Adding upstream version 0.12.1+dfsg.upstream/0.12.1+dfsgupstream

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

4 files changed, 5973 insertions, 0 deletions

diff --git a/lib/includes/CMakeLists.txt b/lib/includes/CMakeLists.txt
new file mode 100644
index 0000000..5eabf73
--- /dev/null
+++ b/lib/includes/CMakeLists.txt
@@ -0,0 +1,4 @@
+install(FILES
+    ngtcp2/ngtcp2.h
+    "${CMAKE_CURRENT_BINARY_DIR}/ngtcp2/version.h"
+  DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/ngtcp2")
diff --git a/lib/includes/Makefile.am b/lib/includes/Makefile.am
new file mode 100644
index 0000000..5ecb6a4
--- /dev/null
+++ b/lib/includes/Makefile.am
@@ -0,0 +1,25 @@
+# ngtcp2
+
+# Copyright (c) 2016 ngtcp2 contributors
+
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+EXTRA_DIST = CMakeLists.txt
+
+nobase_include_HEADERS = ngtcp2/ngtcp2.h ngtcp2/version.h
diff --git a/lib/includes/ngtcp2/ngtcp2.h b/lib/includes/ngtcp2/ngtcp2.h
new file mode 100644
index 0000000..c3bfa58
--- /dev/null
+++ b/lib/includes/ngtcp2/ngtcp2.h
@@ -0,0 +1,5893 @@
+/*
+ * ngtcp2
+ *
+ * Copyright (c) 2017 ngtcp2 contributors
+ * Copyright (c) 2017 nghttp2 contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#ifndef NGTCP2_H
+#define NGTCP2_H
+
+/* Define WIN32 when build target is Win32 API (borrowed from
+   libcurl) */
+#if (defined(_WIN32) || defined(__WIN32__)) && !defined(WIN32)
+#  define WIN32
+#endif
+
+#ifdef _MSC_VER
+#  pragma warning(push)
+#  pragma warning(disable : 4324)
+#endif
+
+#include <stdlib.h>
+#if defined(_MSC_VER) && (_MSC_VER < 1800)
+/* MSVC < 2013 does not have inttypes.h because it is not C99
+   compliant.  See compiler macros and version number in
+   https://sourceforge.net/p/predef/wiki/Compilers/ */
+#  include <stdint.h>
+#else /* !defined(_MSC_VER) || (_MSC_VER >= 1800) */
+#  include <inttypes.h>
+#endif /* !defined(_MSC_VER) || (_MSC_VER >= 1800) */
+#include <sys/types.h>
+#include <stdarg.h>
+#include <stddef.h>
+
+#ifndef NGTCP2_USE_GENERIC_SOCKADDR
+#  ifdef WIN32
+#    ifndef WIN32_LEAN_AND_MEAN
+#      define WIN32_LEAN_AND_MEAN
+#    endif
+#    include <ws2tcpip.h>
+#  else
+#    include <sys/socket.h>
+#    include <netinet/in.h>
+#  endif
+#endif
+
+#ifdef AF_INET
+#  define NGTCP2_AF_INET AF_INET
+#else
+#  define NGTCP2_AF_INET 2
+#endif
+
+#ifdef AF_INET6
+#  define NGTCP2_AF_INET6 AF_INET6
+#else
+#  define NGTCP2_AF_INET6 23
+#  define NGTCP2_USE_GENERIC_IPV6_SOCKADDR
+#endif
+
+#include <ngtcp2/version.h>
+
+#ifdef NGTCP2_STATICLIB
+#  define NGTCP2_EXTERN
+#elif defined(WIN32)
+#  ifdef BUILDING_NGTCP2
+#    define NGTCP2_EXTERN __declspec(dllexport)
+#  else /* !BUILDING_NGTCP2 */
+#    define NGTCP2_EXTERN __declspec(dllimport)
+#  endif /* !BUILDING_NGTCP2 */
+#else    /* !defined(WIN32) */
+#  ifdef BUILDING_NGTCP2
+#    define NGTCP2_EXTERN __attribute__((visibility("default")))
+#  else /* !BUILDING_NGTCP2 */
+#    define NGTCP2_EXTERN
+#  endif /* !BUILDING_NGTCP2 */
+#endif   /* !defined(WIN32) */
+
+#ifdef _MSC_VER
+#  define NGTCP2_ALIGN(N) __declspec(align(N))
+#else /* !_MSC_VER */
+#  define NGTCP2_ALIGN(N) __attribute__((aligned(N)))
+#endif /* !_MSC_VER */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @typedef
+ *
+ * :type:`ngtcp2_ssize` is signed counterpart of size_t.
+ */
+typedef ptrdiff_t ngtcp2_ssize;
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_malloc` is a custom memory allocator to replace
+ * :manpage:`malloc(3)`.  The |user_data| is
+ * :member:`ngtcp2_mem.user_data`.
+ */
+typedef void *(*ngtcp2_malloc)(size_t size, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_free` is a custom memory allocator to replace
+ * :manpage:`free(3)`.  The |user_data| is
+ * :member:`ngtcp2_mem.user_data`.
+ */
+typedef void (*ngtcp2_free)(void *ptr, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_calloc` is a custom memory allocator to replace
+ * :manpage:`calloc(3)`.  The |user_data| is the
+ * :member:`ngtcp2_mem.user_data`.
+ */
+typedef void *(*ngtcp2_calloc)(size_t nmemb, size_t size, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_realloc` is a custom memory allocator to replace
+ * :manpage:`realloc(3)`.  The |user_data| is the
+ * :member:`ngtcp2_mem.user_data`.
+ */
+typedef void *(*ngtcp2_realloc)(void *ptr, size_t size, void *user_data);
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_mem` is a custom memory allocator.  The
+ * :member:`user_data` field is passed to each allocator function.
+ * This can be used, for example, to achieve per-connection memory
+ * pool.
+ *
+ * In the following example code, ``my_malloc``, ``my_free``,
+ * ``my_calloc`` and ``my_realloc`` are the replacement of the
+ * standard allocators :manpage:`malloc(3)`, :manpage:`free(3)`,
+ * :manpage:`calloc(3)` and :manpage:`realloc(3)` respectively::
+ *
+ *     void *my_malloc_cb(size_t size, void *user_data) {
+ *       (void)user_data;
+ *       return my_malloc(size);
+ *     }
+ *
+ *     void my_free_cb(void *ptr, void *user_data) {
+ *       (void)user_data;
+ *       my_free(ptr);
+ *     }
+ *
+ *     void *my_calloc_cb(size_t nmemb, size_t size, void *user_data) {
+ *       (void)user_data;
+ *       return my_calloc(nmemb, size);
+ *     }
+ *
+ *     void *my_realloc_cb(void *ptr, size_t size, void *user_data) {
+ *       (void)user_data;
+ *       return my_realloc(ptr, size);
+ *     }
+ *
+ *     void conn_new() {
+ *       ngtcp2_mem mem = {NULL, my_malloc_cb, my_free_cb, my_calloc_cb,
+ *                          my_realloc_cb};
+ *
+ *       ...
+ *     }
+ */
+typedef struct ngtcp2_mem {
+  /**
+   * :member:`user_data` is an arbitrary user supplied data.  This
+   * is passed to each allocator function.
+   */
+  void *user_data;
+  /**
+   * :member:`malloc` is a custom allocator function to replace
+   * :manpage:`malloc(3)`.
+   */
+  ngtcp2_malloc malloc;
+  /**
+   * :member:`free` is a custom allocator function to replace
+   * :manpage:`free(3)`.
+   */
+  ngtcp2_free free;
+  /**
+   * :member:`calloc` is a custom allocator function to replace
+   * :manpage:`calloc(3)`.
+   */
+  ngtcp2_calloc calloc;
+  /**
+   * :member:`realloc` is a custom allocator function to replace
+   * :manpage:`realloc(3)`.
+   */
+  ngtcp2_realloc realloc;
+} ngtcp2_mem;
+
+/**
+ * @macrosection
+ *
+ * Time related macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_SECONDS` is a count of tick which corresponds to 1 second.
+ */
+#define NGTCP2_SECONDS ((ngtcp2_duration)1000000000ULL)
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MILLISECONDS` is a count of tick which corresponds
+ * to 1 millisecond.
+ */
+#define NGTCP2_MILLISECONDS ((ngtcp2_duration)1000000ULL)
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MICROSECONDS` is a count of tick which corresponds
+ * to 1 microsecond.
+ */
+#define NGTCP2_MICROSECONDS ((ngtcp2_duration)1000ULL)
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_NANOSECONDS` is a count of tick which corresponds to
+ * 1 nanosecond.
+ */
+#define NGTCP2_NANOSECONDS ((ngtcp2_duration)1ULL)
+
+/**
+ * @macrosection
+ *
+ * QUIC protocol version macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PROTO_VER_V1` is the QUIC version 1.
+ */
+#define NGTCP2_PROTO_VER_V1 ((uint32_t)0x00000001u)
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PROTO_VER_V2_DRAFT` is the provisional version
+ * number for QUIC version 2 draft.
+ *
+ * https://quicwg.org/quic-v2/draft-ietf-quic-v2.html
+ */
+#define NGTCP2_PROTO_VER_V2_DRAFT ((uint32_t)0x709a50c4u)
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PROTO_VER_DRAFT_MAX` is the maximum QUIC draft
+ * version that this library supports.
+ */
+#define NGTCP2_PROTO_VER_DRAFT_MAX 0xff000020u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PROTO_VER_DRAFT_MIN` is the minimum QUIC draft
+ * version that this library supports.
+ */
+#define NGTCP2_PROTO_VER_DRAFT_MIN 0xff00001du
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PROTO_VER_MAX` is the highest QUIC version that this
+ * library supports.
+ */
+#define NGTCP2_PROTO_VER_MAX NGTCP2_PROTO_VER_V1
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PROTO_VER_MIN` is the lowest QUIC version that this
+ * library supports.
+ */
+#define NGTCP2_PROTO_VER_MIN NGTCP2_PROTO_VER_DRAFT_MIN
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_RESERVED_VERSION_MASK` is the bit mask of reserved
+ * version.
+ */
+#define NGTCP2_RESERVED_VERSION_MASK 0x0a0a0a0au
+
+/**
+ * @macrosection
+ *
+ * UDP datagram related macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MAX_UDP_PAYLOAD_SIZE` is the default maximum UDP
+ * datagram payload size that this endpoint transmits.
+ */
+#define NGTCP2_MAX_UDP_PAYLOAD_SIZE 1200
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MAX_PMTUD_UDP_PAYLOAD_SIZE` is the maximum UDP
+ * datagram payload size that Path MTU Discovery can discover.
+ */
+#define NGTCP2_MAX_PMTUD_UDP_PAYLOAD_SIZE 1452
+
+/**
+ * @macrosection
+ *
+ * QUIC specific macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MAX_VARINT` is the maximum value which can be
+ * encoded in variable-length integer encoding.
+ */
+#define NGTCP2_MAX_VARINT ((1ULL << 62) - 1)
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_STATELESS_RESET_TOKENLEN` is the length of Stateless
+ * Reset Token.
+ */
+#define NGTCP2_STATELESS_RESET_TOKENLEN 16
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MIN_STATELESS_RESET_RANDLEN` is the minimum length
+ * of random bytes (Unpredictable Bits) in Stateless Reset packet
+ */
+#define NGTCP2_MIN_STATELESS_RESET_RANDLEN 5
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PATH_CHALLENGE_DATALEN` is the length of
+ * PATH_CHALLENGE data.
+ */
+#define NGTCP2_PATH_CHALLENGE_DATALEN 8
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_RETRY_KEY_DRAFT` is an encryption key to create
+ * integrity tag of Retry packet.  It is used for QUIC draft versions.
+ */
+#define NGTCP2_RETRY_KEY_DRAFT                                                 \
+  "\xcc\xce\x18\x7e\xd0\x9a\x09\xd0\x57\x28\x15\x5a\x6c\xb9\x6b\xe1"
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_RETRY_NONCE_DRAFT` is nonce used when generating
+ * integrity tag of Retry packet.  It is used for QUIC draft versions.
+ */
+#define NGTCP2_RETRY_NONCE_DRAFT                                               \
+  "\xe5\x49\x30\xf9\x7f\x21\x36\xf0\x53\x0a\x8c\x1c"
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_RETRY_KEY_V1` is an encryption key to create
+ * integrity tag of Retry packet.  It is used for QUIC v1.
+ */
+#define NGTCP2_RETRY_KEY_V1                                                    \
+  "\xbe\x0c\x69\x0b\x9f\x66\x57\x5a\x1d\x76\x6b\x54\xe3\x68\xc8\x4e"
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_RETRY_NONCE_V1` is nonce used when generating integrity
+ * tag of Retry packet.  It is used for QUIC v1.
+ */
+#define NGTCP2_RETRY_NONCE_V1 "\x46\x15\x99\xd3\x5d\x63\x2b\xf2\x23\x98\x25\xbb"
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_RETRY_KEY_V2_DRAFT` is an encryption key to create
+ * integrity tag of Retry packet.  It is used for QUIC v2 draft.
+ *
+ * https://quicwg.org/quic-v2/draft-ietf-quic-v2.html
+ */
+#define NGTCP2_RETRY_KEY_V2_DRAFT                                              \
+  "\xba\x85\x8d\xc7\xb4\x3d\xe5\xdb\xf8\x76\x17\xff\x4a\xb2\x53\xdb"
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_RETRY_NONCE_V2_DRAFT` is nonce used when generating
+ * integrity tag of Retry packet.  It is used for QUIC v2 draft.
+ *
+ * https://quicwg.org/quic-v2/draft-ietf-quic-v2.html
+ */
+#define NGTCP2_RETRY_NONCE_V2_DRAFT                                            \
+  "\x14\x1b\x99\xc2\x39\xb0\x3e\x78\x5d\x6a\x2e\x9f"
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_HP_MASKLEN` is the length of header protection mask.
+ */
+#define NGTCP2_HP_MASKLEN 5
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_HP_SAMPLELEN` is the number bytes sampled when
+ * encrypting a packet header.
+ */
+#define NGTCP2_HP_SAMPLELEN 16
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_DEFAULT_INITIAL_RTT` is a default initial RTT.
+ */
+#define NGTCP2_DEFAULT_INITIAL_RTT (333 * NGTCP2_MILLISECONDS)
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MAX_CIDLEN` is the maximum length of Connection ID.
+ */
+#define NGTCP2_MAX_CIDLEN 20
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MIN_CIDLEN` is the minimum length of Connection ID.
+ */
+#define NGTCP2_MIN_CIDLEN 1
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_MIN_INITIAL_DCIDLEN` is the minimum length of
+ * Destination Connection ID in Client Initial packet if it does not
+ * bear token from Retry packet.
+ */
+#define NGTCP2_MIN_INITIAL_DCIDLEN 8
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_DEFAULT_HANDSHAKE_TIMEOUT` is the default handshake
+ * timeout.
+ */
+#define NGTCP2_DEFAULT_HANDSHAKE_TIMEOUT (10 * NGTCP2_SECONDS)
+
+/**
+ * @macrosection
+ *
+ * ECN related macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ECN_NOT_ECT` indicates no ECN marking.
+ */
+#define NGTCP2_ECN_NOT_ECT 0x0
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ECN_ECT_1` is ECT(1) codepoint.
+ */
+#define NGTCP2_ECN_ECT_1 0x1
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ECN_ECT_0` is ECT(0) codepoint.
+ */
+#define NGTCP2_ECN_ECT_0 0x2
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ECN_CE` is CE codepoint.
+ */
+#define NGTCP2_ECN_CE 0x3
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ECN_MASK` is a bit mask to get ECN marking.
+ */
+#define NGTCP2_ECN_MASK 0x3
+
+#define NGTCP2_PKT_INFO_VERSION_V1 1
+#define NGTCP2_PKT_INFO_VERSION NGTCP2_PKT_INFO_VERSION_V1
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_pkt_info` is a packet metadata.
+ */
+typedef struct NGTCP2_ALIGN(8) ngtcp2_pkt_info {
+  /**
+   * :member:`ecn` is ECN marking and when passing
+   * `ngtcp2_conn_read_pkt()`, and it should be either
+   * :macro:`NGTCP2_ECN_NOT_ECT`, :macro:`NGTCP2_ECN_ECT_1`,
+   * :macro:`NGTCP2_ECN_ECT_0`, or :macro:`NGTCP2_ECN_CE`.
+   */
+  uint32_t ecn;
+} ngtcp2_pkt_info;
+
+/**
+ * @macrosection
+ *
+ * ngtcp2 library error codes
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT` indicates that a passed
+ * argument is invalid.
+ */
+#define NGTCP2_ERR_INVALID_ARGUMENT -201
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_NOBUF` indicates that a provided buffer does not
+ * have enough space to store data.
+ */
+#define NGTCP2_ERR_NOBUF -203
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_PROTO` indicates a general protocol error.
+ */
+#define NGTCP2_ERR_PROTO -205
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_INVALID_STATE` indicates that a requested
+ * operation is not allowed at the current connection state.
+ */
+#define NGTCP2_ERR_INVALID_STATE -206
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_ACK_FRAME` indicates that an invalid ACK frame
+ * is received.
+ */
+#define NGTCP2_ERR_ACK_FRAME -207
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_STREAM_ID_BLOCKED` indicates that there is no
+ * spare stream ID available.
+ */
+#define NGTCP2_ERR_STREAM_ID_BLOCKED -208
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_STREAM_IN_USE` indicates that a stream ID is
+ * already in use.
+ */
+#define NGTCP2_ERR_STREAM_IN_USE -209
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_STREAM_DATA_BLOCKED` indicates that stream data
+ * cannot be sent because of flow control.
+ */
+#define NGTCP2_ERR_STREAM_DATA_BLOCKED -210
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_FLOW_CONTROL` indicates flow control error.
+ */
+#define NGTCP2_ERR_FLOW_CONTROL -211
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_CONNECTION_ID_LIMIT` indicates that the number
+ * of received Connection ID exceeds acceptable limit.
+ */
+#define NGTCP2_ERR_CONNECTION_ID_LIMIT -212
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_STREAM_LIMIT` indicates that a remote endpoint
+ * opens more streams that is permitted.
+ */
+#define NGTCP2_ERR_STREAM_LIMIT -213
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_FINAL_SIZE` indicates that inconsistent final
+ * size of a stream.
+ */
+#define NGTCP2_ERR_FINAL_SIZE -214
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_CRYPTO` indicates crypto (TLS) related error.
+ */
+#define NGTCP2_ERR_CRYPTO -215
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_PKT_NUM_EXHAUSTED` indicates that packet number
+ * is exhausted.
+ */
+#define NGTCP2_ERR_PKT_NUM_EXHAUSTED -216
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_REQUIRED_TRANSPORT_PARAM` indicates that a
+ * required transport parameter is missing.
+ */
+#define NGTCP2_ERR_REQUIRED_TRANSPORT_PARAM -217
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_MALFORMED_TRANSPORT_PARAM` indicates that a
+ * transport parameter is malformed.
+ */
+#define NGTCP2_ERR_MALFORMED_TRANSPORT_PARAM -218
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_FRAME_ENCODING` indicates there is an error in
+ * frame encoding.
+ */
+#define NGTCP2_ERR_FRAME_ENCODING -219
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_DECRYPT` indicates a decryption failure.
+ */
+#define NGTCP2_ERR_DECRYPT -220
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_STREAM_SHUT_WR` indicates no more data can be
+ * sent to a stream.
+ */
+#define NGTCP2_ERR_STREAM_SHUT_WR -221
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_STREAM_NOT_FOUND` indicates that a stream was not
+ * found.
+ */
+#define NGTCP2_ERR_STREAM_NOT_FOUND -222
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_STREAM_STATE` indicates that a requested
+ * operation is not allowed at the current stream state.
+ */
+#define NGTCP2_ERR_STREAM_STATE -226
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_RECV_VERSION_NEGOTIATION` indicates that Version
+ * Negotiation packet was received.
+ */
+#define NGTCP2_ERR_RECV_VERSION_NEGOTIATION -229
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_CLOSING` indicates that connection is in closing
+ * state.
+ */
+#define NGTCP2_ERR_CLOSING -230
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_DRAINING` indicates that connection is in
+ * draining state.
+ */
+#define NGTCP2_ERR_DRAINING -231
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_TRANSPORT_PARAM` indicates a general transport
+ * parameter error.
+ */
+#define NGTCP2_ERR_TRANSPORT_PARAM -234
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_DISCARD_PKT` indicates a packet was discarded.
+ */
+#define NGTCP2_ERR_DISCARD_PKT -235
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_CONN_ID_BLOCKED` indicates that there is no
+ * spare Connection ID available.
+ */
+#define NGTCP2_ERR_CONN_ID_BLOCKED -237
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_INTERNAL` indicates an internal error.
+ */
+#define NGTCP2_ERR_INTERNAL -238
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_CRYPTO_BUFFER_EXCEEDED` indicates that a crypto
+ * buffer exceeded.
+ */
+#define NGTCP2_ERR_CRYPTO_BUFFER_EXCEEDED -239
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_WRITE_MORE` indicates
+ * :macro:`NGTCP2_WRITE_STREAM_FLAG_MORE` is used and a function call
+ * succeeded.
+ */
+#define NGTCP2_ERR_WRITE_MORE -240
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_RETRY` indicates that server should send Retry
+ * packet.
+ */
+#define NGTCP2_ERR_RETRY -241
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_DROP_CONN` indicates that an endpoint should
+ * drop connection immediately.
+ */
+#define NGTCP2_ERR_DROP_CONN -242
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_AEAD_LIMIT_REACHED` indicates AEAD encryption
+ * limit is reached and key update is not available.  An endpoint
+ * should drop connection immediately.
+ */
+#define NGTCP2_ERR_AEAD_LIMIT_REACHED -243
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_NO_VIABLE_PATH` indicates that path validation
+ * could not probe that a path is capable of sending UDP datagram
+ * payload of size at least 1200 bytes.
+ */
+#define NGTCP2_ERR_NO_VIABLE_PATH -244
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_VERSION_NEGOTIATION` indicates that server
+ * should send Version Negotiation packet.
+ */
+#define NGTCP2_ERR_VERSION_NEGOTIATION -245
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_HANDSHAKE_TIMEOUT` indicates that QUIC
+ * connection is not established before the specified deadline.
+ */
+#define NGTCP2_ERR_HANDSHAKE_TIMEOUT -246
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_VERSION_NEGOTIATION_FAILURE` indicates the
+ * version negotiation failed.
+ */
+#define NGTCP2_ERR_VERSION_NEGOTIATION_FAILURE -247
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_IDLE_CLOSE` indicates the connection should be
+ * closed silently because of idle timeout.
+ */
+#define NGTCP2_ERR_IDLE_CLOSE -248
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_FATAL` indicates that error codes less than this
+ * value is fatal error.  When this error is returned, an endpoint
+ * should drop connection immediately.
+ */
+#define NGTCP2_ERR_FATAL -500
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_NOMEM` indicates out of memory.
+ */
+#define NGTCP2_ERR_NOMEM -501
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` indicates that user defined
+ * callback function failed.
+ */
+#define NGTCP2_ERR_CALLBACK_FAILURE -502
+
+/**
+ * @macrosection
+ *
+ * QUIC packet header flags
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PKT_FLAG_NONE` indicates no flag set.
+ */
+#define NGTCP2_PKT_FLAG_NONE 0x00u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PKT_FLAG_LONG_FORM` indicates the Long header packet
+ * header.
+ */
+#define NGTCP2_PKT_FLAG_LONG_FORM 0x01u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PKT_FLAG_FIXED_BIT_CLEAR` indicates that Fixed Bit
+ * (aka QUIC bit) is not set.
+ */
+#define NGTCP2_PKT_FLAG_FIXED_BIT_CLEAR 0x02u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PKT_FLAG_KEY_PHASE` indicates Key Phase bit set.
+ */
+#define NGTCP2_PKT_FLAG_KEY_PHASE 0x04u
+
+/**
+ * @enum
+ *
+ * :type:`ngtcp2_pkt_type` defines QUIC version-independent QUIC
+ * packet types.
+ */
+typedef enum ngtcp2_pkt_type {
+  /**
+   * :enum:`NGTCP2_PKT_VERSION_NEGOTIATION` is defined by libngtcp2
+   * for convenience.
+   */
+  NGTCP2_PKT_VERSION_NEGOTIATION = 0x80,
+  /**
+   * :enum:`NGTCP2_PKT_STATELESS_RESET` is defined by libngtcp2 for
+   * convenience.
+   */
+  NGTCP2_PKT_STATELESS_RESET = 0x81,
+  /**
+   * :enum:`NGTCP2_PKT_INITIAL` indicates Initial packet.
+   */
+  NGTCP2_PKT_INITIAL = 0x10,
+  /**
+   * :enum:`NGTCP2_PKT_0RTT` indicates 0RTT packet.
+   */
+  NGTCP2_PKT_0RTT = 0x11,
+  /**
+   * :enum:`NGTCP2_PKT_HANDSHAKE` indicates Handshake packet.
+   */
+  NGTCP2_PKT_HANDSHAKE = 0x12,
+  /**
+   * :enum:`NGTCP2_PKT_RETRY` indicates Retry packet.
+   */
+  NGTCP2_PKT_RETRY = 0x13,
+  /**
+   * :enum:`NGTCP2_PKT_1RTT` is defined by libngtcp2 for convenience.
