpcli_t* self);
+void output_tcpcli_destroy(output_tcpcli_t* self);
+int  output_tcpcli_connect(output_tcpcli_t* self, const char* host, const char* port);
+int  output_tcpcli_nonblocking(output_tcpcli_t* self);
+int  output_tcpcli_set_nonblocking(output_tcpcli_t* self, int nonblocking);
+
+core_receiver_t output_tcpcli_receiver(output_tcpcli_t* self);
+core_producer_t output_tcpcli_producer(output_tcpcli_t* self);
diff --git a/src/output/tcpcli.lua b/src/output/tcpcli.lua
new file mode 100644
index 0000000..d57de88
--- /dev/null
+++ b/src/output/tcpcli.lua
@@ -0,0 +1,131 @@
+-- Copyright (c) 2018-2021, OARC, Inc.
+-- All rights reserved.
+--
+-- This file is part of dnsjit.
+--
+-- dnsjit is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation, either version 3 of the License, or
+-- (at your option) any later version.
+--
+-- dnsjit is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License
+-- along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+
+-- dnsjit.output.tcpcli
+-- Simple, length aware, TCP client
+--   local output = require("dnsjit.output.tcpcli").new("127.0.0.1", "53")
+--
+-- Simple TCP client that takes any payload you give it, sends the length of
+-- the payload as an unsigned 16 bit integer and then sends the payload.
+-- When receiving it will first retrieve the length of the payload as an
+-- unsigned 16 bit integer and it will stall until it gets, even if
+-- nonblocking mode is used.
+-- Then it will retrieve at least that amount of bytes, if nonblocking mode
+-- is used here then it will return a payload object with length zero if
+-- there was nothing to receive or if the full payload have not been received
+-- yet.
+-- Additional calls will continue retrieving the payload.
+-- .SS Attributes
+-- .TP
+-- timeout
+-- A
+-- .I core.timespec
+-- that is used when producing objects.
+module(...,package.seeall)
+
+require("dnsjit.output.tcpcli_h")
+local ffi = require("ffi")
+local C = ffi.C
+
+local t_name = "output_tcpcli_t"
+local output_tcpcli_t = ffi.typeof(t_name)
+local Tcpcli = {}
+
+-- Create a new Tcpcli output.
+function Tcpcli.new()
+    local self = {
+        obj = output_tcpcli_t(),
+    }
+    C.output_tcpcli_init(self.obj)
+    ffi.gc(self.obj, C.output_tcpcli_destroy)
+    return setmetatable(self, { __index = Tcpcli })
+end
+
+-- Set the timeout when producing objects.
+function Tcpcli:timeout(seconds, nanoseconds)
+    self.obj.timeout.sec = seconds
+    self.obj.timeout.nsec = nanoseconds
+end
+
+-- Connect to the
+-- .I host
+-- and
+-- .I port
+-- and return 0 if successful.
+function Tcpcli:connect(host, port)
+    return C.output_tcpcli_connect(self.obj, host, port)
+end
+
+-- Enable (true) or disable (false) nonblocking mode and
+-- return 0 if successful, if
+-- .I bool
+-- is not specified then return if nonblocking mode is on (true) or off (false).
+function Tcpcli:nonblocking(bool)
+    if bool == nil then
+        if C.output_tcpcli_nonblocking(self.obj) == 1 then
+            return true
+        end
+        return false
+    elseif bool == true then
+        return C.output_tcpcli_set_nonblocking(self.obj, 1)
+    else
+        return C.output_tcpcli_set_nonblocking(self.obj, 0)
+    end
+end
+
+-- Return the C functions and context for receiving objects, these objects
+-- will be sent.
+function Tcpcli:receive()
+    return C.output_tcpcli_receiver(self.obj), self.obj
+end
+
+-- Return the C functions and context for producing objects, these objects
+-- are received.
+-- If nonblocking mode is enabled the producer will return a payload object
+-- with length zero if there was nothing to receive or if the full payload
+-- have not been received yet.
+-- If nonblocking mode is disabled the producer will wait for data and if
+-- timed out (see
+-- .IR timeout )
+-- it will return a payload object with length zero.
