Adding upstream version 255.4.upstream/255.4

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

1 files changed, 3767 insertions, 0 deletions

diff --git a/src/shared/varlink.c b/src/shared/varlink.c
new file mode 100644
index 0000000..749b644
--- /dev/null
+++ b/src/shared/varlink.c
@@ -0,0 +1,3767 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <malloc.h>
+#include <poll.h>
+
+#include <sd-daemon.h>
+
+#include "alloc-util.h"
+#include "errno-util.h"
+#include "fd-util.h"
+#include "glyph-util.h"
+#include "hashmap.h"
+#include "io-util.h"
+#include "iovec-util.h"
+#include "list.h"
+#include "path-util.h"
+#include "process-util.h"
+#include "selinux-util.h"
+#include "serialize.h"
+#include "set.h"
+#include "socket-util.h"
+#include "string-table.h"
+#include "string-util.h"
+#include "strv.h"
+#include "time-util.h"
+#include "umask-util.h"
+#include "user-util.h"
+#include "varlink.h"
+#include "varlink-internal.h"
+#include "varlink-org.varlink.service.h"
+#include "varlink-io.systemd.h"
+#include "version.h"
+
+#define VARLINK_DEFAULT_CONNECTIONS_MAX 4096U
+#define VARLINK_DEFAULT_CONNECTIONS_PER_UID_MAX 1024U
+
+#define VARLINK_DEFAULT_TIMEOUT_USEC (45U*USEC_PER_SEC)
+#define VARLINK_BUFFER_MAX (16U*1024U*1024U)
+#define VARLINK_READ_SIZE (64U*1024U)
+
+typedef enum VarlinkState {
+        /* Client side states */
+        VARLINK_IDLE_CLIENT,
+        VARLINK_AWAITING_REPLY,
+        VARLINK_AWAITING_REPLY_MORE,
+        VARLINK_CALLING,
+        VARLINK_CALLED,
+        VARLINK_PROCESSING_REPLY,
+
+        /* Server side states */
+        VARLINK_IDLE_SERVER,
+        VARLINK_PROCESSING_METHOD,
+        VARLINK_PROCESSING_METHOD_MORE,
+        VARLINK_PROCESSING_METHOD_ONEWAY,
+        VARLINK_PROCESSED_METHOD,
+        VARLINK_PENDING_METHOD,
+        VARLINK_PENDING_METHOD_MORE,
+
+        /* Common states (only during shutdown) */
+        VARLINK_PENDING_DISCONNECT,
+        VARLINK_PENDING_TIMEOUT,
+        VARLINK_PROCESSING_DISCONNECT,
+        VARLINK_PROCESSING_TIMEOUT,
+        VARLINK_PROCESSING_FAILURE,
+        VARLINK_DISCONNECTED,
+
+        _VARLINK_STATE_MAX,
+        _VARLINK_STATE_INVALID = -EINVAL,
+} VarlinkState;
+
+/* Tests whether we are not yet disconnected. Note that this is true during all states where the connection
+ * is still good for something, and false only when it's dead for good. This means: when we are
+ * asynchronously connecting to a peer and the connect() is still pending, then this will return 'true', as
+ * the connection is still good, and we are likely to be able to properly operate on it soon. */
+#define VARLINK_STATE_IS_ALIVE(state)                   \
+        IN_SET(state,                                   \
+               VARLINK_IDLE_CLIENT,                     \
+               VARLINK_AWAITING_REPLY,                  \
+               VARLINK_AWAITING_REPLY_MORE,             \
+               VARLINK_CALLING,                         \
+               VARLINK_CALLED,                          \
+               VARLINK_PROCESSING_REPLY,                \
+               VARLINK_IDLE_SERVER,                     \
+               VARLINK_PROCESSING_METHOD,               \
+               VARLINK_PROCESSING_METHOD_MORE,          \
+               VARLINK_PROCESSING_METHOD_ONEWAY,        \
+               VARLINK_PROCESSED_METHOD,                \
+               VARLINK_PENDING_METHOD,                  \
+               VARLINK_PENDING_METHOD_MORE)
+
+typedef struct VarlinkJsonQueueItem VarlinkJsonQueueItem;
+
+/* A queued message we shall write into the socket, along with the file descriptors to send at the same
+ * time. This queue item binds them together so that message/fd boundaries are maintained throughout the
+ * whole pipeline. */
+struct VarlinkJsonQueueItem {
+        LIST_FIELDS(VarlinkJsonQueueItem, queue);
+        JsonVariant *data;
+        size_t n_fds;
+        int fds[];
+};
+
+struct Varlink {
+        unsigned n_ref;
+
+        VarlinkServer *server;
+
+        VarlinkState state;
+        bool connecting; /* This boolean indicates whether the socket fd we are operating on is currently
+                          * processing an asynchronous connect(). In that state we watch the socket for
+                          * EPOLLOUT, but we refrain from calling read() or write() on the socket as that
+                          * will trigger ENOTCONN. Note that this boolean is kept separate from the
+                          * VarlinkState above on purpose: while the connect() is still not complete we
+                          * already want to allow queuing of messages and similar. Thus it's nice to keep
+                          * these two state concepts separate: the VarlinkState encodes what our own view of
+                          * the connection is, i.e. whether we think it's a server, a client, and has
+                          * something queued already, while 'connecting' tells us a detail about the
+                          * transport used below, that should have no effect on how we otherwise accept and
+                          * process operations from the user.
+                          *
+                          * Or to say this differently: VARLINK_STATE_IS_ALIVE(state) tells you whether the
+                          * connection is good to use, even if it might not be fully connected
+                          * yet. connecting=true then informs you that actually we are still connecting, and
+                          * the connection is actually not established yet and thus any requests you enqueue
+                          * now will still work fine but will be queued only, not sent yet, but that
+                          * shouldn't stop you from using the connection, since eventually whatever you queue
+                          * *will* be sent.
+                          *
+                          * Or to say this even differently: 'state' is a high-level ("application layer"
+                          * high, if you so will) state, while 'conecting' is a low-level ("transport layer"
+                          * low, if you so will) state, and while they are not entirely unrelated and
+                          * sometimes propagate effects to each other they are only asynchronously connected
+                          * at most. */
+        unsigned n_pending;
+
+        int fd;
+
+        char *input_buffer; /* valid data starts at input_buffer_index, ends at input_buffer_index+input_buffer_size */
+        size_t input_buffer_index;
+        size_t input_buffer_size;
+        size_t input_buffer_unscanned;
+
+        void *input_control_buffer;
+        size_t input_control_buffer_size;
+
+        char *output_buffer; /* valid data starts at output_buffer_index, ends at output_buffer_index+output_buffer_size */
+        size_t output_buffer_index;
+        size_t output_buffer_size;
+
+        int *input_fds; /* file descriptors associated with the data in input_buffer (for fd passing) */
+        size_t n_input_fds;
+
+        int *output_fds; /* file descriptors associated with the data in output_buffer (for fd passing) */
+        size_t n_output_fds;
+
+        /* Further messages to output not yet formatted into text, and thus not included in output_buffer
+         * yet. We keep them separate from output_buffer, to not violate fd message boundaries: we want that
+         * each fd that is sent is associated with its fds, and that fds cannot be accidentally associated
+         * with preceding or following messages. */
+        LIST_HEAD(VarlinkJsonQueueItem, output_queue);
+        VarlinkJsonQueueItem *output_queue_tail;
+
+        /* The fds to associate with the next message that is about to be enqueued. The user first pushes the
+         * fds it intends to send via varlink_push_fd() into this queue, and then once the message data is
+         * submitted we'll combine the fds and the message data into one. */
+        int *pushed_fds;
+        size_t n_pushed_fds;
+
+        VarlinkReply reply_callback;
+
+        JsonVariant *current;
+        VarlinkSymbol *current_method;
+
+        struct ucred ucred;
+        bool ucred_acquired:1;
+
+        bool write_disconnected:1;
+        bool read_disconnected:1;
+        bool prefer_read_write:1;
+        bool got_pollhup:1;
+
+        bool allow_fd_passing_input:1;
+        bool allow_fd_passing_output:1;
+
+        bool output_buffer_sensitive:1; /* whether to erase the output buffer after writing it to the socket */
+
+        int af; /* address family if socket; AF_UNSPEC if not socket; negative if not known */
+
+        usec_t timestamp;
+        usec_t timeout;
+
+        void *userdata;
+        char *description;
+
+        sd_event *event;
+        sd_event_source *io_event_source;
+        sd_event_source *time_event_source;
+        sd_event_source *quit_event_source;
+        sd_event_source *defer_event_source;
+
+        pid_t exec_pid;
+};
+
+typedef struct VarlinkServerSocket VarlinkServerSocket;
+
+struct VarlinkServerSocket {
+        VarlinkServer *server;
+
+        int fd;
+        char *address;
+
+        sd_event_source *event_source;
+
+        LIST_FIELDS(VarlinkServerSocket, sockets);
+};
+
+struct VarlinkServer {
+        unsigned n_ref;
+        VarlinkServerFlags flags;
+
+        LIST_HEAD(VarlinkServerSocket, sockets);
+
+        Hashmap *methods;              /* Fully qualified symbol name of a method → VarlinkMethod */
+        Hashmap *interfaces;           /* Fully qualified interface name → VarlinkInterface* */
+        Hashmap *symbols;              /* Fully qualified symbol name of method/error → VarlinkSymbol* */
+        VarlinkConnect connect_callback;
+        VarlinkDisconnect disconnect_callback;
+
+        sd_event *event;
+        int64_t event_priority;
+
+        unsigned n_connections;
+        Hashmap *by_uid;               /* UID_TO_PTR(uid) → UINT_TO_PTR(n_connections) */
+
+        void *userdata;
+        char *description;
+
+        unsigned connections_max;
+        unsigned connections_per_uid_max;
+
+        bool exit_on_idle;
+};
+
+typedef struct VarlinkCollectContext {
+        JsonVariant *parameters;
+        const char *error_id;
+        VarlinkReplyFlags flags;
+} VarlinkCollectContext ;
+
+static const char* const varlink_state_table[_VARLINK_STATE_MAX] = {
+        [VARLINK_IDLE_CLIENT]              = "idle-client",
+        [VARLINK_AWAITING_REPLY]           = "awaiting-reply",
+        [VARLINK_AWAITING_REPLY_MORE]      = "awaiting-reply-more",
+        [VARLINK_CALLING]                  = "calling",
+        [VARLINK_CALLED]                   = "called",
+        [VARLINK_PROCESSING_REPLY]         = "processing-reply",
+        [VARLINK_IDLE_SERVER]              = "idle-server",
+        [VARLINK_PROCESSING_METHOD]        = "processing-method",
+        [VARLINK_PROCESSING_METHOD_MORE]   = "processing-method-more",
+        [VARLINK_PROCESSING_METHOD_ONEWAY] = "processing-method-oneway",
+        [VARLINK_PROCESSED_METHOD]         = "processed-method",
+        [VARLINK_PENDING_METHOD]           = "pending-method",
+        [VARLINK_PENDING_METHOD_MORE]      = "pending-method-more",
+        [VARLINK_PENDING_DISCONNECT]       = "pending-disconnect",
+        [VARLINK_PENDING_TIMEOUT]          = "pending-timeout",
+        [VARLINK_PROCESSING_DISCONNECT]    = "processing-disconnect",
+        [VARLINK_PROCESSING_TIMEOUT]       = "processing-timeout",
+        [VARLINK_PROCESSING_FAILURE]       = "processing-failure",
+        [VARLINK_DISCONNECTED]             = "disconnected",
+};
+
+DEFINE_PRIVATE_STRING_TABLE_LOOKUP_TO_STRING(varlink_state, VarlinkState);
+
+#define varlink_log_errno(v, error, fmt, ...)                           \
+        log_debug_errno(error, "%s: " fmt, varlink_description(v), ##__VA_ARGS__)
+
+#define varlink_log(v, fmt, ...)                                        \
+        log_debug("%s: " fmt, varlink_description(v), ##__VA_ARGS__)
+
+#define varlink_server_log_errno(s, error, fmt, ...) \
+        log_debug_errno(error, "%s: " fmt, varlink_server_description(s), ##__VA_ARGS__)
+
+#define varlink_server_log(s, fmt, ...) \
+        log_debug("%s: " fmt, varlink_server_description(s), ##__VA_ARGS__)
+
+static int varlink_format_queue(Varlink *v);
+static void varlink_server_test_exit_on_idle(VarlinkServer *s);
+
+static const char *varlink_description(Varlink *v) {
+        return (v ? v->description : NULL) ?: "varlink";
+}
+
+static const char *varlink_server_description(VarlinkServer *s) {
+        return (s ? s->description : NULL) ?: "varlink";
+}
+
+static VarlinkJsonQueueItem *varlink_json_queue_item_free(VarlinkJsonQueueItem *q) {
+        if (!q)
+                return NULL;
+
+        json_variant_unref(q->data);
+        close_many(q->fds, q->n_fds);
+
+        return mfree(q);
+}
+
+static VarlinkJsonQueueItem *varlink_json_queue_item_new(JsonVariant *m, const int fds[], size_t n_fds) {
+        VarlinkJsonQueueItem *q;
+
+        assert(m);
+        assert(fds || n_fds == 0);
+
+        q = malloc(offsetof(VarlinkJsonQueueItem, fds) + sizeof(int) * n_fds);
+        if (!q)
+                return NULL;
+
+        *q = (VarlinkJsonQueueItem) {
+                .data = json_variant_ref(m),
+                .n_fds = n_fds,
+        };
+
+        memcpy_safe(q->fds, fds, n_fds * sizeof(int));
+
+        return TAKE_PTR(q);
+}
+
+static void varlink_set_state(Varlink *v, VarlinkState state) {
+        assert(v);
+        assert(state >= 0 && state < _VARLINK_STATE_MAX);
+
+        if (v->state < 0)
+                varlink_log(v, "Setting state %s",
+                            varlink_state_to_string(state));
+        else
+                varlink_log(v, "Changing state %s %s %s",
+                            varlink_state_to_string(v->state),
+                            special_glyph(SPECIAL_GLYPH_ARROW_RIGHT),
+                            varlink_state_to_string(state));
+
+        v->state = state;
+}
+
+static int varlink_new(Varlink **ret) {
+        Varlink *v;
+
+        assert(ret);
+
+        v = new(Varlink, 1);
+        if (!v)
+                return -ENOMEM;
+
+        *v = (Varlink) {
+                .n_ref = 1,
+                .fd = -EBADF,
+
+                .state = _VARLINK_STATE_INVALID,
+
+                .ucred = UCRED_INVALID,
+
+                .timestamp = USEC_INFINITY,
+                .timeout = VARLINK_DEFAULT_TIMEOUT_USEC,
+
+                .af = -1,
+        };
+
+        *ret = v;
+        return 0;
+}
+
+int varlink_connect_address(Varlink **ret, const char *address) {
+        _cleanup_(varlink_unrefp) Varlink *v = NULL;
+        union sockaddr_union sockaddr;
+        int r;
+
+        assert_return(ret, -EINVAL);
+        assert_return(address, -EINVAL);
+