+   */
+  NGTCP2_PKT_1RTT = 0x40
+} ngtcp2_pkt_type;
+
+/**
+ * @macrosection
+ *
+ * QUIC transport error code
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_NO_ERROR` is QUIC transport error code ``NO_ERROR``.
+ */
+#define NGTCP2_NO_ERROR 0x0u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_INTERNAL_ERROR` is QUIC transport error code
+ * ``INTERNAL_ERROR``.
+ */
+#define NGTCP2_INTERNAL_ERROR 0x1u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_CONNECTION_REFUSED` is QUIC transport error code
+ * ``CONNECTION_REFUSED``.
+ */
+#define NGTCP2_CONNECTION_REFUSED 0x2u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_FLOW_CONTROL_ERROR` is QUIC transport error code
+ * ``FLOW_CONTROL_ERROR``.
+ */
+#define NGTCP2_FLOW_CONTROL_ERROR 0x3u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_STREAM_LIMIT_ERROR` is QUIC transport error code
+ * ``STREAM_LIMIT_ERROR``.
+ */
+#define NGTCP2_STREAM_LIMIT_ERROR 0x4u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_STREAM_STATE_ERROR` is QUIC transport error code
+ * ``STREAM_STATE_ERROR``.
+ */
+#define NGTCP2_STREAM_STATE_ERROR 0x5u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_FINAL_SIZE_ERROR` is QUIC transport error code
+ * ``FINAL_SIZE_ERROR``.
+ */
+#define NGTCP2_FINAL_SIZE_ERROR 0x6u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_FRAME_ENCODING_ERROR` is QUIC transport error code
+ * ``FRAME_ENCODING_ERROR``.
+ */
+#define NGTCP2_FRAME_ENCODING_ERROR 0x7u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_TRANSPORT_PARAMETER_ERROR` is QUIC transport error
+ * code ``TRANSPORT_PARAMETER_ERROR``.
+ */
+#define NGTCP2_TRANSPORT_PARAMETER_ERROR 0x8u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_CONNECTION_ID_LIMIT_ERROR` is QUIC transport error
+ * code ``CONNECTION_ID_LIMIT_ERROR``.
+ */
+#define NGTCP2_CONNECTION_ID_LIMIT_ERROR 0x9u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PROTOCOL_VIOLATION` is QUIC transport error code
+ * ``PROTOCOL_VIOLATION``.
+ */
+#define NGTCP2_PROTOCOL_VIOLATION 0xau
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_INVALID_TOKEN` is QUIC transport error code
+ * ``INVALID_TOKEN``.
+ */
+#define NGTCP2_INVALID_TOKEN 0xbu
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_APPLICATION_ERROR` is QUIC transport error code
+ * ``APPLICATION_ERROR``.
+ */
+#define NGTCP2_APPLICATION_ERROR 0xcu
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_CRYPTO_BUFFER_EXCEEDED` is QUIC transport error code
+ * ``CRYPTO_BUFFER_EXCEEDED``.
+ */
+#define NGTCP2_CRYPTO_BUFFER_EXCEEDED 0xdu
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_KEY_UPDATE_ERROR` is QUIC transport error code
+ * ``KEY_UPDATE_ERROR``.
+ */
+#define NGTCP2_KEY_UPDATE_ERROR 0xeu
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_AEAD_LIMIT_REACHED` is QUIC transport error code
+ * ``AEAD_LIMIT_REACHED``.
+ */
+#define NGTCP2_AEAD_LIMIT_REACHED 0xfu
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_NO_VIABLE_PATH` is QUIC transport error code
+ * ``NO_VIABLE_PATH``.
+ */
+#define NGTCP2_NO_VIABLE_PATH 0x10u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_CRYPTO_ERROR` is QUIC transport error code
+ * ``CRYPTO_ERROR``.
+ */
+#define NGTCP2_CRYPTO_ERROR 0x100u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_VERSION_NEGOTIATION_ERROR_DRAFT` is QUIC transport
+ * error code ``VERSION_NEGOTIATION_ERROR``.
+ *
+ * https://quicwg.org/quic-v2/draft-ietf-quic-v2.html
+ */
+#define NGTCP2_VERSION_NEGOTIATION_ERROR_DRAFT 0x53f8u
+
+/**
+ * @enum
+ *
+ * :type:`ngtcp2_path_validation_result` defines path validation
+ * result code.
+ */
+typedef enum ngtcp2_path_validation_result {
+  /**
+   * :enum:`NGTCP2_PATH_VALIDATION_RESULT_SUCCESS` indicates
+   * successful validation.
+   */
+  NGTCP2_PATH_VALIDATION_RESULT_SUCCESS,
+  /**
+   * :enum:`NGTCP2_PATH_VALIDATION_RESULT_FAILURE` indicates
+   * validation failure.
+   */
+  NGTCP2_PATH_VALIDATION_RESULT_FAILURE,
+  /**
+   * :enum:`NGTCP2_PATH_VALIDATION_RESULT_ABORTED` indicates that path
+   * validation was aborted.
+   */
+  NGTCP2_PATH_VALIDATION_RESULT_ABORTED
+} ngtcp2_path_validation_result;
+
+/**
+ * @typedef
+ *
+ * :type:`ngtcp2_tstamp` is a timestamp with nanosecond resolution.
+ * ``UINT64_MAX`` is an invalid value.
+ */
+typedef uint64_t ngtcp2_tstamp;
+
+/**
+ * @typedef
+ *
+ * :type:`ngtcp2_duration` is a period of time in nanosecond
+ * resolution.  ``UINT64_MAX`` is an invalid value.
+ */
+typedef uint64_t ngtcp2_duration;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_cid` holds a Connection ID.
+ */
+typedef struct ngtcp2_cid {
+  /**
+   * :member:`datalen` is the length of Connection ID.
+   */
+  size_t datalen;
+  /**
+   * :member:`data` is the buffer to store Connection ID.
+   */
+  uint8_t data[NGTCP2_MAX_CIDLEN];
+} ngtcp2_cid;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_vec` is struct iovec compatible structure to
+ * reference arbitrary array of bytes.
+ */
+typedef struct ngtcp2_vec {
+  /**
+   * :member:`base` points to the data.
+   */
+  uint8_t *base;
+  /**
+   * :member:`len` is the number of bytes which the buffer pointed by
+   * base contains.
+   */
+  size_t len;
+} ngtcp2_vec;
+
+/**
+ * @function
+ *
+ * `ngtcp2_cid_init` initializes Connection ID |cid| with the byte
+ * string pointed by |data| and its length is |datalen|.  |datalen|
+ * must be at most :macro:`NGTCP2_MAX_CIDLEN`.
+ */
+NGTCP2_EXTERN void ngtcp2_cid_init(ngtcp2_cid *cid, const uint8_t *data,
+                                   size_t datalen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_cid_eq` returns nonzero if |a| and |b| share the same
+ * Connection ID.
+ */
+NGTCP2_EXTERN int ngtcp2_cid_eq(const ngtcp2_cid *a, const ngtcp2_cid *b);
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_pkt_hd` represents QUIC packet header.
+ */
+typedef struct ngtcp2_pkt_hd {
+  /**
+   * :member:`dcid` is Destination Connection ID.
+   */
+  ngtcp2_cid dcid;
+  /**
+   * :member:`scid` is Source Connection ID.
+   */
+  ngtcp2_cid scid;
+  /**
+   * :member:`pkt_num` is a packet number.
+   */
+  int64_t pkt_num;
+  /**
+   * :member:`token` contains token for Initial
+   * packet.
+   */
+  ngtcp2_vec token;
+  /**
+   * :member:`pkt_numlen` is the number of bytes spent to encode
+   * :member:`pkt_num`.
+   */
+  size_t pkt_numlen;
+  /**
+   * :member:`len` is the sum of :member:`pkt_numlen` and the length
+   * of QUIC packet payload.
+   */
+  size_t len;
+  /**
+   * :member:`version` is QUIC version.
+   */
+  uint32_t version;
+  /**
+   * :member:`type` is a type of QUIC packet.  See
+   * :type:`ngtcp2_pkt_type`.
+   */
+  uint8_t type;
+  /**
+   * :member:`flags` is zero or more of :macro:`NGTCP2_PKT_FLAG_*
+   * <NGTCP2_PKT_FLAG_NONE>`.
+   */
+  uint8_t flags;
+} ngtcp2_pkt_hd;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_pkt_stateless_reset` represents Stateless Reset.
+ */
+typedef struct ngtcp2_pkt_stateless_reset {
+  /**
+   * :member:`stateless_reset_token` contains stateless reset token.
+   */
+  uint8_t stateless_reset_token[NGTCP2_STATELESS_RESET_TOKENLEN];
+  /**
+   * :member:`rand` points a buffer which contains random bytes
+   * section.
+   */
+  const uint8_t *rand;
+  /**
+   * :member:`randlen` is the number of random bytes.
+   */
+  size_t randlen;
+} ngtcp2_pkt_stateless_reset;
+
+/**
+ * @enum
+ *
+ * :type:`ngtcp2_transport_params_type` defines TLS message type which
+ * carries transport parameters.
+ */
+typedef enum ngtcp2_transport_params_type {
+  /**
+   * :enum:`NGTCP2_TRANSPORT_PARAMS_TYPE_CLIENT_HELLO` is Client Hello
+   * TLS message.
+   */
+  NGTCP2_TRANSPORT_PARAMS_TYPE_CLIENT_HELLO,
+  /**
+   * :enum:`NGTCP2_TRANSPORT_PARAMS_TYPE_ENCRYPTED_EXTENSIONS` is
+   * Encrypted Extensions TLS message.
+   */
+  NGTCP2_TRANSPORT_PARAMS_TYPE_ENCRYPTED_EXTENSIONS
+} ngtcp2_transport_params_type;
+
+/**
+ * @macrosection
+ *
+ * QUIC transport parameters related macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_DEFAULT_MAX_RECV_UDP_PAYLOAD_SIZE` is the default
+ * value of max_udp_payload_size transport parameter.
+ */
+#define NGTCP2_DEFAULT_MAX_RECV_UDP_PAYLOAD_SIZE 65527
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_DEFAULT_ACK_DELAY_EXPONENT` is a default value of
+ * scaling factor of ACK Delay field in ACK frame.
+ */
+#define NGTCP2_DEFAULT_ACK_DELAY_EXPONENT 3
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_DEFAULT_MAX_ACK_DELAY` is a default value of the
+ * maximum amount of time in nanoseconds by which endpoint delays
+ * sending acknowledgement.
+ */
+#define NGTCP2_DEFAULT_MAX_ACK_DELAY (25 * NGTCP2_MILLISECONDS)
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_DEFAULT_ACTIVE_CONNECTION_ID_LIMIT` is the default
+ * value of active_connection_id_limit transport parameter value if
+ * omitted.
+ */
+#define NGTCP2_DEFAULT_ACTIVE_CONNECTION_ID_LIMIT 2
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_TLSEXT_QUIC_TRANSPORT_PARAMETERS_V1` is TLS
+ * extension type of quic_transport_parameters.
+ */
+#define NGTCP2_TLSEXT_QUIC_TRANSPORT_PARAMETERS_V1 0x39u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_TLSEXT_QUIC_TRANSPORT_PARAMETERS_DRAFT` is TLS
+ * extension type of quic_transport_parameters used during draft
+ * development.
+ */
+#define NGTCP2_TLSEXT_QUIC_TRANSPORT_PARAMETERS_DRAFT 0xffa5u
+
+#ifdef NGTCP2_USE_GENERIC_SOCKADDR
+typedef struct ngtcp2_sockaddr {
+  uint16_t sa_family;
+  uint8_t sa_data[14];
+} ngtcp2_sockaddr;
+
+typedef struct ngtcp2_in_addr {
+  uint32_t s_addr;
+} ngtcp2_in_addr;
+
+typedef struct ngtcp2_sockaddr_in {
+  uint16_t sin_family;
+  uint16_t sin_port;
+  ngtcp2_in_addr sin_addr;
+  uint8_t sin_zero[8];
+} ngtcp2_sockaddr_in;
+
+#  define NGTCP2_SS_MAXSIZE 128
+#  define NGTCP2_SS_ALIGNSIZE (sizeof(uint64_t))
+#  define NGTCP2_SS_PAD1SIZE (NGTCP2_SS_ALIGNSIZE - sizeof(uint16_t))
+#  define NGTCP2_SS_PAD2SIZE                                                   \
+    (NGTCP2_SS_MAXSIZE -                                                       \
+     (sizeof(uint16_t) + NGTCP2_SS_PAD1SIZE + NGTCP2_SS_ALIGNSIZE))
+
+typedef struct ngtcp2_sockaddr_storage {
+  uint16_t ss_family;
+  uint8_t _ss_pad1[NGTCP2_SS_PAD1SIZE];
+  uint64_t _ss_align;
+  uint8_t _ss_pad2[NGTCP2_SS_PAD2SIZE];
+} ngtcp2_sockaddr_storage;
+
+#  undef NGTCP2_SS_PAD2SIZE
+#  undef NGTCP2_SS_PAD1SIZE
+#  undef NGTCP2_SS_ALIGNSIZE
+#  undef NGTCP2_SS_MAXSIZE
+
+typedef uint32_t ngtcp2_socklen;
+#else
+/**
+ * @typedef
+ *
+ * :type:`ngtcp2_sockaddr` is typedefed to struct sockaddr.  If
+ * :macro:`NGTCP2_USE_GENERIC_SOCKADDR` is defined, it is typedefed to
+ * the generic struct sockaddr defined in ngtcp2.h.
+ */
+typedef struct sockaddr ngtcp2_sockaddr;
+/**
+ * @typedef
+ *
+ * :type:`ngtcp2_sockaddr_storage` is typedefed to struct
+ * sockaddr_storage.  If :macro:`NGTCP2_USE_GENERIC_SOCKADDR` is
+ * defined, it is typedefed to the generic struct sockaddr_storage
+ * defined in ngtcp2.h.
+ */
+typedef struct sockaddr_storage ngtcp2_sockaddr_storage;
+/**
+ * @typedef
+ *
+ * :type:`ngtcp2_sockaddr_in` is typedefed to struct sockaddr_in.  If
+ * :macro:`NGTCP2_USE_GENERIC_SOCKADDR` is defined, it is typedefed to
+ * the generic struct sockaddr_in defined in ngtcp2.h.
+ */
+typedef struct sockaddr_in ngtcp2_sockaddr_in;
+/**
+ * @typedef
+ *
+ * :type:`ngtcp2_socklen` is typedefed to socklen_t.  If
+ * :macro:`NGTCP2_USE_GENERIC_SOCKADDR` is defined, it is typedefed to
+ * uint32_t.
+ */
+typedef socklen_t ngtcp2_socklen;
+#endif
+
+#if defined(NGTCP2_USE_GENERIC_SOCKADDR) ||                                    \
+    defined(NGTCP2_USE_GENERIC_IPV6_SOCKADDR)
+typedef struct ngtcp2_in6_addr {
+  uint8_t in6_addr[16];
+} ngtcp2_in6_addr;
+
+typedef struct ngtcp2_sockaddr_in6 {
+  uint16_t sin6_family;
+  uint16_t sin6_port;
+  uint32_t sin6_flowinfo;
+  ngtcp2_in6_addr sin6_addr;
+  uint32_t sin6_scope_id;
+} ngtcp2_sockaddr_in6;
+#else
+/**
+ * @typedef
+ *
+ * :type:`ngtcp2_sockaddr_in6` is typedefed to struct sockaddr_in6.
+ * If :macro:`NGTCP2_USE_GENERIC_SOCKADDR` is defined, it is typedefed
+ * to the generic struct sockaddr_in6 defined in ngtcp2.h.
+ */
+typedef struct sockaddr_in6 ngtcp2_sockaddr_in6;
+#endif
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_sockaddr_union` conveniently includes all supported
+ * address types.
+ */
+typedef union ngtcp2_sockaddr_union {
+  ngtcp2_sockaddr sa;
+  ngtcp2_sockaddr_in in;
+  ngtcp2_sockaddr_in6 in6;
+} ngtcp2_sockaddr_union;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_preferred_addr` represents preferred address
+ * structure.
+ */
+typedef struct ngtcp2_preferred_addr {
+  /**
+   * :member:`cid` is a Connection ID.
+   */
+  ngtcp2_cid cid;
+  /**
+   * :member:`ipv4` contains IPv4 address and port.
+   */
+  ngtcp2_sockaddr_in ipv4;
+  /**
+   * :member:`ipv6` contains IPv4 address and port.
+   */
+  ngtcp2_sockaddr_in6 ipv6;
+  /**
+   * :member:`ipv4_present` indicates that :member:`ipv4` contains
+   * IPv4 address and port.
+   */
+  uint8_t ipv4_present;
+  /**
+   * :member:`ipv6_present` indicates that :member:`ipv6` contains
+   * IPv6 address and port.
+   */
+  uint8_t ipv6_present;
+  /**
+   * :member:`stateless_reset_token` contains stateless reset token.
+   */
+  uint8_t stateless_reset_token[NGTCP2_STATELESS_RESET_TOKENLEN];
+} ngtcp2_preferred_addr;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_version_info` represents version_information
+ * structure.
+ */
+typedef struct ngtcp2_version_info {
+  /**
+   * :member:`chosen_version` is the version chosen by the sender.
+   */
+  uint32_t chosen_version;
+  /**
+   * :member:`other_versions` points the wire image of other_versions
+   * field.  The each version is therefore in network byte order.
+   */
+  uint8_t *other_versions;
+  /**
+   * :member:`other_versionslen` is the number of bytes pointed by
+   * :member:`other_versions`, not the number of versions included.
+   */
+  size_t other_versionslen;
+} ngtcp2_version_info;
+
+#define NGTCP2_TRANSPORT_PARAMS_VERSION_V1 1
+#define NGTCP2_TRANSPORT_PARAMS_VERSION NGTCP2_TRANSPORT_PARAMS_VERSION_V1
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_transport_params` represents QUIC transport
+ * parameters.
+ */
+typedef struct ngtcp2_transport_params {
+  /**
+   * :member:`preferred_address` contains preferred address if
+   * :member:`preferred_address_present` is nonzero.
+   */
+  ngtcp2_preferred_addr preferred_address;
+  /**
+   * :member:`original_dcid` is the Destination Connection ID field
+   * from the first Initial packet from client.  Server must specify
+   * this field.  It is expected that application knows the original
+   * Destination Connection ID even if it sends Retry packet, for
+   * example, by including it in retry token.  Otherwise, application
+   * should not specify this field.
+   */
+  ngtcp2_cid original_dcid;
+  /**
+   * :member:`initial_scid` is the Source Connection ID field from the
+   * first Initial packet the endpoint sends.  Application should not
+   * specify this field.
+   */
+  ngtcp2_cid initial_scid;
+  /**
+   * :member:`retry_scid` is the Source Connection ID field from Retry
+   * packet.  Only server uses this field.  If server application
+   * received Initial packet with retry token from client and server
+   * verified its token, server application must set Destination
+   * Connection ID field from the Initial packet to this field and set
+   * :member:`retry_scid_present` to nonzero.  Server application must
+   * verify that the Destination Connection ID from Initial packet was
+   * sent in Retry packet by, for example, including the Connection ID
+   * in a token, or including it in AAD when encrypting a token.
+   */
+  ngtcp2_cid retry_scid;
+  /**
+   * :member:`initial_max_stream_data_bidi_local` is the size of flow
+   * control window of locally initiated stream.  This is the number
+   * of bytes that the remote endpoint can send and the local endpoint
+   * must ensure that it has enough buffer to receive them.
+   */
+  uint64_t initial_max_stream_data_bidi_local;
+  /**
+   * :member:`initial_max_stream_data_bidi_remote` is the size of flow
+   * control window of remotely initiated stream.  This is the number
+   * of bytes that the remote endpoint can send and the local endpoint
+   * must ensure that it has enough buffer to receive them.
+   */
+  uint64_t initial_max_stream_data_bidi_remote;
+  /**
+   * :member:`initial_max_stream_data_uni` is the size of flow control
+   * window of remotely initiated unidirectional stream.  This is the
+   * number of bytes that the remote endpoint can send and the local
+   * endpoint must ensure that it has enough buffer to receive them.
+   */
+  uint64_t initial_max_stream_data_uni;
+  /**
+   * :member:`initial_max_data` is the connection level flow control
+   * window.
+   */
+  uint64_t initial_max_data;
+  /**
+   * :member:`initial_max_streams_bidi` is the number of concurrent
+   * streams that the remote endpoint can create.
+   */
+  uint64_t initial_max_streams_bidi;
+  /**
+   * :member:`initial_max_streams_uni` is the number of concurrent
+   * unidirectional streams that the remote endpoint can create.
+   */
+  uint64_t initial_max_streams_uni;
+  /**
+   * :member:`max_idle_timeout` is a duration during which sender
+   * allows quiescent.
+   */
+  ngtcp2_duration max_idle_timeout;
+  /**
+   * :member:`max_udp_payload_size` is the maximum datagram size that
+   * the endpoint can receive.
+   */
+  uint64_t max_udp_payload_size;
+  /**
+   * :member:`active_connection_id_limit` is the maximum number of
+   * Connection ID that sender can store.
+   */
+  uint64_t active_connection_id_limit;
+  /**
+   * :member:`ack_delay_exponent` is the exponent used in ACK Delay
+   * field in ACK frame.
+   */
+  uint64_t ack_delay_exponent;
+  /**
+   * :member:`max_ack_delay` is the maximum acknowledgement delay by
+   * which the endpoint will delay sending acknowledgements.
+   */
+  ngtcp2_duration max_ack_delay;
+  /**
+   * :member:`max_datagram_frame_size` is the maximum size of DATAGRAM
+   * frame that this endpoint willingly receives.  Specifying 0
+   * disables DATAGRAM support.  See
+   * https://datatracker.ietf.org/doc/html/rfc9221
+   */
+  uint64_t max_datagram_frame_size;
+  /**
+   * :member:`stateless_reset_token_present` is nonzero if
+   * :member:`stateless_reset_token` field is set.
+   */
+  uint8_t stateless_reset_token_present;
+  /**
+   * :member:`disable_active_migration` is nonzero if the endpoint
+   * does not support active connection migration.
+   */
+  uint8_t disable_active_migration;
+  /**
+   * :member:`retry_scid_present` is nonzero if :member:`retry_scid`
+   * field is set.
+   */
+  uint8_t retry_scid_present;
+  /**
+   * :member:`preferred_address_present` is nonzero if
+   * :member:`preferred_address` is set.
+   */
+  uint8_t preferred_address_present;
+  /**
+   * :member:`stateless_reset_token` contains stateless reset token.
+   */
+  uint8_t stateless_reset_token[NGTCP2_STATELESS_RESET_TOKENLEN];
+  /**
+   * :member:`grease_quic_bit` is nonzero if sender supports "Greasing
+   * the QUIC Bit" extension.  See :rfc:`9287`.  Note that the local
+   * endpoint always enables greasing QUIC bit regardless of this
+   * field value.
+   */
+  uint8_t grease_quic_bit;
+  /**
+   * :member:`version_info` contains version_information field if
+   * :member:`version_info_present` is nonzero.  Application should
+   * not specify this field.
+   */
+  ngtcp2_version_info version_info;
+  /**
+   * :member:`version_info_present` is nonzero if
+   * :member:`version_info` is set.  Application should not specify
+   * this field.
+   */
+  uint8_t version_info_present;
+} ngtcp2_transport_params;
+
+/**
+ * @enum
+ *
+ * :type:`ngtcp2_pktns_id` defines packet number space identifier.
+ */
+typedef enum ngtcp2_pktns_id {
+  /**
+   * :enum:`NGTCP2_PKTNS_ID_INITIAL` is the Initial packet number
+   * space.
+   */
+  NGTCP2_PKTNS_ID_INITIAL,
+  /**
+   * :enum:`NGTCP2_PKTNS_ID_HANDSHAKE` is the Handshake packet number
+   * space.
+   */
+  NGTCP2_PKTNS_ID_HANDSHAKE,
+  /**
+   * :enum:`NGTCP2_PKTNS_ID_APPLICATION` is the Application data
+   * packet number space.
+   */
+  NGTCP2_PKTNS_ID_APPLICATION,
+  /**
+   * :enum:`NGTCP2_PKTNS_ID_MAX` is defined to get the number of
+   * packet number spaces.
+   */
+  NGTCP2_PKTNS_ID_MAX
+} ngtcp2_pktns_id;
+
+#define NGTCP2_CONN_STAT_VERSION_V1 1
+#define NGTCP2_CONN_STAT_VERSION NGTCP2_CONN_STAT_VERSION_V1
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_conn_stat` holds various connection statistics, and
+ * computed data for recovery and congestion controller.
+ */
+typedef struct ngtcp2_conn_stat {
+  /**
+   * :member:`latest_rtt` is the latest RTT sample which is not
+   * adjusted by acknowledgement delay.
+   */
+  ngtcp2_duration latest_rtt;
+  /**
+   * :member:`min_rtt` is the minimum RTT seen so far.  It is not
+   * adjusted by acknowledgement delay.
+   */
+  ngtcp2_duration min_rtt;
+  /**
+   * :member:`smoothed_rtt` is the smoothed RTT.
+   */
+  ngtcp2_duration smoothed_rtt;
+  /**
+   * :member:`rttvar` is a mean deviation of observed RTT.
+   */
+  ngtcp2_duration rttvar;
+  /**
+   * :member:`initial_rtt` is the initial RTT which is used when no
+   * RTT sample is available.
