/*
 * nghttp3
 *
 * Copyright (c) 2018 nghttp3 contributors
 * 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 NGHTTP3_H
#define NGHTTP3_H

/* Define WIN32 when build target is Win32 API (borrowed from
   libcurl) */
#if (defined(_WIN32) || defined(__WIN32__)) && !defined(WIN32)
#  define WIN32
#endif /* (defined(_WIN32) || defined(__WIN32__)) && !defined(WIN32) */

#ifdef __cplusplus
extern "C" {
#endif /* defined(__cplusplus) */

#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>

#include <nghttp3/version.h>

#ifdef NGHTTP3_STATICLIB
#  define NGHTTP3_EXTERN
#elif defined(WIN32)
#  ifdef BUILDING_NGHTTP3
#    define NGHTTP3_EXTERN __declspec(dllexport)
#  else /* !defined(BUILDING_NGHTTP3) */
#    define NGHTTP3_EXTERN __declspec(dllimport)
#  endif /* !defined(BUILDING_NGHTTP3) */
#else    /* !(defined(NGHTTP3_STATICLIB) || defined(WIN32)) */
#  ifdef BUILDING_NGHTTP3
#    define NGHTTP3_EXTERN __attribute__((visibility("default")))
#  else /* !defined(BUILDING_NGHTTP3) */
#    define NGHTTP3_EXTERN
#  endif /* !defined(BUILDING_NGHTTP3) */
#endif   /* !(defined(NGHTTP3_STATICLIB) || defined(WIN32)) */

#ifdef _MSC_VER
#  define NGHTTP3_ALIGN(N) __declspec(align(N))
#else /* !defined(_MSC_VER) */
#  define NGHTTP3_ALIGN(N) __attribute__((aligned(N)))
#endif /* !defined(_MSC_VER) */

/**
 * @typedef
 *
 * :type:`nghttp3_ssize` is signed counterpart of size_t.
 */
typedef ptrdiff_t nghttp3_ssize;

/**
 * @typedef
 *
 * :type:`nghttp3_tstamp` is a timestamp with nanosecond resolution.
 * ``UINT64_MAX`` is an invalid value, and it is often used to
 * indicate that no value is set.  This type is available since
 * v1.12.0.
 */
typedef uint64_t nghttp3_tstamp;

/**
 * @typedef
 *
 * :type:`nghttp3_duration` is a period of time in nanosecond
 * resolution.  ``UINT64_MAX`` is an invalid value, and it is often
 * used to indicate that no value is set.  This type is available
 * since v1.12.0.
 */
typedef uint64_t nghttp3_duration;

/**
 * @macro
 *
 * :macro:`NGHTTP3_NANOSECONDS` is a count of tick which corresponds
 * to 1 nanosecond.  This macro is available since v1.12.0.
 */
#define NGHTTP3_NANOSECONDS ((nghttp3_duration)1ULL)

/**
 * @macro
 *
 * :macro:`NGHTTP3_MICROSECONDS` is a count of tick which corresponds
 * to 1 microsecond.  This macro is available since v1.12.0.
 */
#define NGHTTP3_MICROSECONDS ((nghttp3_duration)(1000ULL * NGHTTP3_NANOSECONDS))

/**
 * @macro
 *
 * :macro:`NGHTTP3_MILLISECONDS` is a count of tick which corresponds
 * to 1 millisecond.  This macro is available since v1.12.0.
 */
#define NGHTTP3_MILLISECONDS                                                   \
  ((nghttp3_duration)(1000ULL * NGHTTP3_MICROSECONDS))

/**
 * @macro
 *
 * :macro:`NGHTTP3_SECONDS` is a count of tick which corresponds to 1
 * second.  This macro is available since v1.12.0.
 */
#define NGHTTP3_SECONDS ((nghttp3_duration)(1000ULL * NGHTTP3_MILLISECONDS))

/**
 * @macro
 *
 * :macro:`NGHTTP3_ALPN_H3` is a serialized form of HTTP/3 ALPN
 * protocol identifier this library supports.  Notice that the first
 * byte is the length of the following protocol identifier.
 */
#define NGHTTP3_ALPN_H3 "\x2h3"