+        r = varlink_new(&v);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to create varlink object: %m");
+
+        v->fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+        if (v->fd < 0)
+                return log_debug_errno(errno, "Failed to create AF_UNIX socket: %m");
+
+        v->fd = fd_move_above_stdio(v->fd);
+        v->af = AF_UNIX;
+
+        r = sockaddr_un_set_path(&sockaddr.un, address);
+        if (r < 0) {
+                if (r != -ENAMETOOLONG)
+                        return log_debug_errno(r, "Failed to set socket address '%s': %m", address);
+
+                /* This is a file system path, and too long to fit into sockaddr_un. Let's connect via O_PATH
+                 * to this socket. */
+
+                r = connect_unix_path(v->fd, AT_FDCWD, address);
+        } else
+                r = RET_NERRNO(connect(v->fd, &sockaddr.sa, r));
+
+        if (r < 0) {
+                if (!IN_SET(r, -EAGAIN, -EINPROGRESS))
+                        return log_debug_errno(r, "Failed to connect to %s: %m", address);
+
+                v->connecting = true; /* We are asynchronously connecting, i.e. the connect() is being
+                                       * processed in the background. As long as that's the case the socket
+                                       * is in a special state: it's there, we can poll it for EPOLLOUT, but
+                                       * if we attempt to write() to it before we see EPOLLOUT we'll get
+                                       * ENOTCONN (and not EAGAIN, like we would for a normal connected
+                                       * socket that isn't writable at the moment). Since ENOTCONN on write()
+                                       * hence can mean two different things (i.e. connection not complete
+                                       * yet vs. already disconnected again), we store as a boolean whether
+                                       * we are still in connect(). */
+        }
+
+        varlink_set_state(v, VARLINK_IDLE_CLIENT);
+
+        *ret = TAKE_PTR(v);
+        return 0;
+}
+
+int varlink_connect_exec(Varlink **ret, const char *_command, char **_argv) {
+        _cleanup_close_pair_ int pair[2] = EBADF_PAIR;
+        _cleanup_(sigkill_waitp) pid_t pid = 0;
+        _cleanup_free_ char *command = NULL;
+        _cleanup_strv_free_ char **argv = NULL;
+        int r;
+
+        assert_return(ret, -EINVAL);
+        assert_return(_command, -EINVAL);
+
+        /* Copy the strings, in case they point into our own argv[], which we'll invalidate shortly because
+         * we rename the child process */
+        command = strdup(_command);
+        if (!command)
+                return -ENOMEM;
+
+        if (strv_isempty(_argv))
+                argv = strv_new(command);
+        else
+                argv = strv_copy(_argv);
+        if (!argv)
+                return -ENOMEM;
+
+        log_debug("Forking off Varlink child process '%s'.", command);
+
+        if (socketpair(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0, pair) < 0)
+                return log_debug_errno(errno, "Failed to allocate AF_UNIX socket pair: %m");
+
+        r = safe_fork_full(
+                        "(sd-vlexec)",
+                        /* stdio_fds= */ NULL,
+                        /* except_fds= */ (int[]) { pair[1] },
+                        /* n_except_fds= */ 1,
+                        FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_REOPEN_LOG|FORK_LOG|FORK_RLIMIT_NOFILE_SAFE,
+                        &pid);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to spawn process: %m");
+        if (r == 0) {
+                char spid[DECIMAL_STR_MAX(pid_t)+1];
+                const char *setenv_list[] = {
+                        "LISTEN_FDS", "1",
+                        "LISTEN_PID", spid,
+                        "LISTEN_FDNAMES", "varlink",
+                        NULL, NULL,
+                };
+                /* Child */
+
+                pair[0] = -EBADF;
+
+                r = move_fd(pair[1], 3, /* cloexec= */ false);
+                if (r < 0) {
+                        log_debug_errno(r, "Failed to move file descriptor to 3: %m");
+                        _exit(EXIT_FAILURE);
+                }
+
+                xsprintf(spid, PID_FMT, pid);
+
+                STRV_FOREACH_PAIR(a, b, setenv_list) {
+                        if (setenv(*a, *b, /* override= */ true) < 0) {
+                                log_debug_errno(errno, "Failed to set environment variable '%s': %m", *a);
+                                _exit(EXIT_FAILURE);
+                        }
+                }
+
+                execvp(command, argv);
+                log_debug_errno(r, "Failed to invoke process '%s': %m", command);
+                _exit(EXIT_FAILURE);
+        }
+
+        pair[1] = safe_close(pair[1]);
+
+        Varlink *v;
+        r = varlink_new(&v);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to create varlink object: %m");
+
+        v->fd = TAKE_FD(pair[0]);
+        v->af = AF_UNIX;
+        v->exec_pid = TAKE_PID(pid);
+        varlink_set_state(v, VARLINK_IDLE_CLIENT);
+
+        *ret = v;
+        return 0;
+}
+
+int varlink_connect_url(Varlink **ret, const char *url) {
+        _cleanup_free_ char *c = NULL;
+        const char *p;
+        bool exec;
+        int r;
+
+        assert_return(ret, -EINVAL);
+        assert_return(url, -EINVAL);
+
+        // FIXME: Add support for vsock:, ssh-exec:, ssh-unix: URL schemes here. (The latter with OpenSSH
+        // 9.4's -W switch for referencing remote AF_UNIX sockets.)
+
+        /* The Varlink URL scheme is a bit underdefined. We support only the unix: transport for now, plus an
+         * exec: transport we made up ourselves. Strictly speaking this shouldn't even be called URL, since
+         * it has nothing to do with Internet URLs by RFC. */
+
+        p = startswith(url, "unix:");
+        if (p)
+                exec = false;
+        else {
+                p = startswith(url, "exec:");
+                if (!p)
+                        return log_debug_errno(SYNTHETIC_ERRNO(EPROTONOSUPPORT), "URL scheme not supported.");
+
+                exec = true;
+        }
+
+        /* The varlink.org reference C library supports more than just file system paths. We might want to
+         * support that one day too. For now simply refuse that. */
+        if (p[strcspn(p, ";?#")] != '\0')
+                return log_debug_errno(SYNTHETIC_ERRNO(EPROTONOSUPPORT), "URL parameterization with ';', '?', '#' not supported.");
+
+        if (exec || p[0] != '@') { /* no validity checks for abstract namespace */
+
+                if (!path_is_absolute(p))
+                        return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Specified path not absolute, refusing.");
+
+                r = path_simplify_alloc(p, &c);
+                if (r < 0)
+                        return r;
+
+                if (!path_is_normalized(c))
+                        return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Specified path is not normalized, refusing.");
+        }
+
+        if (exec)
+                return varlink_connect_exec(ret, c, NULL);
+
+        return varlink_connect_address(ret, c ?: p);
+}
+
+int varlink_connect_fd(Varlink **ret, int fd) {
+        Varlink *v;
+        int r;
+
+        assert_return(ret, -EINVAL);
+        assert_return(fd >= 0, -EBADF);
+
+        r = fd_nonblock(fd, true);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to make fd %d nonblocking: %m", fd);
+
+        r = varlink_new(&v);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to create varlink object: %m");
+
+        v->fd = fd;
+        v->af = -1,
+        varlink_set_state(v, VARLINK_IDLE_CLIENT);
+
+        /* Note that if this function is called we assume the passed socket (if it is one) is already
+         * properly connected, i.e. any asynchronous connect() done on it already completed. Because of that
+         * we'll not set the 'connecting' boolean here, i.e. we don't need to avoid write()ing to the socket
+         * until the connection is fully set up. Behaviour here is hence a bit different from
+         * varlink_connect_address() above, as there we do handle asynchronous connections ourselves and
+         * avoid doing write() on it before we saw EPOLLOUT for the first time. */
+
+        *ret = v;
+        return 0;
+}
+
+static void varlink_detach_event_sources(Varlink *v) {
+        assert(v);
+
+        v->io_event_source = sd_event_source_disable_unref(v->io_event_source);
+        v->time_event_source = sd_event_source_disable_unref(v->time_event_source);
+        v->quit_event_source = sd_event_source_disable_unref(v->quit_event_source);
+        v->defer_event_source = sd_event_source_disable_unref(v->defer_event_source);
+}
+
+static void varlink_clear_current(Varlink *v) {
+        assert(v);
+
+        /* Clears the currently processed incoming message */
+        v->current = json_variant_unref(v->current);
+        v->current_method = NULL;
+
+        close_many(v->input_fds, v->n_input_fds);
+        v->input_fds = mfree(v->input_fds);
+        v->n_input_fds = 0;
+}
+
+static void varlink_clear(Varlink *v) {
+        assert(v);
+
+        varlink_detach_event_sources(v);
+
+        v->fd = safe_close(v->fd);
+
+        varlink_clear_current(v);
+
+        v->input_buffer = mfree(v->input_buffer);
+        v->output_buffer = v->output_buffer_sensitive ? erase_and_free(v->output_buffer) : mfree(v->output_buffer);
+
+        v->input_control_buffer = mfree(v->input_control_buffer);
+        v->input_control_buffer_size = 0;
+
+        close_many(v->output_fds, v->n_output_fds);
+        v->output_fds = mfree(v->output_fds);
+        v->n_output_fds = 0;
+
+        close_many(v->pushed_fds, v->n_pushed_fds);
+        v->pushed_fds = mfree(v->pushed_fds);
+        v->n_pushed_fds = 0;
+
+        LIST_CLEAR(queue, v->output_queue, varlink_json_queue_item_free);
+        v->output_queue_tail = NULL;
+
+        v->event = sd_event_unref(v->event);
+
+        if (v->exec_pid > 0) {
+                sigterm_wait(v->exec_pid);
+                v->exec_pid = 0;
+        }
+}
+
+static Varlink* varlink_destroy(Varlink *v) {
+        if (!v)
+                return NULL;
+
+        /* If this is called the server object must already been unreffed here. Why that? because when we
+         * linked up the varlink connection with the server object we took one ref in each direction */
+        assert(!v->server);
+
+        varlink_clear(v);
+
+        free(v->description);
+        return mfree(v);
+}
+
+DEFINE_TRIVIAL_REF_UNREF_FUNC(Varlink, varlink, varlink_destroy);
+
+static int varlink_test_disconnect(Varlink *v) {
+        assert(v);
+
+        /* Tests whether we the connection has been terminated. We are careful to not stop processing it
+         * prematurely, since we want to handle half-open connections as well as possible and want to flush
+         * out and read data before we close down if we can. */
+
+        /* Already disconnected? */
+        if (!VARLINK_STATE_IS_ALIVE(v->state))
+                return 0;
+
+        /* Wait until connection setup is complete, i.e. until asynchronous connect() completes */
+        if (v->connecting)
+                return 0;
+
+        /* Still something to write and we can write? Stay around */
+        if (v->output_buffer_size > 0 && !v->write_disconnected)
+                return 0;
+
+        /* Both sides gone already? Then there's no need to stick around */
+        if (v->read_disconnected && v->write_disconnected)
+                goto disconnect;
+
+        /* If we are waiting for incoming data but the read side is shut down, disconnect. */
+        if (IN_SET(v->state, VARLINK_AWAITING_REPLY, VARLINK_AWAITING_REPLY_MORE, VARLINK_CALLING, VARLINK_IDLE_SERVER) && v->read_disconnected)
+                goto disconnect;
+
+        /* Similar, if are a client that hasn't written anything yet but the write side is dead, also
+         * disconnect. We also explicitly check for POLLHUP here since we likely won't notice the write side
+         * being down if we never wrote anything. */
+        if (v->state == VARLINK_IDLE_CLIENT && (v->write_disconnected || v->got_pollhup))
+                goto disconnect;
+
+        /* We are on the server side and still want to send out more replies, but we saw POLLHUP already, and
+         * either got no buffered bytes to write anymore or already saw a write error. In that case we should
+         * shut down the varlink link. */
+        if (IN_SET(v->state, VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE) && (v->write_disconnected || v->output_buffer_size == 0) && v->got_pollhup)
+                goto disconnect;
+
+        return 0;
+
+disconnect:
+        varlink_set_state(v, VARLINK_PENDING_DISCONNECT);
+        return 1;
+}
+
+static int varlink_write(Varlink *v) {
+        ssize_t n;
+        int r;
+
+        assert(v);
+
+        if (!VARLINK_STATE_IS_ALIVE(v->state))
+                return 0;
+        if (v->connecting) /* Writing while we are still wait for a non-blocking connect() to complete will
+                            * result in ENOTCONN, hence exit early here */
+                return 0;
+        if (v->write_disconnected)
+                return 0;
+
+        /* If needed let's convert some output queue json variants into text form */
+        r = varlink_format_queue(v);
+        if (r < 0)
+                return r;
+
+        if (v->output_buffer_size == 0)
+                return 0;
+
+        assert(v->fd >= 0);
+
+        if (v->n_output_fds > 0) { /* If we shall send fds along, we must use sendmsg() */
+                struct iovec iov = {
+                        .iov_base = v->output_buffer + v->output_buffer_index,
+                        .iov_len = v->output_buffer_size,
+                };
+                struct msghdr mh = {
+                        .msg_iov = &iov,
+                        .msg_iovlen = 1,
+                        .msg_controllen = CMSG_SPACE(sizeof(int) * v->n_output_fds),
+                };
+
+                mh.msg_control = alloca0(mh.msg_controllen);
+
+                struct cmsghdr *control = CMSG_FIRSTHDR(&mh);
+                control->cmsg_len = CMSG_LEN(sizeof(int) * v->n_output_fds);
+                control->cmsg_level = SOL_SOCKET;
+                control->cmsg_type = SCM_RIGHTS;
+                memcpy(CMSG_DATA(control), v->output_fds, sizeof(int) * v->n_output_fds);
+
+                n = sendmsg(v->fd, &mh, MSG_DONTWAIT|MSG_NOSIGNAL);
+        } else {
+                /* We generally prefer recv()/send() (mostly because of MSG_NOSIGNAL) but also want to be compatible
+                 * with non-socket IO, hence fall back automatically.