+-- If a timeout happens during during the first stage, getting the length, it
+-- will fail and return nil.
+-- Additional calls will continue retrieving the payload.
+-- The producer returns nil on error.
+function Tcpcli:produce()
+    return C.output_tcpcli_producer(self.obj), self.obj
+end
+
+-- Return the number of "packets" sent, actually the number of completely sent
+-- payloads.
+function Tcpcli:packets()
+    return tonumber(self.obj.pkts)
+end
+
+-- Return the number of "packets" received, actually the number of completely
+-- received DNS messages.
+function Tcpcli:received()
+    return tonumber(self.obj.pkts_recv)
+end
+
+-- Return the number of errors when sending.
+function Tcpcli:errors()
+    return tonumber(self.obj.errs)
+end
+
+return Tcpcli
diff --git a/src/output/tlscli.c b/src/output/tlscli.c
new file mode 100644
index 0000000..8c5947a
--- /dev/null
+++ b/src/output/tlscli.c
@@ -0,0 +1,345 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/tlscli.h"
+#include "core/assert.h"
+#include "core/object/dns.h"
+#include "core/object/payload.h"
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <poll.h>
+
+static core_log_t      _log      = LOG_T_INIT("output.tlscli");
+static output_tlscli_t _defaults = {
+    LOG_T_INIT_OBJ("output.tlscli"),
+    0, 0, -1, 0,
+    { 0 }, CORE_OBJECT_PAYLOAD_INIT(0),
+    0, 0, 0, 0,
+    { 5, 0 },
+    0, 0
+};
+
+core_log_t* output_tlscli_log()
+{
+    return &_log;
+}
+
+void output_tlscli_init(output_tlscli_t* self)
+{
+    int err;
+    mlassert_self();
+
+    *self             = _defaults;
+    self->pkt.payload = self->recvbuf;
+
+    gnutls_global_init();
+    if ((err = gnutls_certificate_allocate_credentials(&self->cred)) != GNUTLS_E_SUCCESS) {
+        lfatal("gnutls_certificate_allocate_credentials() error: %s", gnutls_strerror(err));
+    } else if ((err = gnutls_init(&self->session, GNUTLS_CLIENT)) != GNUTLS_E_SUCCESS) {
+        lfatal("gnutls_init() error: %s", gnutls_strerror(err));
+    } else if ((err = gnutls_set_default_priority(self->session)) != GNUTLS_E_SUCCESS) {
+        lfatal("gnutls_set_default_priority() error: %s", gnutls_strerror(err));
+    } else if ((err = gnutls_credentials_set(self->session, GNUTLS_CRD_CERTIFICATE, self->cred)) != GNUTLS_E_SUCCESS) {
+        lfatal("gnutls_credentials_set() error: %s", gnutls_strerror(err));
+    }
+
+    gnutls_handshake_set_timeout(self->session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);
+}
+
+void output_tlscli_destroy(output_tlscli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd > -1) {
+        if (self->session) {
+            gnutls_bye(self->session, GNUTLS_SHUT_RDWR);
+            gnutls_deinit(self->session);
+        }
+        shutdown(self->fd, SHUT_RDWR);
+        close(self->fd);
+        if (self->cred) {
+            gnutls_certificate_free_credentials(self->cred);
+        }
+    }
+}
+
+int output_tlscli_connect(output_tlscli_t* self, const char* host, const char* port)
+{
+    struct addrinfo* addr;
+    int              err;
+    unsigned int     ms;
+    mlassert_self();
+    lassert(host, "host is nil");
+    lassert(port, "port is nil");
+
+    if (self->fd > -1) {
+        lfatal("already connected");
+    }
+    if (self->tls_ok) {
+        lfatal("TLS already established");
+    }
+
+    if ((err = getaddrinfo(host, port, 0, &addr))) {
+        lcritical("getaddrinfo(%s, %s) error %s", host, port, gai_strerror(err));
+        return -1;
+    }
+    if (!addr) {
+        lcritical("getaddrinfo failed, no address returned");
+        return -1;
+    }
+
+    if ((self->fd = socket(addr->ai_addr->sa_family, SOCK_STREAM, 0)) < 0) {
+        lcritical("socket() error %s", core_log_errstr(errno));
+        freeaddrinfo(addr);
+        return -2;
+    }
+
+    if (connect(self->fd, addr->ai_addr, addr->ai_addrlen)) {
+        lcritical("connect() error %s", core_log_errstr(errno));