/**
 * @macrosection
 *
 * nghttp3 library error codes
 */

/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_INVALID_ARGUMENT` indicates that a passed
 * argument is invalid.
 */
#define NGHTTP3_ERR_INVALID_ARGUMENT -101
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_INVALID_STATE` indicates that a requested
 * operation is not allowed at the current connection state.
 */
#define NGHTTP3_ERR_INVALID_STATE -102
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_WOULDBLOCK` indicates that an operation might
 * block.
 */
#define NGHTTP3_ERR_WOULDBLOCK -103
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_STREAM_IN_USE` indicates that a stream ID is
 * already in use.
 */
#define NGHTTP3_ERR_STREAM_IN_USE -104
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_MALFORMED_HTTP_HEADER` indicates that an HTTP
 * header field is malformed.
 */
#define NGHTTP3_ERR_MALFORMED_HTTP_HEADER -105
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_REMOVE_HTTP_HEADER` indicates that an HTTP
 * header field is discarded.
 */
#define NGHTTP3_ERR_REMOVE_HTTP_HEADER -106
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_MALFORMED_HTTP_MESSAGING` indicates that HTTP
 * messaging is malformed.
 */
#define NGHTTP3_ERR_MALFORMED_HTTP_MESSAGING -107
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_QPACK_FATAL` indicates that a fatal error is
 * occurred during QPACK processing, and it cannot be recoverable.
 */
#define NGHTTP3_ERR_QPACK_FATAL -108
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_QPACK_HEADER_TOO_LARGE` indicates that a header
 * field is too large to process.
 */
#define NGHTTP3_ERR_QPACK_HEADER_TOO_LARGE -109
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_STREAM_NOT_FOUND` indicates that a stream is
 * not found.
 */
#define NGHTTP3_ERR_STREAM_NOT_FOUND -110
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_CONN_CLOSING` indicates that a connection is
 * closing state.
 */
#define NGHTTP3_ERR_CONN_CLOSING -111
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_STREAM_DATA_OVERFLOW` indicates that the length
 * of stream data is too long, and causes overflow.
 */
#define NGHTTP3_ERR_STREAM_DATA_OVERFLOW -112
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_QPACK_DECOMPRESSION_FAILED` indicates that a
 * QPACK decompression failed.
 */
#define NGHTTP3_ERR_QPACK_DECOMPRESSION_FAILED -401
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_QPACK_ENCODER_STREAM_ERROR` indicates that an
 * error occurred while reading QPACK encoder stream.
 */
#define NGHTTP3_ERR_QPACK_ENCODER_STREAM_ERROR -402
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_QPACK_DECODER_STREAM_ERROR` indicates that an
 * error occurred while reading QPACK decoder stream.
 */
#define NGHTTP3_ERR_QPACK_DECODER_STREAM_ERROR -403
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_FRAME_UNEXPECTED` indicates that an
 * unexpected HTTP/3 frame is received.
 */
#define NGHTTP3_ERR_H3_FRAME_UNEXPECTED -601
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_FRAME_ERROR` indicates that an HTTP/3 frame
 * is malformed.
 */
#define NGHTTP3_ERR_H3_FRAME_ERROR -602
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_MISSING_SETTINGS` indicates that an HTTP/3
 * SETTINGS frame is missing.
 */
#define NGHTTP3_ERR_H3_MISSING_SETTINGS -603
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_INTERNAL_ERROR` indicates an internal error.
 */
#define NGHTTP3_ERR_H3_INTERNAL_ERROR -604
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_CLOSED_CRITICAL_STREAM` indicates that a
 * critical stream is closed.
 */
#define NGHTTP3_ERR_H3_CLOSED_CRITICAL_STREAM -605
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_GENERAL_PROTOCOL_ERROR` indicates a general
 * protocol error.  This is typically a catch-all error.
 */
#define NGHTTP3_ERR_H3_GENERAL_PROTOCOL_ERROR -606
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_ID_ERROR` indicates that an ID related error
 * occurred.
 */
#define NGHTTP3_ERR_H3_ID_ERROR -607
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_SETTINGS_ERROR` indicates that an HTTP/3
 * SETTINGS frame is malformed.
 */
#define NGHTTP3_ERR_H3_SETTINGS_ERROR -608
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_STREAM_CREATION_ERROR` indicates that a
 * remote endpoint attempts to create a new stream which is not
 * allowed.
 */
#define NGHTTP3_ERR_H3_STREAM_CREATION_ERROR -609
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_H3_EXCESSIVE_LOAD` indicates that a local
 * endpoint detected that its remote endpoint is exhibiting a behavior
 * that might generating excessive load.
 */
#define NGHTTP3_ERR_H3_EXCESSIVE_LOAD -610
/**
 * @macro
 *
 * :macro:`NGHTTP3_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 NGHTTP3_ERR_FATAL -900
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_NOMEM` indicates out of memory.
 */
#define NGHTTP3_ERR_NOMEM -901
/**
 * @macro
 *
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` indicates that user defined
 * callback function failed.
 */
#define NGHTTP3_ERR_CALLBACK_FAILURE -902

/**
 * @macrosection
 *
 * HTTP/3 application error code
 */

/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_NO_ERROR` is HTTP/3 application error code
 * ``H3_NO_ERROR``.
 */
#define NGHTTP3_H3_NO_ERROR 0x0100
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_GENERAL_PROTOCOL_ERROR` is HTTP/3 application
 * error code ``H3_GENERAL_PROTOCOL_ERROR``.
 */
#define NGHTTP3_H3_GENERAL_PROTOCOL_ERROR 0x0101
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_INTERNAL_ERROR` is HTTP/3 application error code
 * ``H3_INTERNAL_ERROR``.
 */
#define NGHTTP3_H3_INTERNAL_ERROR 0x0102
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_STREAM_CREATION_ERROR` is HTTP/3 application
 * error code ``H3_STREAM_CREATION_ERROR``.
 */
#define NGHTTP3_H3_STREAM_CREATION_ERROR 0x0103
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_CLOSED_CRITICAL_STREAM` is HTTP/3 application
 * error code ``H3_CLOSED_CRITICAL_STREAM``.
 */
#define NGHTTP3_H3_CLOSED_CRITICAL_STREAM 0x0104
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_FRAME_UNEXPECTED` is HTTP/3 application error
 * code ``H3_FRAME_UNEXPECTED``.
 */
#define NGHTTP3_H3_FRAME_UNEXPECTED 0x0105
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_FRAME_ERROR` is HTTP/3 application error code
 * ``H3_FRAME_ERROR``.
 */
#define NGHTTP3_H3_FRAME_ERROR 0x0106
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_EXCESSIVE_LOAD` is HTTP/3 application error code
 * ``H3_EXCESSIVE_LOAD``.
 */
#define NGHTTP3_H3_EXCESSIVE_LOAD 0x0107
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_ID_ERROR` is HTTP/3 application error code
 * ``H3_ID_ERROR``.
 */
#define NGHTTP3_H3_ID_ERROR 0x0108
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_SETTINGS_ERROR` is HTTP/3 application error code
 * ``H3_SETTINGS_ERROR``.
 */
#define NGHTTP3_H3_SETTINGS_ERROR 0x0109
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_MISSING_SETTINGS` is HTTP/3 application error
 * code ``H3_MISSING_SETTINGS``.
 */
#define NGHTTP3_H3_MISSING_SETTINGS 0x010a
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_REQUEST_REJECTED` is HTTP/3 application error
 * code ``H3_REQUEST_REJECTED``.
 */
#define NGHTTP3_H3_REQUEST_REJECTED 0x010b
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_REQUEST_CANCELLED` is HTTP/3 application error
 * code ``H3_REQUEST_CANCELLED``.
 */
#define NGHTTP3_H3_REQUEST_CANCELLED 0x010c
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_REQUEST_INCOMPLETE` is HTTP/3 application error
 * code ``H3_REQUEST_INCOMPLETE``.
 */
#define NGHTTP3_H3_REQUEST_INCOMPLETE 0x010d
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_MESSAGE_ERROR` is HTTP/3 application error code
 * ``H3_MESSAGE_ERROR``.
 */
#define NGHTTP3_H3_MESSAGE_ERROR 0x010e
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_CONNECT_ERROR` is HTTP/3 application error code
 * ``H3_CONNECT_ERROR``.
 */
#define NGHTTP3_H3_CONNECT_ERROR 0x010f
/**
 * @macro
 *
 * :macro:`NGHTTP3_H3_VERSION_FALLBACK` is HTTP/3 application error
 * code ``H3_VERSION_FALLBACK``.
 */
#define NGHTTP3_H3_VERSION_FALLBACK 0x0110
/**
 * @macro
 *
 * :macro:`NGHTTP3_QPACK_DECOMPRESSION_FAILED` is HTTP/3 application
 * error code ``QPACK_DECOMPRESSION_FAILED``.
 */
#define NGHTTP3_QPACK_DECOMPRESSION_FAILED 0x0200
/**
 * @macro
 *
 * :macro:`NGHTTP3_QPACK_ENCODER_STREAM_ERROR` is HTTP/3 application
 * error code ``QPACK_ENCODER_STREAM_ERROR``.
 */
#define NGHTTP3_QPACK_ENCODER_STREAM_ERROR 0x0201
/**
 * @macro
 *
 * :macro:`NGHTTP3_QPACK_DECODER_STREAM_ERROR` is HTTP/3 application
 * error code ``QPACK_DECODER_STREAM_ERROR``.
 */
#define NGHTTP3_QPACK_DECODER_STREAM_ERROR 0x0202