+                 *
+                 * Use a local variable to help gcc figure out that we set 'n' in all cases. */
+                bool prefer_write = v->prefer_read_write;
+                if (!prefer_write) {
+                        n = send(v->fd, v->output_buffer + v->output_buffer_index, v->output_buffer_size, MSG_DONTWAIT|MSG_NOSIGNAL);
+                        if (n < 0 && errno == ENOTSOCK)
+                                prefer_write = v->prefer_read_write = true;
+                }
+                if (prefer_write)
+                        n = write(v->fd, v->output_buffer + v->output_buffer_index, v->output_buffer_size);
+        }
+        if (n < 0) {
+                if (errno == EAGAIN)
+                        return 0;
+
+                if (ERRNO_IS_DISCONNECT(errno)) {
+                        /* If we get informed about a disconnect on write, then let's remember that, but not
+                         * act on it just yet. Let's wait for read() to report the issue first. */
+                        v->write_disconnected = true;
+                        return 1;
+                }
+
+                return -errno;
+        }
+
+        if (v->output_buffer_sensitive)
+                explicit_bzero_safe(v->output_buffer + v->output_buffer_index, n);
+
+        v->output_buffer_size -= n;
+
+        if (v->output_buffer_size == 0) {
+                v->output_buffer_index = 0;
+                v->output_buffer_sensitive = false; /* We can reset the sensitive flag once the buffer is empty */
+        } else
+                v->output_buffer_index += n;
+
+        close_many(v->output_fds, v->n_output_fds);
+        v->n_output_fds = 0;
+
+        v->timestamp = now(CLOCK_MONOTONIC);
+        return 1;
+}
+
+#define VARLINK_FDS_MAX (16U*1024U)
+
+static int varlink_read(Varlink *v) {
+        struct iovec iov;
+        struct msghdr mh;
+        size_t rs;
+        ssize_t n;
+        void *p;
+
+        assert(v);
+
+        if (!IN_SET(v->state, VARLINK_AWAITING_REPLY, VARLINK_AWAITING_REPLY_MORE, VARLINK_CALLING, VARLINK_IDLE_SERVER))
+                return 0;
+        if (v->connecting) /* read() on a socket while we are in connect() will fail with EINVAL, hence exit early here */
+                return 0;
+        if (v->current)
+                return 0;
+        if (v->input_buffer_unscanned > 0)
+                return 0;
+        if (v->read_disconnected)
+                return 0;
+
+        if (v->input_buffer_size >= VARLINK_BUFFER_MAX)
+                return -ENOBUFS;
+
+        assert(v->fd >= 0);
+
+        if (MALLOC_SIZEOF_SAFE(v->input_buffer) <= v->input_buffer_index + v->input_buffer_size) {
+                size_t add;
+
+                add = MIN(VARLINK_BUFFER_MAX - v->input_buffer_size, VARLINK_READ_SIZE);
+
+                if (v->input_buffer_index == 0) {
+
+                        if (!GREEDY_REALLOC(v->input_buffer, v->input_buffer_size + add))
+                                return -ENOMEM;
+
+                } else {
+                        char *b;
+
+                        b = new(char, v->input_buffer_size + add);
+                        if (!b)
+                                return -ENOMEM;
+
+                        memcpy(b, v->input_buffer + v->input_buffer_index, v->input_buffer_size);
+
+                        free_and_replace(v->input_buffer, b);
+                        v->input_buffer_index = 0;
+                }
+        }
+
+        p = v->input_buffer + v->input_buffer_index + v->input_buffer_size;
+        rs = MALLOC_SIZEOF_SAFE(v->input_buffer) - (v->input_buffer_index + v->input_buffer_size);
+
+        if (v->allow_fd_passing_input) {
+                iov = IOVEC_MAKE(p, rs);
+
+                /* Allocate the fd buffer on the heap, since we need a lot of space potentially */
+                if (!v->input_control_buffer) {
+                        v->input_control_buffer_size = CMSG_SPACE(sizeof(int) * VARLINK_FDS_MAX);
+                        v->input_control_buffer = malloc(v->input_control_buffer_size);
+                        if (!v->input_control_buffer)
+                                return -ENOMEM;
+                }
+
+                mh = (struct msghdr) {
+                        .msg_iov = &iov,
+                        .msg_iovlen = 1,
+                        .msg_control = v->input_control_buffer,
+                        .msg_controllen = v->input_control_buffer_size,
+                };
+
+                n = recvmsg_safe(v->fd, &mh, MSG_DONTWAIT|MSG_CMSG_CLOEXEC);
+        } else {
+                bool prefer_read = v->prefer_read_write;
+                if (!prefer_read) {
+                        n = recv(v->fd, p, rs, MSG_DONTWAIT);
+                        if (n < 0 && errno == ENOTSOCK)
+                                prefer_read = v->prefer_read_write = true;
+                }
+                if (prefer_read)
+                        n = read(v->fd, p, rs);
+        }
+        if (n < 0) {
+                if (errno == EAGAIN)
+                        return 0;
+
+                if (ERRNO_IS_DISCONNECT(errno)) {
+                        v->read_disconnected = true;
+                        return 1;
+                }
+
+                return -errno;
+        }
+        if (n == 0) { /* EOF */
+
+                if (v->allow_fd_passing_input)
+                        cmsg_close_all(&mh);
+
+                v->read_disconnected = true;
+                return 1;
+        }
+
+        if (v->allow_fd_passing_input) {
+                struct cmsghdr* cmsg;
+
+                cmsg = cmsg_find(&mh, SOL_SOCKET, SCM_RIGHTS, (socklen_t) -1);
+                if (cmsg) {
+                        size_t add;
+
+                        /* We only allow file descriptors to be passed along with the first byte of a
+                         * message. If they are passed with any other byte this is a protocol violation. */
+                        if (v->input_buffer_size != 0) {
+                                cmsg_close_all(&mh);
+                                return -EPROTO;
+                        }
+
+                        add = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
+                        if (add > INT_MAX - v->n_input_fds) {
+                                cmsg_close_all(&mh);
+                                return -EBADF;
+                        }
+
+                        if (!GREEDY_REALLOC(v->input_fds, v->n_input_fds + add)) {
+                                cmsg_close_all(&mh);
+                                return -ENOMEM;
+                        }
+
+                        memcpy_safe(v->input_fds + v->n_input_fds, CMSG_TYPED_DATA(cmsg, int), add * sizeof(int));
+                        v->n_input_fds += add;
+                }
+        }
+
+        v->input_buffer_size += n;
+        v->input_buffer_unscanned += n;
+
+        return 1;
+}
+
+static int varlink_parse_message(Varlink *v) {
+        const char *e, *begin;
+        size_t sz;
+        int r;
+
+        assert(v);
+
+        if (v->current)
+                return 0;
+        if (v->input_buffer_unscanned <= 0)
+                return 0;
+
+        assert(v->input_buffer_unscanned <= v->input_buffer_size);
+        assert(v->input_buffer_index + v->input_buffer_size <= MALLOC_SIZEOF_SAFE(v->input_buffer));
+
+        begin = v->input_buffer + v->input_buffer_index;
+
+        e = memchr(begin + v->input_buffer_size - v->input_buffer_unscanned, 0, v->input_buffer_unscanned);
+        if (!e) {
+                v->input_buffer_unscanned = 0;
+                return 0;
+        }
+
+        sz = e - begin + 1;
+
+        varlink_log(v, "New incoming message: %s", begin); /* FIXME: should we output the whole message here before validation?
+                                                            * This may produce a non-printable journal entry if the message
+                                                            * is invalid. We may also expose privileged information. */
+
+        r = json_parse(begin, 0, &v->current, NULL, NULL);
+        if (r < 0) {
+                /* If we encounter a parse failure flush all data. We cannot possibly recover from this,
+                 * hence drop all buffered data now. */
+                v->input_buffer_index = v->input_buffer_size = v->input_buffer_unscanned = 0;
+                return varlink_log_errno(v, r, "Failed to parse JSON: %m");
+        }
+
+        v->input_buffer_size -= sz;
+
+        if (v->input_buffer_size == 0)
+                v->input_buffer_index = 0;
+        else
+                v->input_buffer_index += sz;
+
+        v->input_buffer_unscanned = v->input_buffer_size;
+        return 1;
+}
+
+static int varlink_test_timeout(Varlink *v) {
+        assert(v);
+
+        if (!IN_SET(v->state, VARLINK_AWAITING_REPLY, VARLINK_AWAITING_REPLY_MORE, VARLINK_CALLING))
+                return 0;
+        if (v->timeout == USEC_INFINITY)
+                return 0;
+
+        if (now(CLOCK_MONOTONIC) < usec_add(v->timestamp, v->timeout))
+                return 0;
+
+        varlink_set_state(v, VARLINK_PENDING_TIMEOUT);
+
+        return 1;
+}
+
+static int varlink_dispatch_local_error(Varlink *v, const char *error) {
+        int r;
+
+        assert(v);
+        assert(error);
+
+        if (!v->reply_callback)
+                return 0;
+
+        r = v->reply_callback(v, NULL, error, VARLINK_REPLY_ERROR|VARLINK_REPLY_LOCAL, v->userdata);
+        if (r < 0)
+                log_debug_errno(r, "Reply callback returned error, ignoring: %m");
+
+        return 1;
+}
+
+static int varlink_dispatch_timeout(Varlink *v) {
+        assert(v);
+
+        if (v->state != VARLINK_PENDING_TIMEOUT)
+                return 0;
+
+        varlink_set_state(v, VARLINK_PROCESSING_TIMEOUT);
+        varlink_dispatch_local_error(v, VARLINK_ERROR_TIMEOUT);
+        varlink_close(v);
+
+        return 1;
+}
+
+static int varlink_dispatch_disconnect(Varlink *v) {
+        assert(v);
+
+        if (v->state != VARLINK_PENDING_DISCONNECT)
+                return 0;
+
+        varlink_set_state(v, VARLINK_PROCESSING_DISCONNECT);
+        varlink_dispatch_local_error(v, VARLINK_ERROR_DISCONNECTED);
+        varlink_close(v);
+
+        return 1;
+}
+
+static int varlink_sanitize_parameters(JsonVariant **v) {
+        int r;
+
+        assert(v);
+
+        /* Varlink always wants a parameters list, hence make one if the caller doesn't want any */
+        if (!*v)
+                return json_variant_new_object(v, NULL, 0);
+        if (json_variant_is_null(*v)) {
+                JsonVariant *empty;
+
+                r = json_variant_new_object(&empty, NULL, 0);
+                if (r < 0)
+                        return r;
+
+                json_variant_unref(*v);
+                *v = empty;
+                return 0;
+        }
+        if (!json_variant_is_object(*v))
+                return -EINVAL;
+
+        return 0;
+}
+
+static int varlink_dispatch_reply(Varlink *v) {
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        VarlinkReplyFlags flags = 0;
+        const char *error = NULL;
+        JsonVariant *e;
+        const char *k;
+        int r;
+
+        assert(v);
+
+        if (!IN_SET(v->state, VARLINK_AWAITING_REPLY, VARLINK_AWAITING_REPLY_MORE, VARLINK_CALLING))
+                return 0;
+        if (!v->current)
+                return 0;
+
+        assert(v->n_pending > 0);
+
+        if (!json_variant_is_object(v->current))
+                goto invalid;
+
+        JSON_VARIANT_OBJECT_FOREACH(k, e, v->current) {
+
+                if (streq(k, "error")) {
+                        if (error)
+                                goto invalid;
+                        if (!json_variant_is_string(e))
+                                goto invalid;
+
+                        error = json_variant_string(e);
+                        flags |= VARLINK_REPLY_ERROR;
+
+                } else if (streq(k, "parameters")) {
+                        if (parameters)
+                                goto invalid;
+                        if (!json_variant_is_object(e) && !json_variant_is_null(e))
+                                goto invalid;
+
+                        parameters = json_variant_ref(e);
+
+                } else if (streq(k, "continues")) {
+                        if (FLAGS_SET(flags, VARLINK_REPLY_CONTINUES))
+                                goto invalid;
+
+                        if (!json_variant_is_boolean(e))
+                                goto invalid;
+
+                        if (json_variant_boolean(e))
+                                flags |= VARLINK_REPLY_CONTINUES;
+                } else
+                        goto invalid;
+        }
+
+        /* Replies with 'continue' set are only OK if we set 'more' when the method call was initiated */
+        if (v->state != VARLINK_AWAITING_REPLY_MORE && FLAGS_SET(flags, VARLINK_REPLY_CONTINUES))
+                goto invalid;
+
+        /* An error is final */
+        if (error && FLAGS_SET(flags, VARLINK_REPLY_CONTINUES))
+                goto invalid;
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                goto invalid;
+
+        if (IN_SET(v->state, VARLINK_AWAITING_REPLY, VARLINK_AWAITING_REPLY_MORE)) {
+                varlink_set_state(v, VARLINK_PROCESSING_REPLY);
+
+                if (v->reply_callback) {
+                        r = v->reply_callback(v, parameters, error, flags, v->userdata);
+                        if (r < 0)
+                                log_debug_errno(r, "Reply callback returned error, ignoring: %m");
+                }
+
+                varlink_clear_current(v);
+
+                if (v->state == VARLINK_PROCESSING_REPLY) {
+
+                        assert(v->n_pending > 0);
+
+                        if (!FLAGS_SET(flags, VARLINK_REPLY_CONTINUES))
+                                v->n_pending--;
+
+                        varlink_set_state(v,
+                                          FLAGS_SET(flags, VARLINK_REPLY_CONTINUES) ? VARLINK_AWAITING_REPLY_MORE :
+                                          v->n_pending == 0 ? VARLINK_IDLE_CLIENT : VARLINK_AWAITING_REPLY);
+                }
+        } else {
+                assert(v->state == VARLINK_CALLING);
+                varlink_set_state(v, VARLINK_CALLED);
+        }
+
+        return 1;
+
+invalid:
+        varlink_set_state(v, VARLINK_PROCESSING_FAILURE);
+        varlink_dispatch_local_error(v, VARLINK_ERROR_PROTOCOL);
+        varlink_close(v);
+
+        return 1;
+}
+
+static int generic_method_get_info(
+                Varlink *link,
+                JsonVariant *parameters,
+                VarlinkMethodFlags flags,
+                void *userdata) {
+
+        _cleanup_strv_free_ char **interfaces = NULL;
+        _cleanup_free_ char *product = NULL;
+        int r;
+
+        assert(link);
+
+        if (json_variant_elements(parameters) != 0)
+                return varlink_errorb(link, VARLINK_ERROR_INVALID_PARAMETER,
+                                      JSON_BUILD_OBJECT(
+                                                      JSON_BUILD_PAIR_VARIANT("parameter", json_variant_by_index(parameters, 0))));
+
+        product = strjoin("systemd (", program_invocation_short_name, ")");
+        if (!product)
+                return -ENOMEM;
+
+        VarlinkInterface *interface;
+        HASHMAP_FOREACH(interface, ASSERT_PTR(link->server)->interfaces) {
+                r = strv_extend(&interfaces, interface->name);
+                if (r < 0)
+                        return r;
+        }
+
+        strv_sort(interfaces);
+
+        return varlink_replyb(link, JSON_BUILD_OBJECT(
+                                              JSON_BUILD_PAIR_STRING("vendor", "The systemd Project"),
+                                              JSON_BUILD_PAIR_STRING("product", product),
+                                              JSON_BUILD_PAIR_STRING("version", STRINGIFY(PROJECT_VERSION) " (" GIT_VERSION ")"),
+                                              JSON_BUILD_PAIR_STRING("url", "https://systemd.io/"),
+                                              JSON_BUILD_PAIR_STRV("interfaces", interfaces)));
+}
+
+static int generic_method_get_interface_description(
+                Varlink *link,
+                JsonVariant *parameters,
+                VarlinkMethodFlags flags,
+                void *userdata) {