+   */
+  ngtcp2_duration initial_rtt;
+  /**
+   * :member:`first_rtt_sample_ts` is the timestamp when the first RTT
+   * sample is obtained.
+   */
+  ngtcp2_tstamp first_rtt_sample_ts;
+  /**
+   * :member:`pto_count` is the count of successive PTO timer
+   * expiration.
+   */
+  size_t pto_count;
+  /**
+   * :member:`loss_detection_timer` is the deadline of the current
+   * loss detection timer.
+   */
+  ngtcp2_tstamp loss_detection_timer;
+  /**
+   * :member:`last_tx_pkt_ts` corresponds to
+   * time_of_last_ack_eliciting_packet in :rfc:`9002`.
+   */
+  ngtcp2_tstamp last_tx_pkt_ts[NGTCP2_PKTNS_ID_MAX];
+  /**
+   * :member:`loss_time` corresponds to loss_time in :rfc:`9002`.
+   */
+  ngtcp2_tstamp loss_time[NGTCP2_PKTNS_ID_MAX];
+  /**
+   * :member:`cwnd` is the size of congestion window.
+   */
+  uint64_t cwnd;
+  /**
+   * :member:`ssthresh` is slow start threshold.
+   */
+  uint64_t ssthresh;
+  /**
+   * :member:`congestion_recovery_start_ts` is the timestamp when
+   * congestion recovery started.
+   */
+  ngtcp2_tstamp congestion_recovery_start_ts;
+  /**
+   * :member:`bytes_in_flight` is the number in bytes of all sent
+   * packets which have not been acknowledged.
+   */
+  uint64_t bytes_in_flight;
+  /**
+   * :member:`max_tx_udp_payload_size` is the maximum size of UDP
+   * datagram payload that this endpoint transmits.  It is used by
+   * congestion controller to compute congestion window.
+   */
+  size_t max_tx_udp_payload_size;
+  /**
+   * :member:`delivery_rate_sec` is the current sending rate measured
+   * in byte per second.
+   */
+  uint64_t delivery_rate_sec;
+  /**
+   * :member:`pacing_rate` is the current packet sending rate computed
+   * by a congestion controller.  0 if a congestion controller does
+   * not set pacing rate.  Even if this value is set to 0, the library
+   * paces packets.
+   */
+  double pacing_rate;
+  /**
+   * :member:`send_quantum` is the maximum size of a data aggregate
+   * scheduled and transmitted together.
+   */
+  size_t send_quantum;
+} ngtcp2_conn_stat;
+
+/**
+ * @enum
+ *
+ * :type:`ngtcp2_cc_algo` defines congestion control algorithms.
+ */
+typedef enum ngtcp2_cc_algo {
+  /**
+   * :enum:`NGTCP2_CC_ALGO_RENO` represents Reno.
+   */
+  NGTCP2_CC_ALGO_RENO = 0x00,
+  /**
+   * :enum:`NGTCP2_CC_ALGO_CUBIC` represents Cubic.
+   */
+  NGTCP2_CC_ALGO_CUBIC = 0x01,
+  /**
+   * :enum:`NGTCP2_CC_ALGO_BBR` represents BBR.
+   */
+  NGTCP2_CC_ALGO_BBR = 0x02,
+  /**
+   * :enum:`NGTCP2_CC_ALGO_BBR2` represents BBR v2.
+   */
+  NGTCP2_CC_ALGO_BBR2 = 0x03
+} ngtcp2_cc_algo;
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_printf` is a callback function for logging.
+ * |user_data| is the same object passed to `ngtcp2_conn_client_new`
+ * or `ngtcp2_conn_server_new`.
+ */
+typedef void (*ngtcp2_printf)(void *user_data, const char *format, ...);
+
+/**
+ * @macrosection
+ *
+ * QLog related macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_QLOG_WRITE_FLAG_NONE` indicates no flag set.
+ */
+#define NGTCP2_QLOG_WRITE_FLAG_NONE 0x00u
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_QLOG_WRITE_FLAG_FIN` indicates that this is the
+ * final call to :type:`ngtcp2_qlog_write` in the current connection.
+ */
+#define NGTCP2_QLOG_WRITE_FLAG_FIN 0x01u
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_rand_ctx` is a wrapper around native random number
+ * generator.  It is opaque to the ngtcp2 library.  This might be
+ * useful if application needs to specify random number generator per
+ * thread or per connection.
+ */
+typedef struct ngtcp2_rand_ctx {
+  /**
+   * :member:`native_handle` is a pointer to an underlying random
+   * number generator.
+   */
+  void *native_handle;
+} ngtcp2_rand_ctx;
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_qlog_write` is a callback function which is called to
+ * write qlog |data| of length |datalen| bytes.  |flags| is bitwise OR
+ * of zero or more of :macro:`NGTCP2_QLOG_WRITE_FLAG_*
+ * <NGTCP2_QLOG_WRITE_FLAG_NONE>`.  If
+ * :macro:`NGTCP2_QLOG_WRITE_FLAG_FIN` is set, |datalen| may be 0.
+ */
+typedef void (*ngtcp2_qlog_write)(void *user_data, uint32_t flags,
+                                  const void *data, size_t datalen);
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_qlog_settings` is a set of settings for qlog.
+ */
+typedef struct ngtcp2_qlog_settings {
+  /**
+   * :member:`odcid` is Original Destination Connection ID sent by
+   * client.  It is used as group_id and ODCID fields.  Client ignores
+   * this field and uses dcid parameter passed to
+   * `ngtcp2_conn_client_new()`.
+   */
+  ngtcp2_cid odcid;
+  /**
+   * :member:`write` is a callback function to write qlog.  Setting
+   * ``NULL`` disables qlog.
+   */
+  ngtcp2_qlog_write write;
+} ngtcp2_qlog_settings;
+
+#define NGTCP2_SETTINGS_VERSION_V1 1
+#define NGTCP2_SETTINGS_VERSION NGTCP2_SETTINGS_VERSION_V1
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_settings` defines QUIC connection settings.
+ */
+typedef struct ngtcp2_settings {
+  /**
+   * :member:`qlog` is qlog settings.
+   */
+  ngtcp2_qlog_settings qlog;
+  /**
+   * :member:`cc_algo` specifies congestion control algorithm.
+   */
+  ngtcp2_cc_algo cc_algo;
+  /**
+   * :member:`initial_ts` is an initial timestamp given to the
+   * library.
+   */
+  ngtcp2_tstamp initial_ts;
+  /**
+   * :member:`initial_rtt` is an initial RTT.
+   */
+  ngtcp2_duration initial_rtt;
+  /**
+   * :member:`log_printf` is a function that the library uses to write
+   * logs.  ``NULL`` means no logging output.  It is nothing to do
+   * with qlog.
+   */
+  ngtcp2_printf log_printf;
+  /**
+   * :member:`max_tx_udp_payload_size` is the maximum size of UDP
+   * datagram payload that this endpoint transmits.  It is used by
+   * congestion controller to compute congestion window.
+   */
+  size_t max_tx_udp_payload_size;
+  /**
+   * :member:`token` is a token from Retry packet or NEW_TOKEN frame.
+   *
+   * Server sets this field if it received the token in Client Initial
+   * packet and successfully validated.
+   *
+   * Client sets this field if it intends to send token in its Initial
+   * packet.
+   *
+   * `ngtcp2_conn_server_new` and `ngtcp2_conn_client_new` make a copy
+   * of token.
+   */
+  ngtcp2_vec token;
+  /**
+   * :member:`rand_ctx` is an optional random number generator to be
+   * passed to :type:`ngtcp2_rand` callback.
+   */
+  ngtcp2_rand_ctx rand_ctx;
+  /**
+   * :member:`max_window` is the maximum connection-level flow control
+   * window if connection-level window auto-tuning is enabled.  The
+   * connection-level window auto tuning is enabled if nonzero value
+   * is specified in this field.  The initial value of window size is
+   * :member:`ngtcp2_transport_params.initial_max_data`.  The window
+   * size is scaled up to the value specified in this field.
+   */
+  uint64_t max_window;
+  /**
+   * :member:`max_stream_window` is the maximum stream-level flow
+   * control window if stream-level window auto-tuning is enabled.
+   * The stream-level window auto-tuning is enabled if nonzero value
+   * is specified in this field.  The initial value of window size is
+   * :member:`ngtcp2_transport_params.initial_max_stream_data_bidi_remote`,
+   * :member:`ngtcp2_transport_params.initial_max_stream_data_bidi_local`,
+   * or :member:`ngtcp2_transport_params.initial_max_stream_data_uni`,
+   * depending on the type of stream.  The window size is scaled up to
+   * the value specified in this field.
+   */
+  uint64_t max_stream_window;
+  /**
+   * :member:`ack_thresh` is the minimum number of the received ACK
+   * eliciting packets that triggers the immediate acknowledgement.
+   */
+  size_t ack_thresh;
+  /**
+   * :member:`no_tx_udp_payload_size_shaping`, if set to nonzero,
+   * instructs the library not to limit the UDP payload size to
+   * :macro:`NGTCP2_MAX_UDP_PAYLOAD_SIZE` (which can be extended by
+   * Path MTU Discovery) and instead use the mininum size among the
+   * given buffer size, :member:`max_tx_udp_payload_size`, and the
+   * received max_udp_payload QUIC transport parameter.
+   */
+  int no_tx_udp_payload_size_shaping;
+  /**
+   * :member:`handshake_timeout` is the period of time before giving
+   * up QUIC connection establishment.  If QUIC handshake is not
+   * complete within this period, `ngtcp2_conn_handle_expiry` returns
+   * :macro:`NGTCP2_ERR_HANDSHAKE_TIMEOUT` error.  The deadline is
+   * :member:`initial_ts` + :member:`handshake_timeout`.  If this
+   * field is set to ``UINT64_MAX``, no handshake timeout is set.
+   */
+  ngtcp2_duration handshake_timeout;
+  /**
+   * :member:`preferred_versions` is the array of versions that are
+   * preferred by the local endpoint.  All versions set in this array
+   * must be supported by the library, and compatible to QUIC v1.  The
+   * reserved versions are not allowed.  They are sorted in the order
+   * of preference.
+   *
+   * On compatible version negotiation, server will negotiate one of
+   * those versions contained in this array if a client initially
+   * chooses a less preferred version.  This version set corresponds
+   * to Offered Versions in QUIC Version Negotiation draft, and it should
+   * be sent in Version Negotiation packet.
+   *
+   * Client uses this field and :member:`original_version` to prevent
+   * version downgrade attack if it reacted upon Version Negotiation
+   * packet.  If this field is specified, client must include
+   * |client_chosen_version| passed to `ngtcp2_conn_client_new` unless
+   * |client_chosen_version| is a reserved version.
+   */
+  uint32_t *preferred_versions;
+  /**
+   * :member:`preferred_versionslen` is the number of versions that
+   * are contained in the array pointed by
+   * :member:`preferred_versions`.
+   */
+  size_t preferred_versionslen;
+  /**
+   * :member:`other_versions` is the array of versions that are set in
+   * :member:`other_versions <ngtcp2_version_info.other_versions>`
+   * field of outgoing version_information QUIC transport parameter.
+   *
+   * For server, this corresponds to Fully-Deployed Versions in QUIC
+   * Version Negotiation draft.  If this field is set not, it is set
+   * to :member:`preferred_versions` internally if
+   * :member:`preferred_versionslen` is not zero.  If this field is
+   * not set, and :member:`preferred_versionslen` is zero, this field
+   * is set to :macro:`NGTCP2_PROTO_VER_V1` internally.
+   *
+   * Client must include |client_chosen_version| passed to
+   * `ngtcp2_conn_client_new` in this array if this field is set and
+   * |client_chosen_version| is not a reserved version.  If this field
+   * is not set, |client_chosen_version| passed to
+   * `ngtcp2_conn_client_new` will be set in this field internally
+   * unless |client_chosen_version| is a reserved version.
+   */
+  uint32_t *other_versions;
+  /**
+   * :member:`other_versionslen` is the number of versions that are
+   * contained in the array pointed by :member:`other_versions`.
+   */
+  size_t other_versionslen;
+  /**
+   * :member:`original_version` is the original version that client
+   * initially used to make a connection attempt.  If it is set, and
+   * it differs from |client_chosen_version| passed to
+   * `ngtcp2_conn_client_new`, the library assumes that client reacted
+   * upon Version Negotiation packet.  Server does not use this field.
+   */
+  uint32_t original_version;
+  /**
+   * :member:`no_pmtud`, if set to nonzero, disables Path MTU
+   * Discovery.
+   */
+  int no_pmtud;
+} ngtcp2_settings;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_addr` is the endpoint address.
+ */
+typedef struct ngtcp2_addr {
+  /**
+   * :member:`addr` points to the buffer which contains endpoint
+   * address.  It must not be ``NULL``.
+   */
+  ngtcp2_sockaddr *addr;
+  /**
+   * :member:`addrlen` is the length of addr.
+   */
+  ngtcp2_socklen addrlen;
+} ngtcp2_addr;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_path` is the network endpoints where a packet is sent
+ * and received.
+ */
+typedef struct ngtcp2_path {
+  /**
+   * :member:`local` is the address of local endpoint.
+   */
+  ngtcp2_addr local;
+  /**
+   * :member:`remote` is the address of remote endpoint.
+   */
+  ngtcp2_addr remote;
+  /**
+   * :member:`user_data` is an arbitrary data and opaque to the
+   * library.
+   *
+   * Note that :type:`ngtcp2_path` is generally passed to
+   * :type:`ngtcp2_conn` by an application, and :type:`ngtcp2_conn`
+   * stores their copies.  Unfortunately, there is no way for the
+   * application to know when :type:`ngtcp2_conn` finishes using a
+   * specific :type:`ngtcp2_path` object in mid connection, which
+   * means that the application cannot free the data pointed by this
+   * field.  Therefore, it is advised to use this field only when the
+   * data pointed by this field persists in an entire lifetime of the
+   * connection.
+   */
+  void *user_data;
+} ngtcp2_path;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_path_storage` is a convenient struct to have buffers
+ * to store the longest addresses.
+ */
+typedef struct ngtcp2_path_storage {
+  /**
+   * :member:`path` stores network path.
+   */
+  ngtcp2_path path;
+  /**
+   * :member:`local_addrbuf` is a buffer to store local address.
+   */
+  ngtcp2_sockaddr_union local_addrbuf;
+  /**
+   * :member:`remote_addrbuf` is a buffer to store remote address.
+   */
+  ngtcp2_sockaddr_union remote_addrbuf;
+} ngtcp2_path_storage;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_crypto_md` is a wrapper around native message digest
+ * object.
+ */
+typedef struct ngtcp2_crypto_md {
+  /**
+   * :member:`native_handle` is a pointer to an underlying message
+   * digest object.
+   */
+  void *native_handle;
+} ngtcp2_crypto_md;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_crypto_aead` is a wrapper around native AEAD object.
+ */
+typedef struct ngtcp2_crypto_aead {
+  /**
+   * :member:`native_handle` is a pointer to an underlying AEAD
+   * object.
+   */
+  void *native_handle;
+  /**
+   * :member:`max_overhead` is the number of additional bytes which
+   * AEAD encryption needs on encryption.
+   */
+  size_t max_overhead;
+} ngtcp2_crypto_aead;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_crypto_cipher` is a wrapper around native cipher
+ * object.
+ */
+typedef struct ngtcp2_crypto_cipher {
+  /**
+   * :member:`native_handle` is a pointer to an underlying cipher
+   * object.
+   */
+  void *native_handle;
+} ngtcp2_crypto_cipher;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_crypto_aead_ctx` is a wrapper around native AEAD
+ * cipher context object.  It should be initialized with a specific
+ * key.  ngtcp2 library reuses this context object to encrypt or
+ * decrypt multiple packets.
+ */
+typedef struct ngtcp2_crypto_aead_ctx {
+  /**
+   * :member:`native_handle` is a pointer to an underlying AEAD
+   * context object.
+   */
+  void *native_handle;
+} ngtcp2_crypto_aead_ctx;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_crypto_cipher_ctx` is a wrapper around native cipher
+ * context object.  It should be initialized with a specific key.
+ * ngtcp2 library reuses this context object to encrypt or decrypt
+ * multiple packet headers.
+ */
+typedef struct ngtcp2_crypto_cipher_ctx {
+  /**
+   * :member:`native_handle` is a pointer to an underlying cipher
+   * context object.
+   */
+  void *native_handle;
+} ngtcp2_crypto_cipher_ctx;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_crypto_ctx` is a convenient structure to bind all
+ * crypto related objects in one place.  Use
+ * `ngtcp2_crypto_ctx_initial` to initialize this struct for Initial
+ * packet encryption.  For Handshake and 1RTT packets, use
+ * `ngtcp2_crypto_ctx_tls`.
+ */
+typedef struct ngtcp2_crypto_ctx {
+  /**
+   * :member:`aead` is AEAD object.
+   */
+  ngtcp2_crypto_aead aead;
+  /**
+   * :member:`md` is message digest object.
+   */
+  ngtcp2_crypto_md md;
+  /**
+   * :member:`hp` is header protection cipher.
+   */
+  ngtcp2_crypto_cipher hp;
+  /**
+   * :member:`max_encryption` is the number of encryption which this
+   * key can be used with.
+   */
+  uint64_t max_encryption;
+  /**
+   * :member:`max_decryption_failure` is the number of decryption
+   * failure with this key.
+   */
+  uint64_t max_decryption_failure;
+} ngtcp2_crypto_ctx;
+
+/**
+ * @function
+ *
+ * `ngtcp2_encode_transport_params` encodes |params| in |dest| of
+ * length |destlen|.
+ *
+ * If |dest| is NULL, and |destlen| is zero, this function just
+ * returns the number of bytes required to store the encoded transport
+ * parameters.
+ *
+ * This function returns the number of written, or one of the
+ * following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOBUF`
+ *     Buffer is too small.
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     |exttype| is invalid.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_encode_transport_params_versioned(
+    uint8_t *dest, size_t destlen, ngtcp2_transport_params_type exttype,
+    int transport_params_version, const ngtcp2_transport_params *params);
+
+/**
+ * @function
+ *
+ * `ngtcp2_decode_transport_params` decodes transport parameters in
+ * |data| of length |datalen|, and stores the result in the object
+ * pointed by |params|.
+ *
+ * If the optional parameters are missing, the default value is
+ * assigned.
+ *
+ * The following fields may point to somewhere inside the buffer
+ * pointed by |data| of length |datalen|:
+ *
+ * - :member:`ngtcp2_transport_params.version_info.other_versions
+ *   <ngtcp2_version_info.other_versions>`
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_REQUIRED_TRANSPORT_PARAM`
+ *     The required parameter is missing.
+ * :macro:`NGTCP2_ERR_MALFORMED_TRANSPORT_PARAM`
+ *     The input is malformed.
+ */
+NGTCP2_EXTERN int ngtcp2_decode_transport_params_versioned(
+    int transport_params_version, ngtcp2_transport_params *params,
+    ngtcp2_transport_params_type exttype, const uint8_t *data, size_t datalen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_decode_transport_params_new` decodes transport parameters
+ * in |data| of length |datalen|, and stores the result in the object
+ * allocated dynamically.  The pointer to the allocated object is
+ * assigned to |*pparams|.  Unlike `ngtcp2_decode_transport_params`,
+ * all direct and indirect fields are also allocated dynamically if
+ * needed.
+ *
+ * |mem| is a memory allocator to allocate memory.  If |mem| is
+ * ``NULL``, the memory allocator returned by `ngtcp2_mem_default()`
+ * is used.
+ *
+ * If the optional parameters are missing, the default value is
+ * assigned.
+ *
+ * `ngtcp2_transport_params_del` frees the memory allocated by this
+ * function.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_REQUIRED_TRANSPORT_PARAM`
+ *     The required parameter is missing.
+ * :macro:`NGTCP2_ERR_MALFORMED_TRANSPORT_PARAM`
+ *     The input is malformed.
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_decode_transport_params_new(
+    ngtcp2_transport_params **pparams, ngtcp2_transport_params_type exttype,
+    const uint8_t *data, size_t datalen, const ngtcp2_mem *mem);
+
+/**
+ * @function
+ *
+ * `ngtcp2_transport_params_del` frees the |params| which must be
+ * dynamically allocated by `ngtcp2_decode_transport_params_new`.
+ *
+ * |mem| is a memory allocator that allocated |params|.  If |mem| is
+ * ``NULL``, the memory allocator returned by `ngtcp2_mem_default()`
+ * is used.
+ *
+ * If |params| is ``NULL``, this function does nothing.
+ */
+NGTCP2_EXTERN void ngtcp2_transport_params_del(ngtcp2_transport_params *params,
+                                               const ngtcp2_mem *mem);
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_version_cid` is a convenient struct to store the
+ * result of `ngtcp2_pkt_decode_version_cid`.
+ */
+typedef struct ngtcp2_version_cid {
+  /**
+   * :member:`version` stores QUIC version.
+   */
+  uint32_t version;
+  /**
+   * :member:`dcid` points to the Destination Connection ID.
+   */
+  const uint8_t *dcid;
+  /**
+   * :member:`dcidlen` is the length of the Destination Connection ID
+   * pointed by :member:`dcid`.
+   */
+  size_t dcidlen;
+  /**
+   * :member:`scid` points to the Source Connection ID.
+   */
+  const uint8_t *scid;
+  /**
+   * :member:`scidlen` is the length of the Source Connection ID
+   * pointed by :member:`scid`.
+   */
+  size_t scidlen;
+} ngtcp2_version_cid;
+
+/**
+ * @function
+ *
+ * `ngtcp2_pkt_decode_version_cid` extracts QUIC version, Destination
+ * Connection ID and Source Connection ID from the packet pointed by
+ * |data| of length |datalen|.  This function can handle Connection ID
+ * up to 255 bytes unlike `ngtcp2_pkt_decode_hd_long` or
+ * `ngtcp2_pkt_decode_hd_short` which are only capable of handling
+ * Connection ID less than or equal to :macro:`NGTCP2_MAX_CIDLEN`.
+ * Longer Connection ID is only valid if the version is unsupported
+ * QUIC version.
+ *
+ * If the given packet is Long header packet, this function extracts
+ * the version from the packet and assigns it to
+ * :member:`dest->version <ngtcp2_version_cid.version>`.  It also
+ * extracts the pointer to the Destination Connection ID and its
+ * length and assigns them to :member:`dest->dcid
+ * <ngtcp2_version_cid.dcid>` and :member:`dest->dcidlen
+ * <ngtcp2_version_cid.dcidlen>` respectively.  Similarly, it extracts
+ * the pointer to the Source Connection ID and its length and assigns
+ * them to :member:`dest->scid <ngtcp2_version_cid.scid>` and
+ * :member:`dest->scidlen <ngtcp2_version_cid.scidlen>` respectively.
+ *
+ * If the given packet is Short header packet, :member:`dest->version
+ * <ngtcp2_version_cid.version>` will be 0, :member:`dest->scid
+ * <ngtcp2_version_cid.scid>` will be ``NULL``, and
+ * :member:`dest->scidlen <ngtcp2_version_cid.scidlen>` will be 0.
+ * Because the Short header packet does not have the length of
+ * Destination Connection ID, the caller has to pass the length in
+ * |short_dcidlen|.  This function extracts the pointer to the
+ * Destination Connection ID and assigns it to :member:`dest->dcid
+ * <ngtcp2_version_cid.dcid>`.  |short_dcidlen| is assigned to
+ * :member:`dest->dcidlen <ngtcp2_version_cid.dcidlen>`.
+ *
+ * If Version Negotiation is required, this function returns
+ * :macro:`NGTCP2_ERR_VERSION_NEGOTIATION`.  Unlike the other error
+ * cases, all fields of |dest| are assigned as described above.
+ *
+ * This function returns 0 if it succeeds.  Otherwise, one of the
+ * following negative error code:
+ *
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     The function could not decode the packet header.
+ * :macro:`NGTCP2_ERR_VERSION_NEGOTIATION`
+ *     Version Negotiation packet should be sent.
+ */
+NGTCP2_EXTERN int ngtcp2_pkt_decode_version_cid(ngtcp2_version_cid *dest,
+                                                const uint8_t *data,
+                                                size_t datalen,
+                                                size_t short_dcidlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_pkt_decode_hd_long` decodes QUIC long packet header in
+ * |pkt| of length |pktlen|.  This function only parses the input just
+ * before packet number field.
+ *
+ * This function does not verify that length field is correct.  In
+ * other words, this function succeeds even if length > |pktlen|.
+ *
+ * This function can handle Connection ID up to
+ * :macro:`NGTCP2_MAX_CIDLEN`.  Consider to use
+ * `ngtcp2_pkt_decode_version_cid` to get longer Connection ID.
+ *
+ * This function handles Version Negotiation specially.  If version
+ * field is 0, |pkt| must contain Version Negotiation packet.  Version
+ * Negotiation packet has random type in wire format.  For
+ * convenience, this function sets
+ * :enum:`ngtcp2_pkt_type.NGTCP2_PKT_VERSION_NEGOTIATION` to
+ * :member:`dest->type <ngtcp2_pkt_hd.type>`, clears
+ * :macro:`NGTCP2_PKT_FLAG_LONG_FORM` flag from :member:`dest->flags
+ * <ngtcp2_pkt_hd.flags>`, and sets 0 to :member:`dest->len
+ * <ngtcp2_pkt_hd.len>`.  Version Negotiation packet occupies a single
+ * packet.