/**
 * @functypedef
 *
 * :type:`nghttp3_malloc` is a custom memory allocator to replace
 * :manpage:`malloc(3)`.  The |user_data| is the
 * :member:`nghttp3_mem.user_data`.
 */
typedef void *(*nghttp3_malloc)(size_t size, void *user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_free` is a custom memory allocator to replace
 * :manpage:`free(3)`.  The |user_data| is the
 * :member:`nghttp3_mem.user_data`.
 */
typedef void (*nghttp3_free)(void *ptr, void *user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_calloc` is a custom memory allocator to replace
 * :manpage:`calloc(3)`.  The |user_data| is the
 * :member:`nghttp3_mem.user_data`.
 */
typedef void *(*nghttp3_calloc)(size_t nmemb, size_t size, void *user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_realloc` is a custom memory allocator to replace
 * :manpage:`realloc(3)`.  The |user_data| is the
 * :member:`nghttp3_mem.user_data`.
 */
typedef void *(*nghttp3_realloc)(void *ptr, size_t size, void *user_data);

/**
 * @struct
 *
 * :type:`nghttp3_mem` is a custom memory allocator functions and user
 * defined pointer.  The :member:`user_data` field is passed to each
 * allocator function.  This can be used, for example, to achieve
 * per-session 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() {
 *       nghttp3_mem mem = {NULL, my_malloc_cb, my_free_cb, my_calloc_cb,
 *                          my_realloc_cb};
 *
 *       ...
 *     }
 */
typedef struct nghttp3_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)`.
   */
  nghttp3_malloc malloc;
  /**
   * :member:`free` is a custom allocator function to replace
   * :manpage:`free(3)`.
   */
  nghttp3_free free;
  /**
   * :member:`calloc` is a custom allocator function to replace
   * :manpage:`calloc(3)`.
   */
  nghttp3_calloc calloc;
  /**
   * :member:`realloc` is a custom allocator function to replace
   * :manpage:`realloc(3)`.
   */
  nghttp3_realloc realloc;
} nghttp3_mem;

/**
 * @function
 *
 * `nghttp3_mem_default` returns the default memory allocator which
 * uses malloc/calloc/realloc/free.
 */
NGHTTP3_EXTERN const nghttp3_mem *nghttp3_mem_default(void);

/**
 * @struct
 *
 * :type:`nghttp3_vec` is ``struct iovec`` compatible structure to
 * reference arbitrary array of bytes.
 */
typedef struct nghttp3_vec {
  /**
   * :member:`base` points to the data.
   */
  uint8_t *base;
  /**
   * :member:`len` is the number of bytes which the buffer pointed by
   * :member:`base` contains.
   */
  size_t len;
} nghttp3_vec;

/**
 * @struct
 *
 * :type:`nghttp3_rcbuf` is the object representing reference counted
 * buffer.  The details of this structure are intentionally hidden
 * from the public API.
 */
typedef struct nghttp3_rcbuf nghttp3_rcbuf;

/**
 * @function
 *
 * `nghttp3_rcbuf_incref` increments the reference count of |rcbuf| by
 * 1.
 */
NGHTTP3_EXTERN void nghttp3_rcbuf_incref(nghttp3_rcbuf *rcbuf);

/**
 * @function
 *
 * `nghttp3_rcbuf_decref` decrements the reference count of |rcbuf| by
 * 1.  If the reference count becomes zero, the object pointed by
 * |rcbuf| will be freed.  In this case, application must not use
 * |rcbuf| again.
 */
NGHTTP3_EXTERN void nghttp3_rcbuf_decref(nghttp3_rcbuf *rcbuf);

/**
 * @function
 *
 * `nghttp3_rcbuf_get_buf` returns the underlying buffer managed by
 * |rcbuf|.
 */
NGHTTP3_EXTERN nghttp3_vec nghttp3_rcbuf_get_buf(const nghttp3_rcbuf *rcbuf);

/**
 * @function
 *
 * `nghttp3_rcbuf_is_static` returns nonzero if the underlying buffer
 * is statically allocated, and 0 otherwise. This can be useful for
 * language bindings that wish to avoid creating duplicate strings for
 * these buffers.
 */
NGHTTP3_EXTERN int nghttp3_rcbuf_is_static(const nghttp3_rcbuf *rcbuf);