+        freeaddrinfo(addr);
+        return -2;
+    }
+
+    freeaddrinfo(addr);
+
+    gnutls_transport_set_int(self->session, self->fd);
+    ms = (self->timeout.sec * 1000) + (self->timeout.nsec / 1000000);
+    if (!ms && self->timeout.nsec) {
+        ms = 1;
+    }
+    gnutls_record_set_timeout(self->session, ms);
+
+    /* Establish TLS */
+    do {
+        err = gnutls_handshake(self->session);
+    } while (err < 0 && gnutls_error_is_fatal(err) == 0);
+    if (err == GNUTLS_E_PREMATURE_TERMINATION) {
+        lcritical("gnutls_handshake() error: %s", gnutls_strerror(err));
+        return -3;
+    } else if (err < 0) {
+        lcritical("gnutls_handshake() failed: %s (%d)\n", gnutls_strerror(err), err);
+        return -3;
+    }
+
+    self->tls_ok = 1;
+    return 0;
+}
+
+static void _receive(output_tlscli_t* self, const core_object_t* obj)
+{
+    const uint8_t* payload;
+    size_t         len, sent;
+    uint16_t       dnslen;
+    ssize_t        ret;
+    mlassert_self();
+
+    for (; obj;) {
+        switch (obj->obj_type) {
+        case CORE_OBJECT_DNS:
+            obj = obj->obj_prev;
+            continue;
+        case CORE_OBJECT_PAYLOAD:
+            payload = ((core_object_payload_t*)obj)->payload;
+            len     = ((core_object_payload_t*)obj)->len;
+            break;
+        default:
+            return;
+        }
+
+        sent   = 0;
+        dnslen = htons(len);
+
+        for (;;) {
+            ret = gnutls_record_send(self->session, ((uint8_t*)&dnslen) + sent, sizeof(dnslen) - sent);
+            if (ret > -1) {
+                sent += ret;
+                if (sent < sizeof(dnslen))
+                    continue;
+
+                sent = 0;
+                for (;;) {
+                    ret = gnutls_record_send(self->session, payload + sent, len - sent);
+                    if (ret > -1) {
+                        sent += ret;
+                        if (sent < len)
+                            continue;
+                        self->pkts++;
+                        return;
+                    }
+                    switch (ret) {
+                    case GNUTLS_E_AGAIN:
+                    case GNUTLS_E_TIMEDOUT:
+                        continue;
+                    default:
+                        break;
+                    }
+                    break;
+                }
+                self->errs++;
+                return;
+            }
+            switch (ret) {
+            case GNUTLS_E_AGAIN:
+            case GNUTLS_E_TIMEDOUT:
+                continue;
+            default:
+                break;
+            }
+            break;
+        }
+        self->errs++;
+        break;
+    }
+}
+
+core_receiver_t output_tlscli_receiver(output_tlscli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+    if (!self->tls_ok) {
+        lfatal("TLS is not established");
+    }
+
+    return (core_receiver_t)_receive;
+}
+
+static const core_object_t* _produce(output_tlscli_t* self)
+{
+    ssize_t  n, recv = 0;
+    uint16_t dnslen;
+    mlassert_self();
+
+    // Check if last recvfrom() got more then we needed
+    if (!self->have_dnslen && self->recv > self->dnslen) {
+        recv = self->recv - self->dnslen;
+        if (recv < sizeof(dnslen)) {
+            memcpy(((uint8_t*)&dnslen), self->recvbuf + self->dnslen, recv);
+        } else {
+            memcpy(((uint8_t*)&dnslen), self->recvbuf + self->dnslen, sizeof(dnslen));
+
+            if (recv > sizeof(dnslen)) {
+                self->recv = recv - sizeof(dnslen);
+                memmove(self->recvbuf, self->recvbuf + self->dnslen + sizeof(dnslen), self->recv);
+            } else {
+                self->recv = 0;
+            }
+
+            self->dnslen      = ntohs(dnslen);
+            self->have_dnslen = 1;
+
+            if (self->recv > self->dnslen) {
+                self->pkts_recv++;
+                self->pkt.len     = self->dnslen;