+
+        static const struct JsonDispatch dispatch_table[] = {
+                { "interface",  JSON_VARIANT_STRING, json_dispatch_const_string, 0, JSON_MANDATORY },
+                {}
+        };
+        _cleanup_free_ char *text = NULL;
+        const VarlinkInterface *interface;
+        const char *name = NULL;
+        int r;
+
+        assert(link);
+
+        r = json_dispatch(parameters, dispatch_table, 0, &name);
+        if (r < 0)
+                return r;
+
+        interface = hashmap_get(ASSERT_PTR(link->server)->interfaces, name);
+        if (!interface)
+                return varlink_errorb(link, VARLINK_ERROR_INTERFACE_NOT_FOUND,
+                                      JSON_BUILD_OBJECT(
+                                                      JSON_BUILD_PAIR_STRING("interface", name)));
+
+        r = varlink_idl_format(interface, &text);
+        if (r < 0)
+                return r;
+
+        return varlink_replyb(link,
+                           JSON_BUILD_OBJECT(
+                                           JSON_BUILD_PAIR_STRING("description", text)));
+}
+
+static int varlink_dispatch_method(Varlink *v) {
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        VarlinkMethodFlags flags = 0;
+        const char *method = NULL;
+        JsonVariant *e;
+        VarlinkMethod callback;
+        const char *k;
+        int r;
+
+        assert(v);
+
+        if (v->state != VARLINK_IDLE_SERVER)
+                return 0;
+        if (!v->current)
+                return 0;
+
+        if (!json_variant_is_object(v->current))
+                goto invalid;
+
+        JSON_VARIANT_OBJECT_FOREACH(k, e, v->current) {
+
+                if (streq(k, "method")) {
+                        if (method)
+                                goto invalid;
+                        if (!json_variant_is_string(e))
+                                goto invalid;
+
+                        method = json_variant_string(e);
+
+                } else if (streq(k, "parameters")) {
+                        if (parameters)
+                                goto invalid;
+                        if (!json_variant_is_object(e) && !json_variant_is_null(e))
+                                goto invalid;
+
+                        parameters = json_variant_ref(e);
+
+                } else if (streq(k, "oneway")) {
+
+                        if ((flags & (VARLINK_METHOD_ONEWAY|VARLINK_METHOD_MORE)) != 0)
+                                goto invalid;
+
+                        if (!json_variant_is_boolean(e))
+                                goto invalid;
+
+                        if (json_variant_boolean(e))
+                                flags |= VARLINK_METHOD_ONEWAY;
+
+                } else if (streq(k, "more")) {
+
+                        if ((flags & (VARLINK_METHOD_ONEWAY|VARLINK_METHOD_MORE)) != 0)
+                                goto invalid;
+
+                        if (!json_variant_is_boolean(e))
+                                goto invalid;
+
+                        if (json_variant_boolean(e))
+                                flags |= VARLINK_METHOD_MORE;
+
+                } else
+                        goto invalid;
+        }
+
+        if (!method)
+                goto invalid;
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                goto fail;
+
+        varlink_set_state(v, (flags & VARLINK_METHOD_MORE)   ? VARLINK_PROCESSING_METHOD_MORE :
+                             (flags & VARLINK_METHOD_ONEWAY) ? VARLINK_PROCESSING_METHOD_ONEWAY :
+                                                               VARLINK_PROCESSING_METHOD);
+
+        assert(v->server);
+
+        /* First consult user supplied method implementations */
+        callback = hashmap_get(v->server->methods, method);
+        if (!callback) {
+                if (streq(method, "org.varlink.service.GetInfo"))
+                        callback = generic_method_get_info;
+                else if (streq(method, "org.varlink.service.GetInterfaceDescription"))
+                        callback = generic_method_get_interface_description;
+        }
+
+        if (callback) {
+                bool invalid = false;
+
+                v->current_method = hashmap_get(v->server->symbols, method);
+                if (!v->current_method)
+                        log_debug("No interface description defined for method '%s', not validating.", method);
+                else {
+                        const char *bad_field;
+
+                        r = varlink_idl_validate_method_call(v->current_method, parameters, &bad_field);
+                        if (r < 0) {
+                                log_debug_errno(r, "Parameters for method %s() didn't pass validation on field '%s': %m", method, strna(bad_field));
+
+                                if (!FLAGS_SET(flags, VARLINK_METHOD_ONEWAY)) {
+                                        r = varlink_errorb(v, VARLINK_ERROR_INVALID_PARAMETER, JSON_BUILD_OBJECT(JSON_BUILD_PAIR_STRING("parameter", bad_field)));
+                                        if (r < 0)
+                                                return r;
+                                }
+                                invalid = true;
+                        }
+                }
+
+                if (!invalid) {
+                        r = callback(v, parameters, flags, v->userdata);
+                        if (r < 0) {
+                                log_debug_errno(r, "Callback for %s returned error: %m", method);
+
+                                /* We got an error back from the callback. Propagate it to the client if the method call remains unanswered. */
+                                if (v->state == VARLINK_PROCESSED_METHOD)
+                                        r = 0; /* already processed */
+                                else if (!FLAGS_SET(flags, VARLINK_METHOD_ONEWAY)) {
+                                        r = varlink_error_errno(v, r);
+                                        if (r < 0)
+                                                return r;
+                                }
+                        }
+                }
+        } else if (!FLAGS_SET(flags, VARLINK_METHOD_ONEWAY)) {
+                r = varlink_errorb(v, VARLINK_ERROR_METHOD_NOT_FOUND, JSON_BUILD_OBJECT(JSON_BUILD_PAIR("method", JSON_BUILD_STRING(method))));
+                if (r < 0)
+                        return r;
+        } else
+                r = 0;
+
+        switch (v->state) {
+
+        case VARLINK_PROCESSED_METHOD: /* Method call is fully processed */
+        case VARLINK_PROCESSING_METHOD_ONEWAY: /* ditto */
+                varlink_clear_current(v);
+                varlink_set_state(v, VARLINK_IDLE_SERVER);
+                break;
+
+        case VARLINK_PROCESSING_METHOD: /* Method call wasn't replied to, will be replied to later */
+                varlink_set_state(v, VARLINK_PENDING_METHOD);
+                break;
+
+        case VARLINK_PROCESSING_METHOD_MORE: /* No reply for a "more" message was sent, more to come */
+                varlink_set_state(v, VARLINK_PENDING_METHOD_MORE);
+                break;
+
+        default:
+                assert_not_reached();
+        }
+
+        return r;
+
+invalid:
+        r = -EINVAL;
+
+fail:
+        varlink_set_state(v, VARLINK_PROCESSING_FAILURE);
+        varlink_dispatch_local_error(v, VARLINK_ERROR_PROTOCOL);
+        varlink_close(v);
+
+        return r;
+}
+
+int varlink_process(Varlink *v) {
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        varlink_ref(v);
+
+        r = varlink_write(v);
+        if (r < 0)
+                varlink_log_errno(v, r, "Write failed: %m");
+        if (r != 0)
+                goto finish;
+
+        r = varlink_dispatch_reply(v);
+        if (r < 0)
+                varlink_log_errno(v, r, "Reply dispatch failed: %m");
+        if (r != 0)
+                goto finish;
+
+        r = varlink_dispatch_method(v);
+        if (r < 0)
+                varlink_log_errno(v, r, "Method dispatch failed: %m");
+        if (r != 0)
+                goto finish;
+
+        r = varlink_parse_message(v);
+        if (r < 0)
+                varlink_log_errno(v, r, "Message parsing failed: %m");
+        if (r != 0)
+                goto finish;
+
+        r = varlink_read(v);
+        if (r < 0)
+                varlink_log_errno(v, r, "Read failed: %m");
+        if (r != 0)
+                goto finish;
+
+        r = varlink_test_disconnect(v);
+        assert(r >= 0);
+        if (r != 0)
+                goto finish;
+
+        r = varlink_dispatch_disconnect(v);
+        assert(r >= 0);
+        if (r != 0)
+                goto finish;
+
+        r = varlink_test_timeout(v);
+        assert(r >= 0);
+        if (r != 0)
+                goto finish;
+
+        r = varlink_dispatch_timeout(v);
+        assert(r >= 0);
+        if (r != 0)
+                goto finish;
+
+finish:
+        if (r >= 0 && v->defer_event_source) {
+                int q;
+
+                /* If we did some processing, make sure we are called again soon */
+                q = sd_event_source_set_enabled(v->defer_event_source, r > 0 ? SD_EVENT_ON : SD_EVENT_OFF);
+                if (q < 0)
+                        r = varlink_log_errno(v, q, "Failed to enable deferred event source: %m");
+        }
+
+        if (r < 0) {
+                if (VARLINK_STATE_IS_ALIVE(v->state))
+                        /* Initiate disconnection */
+                        varlink_set_state(v, VARLINK_PENDING_DISCONNECT);
+                else
+                        /* We failed while disconnecting, in that case close right away */
+                        varlink_close(v);
+        }
+
+        varlink_unref(v);
+        return r;
+}
+
+static void handle_revents(Varlink *v, int revents) {
+        assert(v);
+
+        if (v->connecting) {
+                /* If we have seen POLLOUT or POLLHUP on a socket we are asynchronously waiting a connect()
+                 * to complete on, we know we are ready. We don't read the connection error here though,
+                 * we'll get the error on the next read() or write(). */
+                if ((revents & (POLLOUT|POLLHUP)) == 0)
+                        return;
+
+                varlink_log(v, "Asynchronous connection completed.");
+                v->connecting = false;
+        } else {
+                /* Note that we don't care much about POLLIN/POLLOUT here, we'll just try reading and writing
+                 * what we can. However, we do care about POLLHUP to detect connection termination even if we
+                 * momentarily don't want to read nor write anything. */
+
+                if (!FLAGS_SET(revents, POLLHUP))
+                        return;
+
+                varlink_log(v, "Got POLLHUP from socket.");
+                v->got_pollhup = true;
+        }
+}
+
+int varlink_wait(Varlink *v, usec_t timeout) {
+        int r, fd, events;
+        usec_t t;
+
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        r = varlink_get_timeout(v, &t);
+        if (r < 0)
+                return r;
+        if (t != USEC_INFINITY) {
+                usec_t n;
+
+                n = now(CLOCK_MONOTONIC);
+                if (t < n)
+                        t = 0;
+                else
+                        t = usec_sub_unsigned(t, n);
+        }
+
+        if (timeout != USEC_INFINITY &&
+            (t == USEC_INFINITY || timeout < t))
+                t = timeout;
+
+        fd = varlink_get_fd(v);
+        if (fd < 0)
+                return fd;
+
+        events = varlink_get_events(v);
+        if (events < 0)
+                return events;
+
+        r = fd_wait_for_event(fd, events, t);
+        if (ERRNO_IS_NEG_TRANSIENT(r)) /* Treat EINTR as not a timeout, but also nothing happened, and
+                                        * the caller gets a chance to call back into us */
+                return 1;
+        if (r <= 0)
+                return r;
+
+        handle_revents(v, r);
+        return 1;
+}
+
+int varlink_is_idle(Varlink *v) {
+        assert_return(v, -EINVAL);
+
+        /* Returns true if there's nothing pending on the connection anymore, i.e. we processed all incoming
+         * or outgoing messages fully, or finished disconnection */
+
+        return IN_SET(v->state, VARLINK_DISCONNECTED, VARLINK_IDLE_CLIENT, VARLINK_IDLE_SERVER);
+}
+
+int varlink_get_fd(Varlink *v) {
+
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+        if (v->fd < 0)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBADF), "No valid fd.");
+
+        return v->fd;
+}
+
+int varlink_get_events(Varlink *v) {
+        int ret = 0;
+
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        if (v->connecting) /* When processing an asynchronous connect(), we only wait for EPOLLOUT, which
+                            * tells us that the connection is now complete. Before that we should neither
+                            * write() or read() from the fd. */
+                return EPOLLOUT;
+
+        if (!v->read_disconnected &&
+            IN_SET(v->state, VARLINK_AWAITING_REPLY, VARLINK_AWAITING_REPLY_MORE, VARLINK_CALLING, VARLINK_IDLE_SERVER) &&
+            !v->current &&
+            v->input_buffer_unscanned <= 0)
+                ret |= EPOLLIN;
+
+        if (!v->write_disconnected &&
+            v->output_buffer_size > 0)
+                ret |= EPOLLOUT;
+
+        return ret;
+}
+
+int varlink_get_timeout(Varlink *v, usec_t *ret) {
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        if (IN_SET(v->state, VARLINK_AWAITING_REPLY, VARLINK_AWAITING_REPLY_MORE, VARLINK_CALLING) &&
+            v->timeout != USEC_INFINITY) {
+                if (ret)
+                        *ret = usec_add(v->timestamp, v->timeout);
+                return 1;
+        } else {
+                if (ret)
+                        *ret = USEC_INFINITY;
+                return 0;
+        }
+}
+
+int varlink_flush(Varlink *v) {
+        int ret = 0, r;
+
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        for (;;) {
+                if (v->output_buffer_size == 0)
+                        break;
+                if (v->write_disconnected)
+                        return -ECONNRESET;
+
+                r = varlink_write(v);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        ret = 1;
+                        continue;
+                }
+
+                r = fd_wait_for_event(v->fd, POLLOUT, USEC_INFINITY);
+                if (ERRNO_IS_NEG_TRANSIENT(r))
+                        continue;
+                if (r < 0)
+                        return varlink_log_errno(v, r, "Poll failed on fd: %m");
+                assert(r > 0);
+
+                handle_revents(v, r);
+        }
+
+        return ret;
+}
+
+static void varlink_detach_server(Varlink *v) {
+        VarlinkServer *saved_server;
+        assert(v);
+
+        if (!v->server)
+                return;
+
+        if (v->server->by_uid &&
+            v->ucred_acquired &&
+            uid_is_valid(v->ucred.uid)) {
+                unsigned c;
+
+                c = PTR_TO_UINT(hashmap_get(v->server->by_uid, UID_TO_PTR(v->ucred.uid)));
+                assert(c > 0);
+
+                if (c == 1)
+                        (void) hashmap_remove(v->server->by_uid, UID_TO_PTR(v->ucred.uid));
+                else
+                        (void) hashmap_replace(v->server->by_uid, UID_TO_PTR(v->ucred.uid), UINT_TO_PTR(c - 1));
+        }
+
+        assert(v->server->n_connections > 0);
+        v->server->n_connections--;
+
+        /* If this is a connection associated to a server, then let's disconnect the server and the
+         * connection from each other. This drops the dangling reference that connect_callback() set up. But
+         * before we release the references, let's call the disconnection callback if it is defined. */
+
+        saved_server = TAKE_PTR(v->server);
+
+        if (saved_server->disconnect_callback)
+                saved_server->disconnect_callback(saved_server, v, saved_server->userdata);
+
+        varlink_server_test_exit_on_idle(saved_server);
+        varlink_server_unref(saved_server);
+        varlink_unref(v);
+}
+
+int varlink_close(Varlink *v) {
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return 0;
+
+        varlink_set_state(v, VARLINK_DISCONNECTED);
+