/**
 * @struct
 *
 * :type:`nghttp3_buf` is the variable size buffer.
 */
typedef struct nghttp3_buf {
  /**
   * :member:`begin` points to the beginning of the buffer.
   */
  uint8_t *begin;
  /**
   * :member:`end` points to the one beyond of the last byte of the
   * buffer
   */
  uint8_t *end;
  /**
   * :member:`pos` points to the start of data.  Typically, this
   * points to the address that next data should be read.  Initially,
   * it points to :member:`begin`.
   */
  uint8_t *pos;
  /**
   * :member:`last` points to the one beyond of the last data of the
   * buffer.  Typically, new data is written at this point.
   * Initially, it points to :member:`begin`.
   */
  uint8_t *last;
} nghttp3_buf;

/**
 * @function
 *
 * `nghttp3_buf_init` initializes empty |buf|.
 */
NGHTTP3_EXTERN void nghttp3_buf_init(nghttp3_buf *buf);

/**
 * @function
 *
 * `nghttp3_buf_free` frees resources allocated for |buf| using |mem|
 * as memory allocator.  :member:`buf->begin <nghttp3_buf.begin>` must
 * be a heap buffer allocated by |mem|.
 */
NGHTTP3_EXTERN void nghttp3_buf_free(nghttp3_buf *buf, const nghttp3_mem *mem);

/**
 * @function
 *
 * `nghttp3_buf_left` returns the number of additional bytes which can
 * be written to the underlying buffer.  In other words, it returns
 * :member:`buf->end <nghttp3_buf.end>` - :member:`buf->last
 * <nghttp3_buf.last>`.
 */
NGHTTP3_EXTERN size_t nghttp3_buf_left(const nghttp3_buf *buf);

/**
 * @function
 *
 * `nghttp3_buf_len` returns the number of bytes left to read.  In
 * other words, it returns :member:`buf->last <nghttp3_buf.last>` -
 * :member:`buf->pos <nghttp3_buf.pos>`.
 */
NGHTTP3_EXTERN size_t nghttp3_buf_len(const nghttp3_buf *buf);

/**
 * @function
 *
 * `nghttp3_buf_reset` sets :member:`buf->pos <nghttp3_buf.pos>` and
 * :member:`buf->last <nghttp3_buf.last>` to :member:`buf->begin
 * <nghttp3_buf.begin>`.
 */
NGHTTP3_EXTERN void nghttp3_buf_reset(nghttp3_buf *buf);

/**
 * @macrosection
 *
 * Flags for HTTP field name/value pair
 */

/**
 * @macro
 *
 * :macro:`NGHTTP3_NV_FLAG_NONE` indicates no flag set.
 */
#define NGHTTP3_NV_FLAG_NONE 0x00u

/**
 * @macro
 *
 * :macro:`NGHTTP3_NV_FLAG_NEVER_INDEX` indicates that this name/value
 * pair must not be indexed.  Other implementation calls this bit as
 * "sensitive".
 */
#define NGHTTP3_NV_FLAG_NEVER_INDEX 0x01u

/**
 * @macro
 *
 * :macro:`NGHTTP3_NV_FLAG_NO_COPY_NAME` is set solely by application.
 * If this flag is set, the library does not make a copy of field
 * name.  This could improve performance.
 */
#define NGHTTP3_NV_FLAG_NO_COPY_NAME 0x02u

/**
 * @macro
 *
 * :macro:`NGHTTP3_NV_FLAG_NO_COPY_VALUE` is set solely by
 * application.  If this flag is set, the library does not make a copy
 * of field value.  This could improve performance.
 */
#define NGHTTP3_NV_FLAG_NO_COPY_VALUE 0x04u

/**
 * @macro
 *
 * :macro:`NGHTTP3_NV_FLAG_TRY_INDEX` gives a hint to QPACK encoder to
 * index an HTTP field which is not indexed by default.  This is just
 * a hint, and QPACK encoder might not encode the field in various
 * reasons.
 */
#define NGHTTP3_NV_FLAG_TRY_INDEX 0x08u

/**
 * @struct
 *
 * :type:`nghttp3_nv` is the name/value pair, which mainly used to
 * represent HTTP fields.
 */
typedef struct nghttp3_nv {
  /**
   * :member:`name` is the HTTP field name.
   */
  const uint8_t *name;
  /**
   * :member:`value` is the HTTP field value.
   */
  const uint8_t *value;
  /**
   * :member:`namelen` is the length of the |name|, excluding
   * terminating NULL.
   */
  size_t namelen;
  /**
   * :member:`valuelen` is the length of the |value|, excluding
   * terminating NULL.
   */
  size_t valuelen;
  /**
   * :member:`flags` is bitwise OR of one or more of
   * :macro:`NGHTTP3_NV_FLAG_* <NGHTTP3_NV_FLAG_NONE>`.
   */
  uint8_t flags;
} nghttp3_nv;