+ *
+ * It stores the result in the object pointed by |dest|, and returns
+ * the number of bytes decoded to read the packet header if it
+ * succeeds, or one of the following error codes:
+ *
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     Packet is too short; or it is not a long header
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_pkt_decode_hd_long(ngtcp2_pkt_hd *dest,
+                                                     const uint8_t *pkt,
+                                                     size_t pktlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_pkt_decode_hd_short` decodes QUIC short header packet
+ * header in |pkt| of length |pktlen|.  |dcidlen| is the length of
+ * DCID in packet header.  Short header packet does not encode the
+ * length of connection ID, thus we need the input from the outside.
+ * This function only parses the input just before packet number
+ * field.  This function can handle Connection ID up to
+ * :macro:`NGTCP2_MAX_CIDLEN`.  Consider to use
+ * `ngtcp2_pkt_decode_version_cid` to get longer Connection ID.  It
+ * stores the result in the object pointed by |dest|, and returns the
+ * number of bytes decoded to read the packet header if it succeeds,
+ * or one of the following error codes:
+ *
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     Packet is too short; or it is not a short header
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_pkt_decode_hd_short(ngtcp2_pkt_hd *dest,
+                                                      const uint8_t *pkt,
+                                                      size_t pktlen,
+                                                      size_t dcidlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_pkt_write_stateless_reset` writes Stateless Reset packet in
+ * the buffer pointed by |dest| whose length is |destlen|.
+ * |stateless_reset_token| is a pointer to the Stateless Reset Token,
+ * and its length must be :macro:`NGTCP2_STATELESS_RESET_TOKENLEN`
+ * bytes long.  |rand| specifies the random octets preceding Stateless
+ * Reset Token.  The length of |rand| is specified by |randlen| which
+ * must be at least :macro:`NGTCP2_MIN_STATELESS_RESET_RANDLEN` bytes
+ * long.
+ *
+ * If |randlen| is too long to write them all in the buffer, |rand| is
+ * written to the buffer as much as possible, and is truncated.
+ *
+ * This function returns the number of bytes written to the buffer, or
+ * one of the following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOBUF`
+ *     Buffer is too small.
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     |randlen| is strictly less than
+ *     :macro:`NGTCP2_MIN_STATELESS_RESET_RANDLEN`.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_pkt_write_stateless_reset(
+    uint8_t *dest, size_t destlen, const uint8_t *stateless_reset_token,
+    const uint8_t *rand, size_t randlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_pkt_write_version_negotiation` writes Version Negotiation
+ * packet in the buffer pointed by |dest| whose length is |destlen|.
+ * |unused_random| should be generated randomly.  |dcid| is the
+ * destination connection ID which appears in a packet as a source
+ * connection ID sent by client which caused version negotiation.
+ * Similarly, |scid| is the source connection ID which appears in a
+ * packet as a destination connection ID sent by client.  |sv| is a
+ * list of supported versions, and |nsv| specifies the number of
+ * supported versions included in |sv|.
+ *
+ * This function returns the number of bytes written to the buffer, or
+ * one of the following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOBUF`
+ *     Buffer is too small.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_pkt_write_version_negotiation(
+    uint8_t *dest, size_t destlen, uint8_t unused_random, const uint8_t *dcid,
+    size_t dcidlen, const uint8_t *scid, size_t scidlen, const uint32_t *sv,
+    size_t nsv);
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_conn` represents a single QUIC connection.
+ */
+typedef struct ngtcp2_conn ngtcp2_conn;
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_client_initial` is invoked when client application
+ * asks TLS stack to produce first TLS cryptographic handshake data.
+ *
+ * This implementation of this callback must get the first handshake
+ * data from TLS stack and pass it to ngtcp2 library using
+ * `ngtcp2_conn_submit_crypto_data` function.  Make sure that before
+ * calling `ngtcp2_conn_submit_crypto_data` function, client
+ * application must create initial packet protection keys and IVs, and
+ * provide them to ngtcp2 library using
+ * `ngtcp2_conn_install_initial_key`.
+ *
+ * This callback function must return 0 if it succeeds, or
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library call
+ * return immediately.
+ */
+typedef int (*ngtcp2_client_initial)(ngtcp2_conn *conn, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_recv_client_initial` is invoked when server receives
+ * Initial packet from client.  An server application must implement
+ * this callback, and generate initial keys and IVs for both
+ * transmission and reception.  Install them using
+ * `ngtcp2_conn_install_initial_key`.  |dcid| is the destination
+ * connection ID which client generated randomly.  It is used to
+ * derive initial packet protection keys.
+ *
+ * The callback function must return 0 if it succeeds.  If an error
+ * occurs, return :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the
+ * library call return immediately.
+ */
+typedef int (*ngtcp2_recv_client_initial)(ngtcp2_conn *conn,
+                                          const ngtcp2_cid *dcid,
+                                          void *user_data);
+
+/**
+ * @enum
+ *
+ * :type:`ngtcp2_crypto_level` is encryption level.
+ */
+typedef enum ngtcp2_crypto_level {
+  /**
+   * :enum:`NGTCP2_CRYPTO_LEVEL_INITIAL` is Initial Keys encryption
+   * level.
+   */
+  NGTCP2_CRYPTO_LEVEL_INITIAL,
+  /**
+   * :enum:`NGTCP2_CRYPTO_LEVEL_HANDSHAKE` is Handshake Keys
+   * encryption level.
+   */
+  NGTCP2_CRYPTO_LEVEL_HANDSHAKE,
+  /**
+   * :enum:`NGTCP2_CRYPTO_LEVEL_APPLICATION` is Application Data
+   * (1-RTT) Keys encryption level.
+   */
+  NGTCP2_CRYPTO_LEVEL_APPLICATION,
+  /**
+   * :enum:`NGTCP2_CRYPTO_LEVEL_EARLY` is Early Data (0-RTT) Keys
+   * encryption level.
+   */
+  NGTCP2_CRYPTO_LEVEL_EARLY
+} ngtcp2_crypto_level;
+
+/**
+ * @functypedef
+ *
+ * :type`ngtcp2_recv_crypto_data` is invoked when crypto data is
+ * received.  The received data is pointed to by |data|, and its
+ * length is |datalen|.  The |offset| specifies the offset where
+ * |data| is positioned.  |user_data| is the arbitrary pointer passed
+ * to `ngtcp2_conn_client_new` or `ngtcp2_conn_server_new`.  The
+ * ngtcp2 library ensures that the crypto data is passed to the
+ * application in the increasing order of |offset|.  |datalen| is
+ * always strictly greater than 0.  |crypto_level| indicates the
+ * encryption level where this data is received.  Crypto data can
+ * never be received in
+ * :enum:`ngtcp2_crypto_level.NGTCP2_CRYPTO_LEVEL_EARLY`.
+ *
+ * The application should provide the given data to TLS stack.
+ *
+ * The callback function must return 0 if it succeeds, or one of the
+ * following negative error codes:
+ *
+ * - :macro:`NGTCP2_ERR_CRYPTO`
+ * - :macro:`NGTCP2_ERR_REQUIRED_TRANSPORT_PARAM`
+ * - :macro:`NGTCP2_ERR_MALFORMED_TRANSPORT_PARAM`
+ * - :macro:`NGTCP2_ERR_TRANSPORT_PARAM`
+ * - :macro:`NGTCP2_ERR_PROTO`
+ * - :macro:`NGTCP2_ERR_VERSION_NEGOTIATION_FAILURE`
+ * - :macro:`NGTCP2_ERR_NOMEM`
+ * - :macro:`NGTCP2_ERR_CALLBACK_FAILURE`
+ *
+ * If the other value is returned, it is treated as
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE`.
+ *
+ * If application encounters fatal error, return
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library call
+ * return immediately.
+ */
+typedef int (*ngtcp2_recv_crypto_data)(ngtcp2_conn *conn,
+                                       ngtcp2_crypto_level crypto_level,
+                                       uint64_t offset, const uint8_t *data,
+                                       size_t datalen, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_handshake_completed` is invoked when QUIC
+ * cryptographic handshake has completed.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_handshake_completed)(ngtcp2_conn *conn, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_handshake_confirmed` is invoked when QUIC
+ * cryptographic handshake is confirmed.  The handshake confirmation
+ * means that both endpoints agree that handshake has finished.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_handshake_confirmed)(ngtcp2_conn *conn, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_recv_version_negotiation` is invoked when Version
+ * Negotiation packet is received.  |hd| is the pointer to the QUIC
+ * packet header object.  The vector |sv| of |nsv| elements contains
+ * the QUIC version the server supports.  Since Version Negotiation is
+ * only sent by server, this callback function is used by client only.
+ *
+ * The callback function must return 0 if it succeeds, or
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library call
+ * return immediately.
+ */
+typedef int (*ngtcp2_recv_version_negotiation)(ngtcp2_conn *conn,
+                                               const ngtcp2_pkt_hd *hd,
+                                               const uint32_t *sv, size_t nsv,
+                                               void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_recv_retry` is invoked when Retry packet is received.
+ * This callback is client use only.
+ *
+ * Application must regenerate packet protection key, IV, and header
+ * protection key for Initial packets using the destination connection
+ * ID obtained by :member:`hd->scid <ngtcp2_pkt_hd.scid>` and install
+ * them by calling `ngtcp2_conn_install_initial_key()`.
+ *
+ * 0-RTT data accepted by the ngtcp2 library will be automatically
+ * retransmitted as 0-RTT data by the library.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_recv_retry)(ngtcp2_conn *conn, const ngtcp2_pkt_hd *hd,
+                                 void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_encrypt` is invoked when the ngtcp2 library asks the
+ * application to encrypt packet payload.  The packet payload to
+ * encrypt is passed as |plaintext| of length |plaintextlen|.  The
+ * AEAD cipher is |aead|.  |aead_ctx| is the AEAD cipher context
+ * object which is initialized with encryption key.  The nonce is
+ * passed as |nonce| of length |noncelen|.  The Additional
+ * Authenticated Data is passed as |aad| of length |aadlen|.
+ *
+ * The implementation of this callback must encrypt |plaintext| using
+ * the negotiated cipher suite and write the ciphertext into the
+ * buffer pointed by |dest|.  |dest| has enough capacity to store the
+ * ciphertext and any additional AEAD tag data.
+ *
+ * |dest| and |plaintext| may point to the same buffer.
+ *
+ * The callback function must return 0 if it succeeds, or
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library call
+ * return immediately.
+ */
+typedef int (*ngtcp2_encrypt)(uint8_t *dest, const ngtcp2_crypto_aead *aead,
+                              const ngtcp2_crypto_aead_ctx *aead_ctx,
+                              const uint8_t *plaintext, size_t plaintextlen,
+                              const uint8_t *nonce, size_t noncelen,
+                              const uint8_t *aad, size_t aadlen);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_decrypt` is invoked when the ngtcp2 library asks the
+ * application to decrypt packet payload.  The packet payload to
+ * decrypt is passed as |ciphertext| of length |ciphertextlen|.  The
+ * AEAD cipher is |aead|.  |aead_ctx| is the AEAD cipher context
+ * object which is initialized with decryption key.  The nonce is
+ * passed as |nonce| of length |noncelen|.  The Additional
+ * Authenticated Data is passed as |aad| of length |aadlen|.
+ *
+ * The implementation of this callback must decrypt |ciphertext| using
+ * the negotiated cipher suite and write the ciphertext into the
+ * buffer pointed by |dest|.  |dest| has enough capacity to store the
+ * cleartext.
+ *
+ * |dest| and |ciphertext| may point to the same buffer.
+ *
+ * The callback function must return 0 if it succeeds.  If TLS stack
+ * fails to decrypt data, return :macro:`NGTCP2_ERR_DECRYPT`.  For any
+ * other errors, return :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which
+ * makes the library call return immediately.
+ */
+typedef int (*ngtcp2_decrypt)(uint8_t *dest, const ngtcp2_crypto_aead *aead,
+                              const ngtcp2_crypto_aead_ctx *aead_ctx,
+                              const uint8_t *ciphertext, size_t ciphertextlen,
+                              const uint8_t *nonce, size_t noncelen,
+                              const uint8_t *aad, size_t aadlen);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_hp_mask` is invoked when the ngtcp2 library asks the
+ * application to produce a mask to encrypt or decrypt packet header.
+ * The encryption cipher is |hp|.  |hp_ctx| is the cipher context
+ * object which is initialized with header protection key.  The sample
+ * is passed as |sample| which is :macro:`NGTCP2_HP_SAMPLELEN` bytes
+ * long.
+ *
+ * The implementation of this callback must produce a mask using the
+ * header protection cipher suite specified by QUIC specification and
+ * write the result into the buffer pointed by |dest|.  The length of
+ * the mask must be at least :macro:`NGTCP2_HP_MASKLEN`.  The library
+ * only uses the first :macro:`NGTCP2_HP_MASKLEN` bytes of the
+ * produced mask.  The buffer pointed by |dest| is guaranteed to have
+ * at least :macro:`NGTCP2_HP_SAMPLELEN` bytes available for
+ * convenience.
+ *
+ * The callback function must return 0 if it succeeds, or
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library call
+ * return immediately.
+ */
+typedef int (*ngtcp2_hp_mask)(uint8_t *dest, const ngtcp2_crypto_cipher *hp,
+                              const ngtcp2_crypto_cipher_ctx *hp_ctx,
+                              const uint8_t *sample);
+
+/**
+ * @macrosection
+ *
+ * Stream data flags
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_STREAM_DATA_FLAG_NONE` indicates no flag set.
+ */
+#define NGTCP2_STREAM_DATA_FLAG_NONE 0x00u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_STREAM_DATA_FLAG_FIN` indicates that this chunk of
+ * data is final piece of an incoming stream.
+ */
+#define NGTCP2_STREAM_DATA_FLAG_FIN 0x01u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_STREAM_DATA_FLAG_EARLY` indicates that this chunk of
+ * data contains data received in 0RTT packet and the handshake has
+ * not completed yet, which means that the data might be replayed.
+ */
+#define NGTCP2_STREAM_DATA_FLAG_EARLY 0x02u
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_recv_stream_data` is invoked when stream data is
+ * received.  The stream is specified by |stream_id|.  |flags| is the
+ * bitwise-OR of zero or more of :macro:`NGTCP2_STREAM_DATA_FLAG_*
+ * <NGTCP2_STREAM_DATA_FLAG_NONE>`.  If |flags| &
+ * :macro:`NGTCP2_STREAM_DATA_FLAG_FIN` is nonzero, this portion of
+ * the data is the last data in this stream.  |offset| is the offset
+ * where this data begins.  The library ensures that data is passed to
+ * the application in the non-decreasing order of |offset| without any
+ * overlap.  The data is passed as |data| of length |datalen|.
+ * |datalen| may be 0 if and only if |fin| is nonzero.
+ *
+ * If :macro:`NGTCP2_STREAM_DATA_FLAG_EARLY` is set in |flags|, it
+ * indicates that a part of or whole data was received in 0RTT packet
+ * and a handshake has not completed yet.
+ *
+ * The callback function must return 0 if it succeeds, or
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library return
+ * immediately.
+ */
+typedef int (*ngtcp2_recv_stream_data)(ngtcp2_conn *conn, uint32_t flags,
+                                       int64_t stream_id, uint64_t offset,
+                                       const uint8_t *data, size_t datalen,
+                                       void *user_data, void *stream_user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_stream_open` is a callback function which is called
+ * when remote stream is opened by peer.  This function is not called
+ * if stream is opened by implicitly (we might reconsider this
+ * behaviour).
+ *
+ * The implementation of this callback should return 0 if it succeeds.
+ * Returning :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library
+ * call return immediately.
+ */
+typedef int (*ngtcp2_stream_open)(ngtcp2_conn *conn, int64_t stream_id,
+                                  void *user_data);
+
+/**
+ * @macrosection
+ *
+ * Stream close flags
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_STREAM_CLOSE_FLAG_NONE` indicates no flag set.
+ */
+#define NGTCP2_STREAM_CLOSE_FLAG_NONE 0x00u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_STREAM_CLOSE_FLAG_APP_ERROR_CODE_SET` indicates that
+ * app_error_code parameter is set.
+ */
+#define NGTCP2_STREAM_CLOSE_FLAG_APP_ERROR_CODE_SET 0x01u
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_stream_close` is invoked when a stream is closed.
+ * This callback is not called when QUIC connection is closed before
+ * existing streams are closed.  |flags| is the bitwise-OR of zero or
+ * more of :macro:`NGTCP2_STREAM_CLOSE_FLAG_*
+ * <NGTCP2_STREAM_CLOSE_FLAG_NONE>`.  |app_error_code| indicates the
+ * error code of this closure if
+ * :macro:`NGTCP2_STREAM_CLOSE_FLAG_APP_ERROR_CODE_SET` is set in
+ * |flags|.  If it is not set, the stream was closed without any error
+ * code, which generally means success.
+ *
+ * |app_error_code| is the first application error code sent by a
+ * local endpoint, or received from a remote endpoint.  If a stream is
+ * closed cleanly, no application error code is exchanged.  Since QUIC
+ * stack does not know the application error code which indicates "no
+ * errors", |app_error_code| is set to 0 and
+ * :macro:`NGTCP2_STREAM_CLOSE_FLAG_APP_ERROR_CODE_SET` is not set in
+ * |flags| in this case.
+ *
+ * The implementation of this callback should return 0 if it succeeds.
+ * Returning :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library
+ * call return immediately.
+ */
+typedef int (*ngtcp2_stream_close)(ngtcp2_conn *conn, uint32_t flags,
+                                   int64_t stream_id, uint64_t app_error_code,
+                                   void *user_data, void *stream_user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_stream_reset` is invoked when a stream identified by
+ * |stream_id| is reset by a remote endpoint.
+ *
+ * The implementation of this callback should return 0 if it succeeds.
+ * Returning :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library
+ * call return immediately.
+ */
+typedef int (*ngtcp2_stream_reset)(ngtcp2_conn *conn, int64_t stream_id,
+                                   uint64_t final_size, uint64_t app_error_code,
+                                   void *user_data, void *stream_user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_acked_stream_data_offset` is a callback function
+ * which is called when stream data is acked, and application can free
+ * the data.  The acked range of data is [offset, offset + datalen).
+ * For a given stream_id, this callback is called sequentially in
+ * increasing order of |offset| without any overlap.  |datalen| is
+ * normally strictly greater than 0.  One exception is that when a
+ * packet which includes STREAM frame which has fin flag set, and 0
+ * length data, this callback is invoked with 0 passed as |datalen|.
+ *
+ * If a stream is closed prematurely and stream data is still
+ * in-flight, this callback function is not called for those data.
+ *
+ * The implementation of this callback should return 0 if it succeeds.
+ * Returning :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library
+ * call return immediately.
+ */
+typedef int (*ngtcp2_acked_stream_data_offset)(
+    ngtcp2_conn *conn, int64_t stream_id, uint64_t offset, uint64_t datalen,
+    void *user_data, void *stream_user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_recv_stateless_reset` is a callback function which is
+ * called when Stateless Reset packet is received.  The stateless
+ * reset details are given in |sr|.
+ *
+ * The implementation of this callback should return 0 if it succeeds.
+ * Returning :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library
+ * call return immediately.
+ */
+typedef int (*ngtcp2_recv_stateless_reset)(ngtcp2_conn *conn,
+                                           const ngtcp2_pkt_stateless_reset *sr,
+                                           void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_extend_max_streams` is a callback function which is
+ * called every time max stream ID is strictly extended.
+ * |max_streams| is the cumulative number of streams which an endpoint
+ * can open.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_extend_max_streams)(ngtcp2_conn *conn,
+                                         uint64_t max_streams, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_extend_max_stream_data` is a callback function which
+ * is invoked when max stream data is extended.  |stream_id|
+ * identifies the stream.  |max_data| is a cumulative number of bytes
+ * the endpoint can send on this stream.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_extend_max_stream_data)(ngtcp2_conn *conn,
+                                             int64_t stream_id,
+                                             uint64_t max_data, void *user_data,
+                                             void *stream_user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_rand` is a callback function to get randomized byte
+ * string from application.  Application must fill random |destlen|
+ * bytes to the buffer pointed by |dest|.  The generated bytes are
+ * used only in non-cryptographic context.
+ */
+typedef void (*ngtcp2_rand)(uint8_t *dest, size_t destlen,
+                            const ngtcp2_rand_ctx *rand_ctx);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_get_new_connection_id` is a callback function to ask
+ * an application for new connection ID.  Application must generate
+ * new unused connection ID with the exact |cidlen| bytes and store it
+ * in |cid|.  It also has to generate stateless reset token into
+ * |token|.  The length of stateless reset token is
+ * :macro:`NGTCP2_STATELESS_RESET_TOKENLEN` and it is guaranteed that
+ * the buffer pointed by |cid| has the sufficient space to store the
+ * token.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_get_new_connection_id)(ngtcp2_conn *conn, ngtcp2_cid *cid,
+                                            uint8_t *token, size_t cidlen,
+                                            void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_remove_connection_id` is a callback function which
+ * notifies the application that connection ID |cid| is no longer used
+ * by remote endpoint.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_remove_connection_id)(ngtcp2_conn *conn,
+                                           const ngtcp2_cid *cid,
+                                           void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_update_key` is a callback function which tells the
+ * application that it must generate new packet protection keying
+ * materials and AEAD cipher context objects with new keys.  The
+ * current set of secrets are given as |current_rx_secret| and
+ * |current_tx_secret| of length |secretlen|.  They are decryption and
+ * encryption secrets respectively.
+ *
+ * The application has to generate new secrets and keys for both
+ * encryption and decryption, and write decryption secret and IV to
+ * the buffer pointed by |rx_secret| and |rx_iv| respectively.  It
+ * also has to create new AEAD cipher context object with new
+ * decryption key and initialize |rx_aead_ctx| with it.  Similarly,
+ * write encryption secret and IV to the buffer pointed by |tx_secret|
+ * and |tx_iv|.  Create new AEAD cipher context object with new
+ * encryption key and initialize |tx_aead_ctx| with it.  All given
+ * buffers have the enough capacity to store secret, key and IV.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_update_key)(
+    ngtcp2_conn *conn, uint8_t *rx_secret, uint8_t *tx_secret,
+    ngtcp2_crypto_aead_ctx *rx_aead_ctx, uint8_t *rx_iv,
+    ngtcp2_crypto_aead_ctx *tx_aead_ctx, uint8_t *tx_iv,
+    const uint8_t *current_rx_secret, const uint8_t *current_tx_secret,
+    size_t secretlen, void *user_data);
+
+/**
+ * @macrosection
+ *
+ * Path validation related macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PATH_VALIDATION_FLAG_NONE` indicates no flag set.
+ */
+#define NGTCP2_PATH_VALIDATION_FLAG_NONE 0x00u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_PATH_VALIDATION_FLAG_PREFERRED_ADDR` indicates the
+ * validation involving server preferred address.  This flag is only
+ * set for client.
+ */
+#define NGTCP2_PATH_VALIDATION_FLAG_PREFERRED_ADDR 0x01u
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_path_validation` is a callback function which tells
+ * the application the outcome of path validation.  |flags| is zero or
+ * more of :macro:`NGTCP2_PATH_VALIDATION_FLAG_*
+ * <NGTCP2_PATH_VALIDATION_FLAG_NONE>`.  |path| is the path that was
+ * validated.  If |res| is
+ * :enum:`ngtcp2_path_validation_result.NGTCP2_PATH_VALIDATION_RESULT_SUCCESS`,
+ * the path validation succeeded.  If |res| is
+ * :enum:`ngtcp2_path_validation_result.NGTCP2_PATH_VALIDATION_RESULT_FAILURE`,
+ * the path validation failed.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_path_validation)(ngtcp2_conn *conn, uint32_t flags,
+                                      const ngtcp2_path *path,
+                                      ngtcp2_path_validation_result res,
+                                      void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_select_preferred_addr` is a callback function which
+ * asks a client application to choose server address from preferred
+ * addresses |paddr| received from server.  An application should
+ * write a network path for a selected preferred address in |dest|.
+ * More specifically, the selected preferred address must be set to
+ * :member:`dest->remote <ngtcp2_path.remote>`, a client source
+ * address must be set to :member:`dest->local <ngtcp2_path.local>`.
+ * If a client source address does not change for the new server
+ * address, leave :member:`dest->local <ngtcp2_path.local>`
+ * unmodified, or copy the value of :member:`local
+ * <ngtcp2_path.local>` field of the current network path obtained
+ * from `ngtcp2_conn_get_path()`.  Both :member:`dest->local.addr
+ * <ngtcp2_addr.addr>` and :member:`dest->remote.addr
+ * <ngtcp2_addr.addr>` point to buffers which are at least
+ * ``sizeof(struct sockaddr_storage)`` bytes long, respectively.  If
+ * an application denies the preferred addresses, just leave |dest|
+ * unmodified (or set :member:`dest->remote.addrlen
+ * <ngtcp2_addr.addrlen>` to 0) and return 0.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_select_preferred_addr)(ngtcp2_conn *conn,
+                                            ngtcp2_path *dest,
+                                            const ngtcp2_preferred_addr *paddr,
+                                            void *user_data);
+
+/**
+ * @enum
+ *
+ * :type:`ngtcp2_connection_id_status_type` defines a set of status
+ * for Destination Connection ID.
+ */
+typedef enum ngtcp2_connection_id_status_type {
+  /**
+   * :enum:`NGTCP2_CONNECTION_ID_STATUS_TYPE_ACTIVATE` indicates that
+   * a local endpoint starts using new destination Connection ID.