+                self->have_dnslen = 0;
+                return (core_object_t*)&self->pkt;
+            }
+        }
+    }
+
+    if (!self->have_dnslen) {
+        for (;;) {
+            n = gnutls_record_recv(self->session, ((uint8_t*)&dnslen) + recv, sizeof(dnslen) - recv);
+            if (n > 0) {
+                recv += n;
+                if (recv < sizeof(dnslen))
+                    continue;
+                break;
+            }
+            if (!n) {
+                break;
+            }
+            switch (n) {
+            case GNUTLS_E_AGAIN:
+            case GNUTLS_E_TIMEDOUT:
+                self->pkt.len = 0;
+                return (core_object_t*)&self->pkt;
+            default:
+                break;
+            }
+            self->errs++;
+            break;
+        }
+
+        if (n < 1) {
+            return 0;
+        }
+
+        self->dnslen      = ntohs(dnslen);
+        self->have_dnslen = 1;
+        self->recv        = 0;
+    }
+
+    for (;;) {
+        n = gnutls_record_recv(self->session, self->recvbuf + self->recv, sizeof(self->recvbuf) - self->recv);
+        if (n > 0) {
+            self->recv += n;
+            if (self->recv < self->dnslen)
+                continue;
+            break;
+        }
+        if (!n) {
+            break;
+        }
+        switch (n) {
+        case GNUTLS_E_AGAIN:
+        case GNUTLS_E_TIMEDOUT:
+            self->pkt.len = 0;
+            return (core_object_t*)&self->pkt;
+        default:
+            break;
+        }
+        self->errs++;
+        break;
+    }
+
+    if (n < 1) {
+        return 0;
+    }
+
+    self->pkts_recv++;
+    self->pkt.len     = self->dnslen;
+    self->have_dnslen = 0;
+    return (core_object_t*)&self->pkt;
+}
+
+core_producer_t output_tlscli_producer(output_tlscli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+    if (!self->tls_ok) {
+        lfatal("TLS is not established");
+    }
+
+    return (core_producer_t)_produce;
+}
diff --git a/src/output/tlscli.h b/src/output/tlscli.h
new file mode 100644
index 0000000..2bdf69f
--- /dev/null
+++ b/src/output/tlscli.h
@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "core/log.h"
+#include "core/receiver.h"
+#include "core/producer.h"
+#include "core/object/payload.h"
+#include "core/timespec.h"
+
+#ifndef __dnsjit_output_tlscli_h
+#define __dnsjit_output_tlscli_h
+
+#include <gnutls/gnutls.h>
+
+#include "output/tlscli.hh"
+
+#endif
diff --git a/src/output/tlscli.hh b/src/output/tlscli.hh
new file mode 100644
index 0000000..4a0c142
--- /dev/null
+++ b/src/output/tlscli.hh
@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+//lua:require("dnsjit.core.compat_h")
+//lua:require("dnsjit.core.log")
+//lua:require("dnsjit.core.receiver_h")
+//lua:require("dnsjit.core.producer_h")
+//lua:require("dnsjit.core.object.payload_h")
+//lua:require("dnsjit.core.timespec_h")
+
+typedef struct output_tlscli {
+    core_log_t _log;
+    size_t     pkts, errs;
+    int        fd, tls_ok;
+
+    uint8_t               recvbuf[64 * 1024];
+    core_object_payload_t pkt;
+    uint16_t              dnslen;
+    uint8_t               have_dnslen;
+    size_t                recv, pkts_recv;
+
+    core_timespec_t timeout;
+
+    gnutls_session_t                 session;
+    gnutls_certificate_credentials_t cred;
+} output_tlscli_t;
+
+core_log_t* output_tlscli_log();
+
+void output_tlscli_init(output_tlscli_t* self);
+void output_tlscli_destroy(output_tlscli_t* self);
+int  output_tlscli_connect(output_tlscli_t* self, const char* host, const char* port);
+
+core_receiver_t output_tlscli_receiver(output_tlscli_t* self);
+core_producer_t output_tlscli_producer(output_tlscli_t* self);
diff --git a/src/output/tlscli.lua b/src/output/tlscli.lua
new file mode 100644
index 0000000..e37439b
--- /dev/null
+++ b/src/output/tlscli.lua
@@ -0,0 +1,103 @@
+-- Copyright (c) 2018-2021, OARC, Inc.