/* Generated by mkstatichdtbl.py */
/**
 * @enum
 *
 * :type:`nghttp3_qpack_token` defines HTTP field name tokens to
 * identify field name quickly.  It appears in
 * :member:`nghttp3_qpack_nv.token`.
 */
typedef enum nghttp3_qpack_token {
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN__AUTHORITY` is a token for
   * ``:authority``.
   */
  NGHTTP3_QPACK_TOKEN__AUTHORITY = 0,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN__PATH` is a token for ``:path``.
   */
  NGHTTP3_QPACK_TOKEN__PATH = 8,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_AGE` is a token for ``age``.
   */
  NGHTTP3_QPACK_TOKEN_AGE = 43,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_CONTENT_DISPOSITION` is a token for
   * ``content-disposition``.
   */
  NGHTTP3_QPACK_TOKEN_CONTENT_DISPOSITION = 52,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_CONTENT_LENGTH` is a token for
   * ``content-length``.
   */
  NGHTTP3_QPACK_TOKEN_CONTENT_LENGTH = 55,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_COOKIE` is a token for ``cookie``.
   */
  NGHTTP3_QPACK_TOKEN_COOKIE = 68,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_DATE` is a token for ``date``.
   */
  NGHTTP3_QPACK_TOKEN_DATE = 69,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ETAG` is a token for ``etag``.
   */
  NGHTTP3_QPACK_TOKEN_ETAG = 71,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_IF_MODIFIED_SINCE` is a token for
   * ``if-modified-since``.
   */
  NGHTTP3_QPACK_TOKEN_IF_MODIFIED_SINCE = 74,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_IF_NONE_MATCH` is a token for
   * ``if-none-match``.
   */
  NGHTTP3_QPACK_TOKEN_IF_NONE_MATCH = 75,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_LAST_MODIFIED` is a token for
   * ``last-modified``.
   */
  NGHTTP3_QPACK_TOKEN_LAST_MODIFIED = 77,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_LINK` is a token for ``link``.
   */
  NGHTTP3_QPACK_TOKEN_LINK = 78,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_LOCATION` is a token for ``location``.
   */
  NGHTTP3_QPACK_TOKEN_LOCATION = 79,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_REFERER` is a token for ``referer``.
   */
  NGHTTP3_QPACK_TOKEN_REFERER = 83,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_SET_COOKIE` is a token for
   * ``set-cookie``.
   */
  NGHTTP3_QPACK_TOKEN_SET_COOKIE = 85,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN__METHOD` is a token for ``:method``.
   */
  NGHTTP3_QPACK_TOKEN__METHOD = 1,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN__SCHEME` is a token for ``:scheme``.
   */
  NGHTTP3_QPACK_TOKEN__SCHEME = 9,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN__STATUS` is a token for ``:status``.
   */
  NGHTTP3_QPACK_TOKEN__STATUS = 11,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCEPT` is a token for ``accept``.
   */
  NGHTTP3_QPACK_TOKEN_ACCEPT = 25,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCEPT_ENCODING` is a token for
   * ``accept-encoding``.
   */
  NGHTTP3_QPACK_TOKEN_ACCEPT_ENCODING = 27,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCEPT_RANGES` is a token for
   * ``accept-ranges``.
   */
  NGHTTP3_QPACK_TOKEN_ACCEPT_RANGES = 29,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_ALLOW_HEADERS` is a
   * token for ``access-control-allow-headers``.
   */
  NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_ALLOW_HEADERS = 32,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_ALLOW_ORIGIN` is a
   * token for ``access-control-allow-origin``.
   */
  NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_ALLOW_ORIGIN = 38,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_CACHE_CONTROL` is a token for
   * ``cache-control``.
   */
  NGHTTP3_QPACK_TOKEN_CACHE_CONTROL = 46,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_CONTENT_ENCODING` is a token for
   * ``content-encoding``.
   */
  NGHTTP3_QPACK_TOKEN_CONTENT_ENCODING = 53,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_CONTENT_TYPE` is a token for
   * ``content-type``.
   */
  NGHTTP3_QPACK_TOKEN_CONTENT_TYPE = 57,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_RANGE` is a token for ``range``.
   */
  NGHTTP3_QPACK_TOKEN_RANGE = 82,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_STRICT_TRANSPORT_SECURITY` is a token
   * for ``strict-transport-security``.
   */
  NGHTTP3_QPACK_TOKEN_STRICT_TRANSPORT_SECURITY = 86,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_VARY` is a token for ``vary``.
   */
  NGHTTP3_QPACK_TOKEN_VARY = 92,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_X_CONTENT_TYPE_OPTIONS` is a token for
   * ``x-content-type-options``.
   */
  NGHTTP3_QPACK_TOKEN_X_CONTENT_TYPE_OPTIONS = 94,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_X_XSS_PROTECTION` is a token for
   * ``x-xss-protection``.
   */
  NGHTTP3_QPACK_TOKEN_X_XSS_PROTECTION = 98,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCEPT_LANGUAGE` is a token for
   * ``accept-language``.
   */
  NGHTTP3_QPACK_TOKEN_ACCEPT_LANGUAGE = 28,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_ALLOW_CREDENTIALS` is a
   * token for ``access-control-allow-credentials``.
   */
  NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_ALLOW_CREDENTIALS = 30,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_ALLOW_METHODS` is a
   * token for ``access-control-allow-methods``.
   */
  NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_ALLOW_METHODS = 35,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_EXPOSE_HEADERS` is a
   * token for ``access-control-expose-headers``.
   */
  NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_EXPOSE_HEADERS = 39,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_REQUEST_HEADERS` is a
   * token for ``access-control-request-headers``.
   */
  NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_REQUEST_HEADERS = 40,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_REQUEST_METHOD` is a
   * token for ``access-control-request-method``.
   */
  NGHTTP3_QPACK_TOKEN_ACCESS_CONTROL_REQUEST_METHOD = 41,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ALT_SVC` is a token for ``alt-svc``.
   */
  NGHTTP3_QPACK_TOKEN_ALT_SVC = 44,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_AUTHORIZATION` is a token for
   * ``authorization``.
   */
  NGHTTP3_QPACK_TOKEN_AUTHORIZATION = 45,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_CONTENT_SECURITY_POLICY` is a token
   * for ``content-security-policy``.
   */
  NGHTTP3_QPACK_TOKEN_CONTENT_SECURITY_POLICY = 56,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_EARLY_DATA` is a token for
   * ``early-data``.
   */
  NGHTTP3_QPACK_TOKEN_EARLY_DATA = 70,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_EXPECT_CT` is a token for
   * ``expect-ct``.
   */
  NGHTTP3_QPACK_TOKEN_EXPECT_CT = 72,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_FORWARDED` is a token for
   * ``forwarded``.
   */
  NGHTTP3_QPACK_TOKEN_FORWARDED = 73,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_IF_RANGE` is a token for ``if-range``.
   */
  NGHTTP3_QPACK_TOKEN_IF_RANGE = 76,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_ORIGIN` is a token for ``origin``.
   */
  NGHTTP3_QPACK_TOKEN_ORIGIN = 80,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_PURPOSE` is a token for ``purpose``.
   */
  NGHTTP3_QPACK_TOKEN_PURPOSE = 81,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_SERVER` is a token for ``server``.
   */
  NGHTTP3_QPACK_TOKEN_SERVER = 84,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_TIMING_ALLOW_ORIGIN` is a token for
   * ``timing-allow-origin``.
   */
  NGHTTP3_QPACK_TOKEN_TIMING_ALLOW_ORIGIN = 89,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_UPGRADE_INSECURE_REQUESTS` is a token
   * for ``upgrade-insecure-requests``.
   */
  NGHTTP3_QPACK_TOKEN_UPGRADE_INSECURE_REQUESTS = 90,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_USER_AGENT` is a token for
   * ``user-agent``.
   */
  NGHTTP3_QPACK_TOKEN_USER_AGENT = 91,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_X_FORWARDED_FOR` is a token for
   * ``x-forwarded-for``.
   */
  NGHTTP3_QPACK_TOKEN_X_FORWARDED_FOR = 95,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_X_FRAME_OPTIONS` is a token for
   * ``x-frame-options``.
   */
  NGHTTP3_QPACK_TOKEN_X_FRAME_OPTIONS = 96,