+        /* Let's take a reference first, since varlink_detach_server() might drop the final (dangling) ref
+         * which would destroy us before we can call varlink_clear() */
+        varlink_ref(v);
+        varlink_detach_server(v);
+        varlink_clear(v);
+        varlink_unref(v);
+
+        return 1;
+}
+
+Varlink* varlink_close_unref(Varlink *v) {
+        if (!v)
+                return NULL;
+
+        (void) varlink_close(v);
+        return varlink_unref(v);
+}
+
+Varlink* varlink_flush_close_unref(Varlink *v) {
+        if (!v)
+                return NULL;
+
+        (void) varlink_flush(v);
+        return varlink_close_unref(v);
+}
+
+static int varlink_format_json(Varlink *v, JsonVariant *m) {
+        _cleanup_(erase_and_freep) char *text = NULL;
+        int r;
+
+        assert(v);
+        assert(m);
+
+        r = json_variant_format(m, 0, &text);
+        if (r < 0)
+                return r;
+        assert(text[r] == '\0');
+
+        if (v->output_buffer_size + r + 1 > VARLINK_BUFFER_MAX)
+                return -ENOBUFS;
+
+        varlink_log(v, "Sending message: %s", text);
+
+        if (v->output_buffer_size == 0) {
+
+                free_and_replace(v->output_buffer, text);
+
+                v->output_buffer_size = r + 1;
+                v->output_buffer_index = 0;
+
+        } else if (v->output_buffer_index == 0) {
+
+                if (!GREEDY_REALLOC(v->output_buffer, v->output_buffer_size + r + 1))
+                        return -ENOMEM;
+
+                memcpy(v->output_buffer + v->output_buffer_size, text, r + 1);
+                v->output_buffer_size += r + 1;
+        } else {
+                char *n;
+                const size_t new_size = v->output_buffer_size + r + 1;
+
+                n = new(char, new_size);
+                if (!n)
+                        return -ENOMEM;
+
+                memcpy(mempcpy(n, v->output_buffer + v->output_buffer_index, v->output_buffer_size), text, r + 1);
+
+                free_and_replace(v->output_buffer, n);
+                v->output_buffer_size = new_size;
+                v->output_buffer_index = 0;
+        }
+
+        if (json_variant_is_sensitive(m))
+                v->output_buffer_sensitive = true; /* Propagate sensitive flag */
+        else
+                text = mfree(text); /* No point in the erase_and_free() destructor declared above */
+
+        return 0;
+}
+
+static int varlink_enqueue_json(Varlink *v, JsonVariant *m) {
+        VarlinkJsonQueueItem *q;
+
+        assert(v);
+        assert(m);
+
+        /* If there are no file descriptors to be queued and no queue entries yet we can shortcut things and
+         * append this entry directly to the output buffer */
+        if (v->n_pushed_fds == 0 && !v->output_queue)
+                return varlink_format_json(v, m);
+
+        /* Otherwise add a queue entry for this */
+        q = varlink_json_queue_item_new(m, v->pushed_fds, v->n_pushed_fds);
+        if (!q)
+                return -ENOMEM;
+
+        v->n_pushed_fds = 0; /* fds now belong to the queue entry */
+
+        LIST_INSERT_AFTER(queue, v->output_queue, v->output_queue_tail, q);
+        v->output_queue_tail = q;
+        return 0;
+}
+
+static int varlink_format_queue(Varlink *v) {
+        int r;
+
+        assert(v);
+
+        /* Takes entries out of the output queue and formats them into the output buffer. But only if this
+         * would not corrupt our fd message boundaries */
+
+        while (v->output_queue) {
+                _cleanup_free_ int *array = NULL;
+                VarlinkJsonQueueItem *q = v->output_queue;
+
+                if (v->n_output_fds > 0) /* unwritten fds? if we'd add more we'd corrupt the fd message boundaries, hence wait */
+                        return 0;
+
+                if (q->n_fds > 0) {
+                        array = newdup(int, q->fds, q->n_fds);
+                        if (!array)
+                                return -ENOMEM;
+                }
+
+                r = varlink_format_json(v, q->data);
+                if (r < 0)
+                        return r;
+
+                /* Take possession of the queue element's fds */
+                free(v->output_fds);
+                v->output_fds = TAKE_PTR(array);
+                v->n_output_fds = q->n_fds;
+                q->n_fds = 0;
+
+                LIST_REMOVE(queue, v->output_queue, q);
+                if (!v->output_queue)
+                        v->output_queue_tail = NULL;
+
+                varlink_json_queue_item_free(q);
+        }
+
+        return 0;
+}
+
+int varlink_send(Varlink *v, const char *method, JsonVariant *parameters) {
+        _cleanup_(json_variant_unrefp) JsonVariant *m = NULL;
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(method, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        /* We allow enqueuing multiple method calls at once! */
+        if (!IN_SET(v->state, VARLINK_IDLE_CLIENT, VARLINK_AWAITING_REPLY))
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBUSY), "Connection busy.");
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to sanitize parameters: %m");
+
+        r = json_build(&m, JSON_BUILD_OBJECT(
+                                       JSON_BUILD_PAIR("method", JSON_BUILD_STRING(method)),
+                                       JSON_BUILD_PAIR("parameters", JSON_BUILD_VARIANT(parameters)),
+                                       JSON_BUILD_PAIR("oneway", JSON_BUILD_BOOLEAN(true))));
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        r = varlink_enqueue_json(v, m);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to enqueue json message: %m");
+
+        /* No state change here, this is one-way only after all */
+        v->timestamp = now(CLOCK_MONOTONIC);
+        return 0;
+}
+
+int varlink_sendb(Varlink *v, const char *method, ...) {
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        va_list ap;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        va_start(ap, method);
+        r = json_buildv(&parameters, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        return varlink_send(v, method, parameters);
+}
+
+int varlink_invoke(Varlink *v, const char *method, JsonVariant *parameters) {
+        _cleanup_(json_variant_unrefp) JsonVariant *m = NULL;
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(method, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        /* We allow enqueuing multiple method calls at once! */
+        if (!IN_SET(v->state, VARLINK_IDLE_CLIENT, VARLINK_AWAITING_REPLY))
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBUSY), "Connection busy.");
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to sanitize parameters: %m");
+
+        r = json_build(&m, JSON_BUILD_OBJECT(
+                                       JSON_BUILD_PAIR("method", JSON_BUILD_STRING(method)),
+                                       JSON_BUILD_PAIR("parameters", JSON_BUILD_VARIANT(parameters))));
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        r = varlink_enqueue_json(v, m);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to enqueue json message: %m");
+
+        varlink_set_state(v, VARLINK_AWAITING_REPLY);
+        v->n_pending++;
+        v->timestamp = now(CLOCK_MONOTONIC);
+
+        return 0;
+}
+
+int varlink_invokeb(Varlink *v, const char *method, ...) {
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        va_list ap;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        va_start(ap, method);
+        r = json_buildv(&parameters, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        return varlink_invoke(v, method, parameters);
+}
+
+int varlink_observe(Varlink *v, const char *method, JsonVariant *parameters) {
+        _cleanup_(json_variant_unrefp) JsonVariant *m = NULL;
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(method, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        /* Note that we don't allow enqueuing multiple method calls when we are in more/continues mode! We
+         * thus insist on an idle client here. */
+        if (v->state != VARLINK_IDLE_CLIENT)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBUSY), "Connection busy.");
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to sanitize parameters: %m");
+
+        r = json_build(&m, JSON_BUILD_OBJECT(
+                                       JSON_BUILD_PAIR("method", JSON_BUILD_STRING(method)),
+                                       JSON_BUILD_PAIR("parameters", JSON_BUILD_VARIANT(parameters)),
+                                       JSON_BUILD_PAIR("more", JSON_BUILD_BOOLEAN(true))));
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        r = varlink_enqueue_json(v, m);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to enqueue json message: %m");
+
+        varlink_set_state(v, VARLINK_AWAITING_REPLY_MORE);
+        v->n_pending++;
+        v->timestamp = now(CLOCK_MONOTONIC);
+
+        return 0;
+}
+
+int varlink_observeb(Varlink *v, const char *method, ...) {
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        va_list ap;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        va_start(ap, method);
+        r = json_buildv(&parameters, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        return varlink_observe(v, method, parameters);
+}
+
+int varlink_call(
+                Varlink *v,
+                const char *method,
+                JsonVariant *parameters,
+                JsonVariant **ret_parameters,
+                const char **ret_error_id,
+                VarlinkReplyFlags *ret_flags) {
+
+        _cleanup_(json_variant_unrefp) JsonVariant *m = NULL;
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(method, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+        if (v->state != VARLINK_IDLE_CLIENT)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBUSY), "Connection busy.");
+
+        assert(v->n_pending == 0); /* n_pending can't be > 0 if we are in VARLINK_IDLE_CLIENT state */
+
+        /* If there was still a reply pinned from a previous call, now it's the time to get rid of it, so
+         * that we can assign a new reply shortly. */
+        varlink_clear_current(v);
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to sanitize parameters: %m");
+
+        r = json_build(&m, JSON_BUILD_OBJECT(
+                                       JSON_BUILD_PAIR("method", JSON_BUILD_STRING(method)),
+                                       JSON_BUILD_PAIR("parameters", JSON_BUILD_VARIANT(parameters))));
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        r = varlink_enqueue_json(v, m);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to enqueue json message: %m");
+
+        varlink_set_state(v, VARLINK_CALLING);
+        v->n_pending++;
+        v->timestamp = now(CLOCK_MONOTONIC);
+
+        while (v->state == VARLINK_CALLING) {
+
+                r = varlink_process(v);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        continue;
+
+                r = varlink_wait(v, USEC_INFINITY);
+                if (r < 0)
+                        return r;
+        }
+
+        switch (v->state) {
+
+        case VARLINK_CALLED:
+                assert(v->current);
+
+                varlink_set_state(v, VARLINK_IDLE_CLIENT);
+                assert(v->n_pending == 1);
+                v->n_pending--;
+
+                if (ret_parameters)
+                        *ret_parameters = json_variant_by_key(v->current, "parameters");
+                if (ret_error_id)
+                        *ret_error_id = json_variant_string(json_variant_by_key(v->current, "error"));
+                if (ret_flags)
+                        *ret_flags = 0;
+
+                return 1;
+
+        case VARLINK_PENDING_DISCONNECT:
+        case VARLINK_DISCONNECTED:
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ECONNRESET), "Connection was closed.");
+
+        case VARLINK_PENDING_TIMEOUT:
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ETIME), "Connection timed out.");
+
+        default:
+                assert_not_reached();
+        }
+}
+
+int varlink_callb(
+                Varlink *v,
+                const char *method,
+                JsonVariant **ret_parameters,
+                const char **ret_error_id,
+                VarlinkReplyFlags *ret_flags, ...) {
+
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        va_list ap;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        va_start(ap, ret_flags);
+        r = json_buildv(&parameters, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        return varlink_call(v, method, parameters, ret_parameters, ret_error_id, ret_flags);
+}
+
+static void varlink_collect_context_free(VarlinkCollectContext *cc) {
+        assert(cc);
+
+        json_variant_unref(cc->parameters);
+        free((char *)cc->error_id);
+}
+
+static int collect_callback(
+                Varlink *v,
+                JsonVariant *parameters,
+                const char *error_id,
+                VarlinkReplyFlags flags,
+                void *userdata) {
+
+        VarlinkCollectContext *context = ASSERT_PTR(userdata);
+        int r;
+
+        assert(v);
+
+        context->flags = flags;
+        /* If we hit an error, we will drop all collected replies and just return the error_id and flags in varlink_collect() */
+        if (error_id) {
+                context->error_id = error_id;
+                return 0;
+        }
+
+        r = json_variant_append_array(&context->parameters, parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to append JSON object to array: %m");
+
+        return 1;
+}
+
+int varlink_collect(
+                Varlink *v,
+                const char *method,
+                JsonVariant *parameters,
+                JsonVariant **ret_parameters,
+                const char **ret_error_id,
+                VarlinkReplyFlags *ret_flags) {
+
+        _cleanup_(varlink_collect_context_free) VarlinkCollectContext context = {};
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(method, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+        if (v->state != VARLINK_IDLE_CLIENT)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBUSY), "Connection busy.");
+
+        assert(v->n_pending == 0); /* n_pending can't be > 0 if we are in VARLINK_IDLE_CLIENT state */
+
+        /* If there was still a reply pinned from a previous call, now it's the time to get rid of it, so
+         * that we can assign a new reply shortly. */
+        varlink_clear_current(v);
+
+        r = varlink_bind_reply(v, collect_callback);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to bind collect callback");
+
+        varlink_set_userdata(v, &context);
+        r = varlink_observe(v, method, parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to collect varlink method: %m");
+
+        while (v->state == VARLINK_AWAITING_REPLY_MORE) {
+
+                r = varlink_process(v);
+                if (r < 0)
+                        return r;
+
+                /* If we get an error from any of the replies, return immediately with just the error_id and flags*/
+                if (context.error_id) {
+                        if (ret_error_id)
+                                *ret_error_id = TAKE_PTR(context.error_id);
+                        if (ret_flags)
+                                *ret_flags = context.flags;
+                        return 0;
+                }
+
+                if (r > 0)
+                        continue;
+
+                r = varlink_wait(v, USEC_INFINITY);
+                if (r < 0)
+                        return r;
+        }
+
+        switch (v->state) {
+
+        case VARLINK_IDLE_CLIENT:
+                break;
+
+        case VARLINK_PENDING_DISCONNECT:
+        case VARLINK_DISCONNECTED:
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ECONNRESET), "Connection was closed.");
+
+        case VARLINK_PENDING_TIMEOUT:
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ETIME), "Connection timed out.");
+
+        default:
+                assert_not_reached();
+        }
+
+        if (ret_parameters)
+                *ret_parameters = TAKE_PTR(context.parameters);
+        if (ret_error_id)
+                *ret_error_id = TAKE_PTR(context.error_id);
+        if (ret_flags)
+                *ret_flags = context.flags;
+        return 1;
+}
+
+int varlink_collectb(
+                Varlink *v,
+                const char *method,