+-- All rights reserved.
+--
+-- This file is part of dnsjit.
+--
+-- dnsjit is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation, either version 3 of the License, or
+-- (at your option) any later version.
+--
+-- dnsjit is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License
+-- along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+
+-- dnsjit.output.tlscli
+-- Simple TLS client
+--   local output = require("dnsjit.output.tlscli").new("127.0.0.1", "853")
+--
+-- Simple TLS client that attempts to do a TLS handshake (without
+-- certificate verification). It behaves the same way as tcpcli, except all
+-- the data is sent over the encrypted channel.
+-- .SS Attributes
+-- .TP
+-- timeout
+-- A
+-- .I core.timespec
+-- that is used when producing objects.
+module(...,package.seeall)
+
+require("dnsjit.output.tlscli_h")
+local ffi = require("ffi")
+local C = ffi.C
+
+local t_name = "output_tlscli_t"
+local output_tlscli_t = ffi.typeof(t_name)
+local Tlscli = {}
+
+-- Create a new Tlscli output.
+function Tlscli.new()
+    local self = {
+        obj = output_tlscli_t(),
+    }
+    C.output_tlscli_init(self.obj)
+    ffi.gc(self.obj, C.output_tlscli_destroy)
+    return setmetatable(self, { __index = Tlscli })
+end
+
+-- Set the timeout when producing objects.
+function Tlscli:timeout(seconds, nanoseconds)
+    self.obj.timeout.sec = seconds
+    self.obj.timeout.nsec = nanoseconds
+end
+
+-- Connect to the
+-- .I host
+-- and
+-- .I port
+-- , perform a TLS handshake and return 0 if successful.
+function Tlscli:connect(host, port)
+    return C.output_tlscli_connect(self.obj, host, port)
+end
+
+-- Return the C functions and context for receiving objects, these objects
+-- will be sent.
+function Tlscli:receive()
+    return C.output_tlscli_receiver(self.obj), self.obj
+end
+
+-- Return the C functions and context for producing objects, these objects
+-- are received.
+-- The producer will wait for data and if timed out (see
+-- .IR timeout )
+-- it will return a payload object with length zero.
+-- If a timeout happens during during the first stage, getting the length, it
+-- will fail and return nil.
+-- Additional calls will continue retrieving the payload.
+-- The producer returns nil on error.
+function Tlscli:produce()
+    return C.output_tlscli_producer(self.obj), self.obj
+end
+
+-- Return the number of "packets" sent, actually the number of completely sent
+-- payloads.
+function Tlscli:packets()
+    return tonumber(self.obj.pkts)
+end
+
+-- Return the number of "packets" received, actually the number of completely
+-- received DNS messages.
+function Tlscli:received()
+    return tonumber(self.obj.pkts_recv)
+end
+
+-- Return the number of errors when sending.