  /* Additional HTTP fields for HTTP messaging validation */

  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_HOST` is a token for ``host``.
   */
  NGHTTP3_QPACK_TOKEN_HOST = 1000,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_CONNECTION` is a token for
   * ``connection``.
   */
  NGHTTP3_QPACK_TOKEN_CONNECTION,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_KEEP_ALIVE` is a token for
   * ``keep-alive``.
   */
  NGHTTP3_QPACK_TOKEN_KEEP_ALIVE,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_PROXY_CONNECTION` is a token for
   * ``proxy-connection``.
   */
  NGHTTP3_QPACK_TOKEN_PROXY_CONNECTION,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_TRANSFER_ENCODING` is a token for
   * ``transfer-encoding``.
   */
  NGHTTP3_QPACK_TOKEN_TRANSFER_ENCODING,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_UPGRADE` is a token for ``upgrade``.
   */
  NGHTTP3_QPACK_TOKEN_UPGRADE,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_TE` is a token for ``te``.
   */
  NGHTTP3_QPACK_TOKEN_TE,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN__PROTOCOL` is a token for
   * ``:protocol``.
   */
  NGHTTP3_QPACK_TOKEN__PROTOCOL,
  /**
   * :enum:`NGHTTP3_QPACK_TOKEN_PRIORITY` is a token for ``priority``.
   */
  NGHTTP3_QPACK_TOKEN_PRIORITY
} nghttp3_qpack_token;

/**
 * @struct
 *
 * :type:`nghttp3_qpack_nv` represents HTTP field name/value pair just
 * like :type:`nghttp3_nv`.  It is an extended version of
 * :type:`nghttp3_nv`, and has reference counted buffers and tokens.
 */
typedef struct nghttp3_qpack_nv {
  /**
   * :member:`name` is the buffer containing HTTP field name.
   * NULL-termination is guaranteed.
   */
  nghttp3_rcbuf *name;
  /**
   * :member:`value` is the buffer containing HTTP field value.
   * NULL-termination is guaranteed.
   */
  nghttp3_rcbuf *value;
  /**
   * :member:`token` is :type:`nghttp3_qpack_token` value of
   * :member:`name`.  It could be -1 if we have no token for that HTTP
   * field name.
   */
  int32_t token;
  /**
   * :member:`flags` is a bitwise OR of one or more of
   * :macro:`NGHTTP3_NV_FLAG_* <NGHTTP3_NV_FLAG_NONE>`.
   */
  uint8_t flags;
} nghttp3_qpack_nv;

/**
 * @struct
 *
 * :type:`nghttp3_qpack_encoder` is QPACK encoder.  The details of
 * this structure are intentionally hidden from the public API.
 */
typedef struct nghttp3_qpack_encoder nghttp3_qpack_encoder;

/**
 * @function
 *
 * `nghttp3_qpack_encoder_new` initializes QPACK encoder.  |pencoder|
 * must be non-NULL pointer.  |hard_max_dtable_capacity| is the upper
 * bound of the dynamic table capacity.  |mem| is a memory allocator.
 * This function allocates memory for :type:`nghttp3_qpack_encoder`
 * itself, and assigns its pointer to |*pencoder| if it succeeds.
 *
 * The maximum dynamic table capacity is still 0.  In order to change
 * the maximum dynamic table capacity, call
 * `nghttp3_qpack_encoder_set_max_dtable_capacity`.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 *
 * See also `nghttp3_qpack_encoder_new2`.  This function calls
 * `nghttp3_qpack_encoder_new2` with the given parameters and 0 as
 * seed.
 */
NGHTTP3_EXTERN int nghttp3_qpack_encoder_new(nghttp3_qpack_encoder **pencoder,
                                             size_t hard_max_dtable_capacity,
                                             const nghttp3_mem *mem);

/**
 * @function
 *
 * `nghttp3_qpack_encoder_new2` initializes QPACK encoder.  |pencoder|
 * must be non-NULL pointer.  |hard_max_dtable_capacity| is the upper
 * bound of the dynamic table capacity.  |seed| must be unpredictable
 * value, and is used to seed the internal data structure.  |mem| is a
 * memory allocator.  This function allocates memory for
 * :type:`nghttp3_qpack_encoder` itself, and assigns its pointer to
 * |*pencoder| if it succeeds.
 *
 * The maximum dynamic table capacity is still 0.  In order to change
 * the maximum dynamic table capacity, call
 * `nghttp3_qpack_encoder_set_max_dtable_capacity`.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 *
 * This function is available since v1.11.0.
 */
NGHTTP3_EXTERN int nghttp3_qpack_encoder_new2(nghttp3_qpack_encoder **pencoder,
                                              size_t hard_max_dtable_capacity,
                                              uint64_t seed,
                                              const nghttp3_mem *mem);

/**
 * @function
 *
 * `nghttp3_qpack_encoder_del` frees memory allocated for |encoder|.
 * This function also frees memory pointed by |encoder| itself.  This
 * function does nothing if |encoder| is NULL.
 */
NGHTTP3_EXTERN void nghttp3_qpack_encoder_del(nghttp3_qpack_encoder *encoder);