+                JsonVariant **ret_parameters,
+                const char **ret_error_id,
+                VarlinkReplyFlags *ret_flags, ...) {
+
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        va_list ap;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        va_start(ap, ret_flags);
+        r = json_buildv(&parameters, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        return varlink_collect(v, method, parameters, ret_parameters, ret_error_id, ret_flags);
+}
+
+int varlink_reply(Varlink *v, JsonVariant *parameters) {
+        _cleanup_(json_variant_unrefp) JsonVariant *m = NULL;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return -ENOTCONN;
+        if (!IN_SET(v->state,
+                    VARLINK_PROCESSING_METHOD, VARLINK_PROCESSING_METHOD_MORE,
+                    VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE))
+                return -EBUSY;
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to sanitize parameters: %m");
+
+        r = json_build(&m, JSON_BUILD_OBJECT(JSON_BUILD_PAIR("parameters", JSON_BUILD_VARIANT(parameters))));
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        if (v->current_method) {
+                const char *bad_field = NULL;
+
+                r = varlink_idl_validate_method_reply(v->current_method, parameters, &bad_field);
+                if (r < 0)
+                        log_debug_errno(r, "Return parameters for method reply %s() didn't pass validation on field '%s', ignoring: %m", v->current_method->name, strna(bad_field));
+        }
+
+        r = varlink_enqueue_json(v, m);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to enqueue json message: %m");
+
+        if (IN_SET(v->state, VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE)) {
+                /* We just replied to a method call that was let hanging for a while (i.e. we were outside of
+                 * the varlink_dispatch_method() stack frame), which means with this reply we are ready to
+                 * process further messages. */
+                varlink_clear_current(v);
+                varlink_set_state(v, VARLINK_IDLE_SERVER);
+        } else
+                /* We replied to a method call from within the varlink_dispatch_method() stack frame), which
+                 * means we should it handle the rest of the state engine. */
+                varlink_set_state(v, VARLINK_PROCESSED_METHOD);
+
+        return 1;
+}
+
+int varlink_replyb(Varlink *v, ...) {
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        va_list ap;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        va_start(ap, v);
+        r = json_buildv(&parameters, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return r;
+
+        return varlink_reply(v, parameters);
+}
+
+int varlink_error(Varlink *v, const char *error_id, JsonVariant *parameters) {
+        _cleanup_(json_variant_unrefp) JsonVariant *m = NULL;
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(error_id, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+        if (!IN_SET(v->state,
+                    VARLINK_PROCESSING_METHOD, VARLINK_PROCESSING_METHOD_MORE,
+                    VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE))
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBUSY), "Connection busy.");
+
+        /* Reset the list of pushed file descriptors before sending an error reply. We do this here to
+         * simplify code that puts together a complex reply message with fds, and half-way something
+         * fails. In that case the pushed fds need to be flushed out again. Under the assumption that it
+         * never makes sense to send fds along with errors we simply flush them out here beforehand, so that
+         * the callers don't need to do this explicitly. */
+        varlink_reset_fds(v);
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to sanitize parameters: %m");
+
+        r = json_build(&m, JSON_BUILD_OBJECT(
+                                       JSON_BUILD_PAIR("error", JSON_BUILD_STRING(error_id)),
+                                       JSON_BUILD_PAIR("parameters", JSON_BUILD_VARIANT(parameters))));
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        VarlinkSymbol *symbol = hashmap_get(v->server->symbols, error_id);
+        if (!symbol)
+                log_debug("No interface description defined for error '%s', not validating.", error_id);
+        else {
+                const char *bad_field = NULL;
+
+                r = varlink_idl_validate_error(symbol, parameters, &bad_field);
+                if (r < 0)
+                        log_debug_errno(r, "Parameters for error %s didn't pass validation on field '%s', ignoring: %m", error_id, strna(bad_field));
+        }
+
+        r = varlink_enqueue_json(v, m);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to enqueue json message: %m");
+
+        if (IN_SET(v->state, VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE)) {
+                varlink_clear_current(v);
+                varlink_set_state(v, VARLINK_IDLE_SERVER);
+        } else
+                varlink_set_state(v, VARLINK_PROCESSED_METHOD);
+
+        return 1;
+}
+
+int varlink_errorb(Varlink *v, const char *error_id, ...) {
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        va_list ap;
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(error_id, -EINVAL);
+
+        va_start(ap, error_id);
+        r = json_buildv(&parameters, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        return varlink_error(v, error_id, parameters);
+}
+
+int varlink_error_invalid_parameter(Varlink *v, JsonVariant *parameters) {
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(parameters, -EINVAL);
+
+        /* We expect to be called in one of two ways: the 'parameters' argument is a string variant in which
+         * case it is the parameter key name that is invalid. Or the 'parameters' argument is an object
+         * variant in which case we'll pull out the first key. The latter mode is useful in functions that
+         * don't expect any arguments. */
+
+        /* varlink_error(...) expects a json object as the third parameter. Passing a string variant causes
+         * parameter sanitization to fail, and it returns -EINVAL. */
+
+        if (json_variant_is_string(parameters)) {
+                _cleanup_(json_variant_unrefp) JsonVariant *parameters_obj = NULL;
+
+                r = json_build(&parameters_obj,
+                                JSON_BUILD_OBJECT(
+                                        JSON_BUILD_PAIR("parameter", JSON_BUILD_VARIANT(parameters))));
+                if (r < 0)
+                        return r;
+
+                return varlink_error(v, VARLINK_ERROR_INVALID_PARAMETER, parameters_obj);
+        }
+
+        if (json_variant_is_object(parameters) &&
+            json_variant_elements(parameters) > 0) {
+                _cleanup_(json_variant_unrefp) JsonVariant *parameters_obj = NULL;
+
+                r = json_build(&parameters_obj,
+                                JSON_BUILD_OBJECT(
+                                        JSON_BUILD_PAIR("parameter", JSON_BUILD_VARIANT(json_variant_by_index(parameters, 0)))));
+                if (r < 0)
+                        return r;
+
+                return varlink_error(v, VARLINK_ERROR_INVALID_PARAMETER, parameters_obj);
+        }
+
+        return -EINVAL;
+}
+
+int varlink_error_errno(Varlink *v, int error) {
+        return varlink_errorb(
+                        v,
+                        VARLINK_ERROR_SYSTEM,
+                        JSON_BUILD_OBJECT(JSON_BUILD_PAIR("errno", JSON_BUILD_INTEGER(abs(error)))));
+}
+
+int varlink_notify(Varlink *v, JsonVariant *parameters) {
+        _cleanup_(json_variant_unrefp) JsonVariant *m = NULL;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        if (v->state == VARLINK_DISCONNECTED)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENOTCONN), "Not connected.");
+
+        /* If we want to reply with a notify connection but the caller didn't set "more", then return an
+         * error indicating that we expected to be called with "more" set */
+        if (IN_SET(v->state, VARLINK_PROCESSING_METHOD, VARLINK_PENDING_METHOD))
+                return varlink_error(v, VARLINK_ERROR_EXPECTED_MORE, NULL);
+
+        if (!IN_SET(v->state, VARLINK_PROCESSING_METHOD_MORE, VARLINK_PENDING_METHOD_MORE))
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBUSY), "Connection busy.");
+
+        r = varlink_sanitize_parameters(&parameters);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to sanitize parameters: %m");
+
+        r = json_build(&m, JSON_BUILD_OBJECT(
+                                       JSON_BUILD_PAIR("parameters", JSON_BUILD_VARIANT(parameters)),
+                                       JSON_BUILD_PAIR("continues", JSON_BUILD_BOOLEAN(true))));
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        if (v->current_method) {
+                const char *bad_field = NULL;
+
+                r = varlink_idl_validate_method_reply(v->current_method, parameters, &bad_field);
+                if (r < 0)
+                        log_debug_errno(r, "Return parameters for method reply %s() didn't pass validation on field '%s', ignoring: %m", v->current_method->name, strna(bad_field));
+        }
+
+        r = varlink_enqueue_json(v, m);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to enqueue json message: %m");
+
+        /* No state change, as more is coming */
+        return 1;
+}
+
+int varlink_notifyb(Varlink *v, ...) {
+        _cleanup_(json_variant_unrefp) JsonVariant *parameters = NULL;
+        va_list ap;
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        va_start(ap, v);
+        r = json_buildv(&parameters, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to build json message: %m");
+
+        return varlink_notify(v, parameters);
+}
+
+int varlink_dispatch(Varlink *v, JsonVariant *parameters, const JsonDispatch table[], void *userdata) {
+        const char *bad_field = NULL;
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(table, -EINVAL);
+
+        /* A wrapper around json_dispatch_full() that returns a nice InvalidParameter error if we hit a problem with some field. */
+
+        r = json_dispatch_full(parameters, table, /* bad= */ NULL, /* flags= */ 0, userdata, &bad_field);
+        if (r < 0) {
+                if (bad_field)
+                        return varlink_errorb(v, VARLINK_ERROR_INVALID_PARAMETER,
+                                              JSON_BUILD_OBJECT(JSON_BUILD_PAIR("parameter", JSON_BUILD_STRING(bad_field))));
+                return r;
+        }
+
+        return 0;
+}
+
+int varlink_bind_reply(Varlink *v, VarlinkReply callback) {
+        assert_return(v, -EINVAL);
+
+        if (callback && v->reply_callback && callback != v->reply_callback)
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(EBUSY), "A different callback was already set.");
+
+        v->reply_callback = callback;
+
+        return 0;
+}
+
+void* varlink_set_userdata(Varlink *v, void *userdata) {
+        void *old;
+
+        assert_return(v, NULL);
+
+        old = v->userdata;
+        v->userdata = userdata;
+
+        return old;
+}
+
+void* varlink_get_userdata(Varlink *v) {
+        assert_return(v, NULL);
+
+        return v->userdata;
+}
+
+static int varlink_acquire_ucred(Varlink *v) {
+        int r;
+
+        assert(v);
+
+        if (v->ucred_acquired)
+                return 0;
+
+        r = getpeercred(v->fd, &v->ucred);
+        if (r < 0)
+                return r;
+
+        v->ucred_acquired = true;
+        return 0;
+}
+
+int varlink_get_peer_uid(Varlink *v, uid_t *ret) {
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(ret, -EINVAL);
+
+        r = varlink_acquire_ucred(v);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to acquire credentials: %m");
+
+        if (!uid_is_valid(v->ucred.uid))
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENODATA), "Peer uid is invalid.");
+
+        *ret = v->ucred.uid;
+        return 0;
+}
+
+int varlink_get_peer_pid(Varlink *v, pid_t *ret) {
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(ret, -EINVAL);
+
+        r = varlink_acquire_ucred(v);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to acquire credentials: %m");
+
+        if (!pid_is_valid(v->ucred.pid))
+                return varlink_log_errno(v, SYNTHETIC_ERRNO(ENODATA), "Peer uid is invalid.");
+
+        *ret = v->ucred.pid;
+        return 0;
+}
+
+int varlink_set_relative_timeout(Varlink *v, usec_t timeout) {
+        assert_return(v, -EINVAL);
+        assert_return(timeout > 0, -EINVAL);
+
+        v->timeout = timeout;
+        return 0;
+}
+
+VarlinkServer *varlink_get_server(Varlink *v) {
+        assert_return(v, NULL);
+
+        return v->server;
+}
+
+int varlink_set_description(Varlink *v, const char *description) {
+        assert_return(v, -EINVAL);
+
+        return free_and_strdup(&v->description, description);
+}
+
+static int io_callback(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
+        Varlink *v = ASSERT_PTR(userdata);
+
+        assert(s);
+
+        handle_revents(v, revents);
+        (void) varlink_process(v);
+
+        return 1;
+}
+
+static int time_callback(sd_event_source *s, uint64_t usec, void *userdata) {
+        Varlink *v = ASSERT_PTR(userdata);
+
+        assert(s);
+
+        (void) varlink_process(v);
+        return 1;
+}
+
+static int defer_callback(sd_event_source *s, void *userdata) {
+        Varlink *v = ASSERT_PTR(userdata);
+
+        assert(s);
+
+        (void) varlink_process(v);
+        return 1;
+}
+
+static int prepare_callback(sd_event_source *s, void *userdata) {
+        Varlink *v = ASSERT_PTR(userdata);
+        int r, e;
+        usec_t until;
+        bool have_timeout;
+
+        assert(s);
+
+        e = varlink_get_events(v);
+        if (e < 0)
+                return e;
+
+        r = sd_event_source_set_io_events(v->io_event_source, e);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to set source events: %m");
+
+        r = varlink_get_timeout(v, &until);
+        if (r < 0)
+                return r;
+        have_timeout = r > 0;
+
+        if (have_timeout) {
+                r = sd_event_source_set_time(v->time_event_source, until);
+                if (r < 0)
+                        return varlink_log_errno(v, r, "Failed to set source time: %m");
+        }
+
+        r = sd_event_source_set_enabled(v->time_event_source, have_timeout ? SD_EVENT_ON : SD_EVENT_OFF);
+        if (r < 0)
+                return varlink_log_errno(v, r, "Failed to enable event source: %m");
+
+        return 1;
+}
+
+static int quit_callback(sd_event_source *event, void *userdata) {
+        Varlink *v = ASSERT_PTR(userdata);
+
+        assert(event);
+
+        varlink_flush(v);
+        varlink_close(v);
+
+        return 1;
+}
+
+int varlink_attach_event(Varlink *v, sd_event *e, int64_t priority) {
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(!v->event, -EBUSY);
+
+        if (e)
+                v->event = sd_event_ref(e);
+        else {
+                r = sd_event_default(&v->event);
+                if (r < 0)
+                        return varlink_log_errno(v, r, "Failed to create event source: %m");
+        }
+
+        r = sd_event_add_time(v->event, &v->time_event_source, CLOCK_MONOTONIC, 0, 0, time_callback, v);
+        if (r < 0)
+                goto fail;
+
+        r = sd_event_source_set_priority(v->time_event_source, priority);
+        if (r < 0)
+                goto fail;
+
+        (void) sd_event_source_set_description(v->time_event_source, "varlink-time");
+
+        r = sd_event_add_exit(v->event, &v->quit_event_source, quit_callback, v);
+        if (r < 0)
+                goto fail;
+
+        r = sd_event_source_set_priority(v->quit_event_source, priority);
+        if (r < 0)
+                goto fail;
+
+        (void) sd_event_source_set_description(v->quit_event_source, "varlink-quit");
+
+        r = sd_event_add_io(v->event, &v->io_event_source, v->fd, 0, io_callback, v);
+        if (r < 0)
+                goto fail;
+
+        r = sd_event_source_set_prepare(v->io_event_source, prepare_callback);
+        if (r < 0)
+                goto fail;
+
+        r = sd_event_source_set_priority(v->io_event_source, priority);
+        if (r < 0)
+                goto fail;