+   */
+  NGTCP2_CONNECTION_ID_STATUS_TYPE_ACTIVATE,
+  /**
+   * :enum:`NGTCP2_CONNECTION_ID_STATUS_TYPE_DEACTIVATE` indicates
+   * that a local endpoint stops using a given destination Connection
+   * ID.
+   */
+  NGTCP2_CONNECTION_ID_STATUS_TYPE_DEACTIVATE
+} ngtcp2_connection_id_status_type;
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_connection_id_status` is a callback function which is
+ * called when the status of Connection ID changes.
+ *
+ * |token| is the associated stateless reset token and it is ``NULL``
+ * if no token is present.
+ *
+ * |type| is the one of the value defined in
+ * :type:`ngtcp2_connection_id_status_type`.  The new value might be
+ * added in the future release.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_connection_id_status)(ngtcp2_conn *conn, int type,
+                                           uint64_t seq, const ngtcp2_cid *cid,
+                                           const uint8_t *token,
+                                           void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_recv_new_token` is a callback function which is
+ * called when new token is received from server.
+ *
+ * |token| is the received token.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_recv_new_token)(ngtcp2_conn *conn, const ngtcp2_vec *token,
+                                     void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_delete_crypto_aead_ctx` is a callback function which
+ * must delete the native object pointed by
+ * :member:`aead_ctx->native_handle
+ * <ngtcp2_crypto_aead_ctx.native_handle>`.
+ */
+typedef void (*ngtcp2_delete_crypto_aead_ctx)(ngtcp2_conn *conn,
+                                              ngtcp2_crypto_aead_ctx *aead_ctx,
+                                              void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_delete_crypto_cipher_ctx` is a callback function
+ * which must delete the native object pointed by
+ * :member:`cipher_ctx->native_handle
+ * <ngtcp2_crypto_cipher_ctx.native_handle>`.
+ */
+typedef void (*ngtcp2_delete_crypto_cipher_ctx)(
+    ngtcp2_conn *conn, ngtcp2_crypto_cipher_ctx *cipher_ctx, void *user_data);
+
+/**
+ * @macrosection
+ *
+ * Datagram flags
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_DATAGRAM_FLAG_NONE` indicates no flag set.
+ */
+#define NGTCP2_DATAGRAM_FLAG_NONE 0x00u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_DATAGRAM_FLAG_EARLY` indicates that DATAGRAM frame
+ * is received in 0RTT packet and the handshake has not completed yet,
+ * which means that the data might be replayed.
+ */
+#define NGTCP2_DATAGRAM_FLAG_EARLY 0x01u
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_recv_datagram` is invoked when DATAGRAM frame is
+ * received.  |flags| is bitwise-OR of zero or more of
+ * :macro:`NGTCP2_DATAGRAM_FLAG_* <NGTCP2_DATAGRAM_FLAG_NONE>`.
+ *
+ * If :macro:`NGTCP2_DATAGRAM_FLAG_EARLY` is set in |flags|, it
+ * indicates that DATAGRAM frame was received in 0RTT packet and a
+ * handshake has not completed yet.
+ *
+ * The callback function must return 0 if it succeeds, or
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library return
+ * immediately.
+ */
+typedef int (*ngtcp2_recv_datagram)(ngtcp2_conn *conn, uint32_t flags,
+                                    const uint8_t *data, size_t datalen,
+                                    void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_ack_datagram` is invoked when a packet which contains
+ * DATAGRAM frame which is identified by |dgram_id| is acknowledged.
+ * |dgram_id| is the valued passed to `ngtcp2_conn_writev_datagram`.
+ *
+ * The callback function must return 0 if it succeeds, or
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library return
+ * immediately.
+ */
+typedef int (*ngtcp2_ack_datagram)(ngtcp2_conn *conn, uint64_t dgram_id,
+                                   void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_lost_datagram` is invoked when a packet which
+ * contains DATAGRAM frame which is identified by |dgram_id| is
+ * declared lost.  |dgram_id| is the valued passed to
+ * `ngtcp2_conn_writev_datagram`.  Note that the loss might be
+ * spurious, and DATAGRAM frame might be acknowledged later.
+ *
+ * The callback function must return 0 if it succeeds, or
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` which makes the library return
+ * immediately.
+ */
+typedef int (*ngtcp2_lost_datagram)(ngtcp2_conn *conn, uint64_t dgram_id,
+                                    void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_get_path_challenge_data` is a callback function to
+ * ask an application for new data that is sent in PATH_CHALLENGE
+ * frame.  Application must generate new unpredictable exactly
+ * :macro:`NGTCP2_PATH_CHALLENGE_DATALEN` bytes of random data and
+ * store them into the buffer pointed by |data|.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_get_path_challenge_data)(ngtcp2_conn *conn, uint8_t *data,
+                                              void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_stream_stop_sending` is invoked when a stream is no
+ * longer read by a local endpoint before it receives all stream data.
+ * This function is called at most once per stream.  |app_error_code|
+ * is the error code passed to `ngtcp2_conn_shutdown_stream_read` or
+ * `ngtcp2_conn_shutdown_stream`.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_stream_stop_sending)(ngtcp2_conn *conn, int64_t stream_id,
+                                          uint64_t app_error_code,
+                                          void *user_data,
+                                          void *stream_user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_version_negotiation` is invoked when the compatible
+ * version negotiation takes place.  For client, it is called when it
+ * sees a change in version field of a long header packet.  This
+ * callback function might be called multiple times for client.  For
+ * server, it is called once when the version is negotiated.
+ *
+ * The implementation of this callback must install new Initial keys
+ * for |version|.  Use `ngtcp2_conn_install_vneg_initial_key` to
+ * install keys.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_version_negotiation)(ngtcp2_conn *conn, uint32_t version,
+                                          const ngtcp2_cid *client_dcid,
+                                          void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_recv_key` is invoked when new key is installed to
+ * |conn| during QUIC cryptographic handshake.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_recv_key)(ngtcp2_conn *conn, ngtcp2_crypto_level level,
+                               void *user_data);
+
+/**
+ * @functypedef
+ *
+ * :type:`ngtcp2_early_data_rejected` is invoked when early data was
+ * rejected by server, or client decided not to attempt early data.
+ *
+ * The callback function must return 0 if it succeeds.  Returning
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE` makes the library call return
+ * immediately.
+ */
+typedef int (*ngtcp2_early_data_rejected)(ngtcp2_conn *conn, void *user_data);
+
+#define NGTCP2_CALLBACKS_VERSION_V1 1
+#define NGTCP2_CALLBACKS_VERSION NGTCP2_CALLBACKS_VERSION_V1
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_callbacks` holds a set of callback functions.
+ */
+typedef struct ngtcp2_callbacks {
+  /**
+   * :member:`client_initial` is a callback function which is invoked
+   * when client asks TLS stack to produce first TLS cryptographic
+   * handshake message.  This callback function must be specified for
+   * a client application.
+   */
+  ngtcp2_client_initial client_initial;
+  /**
+   * :member:`recv_client_initial` is a callback function which is
+   * invoked when a server receives the first packet from client.
+   * This callback function must be specified for a server application.
+   */
+  ngtcp2_recv_client_initial recv_client_initial;
+  /**
+   * :member:`recv_crypto_data` is a callback function which is
+   * invoked when cryptographic data (CRYPTO frame, in other words,
+   * TLS message) is received.  This callback function must be
+   * specified.
+   */
+  ngtcp2_recv_crypto_data recv_crypto_data;
+  /**
+   * :member:`handshake_completed` is a callback function which is
+   * invoked when QUIC cryptographic handshake has completed.  This
+   * callback function is optional.
+   */
+  ngtcp2_handshake_completed handshake_completed;
+  /**
+   * :member:`recv_version_negotiation` is a callback function which
+   * is invoked when Version Negotiation packet is received by a
+   * client.  This callback function is optional.
+   */
+  ngtcp2_recv_version_negotiation recv_version_negotiation;
+  /**
+   * :member:`encrypt` is a callback function which is invoked to
+   * encrypt a QUIC packet.  This callback function must be specified.
+   */
+  ngtcp2_encrypt encrypt;
+  /**
+   * :member:`decrypt` is a callback function which is invoked to
+   * decrypt a QUIC packet.  This callback function must be specified.
+   */
+  ngtcp2_decrypt decrypt;
+  /**
+   * :member:`hp_mask` is a callback function which is invoked to get
+   * a mask to encrypt or decrypt packet header.  This callback
+   * function must be specified.
+   */
+  ngtcp2_hp_mask hp_mask;
+  /**
+   * :member:`recv_stream_data` is a callback function which is
+   * invoked when STREAM data, which includes application data, is
+   * received.  This callback function is optional.
+   */
+  ngtcp2_recv_stream_data recv_stream_data;
+  /**
+   * :member:`acked_stream_data_offset` is a callback function which
+   * is invoked when STREAM data, which includes application data, is
+   * acknowledged by a remote endpoint.  It tells an application the
+   * largest offset of acknowledged STREAM data without a gap so that
+   * application can free memory for the data.  This callback function
+   * is optional.
+   */
+  ngtcp2_acked_stream_data_offset acked_stream_data_offset;
+  /**
+   * :member:`stream_open` is a callback function which is invoked
+   * when new remote stream is opened by a remote endpoint.  This
+   * callback function is optional.
+   */
+  ngtcp2_stream_open stream_open;
+  /**
+   * :member:`stream_close` is a callback function which is invoked
+   * when a stream is closed.  This callback function is optional.
+   */
+  ngtcp2_stream_close stream_close;
+  /**
+   * :member:`recv_stateless_reset` is a callback function which is
+   * invoked when Stateless Reset packet is received.  This callback
+   * function is optional.
+   */
+  ngtcp2_recv_stateless_reset recv_stateless_reset;
+  /**
+   * :member:`recv_retry` is a callback function which is invoked when
+   * a client receives Retry packet.  For client, this callback
+   * function must be specified.  Server never receive Retry packet.
+   */
+  ngtcp2_recv_retry recv_retry;
+  /**
+   * :member:`extend_max_local_streams_bidi` is a callback function
+   * which is invoked when the number of bidirectional stream which a
+   * local endpoint can open is increased.  This callback function is
+   * optional.
+   */
+  ngtcp2_extend_max_streams extend_max_local_streams_bidi;
+  /**
+   * :member:`extend_max_local_streams_uni` is a callback function
+   * which is invoked when the number of unidirectional stream which a
+   * local endpoint can open is increased.  This callback function is
+   * optional.
+   */
+  ngtcp2_extend_max_streams extend_max_local_streams_uni;
+  /**
+   * :member:`rand` is a callback function which is invoked when the
+   * library needs sequence of random data.  This callback function
+   * must be specified.
+   */
+  ngtcp2_rand rand;
+  /**
+   * :member:`get_new_connection_id` is a callback function which is
+   * invoked when the library needs new connection ID.  This callback
+   * function must be specified.
+   */
+  ngtcp2_get_new_connection_id get_new_connection_id;
+  /**
+   * :member:`remove_connection_id` is a callback function which
+   * notifies an application that connection ID is no longer used by a
+   * remote endpoint.  This callback function is optional.
+   */
+  ngtcp2_remove_connection_id remove_connection_id;
+  /**
+   * :member:`update_key` is a callback function which is invoked when
+   * the library tells an application that it must update keying
+   * materials and install new keys.  This callback function must be
+   * specified.
+   */
+  ngtcp2_update_key update_key;
+  /**
+   * :member:`path_validation` is a callback function which is invoked
+   * when path validation completed.  This callback function is
+   * optional.
+   */
+  ngtcp2_path_validation path_validation;
+  /**
+   * :member:`select_preferred_addr` is a callback function which is
+   * invoked when the library asks a client to select preferred
+   * address presented by a server.  This callback function is
+   * optional.
+   */
+  ngtcp2_select_preferred_addr select_preferred_addr;
+  /**
+   * :member:`stream_reset` is a callback function which is invoked
+   * when a stream is reset by a remote endpoint.  This callback
+   * function is optional.
+   */
+  ngtcp2_stream_reset stream_reset;
+  /**
+   * :member:`extend_max_remote_streams_bidi` is a callback function
+   * which is invoked when the number of bidirectional streams which a
+   * remote endpoint can open is increased.  This callback function is
+   * optional.
+   */
+  ngtcp2_extend_max_streams extend_max_remote_streams_bidi;
+  /**
+   * :member:`extend_max_remote_streams_uni` is a callback function
+   * which is invoked when the number of unidirectional streams which
+   * a remote endpoint can open is increased.  This callback function
+   * is optional.
+   */
+  ngtcp2_extend_max_streams extend_max_remote_streams_uni;
+  /**
+   * :member:`extend_max_stream_data` is callback function which is
+   * invoked when the maximum offset of STREAM data that a local
+   * endpoint can send is increased.  This callback function is
+   * optional.
+   */
+  ngtcp2_extend_max_stream_data extend_max_stream_data;
+  /**
+   * :member:`dcid_status` is a callback function which is invoked
+   * when the new destination Connection ID is activated or the
+   * activated destination Connection ID is now deactivated.  This
+   * callback function is optional.
+   */
+  ngtcp2_connection_id_status dcid_status;
+  /**
+   * :member:`handshake_confirmed` is a callback function which is
+   * invoked when both endpoints agree that handshake has finished.
+   * This field is ignored by server because handshake_completed
+   * indicates the handshake confirmation for server.  This callback
+   * function is optional.
+   */
+  ngtcp2_handshake_confirmed handshake_confirmed;
+  /**
+   * :member:`recv_new_token` is a callback function which is invoked
+   * when new token is received from server.  This field is ignored by
+   * server.  This callback function is optional.
+   */
+  ngtcp2_recv_new_token recv_new_token;
+  /**
+   * :member:`delete_crypto_aead_ctx` is a callback function which
+   * deletes a given AEAD cipher context object.  This callback
+   * function must be specified.
+   */
+  ngtcp2_delete_crypto_aead_ctx delete_crypto_aead_ctx;
+  /**
+   * :member:`delete_crypto_cipher_ctx` is a callback function which
+   * deletes a given cipher context object.  This callback function
+   * must be specified.
+   */
+  ngtcp2_delete_crypto_cipher_ctx delete_crypto_cipher_ctx;
+  /**
+   * :member:`recv_datagram` is a callback function which is invoked
+   * when DATAGRAM frame is received.  This callback function is
+   * optional.
+   */
+  ngtcp2_recv_datagram recv_datagram;
+  /**
+   * :member:`ack_datagram` is a callback function which is invoked
+   * when a packet containing DATAGRAM frame is acknowledged.  This
+   * callback function is optional.
+   */
+  ngtcp2_ack_datagram ack_datagram;
+  /**
+   * :member:`lost_datagram` is a callback function which is invoked
+   * when a packet containing DATAGRAM frame is declared lost.  This
+   * callback function is optional.
+   */
+  ngtcp2_lost_datagram lost_datagram;
+  /**
+   * :member:`get_path_challenge_data` is a callback function which is
+   * invoked when the library needs new PATH_CHALLENGE data.  This
+   * callback must be specified.
+   */
+  ngtcp2_get_path_challenge_data get_path_challenge_data;
+  /**
+   * :member:`stream_stop_sending` is a callback function which is
+   * invoked when a local endpoint no longer reads from a stream
+   * before it receives all stream data.  This callback function is
+   * optional.
+   */
+  ngtcp2_stream_stop_sending stream_stop_sending;
+  /**
+   * :member:`version_negotiation` is a callback function which is
+   * invoked when the compatible version negotiation takes place.
+   * This callback function must be specified.
+   */
+  ngtcp2_version_negotiation version_negotiation;
+  /**
+   * :member:`recv_rx_key` is a callback function which is invoked
+   * when a new key for decrypting packets is installed during QUIC
+   * cryptographic handshake.  It is not called for
+   * :enum:`ngtcp2_crypto_level.NGTCP2_CRYPTO_LEVEL_INITIAL`.
+   */
+  ngtcp2_recv_key recv_rx_key;
+  /**
+   * :member:`recv_tx_key` is a callback function which is invoked
+   * when a new key for encrypting packets is installed during QUIC
+   * cryptographic handshake.  It is not called for
+   * :enum:`ngtcp2_crypto_level.NGTCP2_CRYPTO_LEVEL_INITIAL`.
+   */
+  ngtcp2_recv_key recv_tx_key;
+  /**
+   * :member:`ngtcp2_early_data_rejected` is a callback function which
+   * is invoked when an attempt to send early data by client was
+   * rejected by server, or client decided not to attempt early data.
+   * This callback function is only used by client.
+   */
+  ngtcp2_early_data_rejected early_data_rejected;
+} ngtcp2_callbacks;
+
+/**
+ * @function
+ *
+ * `ngtcp2_pkt_write_connection_close` writes Initial packet
+ * containing CONNECTION_CLOSE frame with the given |error_code| and
+ * the optional |reason| of length |reasonlen| to the buffer pointed
+ * by |dest| of length |destlen|.  All encryption parameters are for
+ * Initial packet encryption.  The packet number is always 0.
+ *
+ * The primary use case of this function is for server to send
+ * CONNECTION_CLOSE frame in Initial packet to close connection
+ * without committing the state when validating Retry token fails.
+ *
+ * This function returns the number of bytes written if it succeeds,
+ * or one of the following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOBUF`
+ *     Buffer is too small.
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE`
+ *     Callback function failed.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_pkt_write_connection_close(
+    uint8_t *dest, size_t destlen, uint32_t version, const ngtcp2_cid *dcid,
+    const ngtcp2_cid *scid, uint64_t error_code, const uint8_t *reason,
+    size_t reasonlen, ngtcp2_encrypt encrypt, const ngtcp2_crypto_aead *aead,
+    const ngtcp2_crypto_aead_ctx *aead_ctx, const uint8_t *iv,
+    ngtcp2_hp_mask hp_mask, const ngtcp2_crypto_cipher *hp,
+    const ngtcp2_crypto_cipher_ctx *hp_ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_pkt_write_retry` writes Retry packet in the buffer pointed
+ * by |dest| whose length is |destlen|.  |dcid| is the destination
+ * connection ID which appeared in a packet as a source connection ID
+ * sent by client.  |scid| is a server chosen source connection ID.
+ * |odcid| specifies Original Destination Connection ID which appeared
+ * in a packet as a destination connection ID sent by client.  |token|
+ * specifies Retry Token, and |tokenlen| specifies its length.  |aead|
+ * must be AEAD_AES_128_GCM.  |aead_ctx| must be initialized with
+ * :macro:`NGTCP2_RETRY_KEY` as an encryption key.
+ *
+ * This function returns the number of bytes written to the buffer, or
+ * one of the following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOBUF`
+ *     Buffer is too small.
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE`
+ *     Callback function failed.
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     :member:`odcid->datalen <ngtcp2_cid.datalen>` is less than
+ *     :macro:`NGTCP2_MIN_INITIAL_DCIDLEN`.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_pkt_write_retry(
+    uint8_t *dest, size_t destlen, uint32_t version, const ngtcp2_cid *dcid,
+    const ngtcp2_cid *scid, const ngtcp2_cid *odcid, const uint8_t *token,
+    size_t tokenlen, ngtcp2_encrypt encrypt, const ngtcp2_crypto_aead *aead,
+    const ngtcp2_crypto_aead_ctx *aead_ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_accept` is used by server implementation, and decides
+ * whether packet |pkt| of length |pktlen| from client is acceptable
+ * for the very initial packet to a connection.
+ *
+ * If |dest| is not ``NULL`` and the function returns 0, or
+ * :macro:`NGTCP2_ERR_RETRY`, the decoded packet header is stored to
+ * the object pointed by |dest|.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_RETRY`
+ *     Retry packet should be sent.
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     The packet is not acceptable for the very first packet to a new
+ *     connection; or the function failed to parse the packet header.
+ */
+NGTCP2_EXTERN int ngtcp2_accept(ngtcp2_pkt_hd *dest, const uint8_t *pkt,
+                                size_t pktlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_client_new` creates new :type:`ngtcp2_conn`, and
+ * initializes it as client.  |dcid| is randomized destination
+ * connection ID.  |scid| is source connection ID.
+ * |client_chosen_version| is a QUIC version that a client chooses.
+ * |path| is the network path where this QUIC connection is being
+ * established and must not be ``NULL``.  |callbacks|, |settings|, and
+ * |params| must not be ``NULL``, and the function make a copy of each
+ * of them.  |params| is local QUIC transport parameters and sent to a
+ * remote endpoint during handshake.  |user_data| is the arbitrary
+ * pointer which is passed to the user-defined callback functions.  If
+ * |mem| is ``NULL``, the memory allocator returned by
+ * `ngtcp2_mem_default()` is used.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_client_new_versioned(
+    ngtcp2_conn **pconn, const ngtcp2_cid *dcid, const ngtcp2_cid *scid,
+    const ngtcp2_path *path, uint32_t client_chosen_version,
+    int callbacks_version, const ngtcp2_callbacks *callbacks,
+    int settings_version, const ngtcp2_settings *settings,
+    int transport_params_version, const ngtcp2_transport_params *params,
+    const ngtcp2_mem *mem, void *user_data);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_server_new` creates new :type:`ngtcp2_conn`, and
+ * initializes it as server.  |dcid| is a destination connection ID.
+ * |scid| is a source connection ID.  |path| is the network path where
+ * this QUIC connection is being established and must not be ``NULL``.
+ * |client_chosen_version| is a QUIC version that a client chooses.
+ * |callbacks|, |settings|, and |params| must not be ``NULL``, and the
+ * function make a copy of each of them.  |params| is local QUIC
+ * transport parameters and sent to a remote endpoint during
+ * handshake.  |user_data| is the arbitrary pointer which is passed to
+ * the user-defined callback functions.  If |mem| is ``NULL``, the
+ * memory allocator returned by `ngtcp2_mem_default()` is used.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_server_new_versioned(
+    ngtcp2_conn **pconn, const ngtcp2_cid *dcid, const ngtcp2_cid *scid,
+    const ngtcp2_path *path, uint32_t client_chosen_version,
+    int callbacks_version, const ngtcp2_callbacks *callbacks,
+    int settings_version, const ngtcp2_settings *settings,
+    int transport_params_version, const ngtcp2_transport_params *params,
+    const ngtcp2_mem *mem, void *user_data);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_del` frees resources allocated for |conn|.  It also
+ * frees memory pointed by |conn|.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_del(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_read_pkt` decrypts QUIC packet given in |pkt| of
+ * length |pktlen| and processes it.  |path| is the network path the
+ * packet is delivered and must not be ``NULL``.  |pi| is packet
+ * metadata and may be ``NULL``. This function performs QUIC handshake
+ * as well.
+ *
+ * This function must not be called from inside the callback
+ * functions.
+ *
+ * This function returns 0 if it succeeds, or negative error codes.
+ * If :macro:`NGTCP2_ERR_RETRY` is returned, application must be a
+ * server and it must perform address validation by sending Retry
+ * packet and discard the connection state.  If
+ * :macro:`NGTCP2_ERR_DROP_CONN` is returned, server application must
+ * drop the connection silently (without sending any CONNECTION_CLOSE
+ * frame) and discard connection state.  If
+ * :macro:`NGTCP2_ERR_DRAINING` is returned, a connection has entered
+ * the draining state, and no further packet transmission is allowed.
+ * If :macro:`NGTCP2_ERR_CRYPTO` is returned, the error happened in
+ * TLS stack and `ngtcp2_conn_get_tls_alert` returns TLS alert if set.
+ *
+ * If any other negative errors are returned, call
+ * `ngtcp2_conn_write_connection_close` to get terminal packet, and
+ * sending it makes QUIC connection enter the closing state.
+ */
+NGTCP2_EXTERN int
+ngtcp2_conn_read_pkt_versioned(ngtcp2_conn *conn, const ngtcp2_path *path,
+                               int pkt_info_version, const ngtcp2_pkt_info *pi,
+                               const uint8_t *pkt, size_t pktlen,
+                               ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_write_pkt` is equivalent to calling
+ * `ngtcp2_conn_writev_stream` with -1 as stream_id, no stream data, and
+ * :macro:`NGTCP2_WRITE_STREAM_FLAG_NONE` as flags.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_conn_write_pkt_versioned(
+    ngtcp2_conn *conn, ngtcp2_path *path, int pkt_info_version,
+    ngtcp2_pkt_info *pi, uint8_t *dest, size_t destlen, ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_handshake_completed` tells |conn| that the TLS stack
+ * declares TLS handshake completion.  This does not mean QUIC
+ * handshake has completed.  The library needs extra conditions to be
+ * met.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_handshake_completed(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_handshake_completed` returns nonzero if QUIC handshake
+ * has completed.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_get_handshake_completed(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_install_initial_key` installs packet protection keying
+ * materials for Initial packets.  |rx_aead_ctx| is AEAD cipher
+ * context object and must be initialized with a decryption key.
+ * |rx_iv| is IV of length |rx_ivlen| for decryption.  |rx_hp_ctx| is
+ * a packet header protection cipher context object for decryption.
+ * Similarly, |tx_aead_ctx|, |tx_iv| and |tx_hp_ctx| are for
+ * encrypting outgoing packets and are the same length with the
+ * decryption counterpart .  If they have already been set, they are
+ * overwritten.
+ *
+ * |ivlen| must be the minimum length of AEAD nonce, or 8 bytes if
+ * that is larger.