+function Tlscli:errors()
+    return tonumber(self.obj.errs)
+end
+
+return Tlscli
diff --git a/src/output/udpcli.c b/src/output/udpcli.c
new file mode 100644
index 0000000..b207d9c
--- /dev/null
+++ b/src/output/udpcli.c
@@ -0,0 +1,300 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "output/udpcli.h"
+#include "core/assert.h"
+#include "core/object/dns.h"
+#include "core/object/payload.h"
+
+#include <netdb.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <poll.h>
+
+static core_log_t      _log      = LOG_T_INIT("output.udpcli");
+static output_udpcli_t _defaults = {
+    LOG_T_INIT_OBJ("output.udpcli"),
+    0, 0, -1,
+    { 0 }, 0,
+    { 0 }, CORE_OBJECT_PAYLOAD_INIT(0), 0,
+    { 5, 0 }, 1
+};
+
+core_log_t* output_udpcli_log()
+{
+    return &_log;
+}
+
+void output_udpcli_init(output_udpcli_t* self)
+{
+    mlassert_self();
+
+    *self             = _defaults;
+    self->pkt.payload = self->recvbuf;
+}
+
+void output_udpcli_destroy(output_udpcli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd > -1) {
+        shutdown(self->fd, SHUT_RDWR);
+        close(self->fd);
+    }
+}
+
+int output_udpcli_connect(output_udpcli_t* self, const char* host, const char* port)
+{
+    struct addrinfo* addr;
+    int              err;
+    mlassert_self();
+    lassert(host, "host is nil");
+    lassert(port, "port is nil");
+
+    if (self->fd > -1) {
+        lfatal("already connected");
+    }
+
+    if ((err = getaddrinfo(host, port, 0, &addr))) {
+        lcritical("getaddrinfo(%s, %s) error %s", host, port, gai_strerror(err));
+        return -1;
+    }
+    if (!addr) {
+        lcritical("getaddrinfo failed, no address returned");
+        return -1;
+    }
+
+    memcpy(&self->addr, addr->ai_addr, addr->ai_addrlen);
+    self->addr_len = addr->ai_addrlen;
+    freeaddrinfo(addr);
+
+    if ((self->fd = socket(((struct sockaddr*)&self->addr)->sa_family, SOCK_DGRAM, 0)) < 0) {
+        lcritical("socket() error %s", core_log_errstr(errno));
+        return -2;
+    }
+
+    return 0;
+}
+
+int output_udpcli_nonblocking(output_udpcli_t* self)
+{
+    int flags;
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+
+    flags = fcntl(self->fd, F_GETFL);
+    if (flags != -1) {
+        flags = flags & O_NONBLOCK ? 1 : 0;
+    }
+
+    return flags;
+}
+
+int output_udpcli_set_nonblocking(output_udpcli_t* self, int nonblocking)
+{
+    int flags;
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+
+    if ((flags = fcntl(self->fd, F_GETFL)) == -1) {
+        lcritical("fcntl(FL_GETFL) error %s", core_log_errstr(errno));
+        return -1;
+    }
+
+    if (nonblocking) {
+        flags |= O_NONBLOCK;
+        self->blocking = 0;
+    } else {
+        flags &= ~O_NONBLOCK;
+        self->blocking = 1;
+    }
+
+    if (fcntl(self->fd, F_SETFL, flags | O_NONBLOCK)) {
+        lcritical("fcntl(FL_SETFL, %x) error %s", flags, core_log_errstr(errno));
+        return -1;
+    }
+
+    return 0;
+}
+
+static void _receive(output_udpcli_t* self, const core_object_t* obj)
+{
+    const uint8_t* payload;
+    size_t         len, sent;
+    mlassert_self();
+
+    for (; obj;) {
+        switch (obj->obj_type) {
+        case CORE_OBJECT_DNS:
+            obj = obj->obj_prev;
+            continue;
+        case CORE_OBJECT_PAYLOAD:
+            payload = ((core_object_payload_t*)obj)->payload;
+            len     = ((core_object_payload_t*)obj)->len;
+            break;
+        default:
+            return;
+        }
+
+        sent = 0;
+        for (;;) {
+            ssize_t ret = sendto(self->fd, payload + sent, len - sent, 0, (struct sockaddr*)&self->addr, self->addr_len);
+            if (ret > -1) {
+                sent += ret;
+                if (sent < len)
+                    continue;
+                self->pkts++;
+                return;
+            }
+            switch (errno) {
+            case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+            case EWOULDBLOCK:
+#endif
+                continue;
+            default:
+                break;
+            }
+            break;
+        }
+        self->errs++;
+        break;
+    }
+}
+
+core_receiver_t output_udpcli_receiver(output_udpcli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+
+    return (core_receiver_t)_receive;
+}
+
+static const core_object_t* _produce(output_udpcli_t* self)