+
+        (void) sd_event_source_set_description(v->io_event_source, "varlink-io");
+
+        r = sd_event_add_defer(v->event, &v->defer_event_source, defer_callback, v);
+        if (r < 0)
+                goto fail;
+
+        r = sd_event_source_set_priority(v->defer_event_source, priority);
+        if (r < 0)
+                goto fail;
+
+        (void) sd_event_source_set_description(v->defer_event_source, "varlink-defer");
+
+        return 0;
+
+fail:
+        varlink_log_errno(v, r, "Failed to setup event source: %m");
+        varlink_detach_event(v);
+        return r;
+}
+
+void varlink_detach_event(Varlink *v) {
+        if (!v)
+                return;
+
+        varlink_detach_event_sources(v);
+
+        v->event = sd_event_unref(v->event);
+}
+
+sd_event *varlink_get_event(Varlink *v) {
+        assert_return(v, NULL);
+
+        return v->event;
+}
+
+int varlink_push_fd(Varlink *v, int fd) {
+        int i;
+
+        assert_return(v, -EINVAL);
+        assert_return(fd >= 0, -EBADF);
+
+        /* Takes an fd to send along with the *next* varlink message sent via this varlink connection. This
+         * takes ownership of the specified fd. Use varlink_dup_fd() below to duplicate the fd first. */
+
+        if (!v->allow_fd_passing_output)
+                return -EPERM;
+
+        if (v->n_pushed_fds >= INT_MAX)
+                return -ENOMEM;
+
+        if (!GREEDY_REALLOC(v->pushed_fds, v->n_pushed_fds + 1))
+                return -ENOMEM;
+
+        i = (int) v->n_pushed_fds;
+        v->pushed_fds[v->n_pushed_fds++] = fd;
+        return i;
+}
+
+int varlink_dup_fd(Varlink *v, int fd) {
+        _cleanup_close_ int dp = -1;
+        int r;
+
+        assert_return(v, -EINVAL);
+        assert_return(fd >= 0, -EBADF);
+
+        /* Like varlink_push_fd() but duplicates the specified fd instead of taking possession of it */
+
+        dp = fcntl(fd, F_DUPFD_CLOEXEC, 3);
+        if (dp < 0)
+                return -errno;
+
+        r = varlink_push_fd(v, dp);
+        if (r < 0)
+                return r;
+
+        TAKE_FD(dp);
+        return r;
+}
+
+int varlink_reset_fds(Varlink *v) {
+        assert_return(v, -EINVAL);
+
+        /* Closes all currently pending fds to send. This may be used whenever the caller is in the process
+         * of putting together a message with fds, and then eventually something fails and they need to
+         * rollback the fds. Note that this is implicitly called whenever an error reply is sent, see above. */
+
+        close_many(v->output_fds, v->n_output_fds);
+        v->n_output_fds = 0;
+        return 0;
+}
+
+int varlink_peek_fd(Varlink *v, size_t i) {
+        assert_return(v, -EINVAL);
+
+        /* Returns one of the file descriptors that were received along with the current message. This does
+         * not duplicate the fd nor invalidate it, it hence remains in our possession. */
+
+        if (!v->allow_fd_passing_input)
+                return -EPERM;
+
+        if (i >= v->n_input_fds)
+                return -ENXIO;
+
+        return v->input_fds[i];
+}
+
+int varlink_take_fd(Varlink *v, size_t i) {
+        assert_return(v, -EINVAL);
+
+        /* Similar to varlink_peek_fd() but the file descriptor's ownership is passed to the caller, and
+         * we'll invalidate the reference to it under our possession. If called twice in a row will return
+         * -EBADF */
+
+        if (!v->allow_fd_passing_input)
+                return -EPERM;
+
+        if (i >= v->n_input_fds)
+                return -ENXIO;
+
+        return TAKE_FD(v->input_fds[i]);
+}
+
+static int verify_unix_socket(Varlink *v) {
+        assert(v);
+
+        if (v->af < 0) {
+                struct stat st;
+
+                if (fstat(v->fd, &st) < 0)
+                        return -errno;
+                if (!S_ISSOCK(st.st_mode)) {
+                        v->af = AF_UNSPEC;
+                        return -ENOTSOCK;
+                }
+
+                v->af = socket_get_family(v->fd);
+                if (v->af < 0)
+                        return v->af;
+        }
+
+        return v->af == AF_UNIX ? 0 : -ENOMEDIUM;
+}
+
+int varlink_set_allow_fd_passing_input(Varlink *v, bool b) {
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        if (v->allow_fd_passing_input == b)
+                return 0;
+
+        if (!b) {
+                v->allow_fd_passing_input = false;
+                return 1;
+        }
+
+        r = verify_unix_socket(v);
+        if (r < 0)
+                return r;
+
+        v->allow_fd_passing_input = true;
+        return 0;
+}
+
+int varlink_set_allow_fd_passing_output(Varlink *v, bool b) {
+        int r;
+
+        assert_return(v, -EINVAL);
+
+        if (v->allow_fd_passing_output == b)
+                return 0;
+
+        if (!b) {
+                v->allow_fd_passing_output = false;
+                return 1;
+        }
+
+        r = verify_unix_socket(v);
+        if (r < 0)
+                return r;
+
+        v->allow_fd_passing_output = true;
+        return 0;
+}
+
+int varlink_server_new(VarlinkServer **ret, VarlinkServerFlags flags) {
+        _cleanup_(varlink_server_unrefp) VarlinkServer *s = NULL;
+        int r;
+
+        assert_return(ret, -EINVAL);
+        assert_return((flags & ~_VARLINK_SERVER_FLAGS_ALL) == 0, -EINVAL);
+
+        s = new(VarlinkServer, 1);
+        if (!s)
+                return log_oom_debug();
+
+        *s = (VarlinkServer) {
+                .n_ref = 1,
+                .flags = flags,
+                .connections_max = varlink_server_connections_max(NULL),
+                .connections_per_uid_max = varlink_server_connections_per_uid_max(NULL),
+        };
+
+        r = varlink_server_add_interface_many(
+                        s,
+                        &vl_interface_io_systemd,
+                        &vl_interface_org_varlink_service);
+        if (r < 0)
+                return r;
+
+        *ret = TAKE_PTR(s);
+        return 0;
+}
+
+static VarlinkServer* varlink_server_destroy(VarlinkServer *s) {
+        char *m;
+
+        if (!s)
+                return NULL;
+
+        varlink_server_shutdown(s);
+
+        while ((m = hashmap_steal_first_key(s->methods)))
+                free(m);
+
+        hashmap_free(s->methods);
+        hashmap_free(s->interfaces);
+        hashmap_free(s->symbols);
+        hashmap_free(s->by_uid);
+
+        sd_event_unref(s->event);
+
+        free(s->description);
+
+        return mfree(s);
+}
+
+DEFINE_TRIVIAL_REF_UNREF_FUNC(VarlinkServer, varlink_server, varlink_server_destroy);
+
+static int validate_connection(VarlinkServer *server, const struct ucred *ucred) {
+        int allowed = -1;
+
+        assert(server);
+        assert(ucred);
+
+        if (FLAGS_SET(server->flags, VARLINK_SERVER_ROOT_ONLY))
+                allowed = ucred->uid == 0;
+
+        if (FLAGS_SET(server->flags, VARLINK_SERVER_MYSELF_ONLY))
+                allowed = allowed > 0 || ucred->uid == getuid();
+
+        if (allowed == 0) { /* Allow access when it is explicitly allowed or when neither
+                             * VARLINK_SERVER_ROOT_ONLY nor VARLINK_SERVER_MYSELF_ONLY are specified. */
+                varlink_server_log(server, "Unprivileged client attempted connection, refusing.");
+                return 0;
+        }
+
+        if (server->n_connections >= server->connections_max) {
+                varlink_server_log(server, "Connection limit of %u reached, refusing.", server->connections_max);
+                return 0;
+        }
+
+        if (FLAGS_SET(server->flags, VARLINK_SERVER_ACCOUNT_UID)) {
+                unsigned c;
+
+                if (!uid_is_valid(ucred->uid)) {
+                        varlink_server_log(server, "Client with invalid UID attempted connection, refusing.");
+                        return 0;
+                }
+
+                c = PTR_TO_UINT(hashmap_get(server->by_uid, UID_TO_PTR(ucred->uid)));
+                if (c >= server->connections_per_uid_max) {
+                        varlink_server_log(server, "Per-UID connection limit of %u reached, refusing.",
+                                           server->connections_per_uid_max);
+                        return 0;
+                }
+        }
+
+        return 1;
+}
+
+static int count_connection(VarlinkServer *server, const struct ucred *ucred) {
+        unsigned c;
+        int r;
+
+        assert(server);
+        assert(ucred);
+
+        server->n_connections++;
+
+        if (FLAGS_SET(server->flags, VARLINK_SERVER_ACCOUNT_UID)) {
+                r = hashmap_ensure_allocated(&server->by_uid, NULL);
+                if (r < 0)
+                        return log_debug_errno(r, "Failed to allocate UID hash table: %m");
+
+                c = PTR_TO_UINT(hashmap_get(server->by_uid, UID_TO_PTR(ucred->uid)));
+
+                varlink_server_log(server, "Connections of user " UID_FMT ": %u (of %u max)",
+                                   ucred->uid, c, server->connections_per_uid_max);
+
+                r = hashmap_replace(server->by_uid, UID_TO_PTR(ucred->uid), UINT_TO_PTR(c + 1));
+                if (r < 0)
+                        return log_debug_errno(r, "Failed to increment counter in UID hash table: %m");
+        }
+
+        return 0;
+}
+
+int varlink_server_add_connection(VarlinkServer *server, int fd, Varlink **ret) {
+        _cleanup_(varlink_unrefp) Varlink *v = NULL;
+        struct ucred ucred = UCRED_INVALID;
+        bool ucred_acquired;
+        int r;
+
+        assert_return(server, -EINVAL);
+        assert_return(fd >= 0, -EBADF);
+
+        if ((server->flags & (VARLINK_SERVER_ROOT_ONLY|VARLINK_SERVER_ACCOUNT_UID)) != 0) {
+                r = getpeercred(fd, &ucred);
+                if (r < 0)
+                        return varlink_server_log_errno(server, r, "Failed to acquire peer credentials of incoming socket, refusing: %m");
+
+                ucred_acquired = true;
+
+                r = validate_connection(server, &ucred);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        return -EPERM;
+        } else
+                ucred_acquired = false;
+
+        r = varlink_new(&v);
+        if (r < 0)
+                return varlink_server_log_errno(server, r, "Failed to allocate connection object: %m");
+
+        r = count_connection(server, &ucred);
+        if (r < 0)
+                return r;
+
+        v->fd = fd;
+        if (server->flags & VARLINK_SERVER_INHERIT_USERDATA)
+                v->userdata = server->userdata;
+
+        if (ucred_acquired) {
+                v->ucred = ucred;
+                v->ucred_acquired = true;
+        }
+
+        _cleanup_free_ char *desc = NULL;
+        if (asprintf(&desc, "%s-%i", server->description ?: "varlink", v->fd) >= 0)
+                v->description = TAKE_PTR(desc);
+
+        /* Link up the server and the connection, and take reference in both directions. Note that the
+         * reference on the connection is left dangling. It will be dropped when the connection is closed,
+         * which happens in varlink_close(), including in the event loop quit callback. */
+        v->server = varlink_server_ref(server);
+        varlink_ref(v);
+
+        varlink_set_state(v, VARLINK_IDLE_SERVER);
+
+        if (server->event) {
+                r = varlink_attach_event(v, server->event, server->event_priority);
+                if (r < 0) {
+                        varlink_log_errno(v, r, "Failed to attach new connection: %m");
+                        v->fd = -EBADF; /* take the fd out of the connection again */
+                        varlink_close(v);
+                        return r;
+                }
+        }
+
+        if (ret)
+                *ret = v;
+
+        return 0;
+}
+
+static VarlinkServerSocket *varlink_server_socket_free(VarlinkServerSocket *ss) {
+        if (!ss)
+                return NULL;
+
+        free(ss->address);
+        return mfree(ss);
+}
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(VarlinkServerSocket *, varlink_server_socket_free);
+
+static int connect_callback(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
+        VarlinkServerSocket *ss = ASSERT_PTR(userdata);
+        _cleanup_close_ int cfd = -EBADF;
+        Varlink *v = NULL;
+        int r;
+
+        assert(source);
+
+        varlink_server_log(ss->server, "New incoming connection.");
+
+        cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
+        if (cfd < 0) {
+                if (ERRNO_IS_ACCEPT_AGAIN(errno))
+                        return 0;
+
+                return varlink_server_log_errno(ss->server, errno, "Failed to accept incoming socket: %m");
+        }
+
+        r = varlink_server_add_connection(ss->server, cfd, &v);
+        if (r < 0)
+                return 0;
+
+        TAKE_FD(cfd);
+
+        if (ss->server->connect_callback) {
+                r = ss->server->connect_callback(ss->server, v, ss->server->userdata);
+                if (r < 0) {
+                        varlink_log_errno(v, r, "Connection callback returned error, disconnecting client: %m");
+                        varlink_close(v);
+                        return 0;
+                }
+        }
+
+        return 0;
+}
+
+static int varlink_server_create_listen_fd_socket(VarlinkServer *s, int fd, VarlinkServerSocket **ret_ss) {
+        _cleanup_(varlink_server_socket_freep) VarlinkServerSocket *ss = NULL;
+        int r;
+
+        assert(s);
+        assert(fd >= 0);
+        assert(ret_ss);
+
+        ss = new(VarlinkServerSocket, 1);
+        if (!ss)
+                return log_oom_debug();
+
+        *ss = (VarlinkServerSocket) {
+                .server = s,
+                .fd = fd,
+        };
+
+        if (s->event) {
+                r = sd_event_add_io(s->event, &ss->event_source, fd, EPOLLIN, connect_callback, ss);
+                if (r < 0)
+                        return r;
+
+                r = sd_event_source_set_priority(ss->event_source, s->event_priority);
+                if (r < 0)
+                        return r;
+        }
+
+        *ret_ss = TAKE_PTR(ss);
+        return 0;
+}
+
+int varlink_server_listen_fd(VarlinkServer *s, int fd) {
+        _cleanup_(varlink_server_socket_freep) VarlinkServerSocket *ss = NULL;
+        int r;
+
+        assert_return(s, -EINVAL);
+        assert_return(fd >= 0, -EBADF);
+
+        r = fd_nonblock(fd, true);
+        if (r < 0)
+                return r;
+
+        r = fd_cloexec(fd, true);
+        if (r < 0)
+                return r;
+
+        r = varlink_server_create_listen_fd_socket(s, fd, &ss);
+        if (r < 0)
+                return r;
+
+        LIST_PREPEND(sockets, s->sockets, TAKE_PTR(ss));
+        return 0;
+}
+
+int varlink_server_listen_address(VarlinkServer *s, const char *address, mode_t m) {
+        _cleanup_(varlink_server_socket_freep) VarlinkServerSocket *ss = NULL;
+        union sockaddr_union sockaddr;
+        socklen_t sockaddr_len;
+        _cleanup_close_ int fd = -EBADF;
+        int r;
+
+        assert_return(s, -EINVAL);
+        assert_return(address, -EINVAL);
+        assert_return((m & ~0777) == 0, -EINVAL);
+
+        r = sockaddr_un_set_path(&sockaddr.un, address);
+        if (r < 0)
+                return r;
+        sockaddr_len = r;
+
+        fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+        if (fd < 0)
+                return -errno;
+
+        fd = fd_move_above_stdio(fd);
+
+        (void) sockaddr_un_unlink(&sockaddr.un);
+
+        WITH_UMASK(~m & 0777) {
+                r = mac_selinux_bind(fd, &sockaddr.sa, sockaddr_len);
+                if (r < 0)
+                        return r;
+        }
+
+        if (listen(fd, SOMAXCONN_DELUXE) < 0)
+                return -errno;
+
+        r = varlink_server_create_listen_fd_socket(s, fd, &ss);
+        if (r < 0)
+                return r;
+
+        r = free_and_strdup(&ss->address, address);
+        if (r < 0)
+                return r;
+
+        LIST_PREPEND(sockets, s->sockets, TAKE_PTR(ss));
+        TAKE_FD(fd);
+        return 0;
+}
+
+int varlink_server_listen_auto(VarlinkServer *s) {
+        _cleanup_strv_free_ char **names = NULL;
+        int r, n = 0;
+
+        assert_return(s, -EINVAL);
+
+        /* Adds all passed fds marked as "varlink" to our varlink server. These fds can either refer to a
+         * listening socket or to a connection socket.