+ *
+ * If this function succeeds, |conn| takes ownership of |rx_aead_ctx|,
+ * |rx_hp_ctx|, |tx_aead_ctx|, and |tx_hp_ctx|.
+ * :type:`ngtcp2_delete_crypto_aead_ctx` and
+ * :type:`ngtcp2_delete_crypto_cipher_ctx` will be called to delete
+ * these objects when they are no longer used.  If this function
+ * fails, the caller is responsible to delete them.
+ *
+ * After receiving Retry packet, the DCID most likely changes.  In
+ * that case, client application must generate these keying materials
+ * again based on new DCID and install them again.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_install_initial_key(
+    ngtcp2_conn *conn, const ngtcp2_crypto_aead_ctx *rx_aead_ctx,
+    const uint8_t *rx_iv, const ngtcp2_crypto_cipher_ctx *rx_hp_ctx,
+    const ngtcp2_crypto_aead_ctx *tx_aead_ctx, const uint8_t *tx_iv,
+    const ngtcp2_crypto_cipher_ctx *tx_hp_ctx, size_t ivlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_install_vneg_initial_key` installs packet protection
+ * keying materials for Initial packets on compatible version
+ * negotiation for |version|.  |rx_aead_ctx| is AEAD cipher context
+ * object and must be initialized with a decryption key.  |rx_iv| is
+ * IV of length |rx_ivlen| for decryption.  |rx_hp_ctx| is a packet
+ * header protection cipher context object for decryption.  Similarly,
+ * |tx_aead_ctx|, |tx_iv| and |tx_hp_ctx| are for encrypting outgoing
+ * packets and are the same length with the decryption counterpart .
+ * If they have already been set, they are overwritten.
+ *
+ * |ivlen| must be the minimum length of AEAD nonce, or 8 bytes if
+ * that is larger.
+ *
+ * If this function succeeds, |conn| takes ownership of |rx_aead_ctx|,
+ * |rx_hp_ctx|, |tx_aead_ctx|, and |tx_hp_ctx|.
+ * :type:`ngtcp2_delete_crypto_aead_ctx` and
+ * :type:`ngtcp2_delete_crypto_cipher_ctx` will be called to delete
+ * these objects when they are no longer used.  If this function
+ * fails, the caller is responsible to delete them.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_install_vneg_initial_key(
+    ngtcp2_conn *conn, uint32_t version,
+    const ngtcp2_crypto_aead_ctx *rx_aead_ctx, const uint8_t *rx_iv,
+    const ngtcp2_crypto_cipher_ctx *rx_hp_ctx,
+    const ngtcp2_crypto_aead_ctx *tx_aead_ctx, const uint8_t *tx_iv,
+    const ngtcp2_crypto_cipher_ctx *tx_hp_ctx, size_t ivlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_install_rx_handshake_key` installs packet protection
+ * keying materials for decrypting incoming Handshake packets.
+ * |aead_ctx| is AEAD cipher context object which must be initialized
+ * with a decryption key.  |iv| is IV of length |ivlen|.  |hp_ctx| is
+ * a packet header protection cipher context object.
+ *
+ * |ivlen| must be the minimum length of AEAD nonce, or 8 bytes if
+ * that is larger.
+ *
+ * If this function succeeds, |conn| takes ownership of |aead_ctx|,
+ * and |hp_ctx|.  :type:`ngtcp2_delete_crypto_aead_ctx` and
+ * :type:`ngtcp2_delete_crypto_cipher_ctx` will be called to delete
+ * these objects when they are no longer used.  If this function
+ * fails, the caller is responsible to delete them.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_install_rx_handshake_key(
+    ngtcp2_conn *conn, const ngtcp2_crypto_aead_ctx *aead_ctx,
+    const uint8_t *iv, size_t ivlen, const ngtcp2_crypto_cipher_ctx *hp_ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_install_tx_handshake_key` installs packet protection
+ * keying materials for encrypting outgoing Handshake packets.
+ * |aead_ctx| is AEAD cipher context object which must be initialized
+ * with an encryption key.  |iv| is IV of length |ivlen|.  |hp_ctx| is
+ * a packet header protection cipher context object.
+ *
+ * |ivlen| must be the minimum length of AEAD nonce, or 8 bytes if
+ * that is larger.
+ *
+ * If this function succeeds, |conn| takes ownership of |aead_ctx| and
+ * |hp_ctx|.  :type:`ngtcp2_delete_crypto_aead_ctx` and
+ * :type:`ngtcp2_delete_crypto_cipher_ctx` will be called to delete
+ * these objects when they are no longer used.  If this function
+ * fails, the caller is responsible to delete them.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_install_tx_handshake_key(
+    ngtcp2_conn *conn, const ngtcp2_crypto_aead_ctx *aead_ctx,
+    const uint8_t *iv, size_t ivlen, const ngtcp2_crypto_cipher_ctx *hp_ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_install_early_key` installs packet protection AEAD
+ * cipher context object |aead_ctx|, IV |iv| of length |ivlen|, and
+ * packet header protection cipher context object |hp_ctx| to encrypt
+ * (for client) or decrypt (for server) 0RTT packets.
+ *
+ * |ivlen| must be the minimum length of AEAD nonce, or 8 bytes if
+ * that is larger.
+ *
+ * If this function succeeds, |conn| takes ownership of |aead_ctx| and
+ * |hp_ctx|.  :type:`ngtcp2_delete_crypto_aead_ctx` and
+ * :type:`ngtcp2_delete_crypto_cipher_ctx` will be called to delete
+ * these objects when they are no longer used.  If this function
+ * fails, the caller is responsible to delete them.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_install_early_key(
+    ngtcp2_conn *conn, const ngtcp2_crypto_aead_ctx *aead_ctx,
+    const uint8_t *iv, size_t ivlen, const ngtcp2_crypto_cipher_ctx *hp_ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_install_rx_key` installs packet protection keying
+ * materials for decrypting Short header packets.  |secret| of length
+ * |secretlen| is the decryption secret which is used to derive keying
+ * materials passed to this function.  |aead_ctx| is AEAD cipher
+ * context object which must be initialized with a decryption key.
+ * |iv| is IV of length |ivlen|.  |hp_ctx| is a packet header
+ * protection cipher context object.
+ *
+ * |ivlen| must be the minimum length of AEAD nonce, or 8 bytes if
+ * that is larger.
+ *
+ * If this function succeeds, |conn| takes ownership of |aead_ctx| and
+ * |hp_ctx|.  :type:`ngtcp2_delete_crypto_aead_ctx` and
+ * :type:`ngtcp2_delete_crypto_cipher_ctx` will be called to delete
+ * these objects when they are no longer used.  If this function
+ * fails, the caller is responsible to delete them.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_install_rx_key(
+    ngtcp2_conn *conn, const uint8_t *secret, size_t secretlen,
+    const ngtcp2_crypto_aead_ctx *aead_ctx, const uint8_t *iv, size_t ivlen,
+    const ngtcp2_crypto_cipher_ctx *hp_ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_install_tx_key` installs packet protection keying
+ * materials for encrypting Short header packets.  |secret| of length
+ * |secretlen| is the encryption secret which is used to derive keying
+ * materials passed to this function.  |aead_ctx| is AEAD cipher
+ * context object which must be initialized with an encryption key.
+ * |iv| is IV of length |ivlen|.  |hp_ctx| is a packet header
+ * protection cipher context object.
+ *
+ * |ivlen| must be the minimum length of AEAD nonce, or 8 bytes if
+ * that is larger.
+ *
+ * If this function succeeds, |conn| takes ownership of |aead_ctx| and
+ * |hp_ctx|.  :type:`ngtcp2_delete_crypto_aead_ctx` and
+ * :type:`ngtcp2_delete_crypto_cipher_ctx` will be called to delete
+ * these objects when they are no longer used.  If this function
+ * fails, the caller is responsible to delete them.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_install_tx_key(
+    ngtcp2_conn *conn, const uint8_t *secret, size_t secretlen,
+    const ngtcp2_crypto_aead_ctx *aead_ctx, const uint8_t *iv, size_t ivlen,
+    const ngtcp2_crypto_cipher_ctx *hp_ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_initiate_key_update` initiates the key update.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_INVALID_STATE`
+ *     The previous key update has not been confirmed yet; or key
+ *     update is too frequent; or new keys are not available yet.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_initiate_key_update(ngtcp2_conn *conn,
+                                                  ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_tls_error` sets the TLS related error |liberr| in
+ * |conn|.  |liberr| must be one of ngtcp2 library error codes (which
+ * is defined as NGTCP2_ERR_* macro, such as
+ * :macro:`NGTCP2_ERR_DECRYPT`).  In general, error code should be
+ * propagated via return value, but sometimes ngtcp2 API is called
+ * inside callback function of TLS stack and it does not allow to
+ * return ngtcp2 error code directly.  In this case, implementation
+ * can set the error code (e.g.,
+ * :macro:`NGTCP2_ERR_MALFORMED_TRANSPORT_PARAM`) using this function.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_set_tls_error(ngtcp2_conn *conn, int liberr);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_tls_error` returns the value set by
+ * `ngtcp2_conn_set_tls_error`.  If no value is set, this function
+ * returns 0.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_get_tls_error(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_tls_alert` sets a TLS alert |alert| generated by a
+ * local endpoint to |conn|.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_set_tls_alert(ngtcp2_conn *conn, uint8_t alert);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_tls_alert` returns the value set by
+ * `ngtcp2_conn_set_tls_alert`.  If no value is set, this function
+ * returns 0.
+ */
+NGTCP2_EXTERN uint8_t ngtcp2_conn_get_tls_alert(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_keep_alive_timeout` sets keep-alive timeout.  If
+ * nonzero value is given, after a connection is idle at least in a
+ * given amount of time, a keep-alive packet is sent.  If 0 is set,
+ * keep-alive functionality is disabled and this is the default.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_set_keep_alive_timeout(ngtcp2_conn *conn,
+                                                      ngtcp2_duration timeout);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_expiry` returns the next expiry time.  It returns
+ * ``UINT64_MAX`` if there is no next expiry.
+ *
+ * Call `ngtcp2_conn_handle_expiry()` and `ngtcp2_conn_write_pkt` (or
+ * `ngtcp2_conn_writev_stream`) if expiry time is passed.
+ */
+NGTCP2_EXTERN ngtcp2_tstamp ngtcp2_conn_get_expiry(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_handle_expiry` handles expired timer.  It does nothing
+ * if timer is not expired.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_handle_expiry(ngtcp2_conn *conn,
+                                            ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_pto` returns Probe Timeout (PTO).
+ */
+NGTCP2_EXTERN ngtcp2_duration ngtcp2_conn_get_pto(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_decode_remote_transport_params` decodes QUIC transport
+ * parameters from the buffer pointed by |data| of length |datalen|,
+ * and sets the result to |conn|.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_REQUIRED_TRANSPORT_PARAM`
+ *     The required parameter is missing.
+ * :macro:`NGTCP2_ERR_MALFORMED_TRANSPORT_PARAM`
+ *     The input is malformed.
+ * :macro:`NGTCP2_ERR_TRANSPORT_PARAM`
+ *     Failed to validate the remote QUIC transport parameters.
+ * :macro:`NGTCP2_ERR_VERSION_NEGOTIATION_FAILURE`
+ *     Version negotiation failure.
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE`
+ *     User callback failed
+ */
+NGTCP2_EXTERN int
+ngtcp2_conn_decode_remote_transport_params(ngtcp2_conn *conn,
+                                           const uint8_t *data, size_t datalen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_remote_transport_params` returns a pointer to the
+ * remote QUIC transport parameters.  If no remote transport
+ * parameters are set, it returns NULL.
+ */
+NGTCP2_EXTERN const ngtcp2_transport_params *
+ngtcp2_conn_get_remote_transport_params(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_early_remote_transport_params` sets |params| as
+ * transport parameters previously received from a server.  The
+ * parameters are used to send early data.  QUIC requires that client
+ * application should remember transport parameters along with a
+ * session ticket.
+ *
+ * At least following fields should be set:
+ *
+ * - initial_max_stream_id_bidi
+ * - initial_max_stream_id_uni
+ * - initial_max_stream_data_bidi_local
+ * - initial_max_stream_data_bidi_remote
+ * - initial_max_stream_data_uni
+ * - initial_max_data
+ * - active_connection_id_limit
+ * - max_datagram_frame_size (if DATAGRAM extension was negotiated)
+ *
+ * The following fields are ignored:
+ *
+ * - ack_delay_exponent
+ * - max_ack_delay
+ * - initial_scid
+ * - original_dcid
+ * - preferred_address and preferred_address_present
+ * - retry_scid and retry_scid_present
+ * - stateless_reset_token and stateless_reset_token_present
+ */
+NGTCP2_EXTERN void ngtcp2_conn_set_early_remote_transport_params_versioned(
+    ngtcp2_conn *conn, int transport_params_version,
+    const ngtcp2_transport_params *params);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_local_transport_params` sets the local transport
+ * parameters |params|.  This function can only be called by server.
+ * Although the local transport parameters are passed to
+ * `ngtcp2_conn_server_new`, server might want to update them after
+ * ALPN is chosen.  In that case, server can update the transport
+ * parameter with this function.  Server must call this function
+ * before calling `ngtcp2_conn_install_tx_handshake_key`.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_INVALID_STATE`
+ *     `ngtcp2_conn_install_tx_handshake_key` has been called.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_set_local_transport_params_versioned(
+    ngtcp2_conn *conn, int transport_params_version,
+    const ngtcp2_transport_params *params);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_local_transport_params` returns a pointer to the
+ * local QUIC transport parameters.
+ */
+NGTCP2_EXTERN const ngtcp2_transport_params *
+ngtcp2_conn_get_local_transport_params(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_encode_local_transport_params` encodes the local QUIC
+ * transport parameters in |dest| of length |destlen|.  This is
+ * equivalent to calling `ngtcp2_conn_get_local_transport_params` and
+ * then `ngtcp2_encode_transport_params`.
+ *
+ * This function returns the number of written, or one of the
+ * following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOBUF`
+ *     Buffer is too small.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_conn_encode_local_transport_params(
+    ngtcp2_conn *conn, uint8_t *dest, size_t destlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_open_bidi_stream` opens new bidirectional stream.  The
+ * |stream_user_data| is the user data specific to the stream.  The
+ * open stream ID is stored in |*pstream_id|.
+ *
+ * Application can call this function before handshake completes.  For
+ * 0RTT packet, application can call this function after calling
+ * `ngtcp2_conn_set_early_remote_transport_params`.  For 1RTT packet,
+ * application can call this function after calling
+ * `ngtcp2_conn_decode_remote_transport_params` and
+ * `ngtcp2_conn_install_tx_key`.  If ngtcp2 crypto support library is
+ * used, application can call this function after calling
+ * `ngtcp2_crypto_derive_and_install_tx_key` for 1RTT packet.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ * :macro:`NGTCP2_ERR_STREAM_ID_BLOCKED`
+ *     The remote peer does not allow |stream_id| yet.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_open_bidi_stream(ngtcp2_conn *conn,
+                                               int64_t *pstream_id,
+                                               void *stream_user_data);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_open_uni_stream` opens new unidirectional stream.  The
+ * |stream_user_data| is the user data specific to the stream.  The
+ * open stream ID is stored in |*pstream_id|.
+ *
+ * Application can call this function before handshake completes.  For
+ * 0RTT packet, application can call this function after calling
+ * `ngtcp2_conn_set_early_remote_transport_params`.  For 1RTT packet,
+ * application can call this function after calling
+ * `ngtcp2_conn_decode_remote_transport_params` and
+ * `ngtcp2_conn_install_tx_key`.  If ngtcp2 crypto support library is
+ * used, application can call this function after calling
+ * `ngtcp2_crypto_derive_and_install_tx_key` for 1RTT packet.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ * :macro:`NGTCP2_ERR_STREAM_ID_BLOCKED`
+ *     The remote peer does not allow |stream_id| yet.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_open_uni_stream(ngtcp2_conn *conn,
+                                              int64_t *pstream_id,
+                                              void *stream_user_data);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_shutdown_stream` closes stream denoted by |stream_id|
+ * abruptly.  |app_error_code| is one of application error codes, and
+ * indicates the reason of shutdown.  Successful call of this function
+ * does not immediately erase the state of the stream.  The actual
+ * deletion is done when the remote endpoint sends acknowledgement.
+ * Calling this function is equivalent to call
+ * `ngtcp2_conn_shutdown_stream_read`, and
+ * `ngtcp2_conn_shutdown_stream_write` sequentially with the following
+ * differences.  If |stream_id| refers to a local unidirectional
+ * stream, this function only shutdowns write side of the stream.  If
+ * |stream_id| refers to a remote unidirectional stream, this function
+ * only shutdowns read side of the stream.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ */
+NGTCP2_EXTERN int ngtcp2_conn_shutdown_stream(ngtcp2_conn *conn,
+                                              int64_t stream_id,
+                                              uint64_t app_error_code);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_shutdown_stream_write` closes write-side of stream
+ * denoted by |stream_id| abruptly.  |app_error_code| is one of
+ * application error codes, and indicates the reason of shutdown.  If
+ * this function succeeds, no application data is sent to the remote
+ * endpoint.  It discards all data which has not been acknowledged
+ * yet.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     |stream_id| refers to a remote unidirectional stream.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_shutdown_stream_write(ngtcp2_conn *conn,
+                                                    int64_t stream_id,
+                                                    uint64_t app_error_code);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_shutdown_stream_read` closes read-side of stream
+ * denoted by |stream_id| abruptly.  |app_error_code| is one of
+ * application error codes, and indicates the reason of shutdown.  If
+ * this function succeeds, no application data is forwarded to an
+ * application layer.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     |stream_id| refers to a local unidirectional stream.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_shutdown_stream_read(ngtcp2_conn *conn,
+                                                   int64_t stream_id,
+                                                   uint64_t app_error_code);
+
+/**
+ * @macrosection
+ *
+ * Write stream data flags
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_WRITE_STREAM_FLAG_NONE` indicates no flag set.
+ */
+#define NGTCP2_WRITE_STREAM_FLAG_NONE 0x00u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_WRITE_STREAM_FLAG_MORE` indicates that more data may
+ * come and should be coalesced into the same packet if possible.
+ */
+#define NGTCP2_WRITE_STREAM_FLAG_MORE 0x01u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_WRITE_STREAM_FLAG_FIN` indicates that the passed
+ * data is the final part of a stream.
+ */
+#define NGTCP2_WRITE_STREAM_FLAG_FIN 0x02u
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_write_stream` is just like
+ * `ngtcp2_conn_writev_stream`.  The only difference is that it
+ * conveniently accepts a single buffer.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_conn_write_stream_versioned(
+    ngtcp2_conn *conn, ngtcp2_path *path, int pkt_info_version,
+    ngtcp2_pkt_info *pi, uint8_t *dest, size_t destlen, ngtcp2_ssize *pdatalen,
+    uint32_t flags, int64_t stream_id, const uint8_t *data, size_t datalen,
+    ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_writev_stream` writes a packet containing stream data
+ * of stream denoted by |stream_id|.  The buffer of the packet is
+ * pointed by |dest| of length |destlen|.  This function performs QUIC
+ * handshake as well.
+ *
+ * |destlen| should be at least
+ * :member:`ngtcp2_settings.max_tx_udp_payload_size`.
+ *
+ * Specifying -1 to |stream_id| means no new stream data to send.
+ *
+ * If |path| is not ``NULL``, this function stores the network path
+ * with which the packet should be sent.  Each addr field must point
+ * to the buffer which should be at least ``sizeof(struct
+ * sockaddr_storage)`` bytes long.  The assignment might not be done
+ * if nothing is written to |dest|.
+ *
+ * If |pi| is not ``NULL``, this function stores packet metadata in it
+ * if it succeeds.  The metadata includes ECN markings.  When calling
+ * this function again after it returns
+ * :macro:`NGTCP2_ERR_WRITE_MORE`, caller must pass the same |pi| to
+ * this function.
+ *
+ * If the all given data is encoded as STREAM frame in |dest|, and if
+ * |flags| & :macro:`NGTCP2_WRITE_STREAM_FLAG_FIN` is nonzero, fin
+ * flag is set to outgoing STREAM frame.  Otherwise, fin flag in
+ * STREAM frame is not set.
+ *
+ * This packet may contain frames other than STREAM frame.  The packet
+ * might not contain STREAM frame if other frames occupy the packet.
+ * In that case, |*pdatalen| would be -1 if |pdatalen| is not
+ * ``NULL``.
+ *
+ * If |flags| & :macro:`NGTCP2_WRITE_STREAM_FLAG_FIN` is nonzero, and
+ * 0 length STREAM frame is successfully serialized, |*pdatalen| would
+ * be 0.
+ *
+ * The number of data encoded in STREAM frame is stored in |*pdatalen|
+ * if it is not ``NULL``.  The caller must keep the portion of data
+ * covered by |*pdatalen| bytes in tact until
+ * :type:`ngtcp2_acked_stream_data_offset` indicates that they are
+ * acknowledged by a remote endpoint or the stream is closed.
+ *
+ * If |flags| equals to :macro:`NGTCP2_WRITE_STREAM_FLAG_NONE`, this
+ * function produces a single payload of UDP packet.  If the given
+ * stream data is small (e.g., few bytes), the packet might be
+ * severely under filled.  Too many small packet might increase
+ * overall packet processing costs.  Unless there are retransmissions,
+ * by default, application can only send 1 STREAM frame in one QUIC
+ * packet.  In order to include more than 1 STREAM frame in one QUIC
+ * packet, specify :macro:`NGTCP2_WRITE_STREAM_FLAG_MORE` in |flags|.
+ * This is analogous to ``MSG_MORE`` flag in :manpage:`send(2)`.  If
+ * the :macro:`NGTCP2_WRITE_STREAM_FLAG_MORE` is used, there are 4
+ * outcomes:
+ *
+ * - The function returns the written length of packet just like
+ *   without :macro:`NGTCP2_WRITE_STREAM_FLAG_MORE`.  This is because
+ *   packet is nearly full and the library decided to make a complete
+ *   packet.  |*pdatalen| might be -1 or >= 0.  It may return 0 which
+ *   indicates that no packet transmission is possible at the moment
+ *   for some reason.
+ *
+ * - The function returns :macro:`NGTCP2_ERR_WRITE_MORE`.  In this
+ *   case, |*pdatalen| >= 0 is asserted.  It indicates that
+ *   application can still call this function with different stream
+ *   data (or `ngtcp2_conn_writev_datagram` if it has data to send in
+ *   unreliable datagram) to pack them into the same packet.
+ *   Application has to specify the same |conn|, |path|, |pi|, |dest|,
+ *   |destlen|, and |ts| parameters, otherwise the behaviour is
+ *   undefined.  The application can change |flags|.
+ *
+ * - The function returns one of the following negative error codes:
+ *   :macro:`NGTCP2_ERR_STREAM_DATA_BLOCKED`,
+ *   :macro:`NGTCP2_ERR_STREAM_NOT_FOUND`,
+ *   :macro:`NGTCP2_ERR_STREAM_SHUT_WR`.  In this case, |*pdatalen| ==
+ *   -1 is asserted.  Application can still write the stream data of
+ *   the other streams by calling this function (or
+ *   `ngtcp2_conn_writev_datagram` if it has data to send in
+ *   unreliable datagram) to pack them into the same packet.
+ *   Application has to specify the same |conn|, |path|, |pi|, |dest|,
+ *   |destlen|, and |ts| parameters, otherwise the behaviour is
+ *   undefined.  The application can change |flags|.
+ *
+ * - The other negative error codes might be returned just like
+ *   without :macro:`NGTCP2_WRITE_STREAM_FLAG_MORE`.  These errors
+ *   should be treated as a connection error.
+ *
+ * When application uses :macro:`NGTCP2_WRITE_STREAM_FLAG_MORE` at
+ * least once, it must not call other ngtcp2 API functions
+ * (application can still call `ngtcp2_conn_write_connection_close` to
+ * handle error from this function), just keep calling this function
+ * (or `ngtcp2_conn_write_pkt`, or `ngtcp2_conn_writev_datagram`)
+ * until it returns 0, a positive number (which indicates a complete
+ * packet is ready), or the error codes other than
+ * :macro:`NGTCP2_ERR_WRITE_MORE`,
+ * :macro:`NGTCP2_ERR_STREAM_DATA_BLOCKED`,
+ * :macro:`NGTCP2_ERR_STREAM_NOT_FOUND`, and
+ * :macro:`NGTCP2_ERR_STREAM_SHUT_WR`.  If there is no stream data to
+ * include, call this function with |stream_id| as -1 to stop
+ * coalescing and write a packet.
+ *
+ * This function returns 0 if it cannot write any frame because buffer
+ * is too small, or packet is congestion limited.  Application should
+ * keep reading and wait for congestion window to grow.
+ *
+ * This function must not be called from inside the callback
+ * functions.
+ *
+ * `ngtcp2_conn_update_pkt_tx_time` must be called after this
+ * function.  Application may call this function multiple times before
+ * calling `ngtcp2_conn_update_pkt_tx_time`.
+ *
+ * This function returns the number of bytes written in |dest| if it
+ * succeeds, or one of the following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ * :macro:`NGTCP2_ERR_STREAM_NOT_FOUND`
+ *     Stream does not exist
+ * :macro:`NGTCP2_ERR_STREAM_SHUT_WR`
+ *     Stream is half closed (local); or stream is being reset.
+ * :macro:`NGTCP2_ERR_PKT_NUM_EXHAUSTED`
+ *     Packet number is exhausted, and cannot send any more packet.