+{
+    ssize_t n;
+    mlassert_self();
+
+    for (;;) {
+        n = recvfrom(self->fd, self->recvbuf, sizeof(self->recvbuf), 0, 0, 0);
+        if (n > -1) {
+            break;
+        }
+        switch (errno) {
+        case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+        case EWOULDBLOCK:
+#endif
+            self->pkt.len = 0;
+            return (core_object_t*)&self->pkt;
+        default:
+            break;
+        }
+        self->errs++;
+        break;
+    }
+
+    if (n < 1) {
+        return 0;
+    }
+
+    self->pkts_recv++;
+    self->pkt.len = n;
+    return (core_object_t*)&self->pkt;
+}
+
+static const core_object_t* _produce_block(output_udpcli_t* self)
+{
+    ssize_t       n;
+    struct pollfd p;
+    int           to;
+    mlassert_self();
+
+    p.fd      = self->fd;
+    p.events  = POLLIN;
+    p.revents = 0;
+    to        = (self->timeout.sec * 1e3) + (self->timeout.nsec / 1e6); //NOSONAR
+    if (!to) {
+        to = 1;
+    }
+
+    n = poll(&p, 1, to);
+    if (n < 0 || (p.revents & (POLLERR | POLLHUP | POLLNVAL))) {
+        self->errs++;
+        return 0;
+    }
+    if (!n || !(p.revents & POLLIN)) {
+        self->pkt.len = 0;
+        return (core_object_t*)&self->pkt;
+    }
+
+    for (;;) {
+        n = recvfrom(self->fd, self->recvbuf, sizeof(self->recvbuf), 0, 0, 0);
+        if (n > -1) {
+            break;
+        }
+        switch (errno) {
+        case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+        case EWOULDBLOCK:
+#endif
+            self->pkt.len = 0;
+            return (core_object_t*)&self->pkt;
+        default:
+            break;
+        }
+        self->errs++;
+        break;
+    }
+
+    if (n < 1) {
+        return 0;
+    }
+
+    self->pkts_recv++;
+    self->pkt.len = n;
+    return (core_object_t*)&self->pkt;
+}
+
+core_producer_t output_udpcli_producer(output_udpcli_t* self)
+{
+    mlassert_self();
+
+    if (self->fd < 0) {
+        lfatal("not connected");
+    }
+
+    if (self->blocking) {
+        return (core_producer_t)_produce_block;
+    }
+    return (core_producer_t)_produce;
+}
diff --git a/src/output/udpcli.h b/src/output/udpcli.h
new file mode 100644
index 0000000..4cb7af2
--- /dev/null
+++ b/src/output/udpcli.h
@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "core/log.h"
+#include "core/receiver.h"
+#include "core/producer.h"
+#include "core/object/payload.h"
+#include "core/timespec.h"
+
+#ifndef __dnsjit_output_udpcli_h
+#define __dnsjit_output_udpcli_h
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include "output/udpcli.hh"
+
+#endif
diff --git a/src/output/udpcli.hh b/src/output/udpcli.hh
new file mode 100644
index 0000000..084a5b6
--- /dev/null
+++ b/src/output/udpcli.hh
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2018-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * This file is part of dnsjit.
+ *
+ * dnsjit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dnsjit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+//lua:require("dnsjit.core.compat_h")
+//lua:require("dnsjit.core.log")
+//lua:require("dnsjit.core.receiver_h")
+//lua:require("dnsjit.core.producer_h")
+//lua:require("dnsjit.core.object.payload_h")
+//lua:require("dnsjit.core.timespec_h")
+
+typedef struct output_udpcli {
+    core_log_t _log;
+    size_t     pkts, errs;
+    int        fd;
+
+    struct sockaddr_storage addr;
+    size_t                  addr_len;
+
+    uint8_t               recvbuf[4 * 1024];
+    core_object_payload_t pkt;
+    size_t                pkts_recv;
+
+    core_timespec_t timeout;
+    int8_t          blocking;
+} output_udpcli_t;
+
+core_log_t* output_udpcli_log();
+
+void output_udpcli_init(output_udpcli_t* self);
+void output_udpcli_destroy(output_udpcli_t* self);
+int  output_udpcli_connect(output_udpcli_t* self, const char* host, const char* port);
+int  output_udpcli_nonblocking(output_udpcli_t* self);
+int  output_udpcli_set_nonblocking(output_udpcli_t* self, int nonblocking);
+
+core_receiver_t output_udpcli_receiver(output_udpcli_t* self);
+core_producer_t output_udpcli_producer(output_udpcli_t* self);
diff --git a/src/output/udpcli.lua b/src/output/udpcli.lua
new file mode 100644
index 0000000..0584725
--- /dev/null
+++ b/src/output/udpcli.lua
@@ -0,0 +1,121 @@
+-- Copyright (c) 2018-2021, OARC, Inc.