/**
 * @function
 *
 * `nghttp3_qpack_encoder_encode` encodes the list of HTTP fields
 * |nva|.  |nvlen| is the length of |nva|.  |stream_id| is the
 * identifier of the stream which these HTTP fields belong to.  This
 * function writes field section prefix, encoded HTTP field section,
 * and encoder stream to |pbuf|, |rbuf|, and |ebuf| respectively.
 * Each :member:`nghttp3_buf.last` will be adjusted when data is
 * written.  An application should write |pbuf| and |rbuf| to the
 * request stream in this order.
 *
 * The buffer pointed by |pbuf|, |rbuf|, and |ebuf| can be empty
 * buffer.  It is fine to pass a buffer initialized by
 * `nghttp3_buf_init(buf) <nghttp3_buf_init>`.  This function
 * allocates memory for these buffers as necessary.  In particular, it
 * frees and expands buffer if the current capacity of buffer is not
 * enough.  If :member:`nghttp3_buf.begin` of any buffer is not NULL,
 * it must be allocated by the same memory allocator passed to
 * `nghttp3_qpack_encoder_new`.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory
 * :macro:`NGHTTP3_ERR_QPACK_FATAL`
 *      |encoder| is in unrecoverable error state, and cannot be used
 *      anymore.
 */
NGHTTP3_EXTERN int nghttp3_qpack_encoder_encode(
  nghttp3_qpack_encoder *encoder, nghttp3_buf *pbuf, nghttp3_buf *rbuf,
  nghttp3_buf *ebuf, int64_t stream_id, const nghttp3_nv *nva, size_t nvlen);

/**
 * @function
 *
 * `nghttp3_qpack_encoder_read_decoder` reads decoder stream.  The
 * buffer pointed by |src| of length |srclen| contains decoder stream.
 *
 * This function returns the number of bytes read, or one of the
 * following negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory
 * :macro:`NGHTTP3_ERR_QPACK_FATAL`
 *     |encoder| is in unrecoverable error state, and cannot be used
 *     anymore.
 * :macro:`NGHTTP3_ERR_QPACK_DECODER_STREAM`
 *     |encoder| is unable to process input because it is malformed.
 */
NGHTTP3_EXTERN nghttp3_ssize nghttp3_qpack_encoder_read_decoder(
  nghttp3_qpack_encoder *encoder, const uint8_t *src, size_t srclen);

/**
 * @function
 *
 * `nghttp3_qpack_encoder_set_max_dtable_capacity` sets max dynamic
 * table capacity to |max_dtable_capacity|.  If |max_dtable_capacity|
 * is larger than ``hard_max_dtable_capacity`` parameter of
 * `nghttp3_qpack_encoder_new`, it is truncated to the latter.
 */
NGHTTP3_EXTERN void
nghttp3_qpack_encoder_set_max_dtable_capacity(nghttp3_qpack_encoder *encoder,
                                              size_t max_dtable_capacity);

/**
 * @function
 *
 * `nghttp3_qpack_encoder_set_max_blocked_streams` sets the number of
 * streams which can be blocked to |max_blocked_streams|.
 */
NGHTTP3_EXTERN void
nghttp3_qpack_encoder_set_max_blocked_streams(nghttp3_qpack_encoder *encoder,
                                              size_t max_blocked_streams);

/**
 * @function
 *
 * `nghttp3_qpack_encoder_ack_everything` tells |encoder| that all
 * encoded HTTP field sections are acknowledged.  This function is
 * provided for debugging purpose only.  In HTTP/3, |encoder| knows
 * this by reading decoder stream with
 * `nghttp3_qpack_encoder_read_decoder`.
 */
NGHTTP3_EXTERN void
nghttp3_qpack_encoder_ack_everything(nghttp3_qpack_encoder *encoder);

/**
 * @function
 *
 * `nghttp3_qpack_encoder_get_num_blocked_streams` returns the number
 * of streams which are potentially blocked at decoder side.
 */
NGHTTP3_EXTERN size_t
nghttp3_qpack_encoder_get_num_blocked_streams(nghttp3_qpack_encoder *encoder);

/**
 * @struct
 *
 * :type:`nghttp3_qpack_stream_context` is a decoder context for an
 * individual stream.  Its state is per HTTP field section.  In order
 * to reuse this object for another HTTP field section, call
 * `nghttp3_qpack_stream_context_reset`.  The details of this
 * structure are intentionally hidden from the public API.
 */
typedef struct nghttp3_qpack_stream_context nghttp3_qpack_stream_context;

/**
 * @function
 *
 * `nghttp3_qpack_stream_context_new` initializes stream context.
 * |psctx| must be non-NULL pointer.  |stream_id| is stream ID.  |mem|
 * is a memory allocator.  This function allocates memory for
 * :type:`nghttp3_qpack_stream_context` itself, and assigns its
 * pointer to |*psctx| if it succeeds.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int
nghttp3_qpack_stream_context_new(nghttp3_qpack_stream_context **psctx,
                                 int64_t stream_id, const nghttp3_mem *mem);

/**
 * @function
 *
 * `nghttp3_qpack_stream_context_del` frees memory allocated for
 * |sctx|.  This function frees memory pointed by |sctx| itself.  This
 * function does nothing if |sctx| is NULL.
 */
NGHTTP3_EXTERN void
nghttp3_qpack_stream_context_del(nghttp3_qpack_stream_context *sctx);

/**
 * @function
 *
 * `nghttp3_qpack_stream_context_get_ricnt` returns required insert
 * count.
 */
NGHTTP3_EXTERN uint64_t
nghttp3_qpack_stream_context_get_ricnt(nghttp3_qpack_stream_context *sctx);

/**
 * @function
 *
 * `nghttp3_qpack_stream_context_reset` resets the state of |sctx|.
 * Then it can be reused for decoding an another HTTP field section in
 * the same stream.
 */
NGHTTP3_EXTERN
void nghttp3_qpack_stream_context_reset(nghttp3_qpack_stream_context *sctx);

/**
 * @struct
 *
 * :type:`nghttp3_qpack_decoder` is QPACK decoder.  The details of
 * this structure are intentionally hidden from the public API.
 */
typedef struct nghttp3_qpack_decoder nghttp3_qpack_decoder;