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE`
+ *     User callback failed
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     The total length of stream data is too large.
+ * :macro:`NGTCP2_ERR_STREAM_DATA_BLOCKED`
+ *     Stream is blocked because of flow control.
+ * :macro:`NGTCP2_ERR_WRITE_MORE`
+ *     (Only when :macro:`NGTCP2_WRITE_STREAM_FLAG_MORE` is specified)
+ *     Application can call this function to pack more stream data
+ *     into the same packet.  See above to know how it works.
+ *
+ * In general, if the error code which satisfies
+ * `ngtcp2_err_is_fatal(err) <ngtcp2_err_is_fatal>` != 0 is returned,
+ * the application should just close the connection by calling
+ * `ngtcp2_conn_write_connection_close` or just delete the QUIC
+ * connection using `ngtcp2_conn_del`.  It is undefined to call the
+ * other library functions.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_conn_writev_stream_versioned(
+    ngtcp2_conn *conn, ngtcp2_path *path, int pkt_info_version,
+    ngtcp2_pkt_info *pi, uint8_t *dest, size_t destlen, ngtcp2_ssize *pdatalen,
+    uint32_t flags, int64_t stream_id, const ngtcp2_vec *datav, size_t datavcnt,
+    ngtcp2_tstamp ts);
+
+/**
+ * @macrosection
+ *
+ * Write datagram flags
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_WRITE_DATAGRAM_FLAG_NONE` indicates no flag set.
+ */
+#define NGTCP2_WRITE_DATAGRAM_FLAG_NONE 0x00u
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_WRITE_DATAGRAM_FLAG_MORE` indicates that more data
+ * may come and should be coalesced into the same packet if possible.
+ */
+#define NGTCP2_WRITE_DATAGRAM_FLAG_MORE 0x01u
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_writev_datagram` writes a packet containing unreliable
+ * data in DATAGRAM frame.  The buffer of the packet is pointed by
+ * |dest| of length |destlen|.  This function performs QUIC handshake
+ * as well.
+ *
+ * |destlen| should be at least
+ * :member:`ngtcp2_settings.max_tx_udp_payload_size`.
+ *
+ * For |path| and |pi| parameters, refer to
+ * `ngtcp2_conn_writev_stream`.
+ *
+ * If the given data is written to the buffer, nonzero value is
+ * assigned to |*paccepted| if it is not NULL.  The data in DATAGRAM
+ * frame cannot be fragmented; writing partial data is not possible.
+ *
+ * |dgram_id| is an opaque identifier which should uniquely identify
+ * the given DATAGRAM.  It is passed to :type:`ngtcp2_ack_datagram`
+ * callback when a packet that contains DATAGRAM frame is
+ * acknowledged.  It is passed to :type:`ngtcp2_lost_datagram`
+ * callback when a packet that contains DATAGRAM frame is declared
+ * lost.  If an application uses neither of those callbacks, it can
+ * sets 0 to this parameter.
+ *
+ * This function might write other frames other than DATAGRAM, just
+ * like `ngtcp2_conn_writev_stream`.
+ *
+ * If the function returns 0, it means that no more data cannot be
+ * sent because of congestion control limit; or, data does not fit
+ * into the provided buffer; or, a local endpoint, as a server, is
+ * unable to send data because of its amplification limit.  In this
+ * case, |*paccepted| is assigned zero if it is not NULL.
+ *
+ * If :macro:`NGTCP2_WRITE_DATAGRAM_FLAG_MORE` is set in |flags|,
+ * there are 3 outcomes:
+ *
+ * - The function returns the written length of packet just like
+ *   without :macro:`NGTCP2_WRITE_DATAGRAM_FLAG_MORE`.  This is
+ *   because packet is nearly full and the library decided to make a
+ *   complete packet.  |*paccepted| might be zero or nonzero.
+ *
+ * - The function returns :macro:`NGTCP2_ERR_WRITE_MORE`.  In this
+ *   case, |*paccepted| != 0 is asserted.  This indicates that
+ *   application can call this function with another unreliable data
+ *   (or `ngtcp2_conn_writev_stream` if it has stream data to send) to
+ *   pack them into the same packet.  Application has to specify the
+ *   same |conn|, |path|, |pi|, |dest|, |destlen|, and |ts|
+ *   parameters, otherwise the behaviour is undefined.  The
+ *   application can change |flags|.
+ *
+ * - The other error might be returned just like without
+ *   :macro:`NGTCP2_WRITE_DATAGRAM_FLAG_MORE`.
+ *
+ * When application sees :macro:`NGTCP2_ERR_WRITE_MORE`, it must not
+ * call other ngtcp2 API functions (application can still call
+ * `ngtcp2_conn_write_connection_close` to handle error from this
+ * function).  Just keep calling `ngtcp2_conn_writev_datagram`,
+ * `ngtcp2_conn_writev_stream` or `ngtcp2_conn_write_pkt` until it
+ * returns a positive number (which indicates a complete packet is
+ * ready).
+ *
+ * This function returns the number of bytes written in |dest| if it
+ * succeeds, or one of the following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ * :macro:`NGTCP2_ERR_PKT_NUM_EXHAUSTED`
+ *     Packet number is exhausted, and cannot send any more packet.
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE`
+ *     User callback failed
+ * :macro:`NGTCP2_ERR_WRITE_MORE`
+ *     (Only when :macro:`NGTCP2_WRITE_DATAGRAM_FLAG_MORE` is
+ *     specified) Application can call this function to pack more data
+ *     into the same packet.  See above to know how it works.
+ * :macro:`NGTCP2_ERR_INVALID_STATE`
+ *     A remote endpoint did not express the DATAGRAM frame support.
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     The provisional DATAGRAM frame size exceeds the maximum
+ *     DATAGRAM frame size that a remote endpoint can receive.
+ *
+ * In general, if the error code which satisfies
+ * `ngtcp2_err_is_fatal(err) <ngtcp2_err_is_fatal>` != 0 is returned,
+ * the application should just close the connection by calling
+ * `ngtcp2_conn_write_connection_close` or just delete the QUIC
+ * connection using `ngtcp2_conn_del`.  It is undefined to call the
+ * other library functions.
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_conn_writev_datagram_versioned(
+    ngtcp2_conn *conn, ngtcp2_path *path, int pkt_info_version,
+    ngtcp2_pkt_info *pi, uint8_t *dest, size_t destlen, int *paccepted,
+    uint32_t flags, uint64_t dgram_id, const ngtcp2_vec *datav, size_t datavcnt,
+    ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_is_in_closing_period` returns nonzero if |conn| is in
+ * the closing period.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_is_in_closing_period(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_is_in_draining_period` returns nonzero if |conn| is in
+ * the draining period.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_is_in_draining_period(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_extend_max_stream_offset` extends stream's max stream
+ * data value by |datalen|.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_extend_max_stream_offset(ngtcp2_conn *conn,
+                                                       int64_t stream_id,
+                                                       uint64_t datalen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_extend_max_offset` extends max data offset by
+ * |datalen|.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_extend_max_offset(ngtcp2_conn *conn,
+                                                 uint64_t datalen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_extend_max_streams_bidi` extends the number of maximum
+ * local bidirectional streams that a remote endpoint can open by |n|.
+ *
+ * The library does not increase maximum stream limit automatically.
+ * The exception is when a stream is closed without
+ * :type:`ngtcp2_stream_open` callback being called.  In this case,
+ * stream limit is increased automatically.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_extend_max_streams_bidi(ngtcp2_conn *conn,
+                                                       size_t n);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_extend_max_streams_uni` extends the number of maximum
+ * local unidirectional streams that a remote endpoint can open by
+ * |n|.
+ *
+ * The library does not increase maximum stream limit automatically.
+ * The exception is when a stream is closed without
+ * :type:`ngtcp2_stream_open` callback being called.  In this case,
+ * stream limit is increased automatically.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_extend_max_streams_uni(ngtcp2_conn *conn,
+                                                      size_t n);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_dcid` returns the non-NULL pointer to destination
+ * connection ID.  If no destination connection ID is present, the
+ * return value is not ``NULL``, and its datalen field is 0.
+ */
+NGTCP2_EXTERN const ngtcp2_cid *ngtcp2_conn_get_dcid(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_client_initial_dcid` returns the non-NULL pointer
+ * to the Destination Connection ID that client sent in its Initial
+ * packet.
+ */
+NGTCP2_EXTERN const ngtcp2_cid *
+ngtcp2_conn_get_client_initial_dcid(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_num_scid` returns the number of source connection
+ * IDs which the local endpoint has provided to the peer and have not
+ * retired.
+ */
+NGTCP2_EXTERN size_t ngtcp2_conn_get_num_scid(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_scid` writes the all source connection IDs which
+ * the local endpoint has provided to the peer and have not retired in
+ * |dest|.  The buffer pointed by |dest| must have
+ * ``sizeof(ngtcp2_cid) * n`` bytes available, where n is the return
+ * value of `ngtcp2_conn_get_num_scid()`.
+ */
+NGTCP2_EXTERN size_t ngtcp2_conn_get_scid(ngtcp2_conn *conn, ngtcp2_cid *dest);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_num_active_dcid` returns the number of the active
+ * destination connection ID.
+ */
+NGTCP2_EXTERN size_t ngtcp2_conn_get_num_active_dcid(ngtcp2_conn *conn);
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_cid_token` is the convenient struct to store
+ * Connection ID, its associated path, and stateless reset token.
+ */
+typedef struct ngtcp2_cid_token {
+  /**
+   * :member:`seq` is the sequence number of this Connection ID.
+   */
+  uint64_t seq;
+  /**
+   * :member:`cid` is Connection ID.
+   */
+  ngtcp2_cid cid;
+  /**
+   * :member:`ps` is the path which is associated to this Connection
+   * ID.
+   */
+  ngtcp2_path_storage ps;
+  /**
+   * :member:`token` is the stateless reset token for this Connection
+   * ID.
+   */
+  uint8_t token[NGTCP2_STATELESS_RESET_TOKENLEN];
+  /**
+   * :member:`token_present` is nonzero if token contains stateless
+   * reset token.
+   */
+  uint8_t token_present;
+} ngtcp2_cid_token;
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_active_dcid` writes the all active destination
+ * connection IDs and tokens to |dest|.  The buffer pointed by |dest|
+ * must have ``sizeof(ngtcp2_cid_token) * n`` bytes available, where n
+ * is the return value of `ngtcp2_conn_get_num_active_dcid()`.
+ */
+NGTCP2_EXTERN size_t ngtcp2_conn_get_active_dcid(ngtcp2_conn *conn,
+                                                 ngtcp2_cid_token *dest);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_client_chosen_version` returns the client chosen
+ * version.
+ */
+NGTCP2_EXTERN uint32_t ngtcp2_conn_get_client_chosen_version(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_negotiated_version` returns the negotiated version.
+ *
+ * Until the version is negotiated, this function returns 0.
+ */
+NGTCP2_EXTERN uint32_t ngtcp2_conn_get_negotiated_version(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_early_data_rejected` tells |conn| that early data was
+ * rejected by a server, or client decided not to attempt early data
+ * for some reason.  |conn| discards the following connection states:
+ *
+ * - Any opended streams.
+ * - Stream identifier allocations.
+ * - Max data extended by `ngtcp2_conn_extend_max_offset`.
+ * - Max bidi streams extended by `ngtcp2_conn_extend_max_streams_bidi`.
+ * - Max uni streams extended by `ngtcp2_conn_extend_max_streams_uni`.
+ *
+ * Application which wishes to retransmit early data, it has to open
+ * streams and send stream data again.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE`
+ *     User callback failed
+ */
+NGTCP2_EXTERN int ngtcp2_conn_early_data_rejected(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_early_data_rejected` returns nonzero if
+ * `ngtcp2_conn_early_data_rejected` has been called.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_get_early_data_rejected(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_conn_stat` assigns connection statistics data to
+ * |*cstat|.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_get_conn_stat_versioned(ngtcp2_conn *conn,
+                                                       int conn_stat_version,
+                                                       ngtcp2_conn_stat *cstat);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_submit_crypto_data` submits crypto stream data |data|
+ * of length |datalen| to the library for transmission.  The
+ * encryption level is given in |crypto_level|.
+ *
+ * The library makes a copy of the buffer pointed by |data| of length
+ * |datalen|.  Application can discard |data|.
+ */
+NGTCP2_EXTERN int
+ngtcp2_conn_submit_crypto_data(ngtcp2_conn *conn,
+                               ngtcp2_crypto_level crypto_level,
+                               const uint8_t *data, const size_t datalen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_submit_new_token` submits address validation token.
+ * It is sent in NEW_TOKEN frame.  Only server can call this function.
+ * |tokenlen| must not be 0.
+ *
+ * This function makes a copy of the buffer pointed by |token| of
+ * length |tokenlen|.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_submit_new_token(ngtcp2_conn *conn,
+                                               const uint8_t *token,
+                                               size_t tokenlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_local_addr` sets local endpoint address |addr| to
+ * the current path of |conn|.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_set_local_addr(ngtcp2_conn *conn,
+                                              const ngtcp2_addr *addr);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_path_user_data` sets the |path_user_data| to the
+ * current path (see :member:`ngtcp2_path.user_data`).
+ */
+NGTCP2_EXTERN void ngtcp2_conn_set_path_user_data(ngtcp2_conn *conn,
+                                                  void *path_user_data);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_path` returns the current path.
+ */
+NGTCP2_EXTERN const ngtcp2_path *ngtcp2_conn_get_path(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_max_tx_udp_payload_size` returns the maximum UDP
+ * payload size that this local endpoint would send.  This is the
+ * value of :member:`ngtcp2_settings.max_tx_udp_payload_size` that is
+ * passed to `ngtcp2_conn_client_new` or `ngtcp2_conn_server_new`.
+ */
+NGTCP2_EXTERN size_t ngtcp2_conn_get_max_tx_udp_payload_size(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_path_max_tx_udp_payload_size` returns the maximum
+ * UDP payload size for the current path.  If
+ * :member:`ngtcp2_settings.no_tx_udp_payload_size_shaping` is set to
+ * nonzero, this function is equivalent to
+ * `ngtcp2_conn_get_max_tx_udp_payload_size`.  Otherwise, it returns
+ * the maximum UDP payload size that is probed for the current path.
+ */
+NGTCP2_EXTERN size_t
+ngtcp2_conn_get_path_max_tx_udp_payload_size(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_initiate_immediate_migration` starts connection
+ * migration to the given |path|.  Only client can initiate migration.
+ * This function does immediate migration; while the path validation
+ * is nonetheless performed, this function does not wait for it to
+ * succeed.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_INVALID_STATE`
+ *     Migration is disabled; or handshake is not yet confirmed; or
+ *     client is migrating to server's preferred address.
+ * :macro:`NGTCP2_ERR_CONN_ID_BLOCKED`
+ *     No unused connection ID is available.
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     |local_addr| equals the current local address.
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ */
+NGTCP2_EXTERN int ngtcp2_conn_initiate_immediate_migration(
+    ngtcp2_conn *conn, const ngtcp2_path *path, ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_initiate_migration` starts connection migration to the
+ * given |path|.  Only client can initiate migration.  Unlike
+ * `ngtcp2_conn_initiate_immediate_migration`, this function starts a
+ * path validation with a new path and migrate to the new path after
+ * successful path validation.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_INVALID_STATE`
+ *     Migration is disabled; or handshake is not yet confirmed; or
+ *     client is migrating to server's preferred address.
+ * :macro:`NGTCP2_ERR_CONN_ID_BLOCKED`
+ *     No unused connection ID is available.
+ * :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
+ *     |local_addr| equals the current local address.
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ */
+NGTCP2_EXTERN int ngtcp2_conn_initiate_migration(ngtcp2_conn *conn,
+                                                 const ngtcp2_path *path,
+                                                 ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_max_local_streams_uni` returns the cumulative
+ * number of streams which local endpoint can open.
+ */
+NGTCP2_EXTERN uint64_t ngtcp2_conn_get_max_local_streams_uni(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_max_data_left` returns the number of bytes that
+ * this local endpoint can send in this connection.
+ */
+NGTCP2_EXTERN uint64_t ngtcp2_conn_get_max_data_left(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_max_stream_data_left` returns the number of bytes
+ * that this local endpoint can send to a stream identified by
+ * |stream_id|.  If no such stream is found, this function returns 0.
+ */
+NGTCP2_EXTERN uint64_t ngtcp2_conn_get_max_stream_data_left(ngtcp2_conn *conn,
+                                                            int64_t stream_id);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_streams_bidi_left` returns the number of
+ * bidirectional streams which the local endpoint can open without
+ * violating stream concurrency limit.
+ */
+NGTCP2_EXTERN uint64_t ngtcp2_conn_get_streams_bidi_left(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_streams_uni_left` returns the number of
+ * unidirectional streams which the local endpoint can open without
+ * violating stream concurrency limit.
+ */
+NGTCP2_EXTERN uint64_t ngtcp2_conn_get_streams_uni_left(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_cwnd_left` returns the cwnd minus the number of
+ * bytes in flight on the current path.  If the former is smaller than
+ * the latter, this function returns 0.
+ */
+NGTCP2_EXTERN uint64_t ngtcp2_conn_get_cwnd_left(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_initial_crypto_ctx` sets |ctx| for Initial packet
+ * encryption.  The passed data will be passed to
+ * :type:`ngtcp2_encrypt`, :type:`ngtcp2_decrypt` and
+ * :type:`ngtcp2_hp_mask` callbacks.
+ */
+NGTCP2_EXTERN void
+ngtcp2_conn_set_initial_crypto_ctx(ngtcp2_conn *conn,
+                                   const ngtcp2_crypto_ctx *ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_initial_crypto_ctx` returns
+ * :type:`ngtcp2_crypto_ctx` object for Initial packet encryption.
+ */
+NGTCP2_EXTERN const ngtcp2_crypto_ctx *
+ngtcp2_conn_get_initial_crypto_ctx(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_crypto_ctx` sets |ctx| for Handshake/1RTT packet
+ * encryption.  The passed data will be passed to
+ * :type:`ngtcp2_encrypt`, :type:`ngtcp2_decrypt` and
+ * :type:`ngtcp2_hp_mask` callbacks.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_set_crypto_ctx(ngtcp2_conn *conn,
+                                              const ngtcp2_crypto_ctx *ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_tls_native_handle` returns TLS native handle set by
+ * `ngtcp2_conn_set_tls_native_handle()`.
+ */
+NGTCP2_EXTERN void *ngtcp2_conn_get_tls_native_handle(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_tls_native_handle` sets TLS native handle
+ * |tls_native_handle| to |conn|.  Internally, it is used as an opaque
+ * pointer.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_set_tls_native_handle(ngtcp2_conn *conn,
+                                                     void *tls_native_handle);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_retry_aead` sets |aead| and |aead_ctx| for Retry
+ * integrity tag verification.  |aead| must be AEAD_AES_128_GCM.
+ * |aead_ctx| must be initialized with :macro:`NGTCP2_RETRY_KEY` as
+ * encryption key.  This function must be called if |conn| is
+ * initialized as client.  Server does not verify the tag and has no
+ * need to call this function.
+ *
+ * If this function succeeds, |conn| takes ownership of |aead_ctx|.
+ * :type:`ngtcp2_delete_crypto_aead_ctx` will be called to delete this
+ * object when it is no longer used.  If this function fails, the
+ * caller is responsible to delete it.
+ */
+NGTCP2_EXTERN void
+ngtcp2_conn_set_retry_aead(ngtcp2_conn *conn, const ngtcp2_crypto_aead *aead,
+                           const ngtcp2_crypto_aead_ctx *aead_ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_crypto_ctx` returns :type:`ngtcp2_crypto_ctx`
+ * object for Handshake/1RTT packet encryption.
+ */
+NGTCP2_EXTERN const ngtcp2_crypto_ctx *
+ngtcp2_conn_get_crypto_ctx(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_early_crypto_ctx` sets |ctx| for 0RTT packet
+ * encryption.  The passed data will be passed to
+ * :type:`ngtcp2_encrypt`, :type:`ngtcp2_decrypt` and
+ * :type:`ngtcp2_hp_mask` callbacks.
+ */
+NGTCP2_EXTERN void
+ngtcp2_conn_set_early_crypto_ctx(ngtcp2_conn *conn,
+                                 const ngtcp2_crypto_ctx *ctx);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_early_crypto_ctx` returns
+ * :type:`ngtcp2_crypto_ctx` object for 0RTT packet encryption.
+ */
+NGTCP2_EXTERN const ngtcp2_crypto_ctx *
+ngtcp2_conn_get_early_crypto_ctx(ngtcp2_conn *conn);
+
+/**
+ * @enum
+ *
+ * :type:`ngtcp2_connection_close_error_code_type` defines connection
+ * error code type.
+ */
+typedef enum ngtcp2_connection_close_error_code_type {
+  /**
+   * :enum:`NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT`
+   * indicates the error code is QUIC transport error code.
+   */
+  NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT,
+  /**
+   * :enum:`NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_APPLICATION`
+   * indicates the error code is application error code.
+   */
+  NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_APPLICATION,
+  /**
+   * :enum:`NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT_VERSION_NEGOTIATION`
+   * is a special case of QUIC transport error, and it indicates that
+   * client receives Version Negotiation packet.
+   */
+  NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT_VERSION_NEGOTIATION,
+  /**
+   * :enum:`NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT_IDLE_CLOSE`
+   * is a special case of QUIC transport error, and it indicates that
+   * connection is closed because of idle timeout.
+   */
+  NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT_IDLE_CLOSE
+} ngtcp2_connection_close_error_code_type;
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_connection_close_error` contains connection
+ * error code, its type, and the optional reason phrase.
+ */
+typedef struct ngtcp2_connection_close_error {
+  /**
+   * :member:`type` is the type of :member:`error_code`.
+   */
+  ngtcp2_connection_close_error_code_type type;
+  /**
+   * :member:`error_code` is the error code for connection closure.
+   */
+  uint64_t error_code;
+  /**
+   * :member:`frame_type` is the type of QUIC frame which triggers
+   * this connection error.  This field is set to 0 if the frame type
+   * is unknown.
+   */
+  uint64_t frame_type;
+  /**
+   * :member:`reason` points to the buffer which contains a reason
+   * phrase.  It may be NULL if there is no reason phrase.  If it is
+   * received from a remote endpoint, it is truncated to at most 1024
+   * bytes.
+   */
+  uint8_t *reason;
+  /**
+   * :member:`reasonlen` is the length of data pointed by
+   * :member:`reason`.
+   */
+  size_t reasonlen;
+} ngtcp2_connection_close_error;
+
+/**
+ * @function
+ *
+ * `ngtcp2_connection_close_error_default` initializes |ccerr| with
+ * the default values.  It sets the following fields:
+ *
+ * - :member:`type <ngtcp2_connection_close_error.type>` =
+ *   :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT`
+ * - :member:`error_code <ngtcp2_connection_close_error.error_code>` =
+ *   :macro:`NGTCP2_NO_ERROR`.
+ * - :member:`frame_type <ngtcp2_connection_close_error.frame_type>` =
+ *   0
+ * - :member:`reason <ngtcp2_connection_close_error.reason>` = NULL
+ * - :member:`reasonlen <ngtcp2_connection_close_error.reasonlen>` = 0
+ */
+NGTCP2_EXTERN void
+ngtcp2_connection_close_error_default(ngtcp2_connection_close_error *ccerr);
+
+/**
+ * @function
+ *
+ * `ngtcp2_connection_close_error_set_transport_error` sets
+ * :member:`ccerr->type <ngtcp2_connection_close_error.type>` to
+ * :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT`,
+ * and :member:`ccerr->error_code
+ * <ngtcp2_connection_close_error.error_code>` to |error_code|.
+ * |reason| is the reason phrase of length |reasonlen|.  This function
+ * does not make a copy of the reason phrase.
+ */
+NGTCP2_EXTERN void ngtcp2_connection_close_error_set_transport_error(
+    ngtcp2_connection_close_error *ccerr, uint64_t error_code,
+    const uint8_t *reason, size_t reasonlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_connection_close_error_set_transport_error_liberr` sets
+ * type and error_code based on |liberr|.
+ *
+ * If |liberr| is :macro:`NGTCP2_ERR_RECV_VERSION_NEGOTIATION`,
+ * :member:`ccerr->type <ngtcp2_connection_close_error.type>` is set
+ * to
+ * :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT_VERSION_NEGOTIATION`,
+ * and :member:`ccerr->error_code
+ * <ngtcp2_connection_close_error.error_code>` to
+ * :macro:`NGTCP2_NO_ERROR`.  If |liberr| is
+ * :macro:`NGTCP2_ERR_IDLE_CLOSE`, :member:`ccerr->type
+ * <ngtcp2_connection_close_error.type>` is set to
+ * :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT_IDLE_CLOSE`,
+ * and :member:`ccerr->error_code
+ * <ngtcp2_connection_close_error.error_code>` to
+ * :macro:`NGTCP2_NO_ERROR`.  Otherwise, :member:`ccerr->type
+ * <ngtcp2_connection_close_error.type>` is set to
+ * :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT`,
+ * and :member:`ccerr->error_code
+ * <ngtcp2_connection_close_error.error_code>` is set to an error code
+ * inferred by |liberr| (see
+ * `ngtcp2_err_infer_quic_transport_error_code`).  |reason| is the
+ * reason phrase of length |reasonlen|.  This function does not make a
+ * copy of the reason phrase.