+-- All rights reserved.
+--
+-- This file is part of dnsjit.
+--
+-- dnsjit is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation, either version 3 of the License, or
+-- (at your option) any later version.
+--
+-- dnsjit is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License
+-- along with dnsjit.  If not, see <http://www.gnu.org/licenses/>.
+
+-- dnsjit.output.udpcli
+-- Simple and dumb UDP DNS client
+--   local output = require("dnsjit.output.udpcli").new("127.0.0.1", "53")
+--
+-- Simple and rather dumb DNS client that takes any payload you give it and
+-- sends the full payload over UDP.
+-- .SS Attributes
+-- .TP
+-- timeout
+-- A
+-- .I core.timespec
+-- that is used when producing objects.
+module(...,package.seeall)
+
+require("dnsjit.output.udpcli_h")
+local ffi = require("ffi")
+local C = ffi.C
+
+local t_name = "output_udpcli_t"
+local output_udpcli_t = ffi.typeof(t_name)
+local Udpcli = {}
+
+-- Create a new Udpcli output.
+function Udpcli.new()
+    local self = {
+        obj = output_udpcli_t(),
+    }
+    C.output_udpcli_init(self.obj)
+    ffi.gc(self.obj, C.output_udpcli_destroy)
+    return setmetatable(self, { __index = Udpcli })
+end
+
+-- Set the timeout when producing objects.
+function Udpcli:timeout(seconds, nanoseconds)
+    self.obj.timeout.sec = seconds
+    self.obj.timeout.nsec = nanoseconds
+end
+
+-- Connect to the
+-- .I host
+-- and
+-- .I port
+-- and return 0 if successful.
+function Udpcli:connect(host, port)
+    return C.output_udpcli_connect(self.obj, host, port)
+end
+
+-- Enable (true) or disable (false) nonblocking mode and
+-- return 0 if successful, if
+-- .I bool
+-- is not specified then return if nonblocking mode is on (true) or off (false).
+function Udpcli:nonblocking(bool)
+    if bool == nil then
+        if C.output_udpcli_nonblocking(self.obj) == 1 then
+            return true
+        end
+        return false
+    elseif bool == true then
+        return C.output_udpcli_set_nonblocking(self.obj, 1)
+    else
+        return C.output_udpcli_set_nonblocking(self.obj, 0)
+    end
+end
+
+-- Return the C functions and context for receiving objects, these objects
+-- will be sent.
+function Udpcli:receive()
+    return C.output_udpcli_receiver(self.obj), self.obj
+end
+
+-- Return the C functions and context for producing objects, these objects
+-- are received.
+-- If nonblocking mode is enabled the producer will return a payload object
+-- with length zero if there was nothing to receive.
+-- If nonblocking mode is disabled the producer will wait for data and if
+-- timed out (see
+-- .IR timeout )
+-- it will return a payload object with length zero.
+-- The producer returns nil on error.
+function Udpcli:produce()
+    return C.output_udpcli_producer(self.obj), self.obj
+end
+
+-- Return the number of "packets" sent, actually the number of completely sent
+-- payloads.
+function Udpcli:packets()
+    return tonumber(self.obj.pkts)
+end
+
+-- Return the number of "packets" received, actually the number of successful
+-- calls to
+-- .IR recvfrom (2)
+-- that returned data.
+function Udpcli:received()
+    return tonumber(self.obj.pkts_recv)
+end
+
+-- Return the number of errors when sending or receiving.
+function Udpcli:errors()
+    return tonumber(self.obj.errs)
+end
+
+return Udpcli