+         *
+         * See https://varlink.org/#activation for the environment variables this is backed by and the
+         * recommended "varlink" identifier in $LISTEN_FDNAMES. */
+
+        r = sd_listen_fds_with_names(/* unset_environment= */ false, &names);
+        if (r < 0)
+                return r;
+
+        for (int i = 0; i < r; i++) {
+                int b, fd;
+                socklen_t l = sizeof(b);
+
+                if (!streq(names[i], "varlink"))
+                        continue;
+
+                fd = SD_LISTEN_FDS_START + i;
+
+                if (getsockopt(fd, SOL_SOCKET, SO_ACCEPTCONN, &b, &l) < 0)
+                        return -errno;
+
+                assert(l == sizeof(b));
+
+                if (b) /* Listening socket? */
+                        r = varlink_server_listen_fd(s, fd);
+                else /* Otherwise assume connection socket */
+                        r = varlink_server_add_connection(s, fd, NULL);
+                if (r < 0)
+                        return r;
+
+                n++;
+        }
+
+        return n;
+}
+
+void* varlink_server_set_userdata(VarlinkServer *s, void *userdata) {
+        void *ret;
+
+        assert_return(s, NULL);
+
+        ret = s->userdata;
+        s->userdata = userdata;
+
+        return ret;
+}
+
+void* varlink_server_get_userdata(VarlinkServer *s) {
+        assert_return(s, NULL);
+
+        return s->userdata;
+}
+
+int varlink_server_loop_auto(VarlinkServer *server) {
+        _cleanup_(sd_event_unrefp) sd_event *event = NULL;
+        int r;
+
+        assert_return(server, -EINVAL);
+        assert_return(!server->event, -EBUSY);
+
+        /* Runs a Varlink service event loop populated with a passed fd. Exits on the last connection. */
+
+        r = sd_event_new(&event);
+        if (r < 0)
+                return r;
+
+        r = varlink_server_set_exit_on_idle(server, true);
+        if (r < 0)
+                return r;
+
+        r = varlink_server_attach_event(server, event, 0);
+        if (r < 0)
+                return r;
+
+        r = varlink_server_listen_auto(server);
+        if (r < 0)
+                return r;
+
+        return sd_event_loop(event);
+}
+
+static VarlinkServerSocket* varlink_server_socket_destroy(VarlinkServerSocket *ss) {
+        if (!ss)
+                return NULL;
+
+        if (ss->server)
+                LIST_REMOVE(sockets, ss->server->sockets, ss);
+
+        sd_event_source_disable_unref(ss->event_source);
+
+        free(ss->address);
+        safe_close(ss->fd);
+
+        return mfree(ss);
+}
+
+int varlink_server_shutdown(VarlinkServer *s) {
+        assert_return(s, -EINVAL);
+
+        while (s->sockets)
+                varlink_server_socket_destroy(s->sockets);
+
+        return 0;
+}
+
+static void varlink_server_test_exit_on_idle(VarlinkServer *s) {
+        assert(s);
+
+        if (s->exit_on_idle && s->event && s->n_connections == 0)
+                (void) sd_event_exit(s->event, 0);
+}
+
+int varlink_server_set_exit_on_idle(VarlinkServer *s, bool b) {
+        assert_return(s, -EINVAL);
+
+        s->exit_on_idle = b;
+        varlink_server_test_exit_on_idle(s);
+        return 0;
+}
+
+static int varlink_server_add_socket_event_source(VarlinkServer *s, VarlinkServerSocket *ss, int64_t priority) {
+        _cleanup_(sd_event_source_unrefp) sd_event_source *es = NULL;
+        int r;
+
+        assert(s);
+        assert(s->event);
+        assert(ss);
+        assert(ss->fd >= 0);
+        assert(!ss->event_source);
+
+        r = sd_event_add_io(s->event, &es, ss->fd, EPOLLIN, connect_callback, ss);
+        if (r < 0)
+                return r;
+
+        r = sd_event_source_set_priority(es, priority);
+        if (r < 0)
+                return r;
+
+        ss->event_source = TAKE_PTR(es);
+        return 0;
+}
+
+int varlink_server_attach_event(VarlinkServer *s, sd_event *e, int64_t priority) {
+        int r;
+
+        assert_return(s, -EINVAL);
+        assert_return(!s->event, -EBUSY);
+
+        if (e)
+                s->event = sd_event_ref(e);
+        else {
+                r = sd_event_default(&s->event);
+                if (r < 0)
+                        return r;
+        }
+
+        LIST_FOREACH(sockets, ss, s->sockets) {
+                r = varlink_server_add_socket_event_source(s, ss, priority);
+                if (r < 0)
+                        goto fail;
+        }
+
+        s->event_priority = priority;
+        return 0;
+
+fail:
+        varlink_server_detach_event(s);
+        return r;
+}
+
+int varlink_server_detach_event(VarlinkServer *s) {
+        assert_return(s, -EINVAL);
+
+        LIST_FOREACH(sockets, ss, s->sockets)
+                ss->event_source = sd_event_source_disable_unref(ss->event_source);
+
+        sd_event_unref(s->event);
+        return 0;
+}
+
+sd_event *varlink_server_get_event(VarlinkServer *s) {
+        assert_return(s, NULL);
+
+        return s->event;
+}
+
+static bool varlink_symbol_in_interface(const char *method, const char *interface) {
+        const char *p;
+
+        assert(method);
+        assert(interface);
+
+        p = startswith(method, interface);
+        if (!p)
+                return false;
+
+        if (*p != '.')
+                return false;
+
+        return !strchr(p+1, '.');
+}
+
+int varlink_server_bind_method(VarlinkServer *s, const char *method, VarlinkMethod callback) {
+        _cleanup_free_ char *m = NULL;
+        int r;
+
+        assert_return(s, -EINVAL);
+        assert_return(method, -EINVAL);
+        assert_return(callback, -EINVAL);
+
+        if (varlink_symbol_in_interface(method, "org.varlink.service") ||
+            varlink_symbol_in_interface(method, "io.systemd"))
+                return log_debug_errno(SYNTHETIC_ERRNO(EEXIST), "Cannot bind server to '%s'.", method);
+
+        m = strdup(method);
+        if (!m)
+                return log_oom_debug();
+
+        r = hashmap_ensure_put(&s->methods, &string_hash_ops, m, callback);
+        if (r == -ENOMEM)
+                return log_oom_debug();
+        if (r < 0)
+                return log_debug_errno(r, "Failed to register callback: %m");
+        if (r > 0)
+                TAKE_PTR(m);
+
+        return 0;
+}
+
+int varlink_server_bind_method_many_internal(VarlinkServer *s, ...) {
+        va_list ap;
+        int r = 0;
+
+        assert_return(s, -EINVAL);
+
+        va_start(ap, s);
+        for (;;) {
+                VarlinkMethod callback;
+                const char *method;
+
+                method = va_arg(ap, const char *);
+                if (!method)
+                        break;
+
+                callback = va_arg(ap, VarlinkMethod);
+
+                r = varlink_server_bind_method(s, method, callback);
+                if (r < 0)
+                        break;
+        }
+        va_end(ap);
+
+        return r;
+}
+
+int varlink_server_bind_connect(VarlinkServer *s, VarlinkConnect callback) {
+        assert_return(s, -EINVAL);
+
+        if (callback && s->connect_callback && callback != s->connect_callback)
+                return log_debug_errno(SYNTHETIC_ERRNO(EBUSY), "A different callback was already set.");
+
+        s->connect_callback = callback;
+        return 0;
+}
+
+int varlink_server_bind_disconnect(VarlinkServer *s, VarlinkDisconnect callback) {
+        assert_return(s, -EINVAL);
+
+        if (callback && s->disconnect_callback && callback != s->disconnect_callback)
+                return log_debug_errno(SYNTHETIC_ERRNO(EBUSY), "A different callback was already set.");
+
+        s->disconnect_callback = callback;
+        return 0;
+}
+
+int varlink_server_add_interface(VarlinkServer *s, const VarlinkInterface *interface) {
+        int r;
+
+        assert_return(s, -EINVAL);
+        assert_return(interface, -EINVAL);
+        assert_return(interface->name, -EINVAL);
+
+        if (hashmap_contains(s->interfaces, interface->name))
+                return log_debug_errno(SYNTHETIC_ERRNO(EEXIST), "Duplicate registration of interface '%s'.", interface->name);
+
+        r = hashmap_ensure_put(&s->interfaces, &string_hash_ops, interface->name, (void*) interface);
+        if (r < 0)
+                return r;
+
+        for (const VarlinkSymbol *const*symbol = interface->symbols; *symbol; symbol++) {
+                _cleanup_free_ char *j = NULL;
+
+                /* We only ever want to validate method calls/replies and errors against the interface
+                 * definitions, hence don't bother with the type symbols */
+                if (!IN_SET((*symbol)->symbol_type, VARLINK_METHOD, VARLINK_ERROR))
+                        continue;
+
+                j = strjoin(interface->name, ".", (*symbol)->name);
+                if (!j)
+                        return -ENOMEM;
+
+                r = hashmap_ensure_put(&s->symbols, &string_hash_ops_free, j, (void*) *symbol);
+                if (r < 0)
+                        return r;
+
+                TAKE_PTR(j);
+        }
+
+        return 0;
+}
+
+int varlink_server_add_interface_many_internal(VarlinkServer *s, ...) {
+        va_list ap;
+        int r = 0;
+
+        assert_return(s, -EINVAL);
+
+        va_start(ap, s);
+        for (;;) {
+                const VarlinkInterface *interface = va_arg(ap, const VarlinkInterface*);
+                if (!interface)
+                        break;
+
+                r = varlink_server_add_interface(s, interface);
+                if (r < 0)
+                        break;
+        }
+        va_end(ap);
+
+        return r;
+}
+
+unsigned varlink_server_connections_max(VarlinkServer *s) {
+        int dts;
+
+        /* If a server is specified, return the setting for that server, otherwise the default value */
+        if (s)
+                return s->connections_max;
+
+        dts = getdtablesize();
+        assert_se(dts > 0);
+
+        /* Make sure we never use up more than ¾th of RLIMIT_NOFILE for IPC */
+        if (VARLINK_DEFAULT_CONNECTIONS_MAX > (unsigned) dts / 4 * 3)
+                return dts / 4 * 3;
+
+        return VARLINK_DEFAULT_CONNECTIONS_MAX;
+}
+
+unsigned varlink_server_connections_per_uid_max(VarlinkServer *s) {
+        unsigned m;
+
+        if (s)
+                return s->connections_per_uid_max;
+
+        /* Make sure to never use up more than ¾th of available connections for a single user */
+        m = varlink_server_connections_max(NULL);
+        if (VARLINK_DEFAULT_CONNECTIONS_PER_UID_MAX > m)
+                return m / 4 * 3;
+
+        return VARLINK_DEFAULT_CONNECTIONS_PER_UID_MAX;
+}
+
+int varlink_server_set_connections_per_uid_max(VarlinkServer *s, unsigned m) {
+        assert_return(s, -EINVAL);
+        assert_return(m > 0, -EINVAL);
+
+        s->connections_per_uid_max = m;
+        return 0;
+}
+
+int varlink_server_set_connections_max(VarlinkServer *s, unsigned m) {
+        assert_return(s, -EINVAL);
+        assert_return(m > 0, -EINVAL);
+
+        s->connections_max = m;
+        return 0;
+}
+
+unsigned varlink_server_current_connections(VarlinkServer *s) {
+        assert_return(s, UINT_MAX);
+
+        return s->n_connections;
+}
+
+int varlink_server_set_description(VarlinkServer *s, const char *description) {
+        assert_return(s, -EINVAL);
+
+        return free_and_strdup(&s->description, description);
+}
+
+int varlink_server_serialize(VarlinkServer *s, FILE *f, FDSet *fds) {
+        assert(f);
+        assert(fds);
+
+        if (!s)
+                return 0;
+
+        LIST_FOREACH(sockets, ss, s->sockets) {
+                int copy;
+
+                assert(ss->address);
+                assert(ss->fd >= 0);
+
+                fprintf(f, "varlink-server-socket-address=%s", ss->address);
+
+                /* If we fail to serialize the fd, it will be considered an error during deserialization */
+                copy = fdset_put_dup(fds, ss->fd);
+                if (copy < 0)
+                        return copy;
+
+                fprintf(f, " varlink-server-socket-fd=%i", copy);
+
+                fputc('\n', f);
+        }
+
+        return 0;
+}
+
+int varlink_server_deserialize_one(VarlinkServer *s, const char *value, FDSet *fds) {
+        _cleanup_(varlink_server_socket_freep) VarlinkServerSocket *ss = NULL;
+        _cleanup_free_ char *address = NULL;
+        const char *v = ASSERT_PTR(value);
+        int r, fd = -EBADF;
+        char *buf;
+        size_t n;
+
+        assert(s);
+        assert(fds);
+
+        n = strcspn(v, " ");
+        address = strndup(v, n);
+        if (!address)
+                return log_oom_debug();
+
+        if (v[n] != ' ')
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "Failed to deserialize VarlinkServerSocket: %s: %m", value);
+        v = startswith(v + n + 1, "varlink-server-socket-fd=");
+        if (!v)
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "Failed to deserialize VarlinkServerSocket fd %s: %m", value);
+
+        n = strcspn(v, " ");
+        buf = strndupa_safe(v, n);
+
+        fd = parse_fd(buf);
+        if (fd < 0)
+                return log_debug_errno(fd, "Unable to parse VarlinkServerSocket varlink-server-socket-fd=%s: %m", buf);
+        if (!fdset_contains(fds, fd))
+                return log_debug_errno(SYNTHETIC_ERRNO(EBADF),
+                                       "VarlinkServerSocket varlink-server-socket-fd= has unknown fd %d: %m", fd);
+
+        ss = new(VarlinkServerSocket, 1);
+        if (!ss)
+                return log_oom_debug();
+
+        *ss = (VarlinkServerSocket) {
+                .server = s,
+                .address = TAKE_PTR(address),
+                .fd = fdset_remove(fds, fd),
+        };
+
+        r = varlink_server_add_socket_event_source(s, ss, SD_EVENT_PRIORITY_NORMAL);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to add VarlinkServerSocket event source to the event loop: %m");
+
+        LIST_PREPEND(sockets, s->sockets, TAKE_PTR(ss));
+        return 0;
+}
+
+int varlink_invocation(VarlinkInvocationFlags flags) {
+        _cleanup_strv_free_ char **names = NULL;
+        int r, b;
+        socklen_t l = sizeof(b);
+
+        /* Returns true if this is a "pure" varlink server invocation, i.e. with one fd passed. */
+
+        r = sd_listen_fds_with_names(/* unset_environment= */ false, &names);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return false;
+        if (r > 1)
+                return -ETOOMANYREFS;
+
+        if (!strv_equal(names, STRV_MAKE("varlink")))
+                return false;
+
+        if (FLAGS_SET(flags, VARLINK_ALLOW_LISTEN|VARLINK_ALLOW_ACCEPT)) /* Both flags set? Then allow everything */
+                return true;
+
+        if ((flags & (VARLINK_ALLOW_LISTEN|VARLINK_ALLOW_ACCEPT)) == 0) /* Neither is set, then fail */
+                return -EISCONN;
+
+        if (getsockopt(SD_LISTEN_FDS_START, SOL_SOCKET, SO_ACCEPTCONN, &b, &l) < 0)
+                return -errno;
+
+        assert(l == sizeof(b));
+
+        if (!FLAGS_SET(flags, b ? VARLINK_ALLOW_LISTEN : VARLINK_ALLOW_ACCEPT))
+                return -EISCONN;
+
+        return true;
+}