+ */
+NGTCP2_EXTERN void ngtcp2_connection_close_error_set_transport_error_liberr(
+    ngtcp2_connection_close_error *ccerr, int liberr, const uint8_t *reason,
+    size_t reasonlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_connection_close_error_set_transport_error_tls_alert` sets
+ * :member:`ccerr->type <ngtcp2_connection_close_error.type>` to
+ * :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT`,
+ * and :member:`ccerr->error_code
+ * <ngtcp2_connection_close_error.error_code>` to bitwise-OR of
+ * :macro:`NGTCP2_CRYPTO_ERROR` and |tls_alert|.  |reason| is the
+ * reason phrase of length |reasonlen|.  This function does not make a
+ * copy of the reason phrase.
+ */
+NGTCP2_EXTERN void ngtcp2_connection_close_error_set_transport_error_tls_alert(
+    ngtcp2_connection_close_error *ccerr, uint8_t tls_alert,
+    const uint8_t *reason, size_t reasonlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_connection_close_error_set_application_error` sets
+ * :member:`ccerr->type <ngtcp2_connection_close_error.type>` to
+ * :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_APPLICATION`,
+ * and :member:`ccerr->error_code
+ * <ngtcp2_connection_close_error.error_code>` to |error_code|.
+ * |reason| is the reason phrase of length |reasonlen|.  This function
+ * does not make a copy of the reason phrase.
+ */
+NGTCP2_EXTERN void ngtcp2_connection_close_error_set_application_error(
+    ngtcp2_connection_close_error *ccerr, uint64_t error_code,
+    const uint8_t *reason, size_t reasonlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_write_connection_close` writes a packet which contains
+ * CONNECTION_CLOSE frame(s) (type 0x1c or 0x1d) in the buffer pointed
+ * by |dest| whose capacity is |destlen|.
+ *
+ * For client, |destlen| should be at least
+ * :macro:`NGTCP2_MAX_UDP_PAYLOAD_SIZE`.
+ *
+ * If |path| is not ``NULL``, this function stores the network path
+ * with which the packet should be sent.  Each addr field must point
+ * to the buffer which should be at least ``sizeof(struct
+ * sockaddr_storage)`` bytes long.  The assignment might not be done
+ * if nothing is written to |dest|.
+ *
+ * If |pi| is not ``NULL``, this function stores packet metadata in it
+ * if it succeeds.  The metadata includes ECN markings.
+ *
+ * If :member:`ccerr->type <ngtcp2_connection_close_error.type>` ==
+ * :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_TRANSPORT`,
+ * this function sends CONNECTION_CLOSE (type 0x1c) frame.  If
+ * :member:`ccerr->type <ngtcp2_connection_close_error.type>` ==
+ * :enum:`ngtcp2_connection_close_error_code_type.NGTCP2_CONNECTION_CLOSE_ERROR_CODE_TYPE_APPLICATION`,
+ * it sends CONNECTION_CLOSE (type 0x1d) frame.  Otherwise, it does
+ * not produce any data, and returns 0.
+ *
+ * This function must not be called from inside the callback
+ * functions.
+ *
+ * At the moment, successful call to this function makes connection
+ * close.  We may change this behaviour in the future to allow
+ * graceful shutdown.
+ *
+ * This function returns the number of bytes written in |dest| if it
+ * succeeds, or one of the following negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_NOMEM`
+ *     Out of memory
+ * :macro:`NGTCP2_ERR_NOBUF`
+ *     Buffer is too small
+ * :macro:`NGTCP2_ERR_INVALID_STATE`
+ *     The current state does not allow sending CONNECTION_CLOSE.
+ * :macro:`NGTCP2_ERR_PKT_NUM_EXHAUSTED`
+ *     Packet number is exhausted, and cannot send any more packet.
+ * :macro:`NGTCP2_ERR_CALLBACK_FAILURE`
+ *     User callback failed
+ */
+NGTCP2_EXTERN ngtcp2_ssize ngtcp2_conn_write_connection_close_versioned(
+    ngtcp2_conn *conn, ngtcp2_path *path, int pkt_info_version,
+    ngtcp2_pkt_info *pi, uint8_t *dest, size_t destlen,
+    const ngtcp2_connection_close_error *ccerr, ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_connection_close_error` stores the received
+ * connection close error in |ccerr|.
+ */
+NGTCP2_EXTERN void
+ngtcp2_conn_get_connection_close_error(ngtcp2_conn *conn,
+                                       ngtcp2_connection_close_error *ccerr);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_is_local_stream` returns nonzero if |stream_id| denotes the
+ * stream which a local endpoint issues.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_is_local_stream(ngtcp2_conn *conn,
+                                              int64_t stream_id);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_is_server` returns nonzero if |conn| is initialized as
+ * server.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_is_server(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_after_retry` returns nonzero if |conn| as a client has
+ * received Retry packet from server and successfully validated it.
+ */
+NGTCP2_EXTERN int ngtcp2_conn_after_retry(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_set_stream_user_data` sets |stream_user_data| to the
+ * stream identified by |stream_id|.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :macro:`NGTCP2_ERR_STREAM_NOT_FOUND`
+ *     Stream does not exist
+ */
+NGTCP2_EXTERN int ngtcp2_conn_set_stream_user_data(ngtcp2_conn *conn,
+                                                   int64_t stream_id,
+                                                   void *stream_user_data);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_update_pkt_tx_time` sets the time instant of the next
+ * packet transmission.  This function must be called after (multiple
+ * invocation of) `ngtcp2_conn_writev_stream`.  If packet aggregation
+ * (e.g., packet batching, GSO) is used, call this function after all
+ * aggregated datagrams are sent, which indicates multiple invocation
+ * of `ngtcp2_conn_writev_stream`.
+ */
+NGTCP2_EXTERN void ngtcp2_conn_update_pkt_tx_time(ngtcp2_conn *conn,
+                                                  ngtcp2_tstamp ts);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_send_quantum` returns the maximum number of bytes
+ * that can be sent in one go without packet spacing.
+ */
+NGTCP2_EXTERN size_t ngtcp2_conn_get_send_quantum(ngtcp2_conn *conn);
+
+/**
+ * @function
+ *
+ * `ngtcp2_conn_get_stream_loss_count` returns the number of packets
+ * that contain STREAM frame for a stream identified by |stream_id|
+ * and are declared to be lost.  The number may include the spurious
+ * losses.  If no stream identified by |stream_id| is found, this
+ * function returns 0.
+ */
+NGTCP2_EXTERN size_t ngtcp2_conn_get_stream_loss_count(ngtcp2_conn *conn,
+                                                       int64_t stream_id);
+
+/**
+ * @function
+ *
+ * `ngtcp2_strerror` returns the text representation of |liberr|.
+ * |liberr| must be one of ngtcp2 library error codes (which is
+ * defined as NGTCP2_ERR_* macro, such as
+ * :macro:`NGTCP2_ERR_DECRYPT`).
+ */
+NGTCP2_EXTERN const char *ngtcp2_strerror(int liberr);
+
+/**
+ * @function
+ *
+ * `ngtcp2_err_is_fatal` returns nonzero if |liberr| is a fatal error.
+ * |liberr| must be one of ngtcp2 library error codes (which is
+ * defined as NGTCP2_ERR_* macro, such as
+ * :macro:`NGTCP2_ERR_DECRYPT`).
+ */
+NGTCP2_EXTERN int ngtcp2_err_is_fatal(int liberr);
+
+/**
+ * @function
+ *
+ * `ngtcp2_err_infer_quic_transport_error_code` returns a QUIC
+ * transport error code which corresponds to |liberr|.  |liberr| must
+ * be one of ngtcp2 library error codes (which is defined as
+ * NGTCP2_ERR_* macro, such as :macro:`NGTCP2_ERR_DECRYPT`).
+ */
+NGTCP2_EXTERN uint64_t ngtcp2_err_infer_quic_transport_error_code(int liberr);
+
+/**
+ * @function
+ *
+ * `ngtcp2_addr_init` initializes |dest| with the given arguments and
+ * returns |dest|.
+ */
+NGTCP2_EXTERN ngtcp2_addr *ngtcp2_addr_init(ngtcp2_addr *dest,
+                                            const ngtcp2_sockaddr *addr,
+                                            ngtcp2_socklen addrlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_addr_copy_byte` copies |addr| of length |addrlen| into the
+ * buffer pointed by :member:`dest->addr <ngtcp2_addr.addr>`.
+ * :member:`dest->addrlen <ngtcp2_addr.addrlen>` is updated to have
+ * |addrlen|.  This function assumes that :member:`dest->addr
+ * <ngtcp2_addr.addr>` points to a buffer which has a sufficient
+ * capacity to store the copy.
+ */
+NGTCP2_EXTERN void ngtcp2_addr_copy_byte(ngtcp2_addr *dest,
+                                         const ngtcp2_sockaddr *addr,
+                                         ngtcp2_socklen addrlen);
+
+/**
+ * @function
+ *
+ * `ngtcp2_path_storage_init` initializes |ps| with the given
+ * arguments.  This function copies |local_addr| and |remote_addr|.
+ */
+NGTCP2_EXTERN void ngtcp2_path_storage_init(ngtcp2_path_storage *ps,
+                                            const ngtcp2_sockaddr *local_addr,
+                                            ngtcp2_socklen local_addrlen,
+                                            const ngtcp2_sockaddr *remote_addr,
+                                            ngtcp2_socklen remote_addrlen,
+                                            void *user_data);
+
+/**
+ * @function
+ *
+ * `ngtcp2_path_storage_zero` initializes |ps| with the zero length
+ * addresses.
+ */
+NGTCP2_EXTERN void ngtcp2_path_storage_zero(ngtcp2_path_storage *ps);
+
+/**
+ * @function
+ *
+ * `ngtcp2_settings_default` initializes |settings| with the default
+ * values.  First this function fills |settings| with 0 and set the
+ * default value to the following fields:
+ *
+ * * :type:`cc_algo <ngtcp2_settings.cc_algo>` =
+ *   :enum:`ngtcp2_cc_algo.NGTCP2_CC_ALGO_CUBIC`
+ * * :type:`initial_rtt <ngtcp2_settings.initial_rtt>` =
+ *   :macro:`NGTCP2_DEFAULT_INITIAL_RTT`
+ * * :type:`ack_thresh <ngtcp2_settings.ack_thresh>` = 2
+ * * :type:`max_tx_udp_payload_size
+ *   <ngtcp2_settings.max_tx_udp_payload_size>` = 1452
+ * * :type:`handshake_timeout <ngtcp2_settings.handshake_timeout>` =
+ *   :macro:`NGTCP2_DEFAULT_HANDSHAKE_TIMEOUT`.
+ */
+NGTCP2_EXTERN void ngtcp2_settings_default_versioned(int settings_version,
+                                                     ngtcp2_settings *settings);
+
+/**
+ * @function
+ *
+ * `ngtcp2_transport_params_default` initializes |params| with the
+ * default values.  First this function fills |params| with 0 and set
+ * the default value to the following fields:
+ *
+ * * :type:`max_udp_payload_size
+ *   <ngtcp2_transport_params.max_udp_payload_size>` =
+ *   :macro:`NGTCP2_DEFAULT_MAX_RECV_UDP_PAYLOAD_SIZE`
+ * * :type:`ack_delay_exponent
+ *   <ngtcp2_transport_params.ack_delay_exponent>` =
+ *   :macro:`NGTCP2_DEFAULT_ACK_DELAY_EXPONENT`
+ * * :type:`max_ack_delay <ngtcp2_transport_params.max_ack_delay>` =
+ *   :macro:`NGTCP2_DEFAULT_MAX_ACK_DELAY`
+ * * :type:`active_connection_id_limit
+ *   <ngtcp2_transport_params.active_connection_id_limit>` =
+ *   :macro:`NGTCP2_DEFAULT_ACTIVE_CONNECTION_ID_LIMIT`
+ */
+NGTCP2_EXTERN void
+ngtcp2_transport_params_default_versioned(int transport_params_version,
+                                          ngtcp2_transport_params *params);
+
+/**
+ * @function
+ *
+ * `ngtcp2_mem_default` returns the default, system standard memory
+ * allocator.
+ */
+NGTCP2_EXTERN const ngtcp2_mem *ngtcp2_mem_default(void);
+
+/**
+ * @macrosection
+ *
+ * ngtcp2_info macros
+ */
+
+/**
+ * @macro
+ *
+ * :macro:`NGTCP2_VERSION_AGE` is the age of :type:`ngtcp2_info`
+ */
+#define NGTCP2_VERSION_AGE 1
+
+/**
+ * @struct
+ *
+ * :type:`ngtcp2_info` is what `ngtcp2_version()` returns.  It holds
+ * information about the particular ngtcp2 version.
+ */
+typedef struct ngtcp2_info {
+  /**
+   * :member:`age` is the age of this struct.  This instance of ngtcp2
+   * sets it to :macro:`NGTCP2_VERSION_AGE` but a future version may
+   * bump it and add more struct fields at the bottom
+   */
+  int age;
+  /**
+   * :member:`version_num` is the :macro:`NGTCP2_VERSION_NUM` number
+   * (since age ==1)
+   */
+  int version_num;
+  /**
+   * :member:`version_str` points to the :macro:`NGTCP2_VERSION`
+   * string (since age ==1)
+   */
+  const char *version_str;
+  /* -------- the above fields all exist when age == 1 */
+} ngtcp2_info;
+
+/**
+ * @function
+ *
+ * `ngtcp2_version` returns a pointer to a ngtcp2_info struct with
+ * version information about the run-time library in use.  The
+ * |least_version| argument can be set to a 24 bit numerical value for
+ * the least accepted version number and if the condition is not met,
+ * this function will return a ``NULL``.  Pass in 0 to skip the
+ * version checking.
+ */
+NGTCP2_EXTERN const ngtcp2_info *ngtcp2_version(int least_version);
+
+/**
+ * @function
+ *
+ * `ngtcp2_is_bidi_stream` returns nonzero if |stream_id| denotes
+ * bidirectional stream.
+ */
+NGTCP2_EXTERN int ngtcp2_is_bidi_stream(int64_t stream_id);
+
+/**
+ * @function
+ *
+ * `ngtcp2_path_copy` copies |src| into |dest|.  This function assumes
+ * that |dest| has enough buffer to store the deep copy of
+ * :member:`src->local <ngtcp2_path.local>` and :member:`src->remote
+ * <ngtcp2_path.remote>`.
+ */
+NGTCP2_EXTERN void ngtcp2_path_copy(ngtcp2_path *dest, const ngtcp2_path *src);
+
+/**
+ * @function
+ *
+ * `ngtcp2_path_eq` returns nonzero if |a| and |b| shares the same
+ * local and remote addresses.
+ */
+NGTCP2_EXTERN int ngtcp2_path_eq(const ngtcp2_path *a, const ngtcp2_path *b);
+
+/**
+ * @function
+ *
+ * `ngtcp2_is_supported_version` returns nonzero if the library supports
+ * QUIC version |version|.
+ */
+NGTCP2_EXTERN int ngtcp2_is_supported_version(uint32_t version);
+
+/*
+ * @function
+ *
+ * `ngtcp2_is_reserved_version` returns nonzero if |version| is a
+ * reserved version.
+ */
+NGTCP2_EXTERN int ngtcp2_is_reserved_version(uint32_t version);
+
+/**
+ * @function
+ *
+ * `ngtcp2_select_version` selects and returns a version from the
+ * version set |offered_versions| of |offered_versionslen| elements.
+ * |preferred_versions| of |preferred_versionslen| elements specifies
+ * the preference of versions, which is sorted in the order of
+ * preference.  All versions included in |preferred_versions| must be
+ * supported by the library, that is, passing a version to
+ * `ngtcp2_is_supported_version` must return nonzero.  This function
+ * is intended to be used by client when it receives Version
+ * Negotiation packet.  If no version is selected, this function
+ * returns 0.
+ */
+NGTCP2_EXTERN uint32_t ngtcp2_select_version(const uint32_t *preferred_versions,
+                                             size_t preferred_versionslen,
+                                             const uint32_t *offered_versions,
+                                             size_t offered_versionslen);
+
+/*
+ * Versioned function wrappers
+ */
+
+/*
+ * `ngtcp2_conn_read_pkt` is a wrapper around
+ * `ngtcp2_conn_read_pkt_versioned` to set the correct struct version.
+ */
+#define ngtcp2_conn_read_pkt(CONN, PATH, PI, PKT, PKTLEN, TS)                  \
+  ngtcp2_conn_read_pkt_versioned((CONN), (PATH), NGTCP2_PKT_INFO_VERSION,      \
+                                 (PI), (PKT), (PKTLEN), (TS))
+
+/*
+ * `ngtcp2_conn_write_pkt` is a wrapper around
+ * `ngtcp2_conn_write_pkt_versioned` to set the correct struct
+ * version.
+ */
+#define ngtcp2_conn_write_pkt(CONN, PATH, PI, DEST, DESTLEN, TS)               \
+  ngtcp2_conn_write_pkt_versioned((CONN), (PATH), NGTCP2_PKT_INFO_VERSION,     \
+                                  (PI), (DEST), (DESTLEN), (TS))
+
+/*
+ * `ngtcp2_conn_write_stream` is a wrapper around
+ * `ngtcp2_conn_write_stream_versioned` to set the correct struct
+ * version.
+ */
+#define ngtcp2_conn_write_stream(CONN, PATH, PI, DEST, DESTLEN, PDATALEN,      \
+                                 FLAGS, STREAM_ID, DATA, DATALEN, TS)          \
+  ngtcp2_conn_write_stream_versioned(                                          \
+      (CONN), (PATH), NGTCP2_PKT_INFO_VERSION, (PI), (DEST), (DESTLEN),        \
+      (PDATALEN), (FLAGS), (STREAM_ID), (DATA), (DATALEN), (TS))
+
+/*
+ * `ngtcp2_conn_writev_stream` is a wrapper around
+ * `ngtcp2_conn_writev_stream_versioned` to set the correct struct
+ * version.
+ */
+#define ngtcp2_conn_writev_stream(CONN, PATH, PI, DEST, DESTLEN, PDATALEN,     \
+                                  FLAGS, STREAM_ID, DATAV, DATAVCNT, TS)       \
+  ngtcp2_conn_writev_stream_versioned(                                         \
+      (CONN), (PATH), NGTCP2_PKT_INFO_VERSION, (PI), (DEST), (DESTLEN),        \
+      (PDATALEN), (FLAGS), (STREAM_ID), (DATAV), (DATAVCNT), (TS))
+
+/*
+ * `ngtcp2_conn_writev_datagram` is a wrapper around
+ * `ngtcp2_conn_writev_datagram_versioned` to set the correct struct
+ * version.
+ */
+#define ngtcp2_conn_writev_datagram(CONN, PATH, PI, DEST, DESTLEN, PACCEPTED,  \
+                                    FLAGS, DGRAM_ID, DATAV, DATAVCNT, TS)      \
+  ngtcp2_conn_writev_datagram_versioned(                                       \
+      (CONN), (PATH), NGTCP2_PKT_INFO_VERSION, (PI), (DEST), (DESTLEN),        \
+      (PACCEPTED), (FLAGS), (DGRAM_ID), (DATAV), (DATAVCNT), (TS))
+
+/*
+ * `ngtcp2_conn_write_connection_close` is a wrapper around
+ * `ngtcp2_conn_write_connection_close_versioned` to set the correct
+ * struct version.
+ */
+#define ngtcp2_conn_write_connection_close(CONN, PATH, PI, DEST, DESTLEN,      \
+                                           CCERR, TS)                          \
+  ngtcp2_conn_write_connection_close_versioned(                                \
+      (CONN), (PATH), NGTCP2_PKT_INFO_VERSION, (PI), (DEST), (DESTLEN),        \
+      (CCERR), (TS))
+
+/*
+ * `ngtcp2_encode_transport_params` is a wrapper around
+ * `ngtcp2_encode_transport_params_versioned` to set the correct
+ * struct version.
+ */
+#define ngtcp2_encode_transport_params(DEST, DESTLEN, EXTTYPE, PARAMS)         \
+  ngtcp2_encode_transport_params_versioned(                                    \
+      (DEST), (DESTLEN), (EXTTYPE), NGTCP2_TRANSPORT_PARAMS_VERSION, (PARAMS))
+
+/*
+ * `ngtcp2_decode_transport_params` is a wrapper around
+ * `ngtcp2_decode_transport_params_versioned` to set the correct
+ * struct version.
+ */
+#define ngtcp2_decode_transport_params(PARAMS, EXTTYPE, DATA, DATALEN)         \
+  ngtcp2_decode_transport_params_versioned(                                    \
+      NGTCP2_TRANSPORT_PARAMS_VERSION, (PARAMS), (EXTTYPE), (DATA), (DATALEN))
+
+/*
+ * `ngtcp2_conn_client_new` is a wrapper around
+ * `ngtcp2_conn_client_new_versioned` to set the correct struct
+ * version.
+ */
+#define ngtcp2_conn_client_new(PCONN, DCID, SCID, PATH, VERSION, CALLBACKS,    \
+                               SETTINGS, PARAMS, MEM, USER_DATA)               \
+  ngtcp2_conn_client_new_versioned(                                            \
+      (PCONN), (DCID), (SCID), (PATH), (VERSION), NGTCP2_CALLBACKS_VERSION,    \
+      (CALLBACKS), NGTCP2_SETTINGS_VERSION, (SETTINGS),                        \
+      NGTCP2_TRANSPORT_PARAMS_VERSION, (PARAMS), (MEM), (USER_DATA))
+
+/*
+ * `ngtcp2_conn_server_new` is a wrapper around
+ * `ngtcp2_conn_server_new_versioned` to set the correct struct
+ * version.
+ */
+#define ngtcp2_conn_server_new(PCONN, DCID, SCID, PATH, VERSION, CALLBACKS,    \
+                               SETTINGS, PARAMS, MEM, USER_DATA)               \
+  ngtcp2_conn_server_new_versioned(                                            \
+      (PCONN), (DCID), (SCID), (PATH), (VERSION), NGTCP2_CALLBACKS_VERSION,    \
+      (CALLBACKS), NGTCP2_SETTINGS_VERSION, (SETTINGS),                        \
+      NGTCP2_TRANSPORT_PARAMS_VERSION, (PARAMS), (MEM), (USER_DATA))
+
+/*
+ * `ngtcp2_conn_set_early_remote_transport_params` is a wrapper around
+ * `ngtcp2_conn_set_early_remote_transport_params_versioned` to set
+ * the correct struct version.
+ */
+#define ngtcp2_conn_set_early_remote_transport_params(CONN, PARAMS)            \
+  ngtcp2_conn_set_early_remote_transport_params_versioned(                     \
+      (CONN), NGTCP2_TRANSPORT_PARAMS_VERSION, (PARAMS))
+
+/*
+ * `ngtcp2_conn_set_local_transport_params` is a wrapper around
+ * `ngtcp2_conn_set_local_transport_params_versioned` to set the
+ * correct struct version.
+ */
+#define ngtcp2_conn_set_local_transport_params(CONN, PARAMS)                   \
+  ngtcp2_conn_set_local_transport_params_versioned(                            \
+      (CONN), NGTCP2_TRANSPORT_PARAMS_VERSION, (PARAMS))
+
+/*
+ * `ngtcp2_transport_params_default` is a wrapper around
+ * `ngtcp2_transport_params_default_versioned` to set the correct
+ * struct version.
+ */
+#define ngtcp2_transport_params_default(PARAMS)                                \
+  ngtcp2_transport_params_default_versioned(NGTCP2_TRANSPORT_PARAMS_VERSION,   \
+                                            (PARAMS))
+
+/*
+ * `ngtcp2_conn_get_conn_stat` is a wrapper around
+ * `ngtcp2_conn_get_conn_stat_versioned` to set the correct struct
+ * version.
+ */
+#define ngtcp2_conn_get_conn_stat(CONN, CSTAT)                                 \
+  ngtcp2_conn_get_conn_stat_versioned((CONN), NGTCP2_CONN_STAT_VERSION, (CSTAT))
+
+/*
+ * `ngtcp2_settings_default` is a wrapper around
+ * `ngtcp2_settings_default_versioned` to set the correct struct
+ * version.
+ */
+#define ngtcp2_settings_default(SETTINGS)                                      \
+  ngtcp2_settings_default_versioned(NGTCP2_SETTINGS_VERSION, (SETTINGS))
+
+#ifdef _MSC_VER
+#  pragma warning(pop)
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* NGTCP2_H */
diff --git a/lib/includes/ngtcp2/version.h.in b/lib/includes/ngtcp2/version.h.in
new file mode 100644
index 0000000..8afe88f
--- /dev/null
+++ b/lib/includes/ngtcp2/version.h.in
@@ -0,0 +1,51 @@
+/*
+ * ngtcp2
+ *
+ * Copyright (c) 2016 ngtcp2 contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#ifndef VERSION_H
+#define VERSION_H
+
+/**
+ * @macrosection
+ *
+ * Library version macros
+ */
+
+/**
+ * @macro
+ *
+ * Version number of the ngtcp2 library release.
+ */
+#define NGTCP2_VERSION "@PACKAGE_VERSION@"
+
+/**
+ * @macro
+ *
+ * Numerical representation of the version number of the ngtcp2
+ * library release. This is a 24 bit number with 8 bits for major
+ * number, 8 bits for minor and 8 bits for patch. Version 1.2.3
+ * becomes 0x010203.
+ */
+#define NGTCP2_VERSION_NUM @PACKAGE_VERSION_NUM@
+
+#endif /* VERSION_H */