/**
 * @function
 *
 * `nghttp3_qpack_decoder_new` initializes QPACK decoder.  |pdecoder|
 * must be non-NULL pointer.  |hard_max_dtable_capacity| is the upper
 * bound of the dynamic table capacity.  |max_blocked_streams| is the
 * maximum number of streams which can be blocked.  |mem| is a memory
 * allocator.  This function allocates memory for
 * :type:`nghttp3_qpack_decoder` itself, and assigns its pointer to
 * |*pdecoder| if it succeeds.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_qpack_decoder_new(nghttp3_qpack_decoder **pdecoder,
                                             size_t hard_max_dtable_capacity,
                                             size_t max_blocked_streams,
                                             const nghttp3_mem *mem);

/**
 * @function
 *
 * `nghttp3_qpack_decoder_del` frees memory allocated for |decoder|.
 * This function frees memory pointed by |decoder| itself.  This
 * function does nothing if |decoder| is NULL.
 */
NGHTTP3_EXTERN void nghttp3_qpack_decoder_del(nghttp3_qpack_decoder *decoder);

/**
 * @function
 *
 * `nghttp3_qpack_decoder_read_encoder` reads encoder stream.  The
 * buffer pointed by |src| of length |srclen| contains encoder stream.
 *
 * This function returns the number of bytes read, or one of the
 * following negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 * :macro:`NGHTTP3_ERR_QPACK_FATAL`
 *     |decoder| is in unrecoverable error state, and cannot be used
 *     anymore.
 * :macro:`NGHTTP3_ERR_QPACK_ENCODER_STREAM`
 *     Could not interpret encoder stream instruction.
 */
NGHTTP3_EXTERN nghttp3_ssize nghttp3_qpack_decoder_read_encoder(
  nghttp3_qpack_decoder *decoder, const uint8_t *src, size_t srclen);

/**
 * @function
 *
 * `nghttp3_qpack_decoder_get_icnt` returns insert count.
 */
NGHTTP3_EXTERN uint64_t
nghttp3_qpack_decoder_get_icnt(const nghttp3_qpack_decoder *decoder);

/**
 * @macrosection
 *
 * Flags for QPACK decoder
 */

/**
 * @macro
 *
 * :macro:`NGHTTP3_QPACK_DECODE_FLAG_NONE` indicates that no flag set.
 */
#define NGHTTP3_QPACK_DECODE_FLAG_NONE 0x00u

/**
 * @macro
 *
 * :macro:`NGHTTP3_QPACK_DECODE_FLAG_EMIT` indicates that an HTTP
 * field is successfully decoded.
 */
#define NGHTTP3_QPACK_DECODE_FLAG_EMIT 0x01u

/**
 * @macro
 *
 * :macro:`NGHTTP3_QPACK_DECODE_FLAG_FINAL` indicates that an entire
 * HTTP field section has been decoded.
 */
#define NGHTTP3_QPACK_DECODE_FLAG_FINAL 0x02u

/**
 * @macro
 *
 * :macro:`NGHTTP3_QPACK_DECODE_FLAG_BLOCKED` indicates that decoding
 * has been blocked.
 */
#define NGHTTP3_QPACK_DECODE_FLAG_BLOCKED 0x04u

/**
 * @function
 *
 * `nghttp3_qpack_decoder_read_request` reads request stream.  The
 * request stream is given as the buffer pointed by |src| of length
 * |srclen|.  |sctx| is the stream context, and it must be created by
 * `nghttp3_qpack_stream_context_new`.  |*pflags| must be non-NULL
 * pointer.  |nv| must be non-NULL pointer.
 *
 * If this function succeeds, it assigns flags to |*pflags|.  If
 * |*pflags| has :macro:`NGHTTP3_QPACK_DECODE_FLAG_EMIT` set, a
 * decoded HTTP field is assigned to |nv|.  If |*pflags| has
 * :macro:`NGHTTP3_QPACK_DECODE_FLAG_FINAL` set, an entire HTTP field
 * section has been successfully decoded.  If |*pflags| has
 * :macro:`NGHTTP3_QPACK_DECODE_FLAG_BLOCKED` set, decoding is blocked
 * due to required insert count.
 *
 * When an HTTP field is decoded, an application receives it in |nv|.
 * :member:`nv->name <nghttp3_qpack_nv.name>` and :member:`nv->value
 * <nghttp3_qpack_nv.value>` are reference counted buffer, and their
 * reference counts are already incremented for application use.
 * Therefore, when application finishes processing |nv|, it must call
 * `nghttp3_rcbuf_decref(nv->name) <nghttp3_rcbuf_decref>` and
 * `nghttp3_rcbuf_decref(nv->value) <nghttp3_rcbuf_decref>`, or memory
 * leak might occur.  These :type:`nghttp3_rcbuf` objects hold the
 * pointer to :type:`nghttp3_mem` that is passed to
 * `nghttp3_qpack_decoder_new` (or either `nghttp3_conn_client_new` or
 * `nghttp3_conn_server_new` if it is used indirectly).  As long as
 * these objects are alive, the pointed :type:`nghttp3_mem` object
 * must be available.  Otherwise, `nghttp3_rcbuf_decref` will cause
 * undefined behavior.
 *
 * This function returns the number of bytes read, or one of the
 * following negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 * :macro:`NGHTTP3_ERR_QPACK_FATAL`
 *     |decoder| is in unrecoverable error state, and cannot be used
 *     anymore.
 * :macro:`NGHTTP3_ERR_QPACK_DECOMPRESSION_FAILED`
 *     Could not interpret field line representations.
 * :macro:`NGHTTP3_ERR_QPACK_HEADER_TOO_LARGE`
 *     HTTP field is too large.
 */
NGHTTP3_EXTERN nghttp3_ssize nghttp3_qpack_decoder_read_request(
  nghttp3_qpack_decoder *decoder, nghttp3_qpack_stream_context *sctx,
  nghttp3_qpack_nv *nv, uint8_t *pflags, const uint8_t *src, size_t srclen,
  int fin);

/**
 * @function
 *
 * `nghttp3_qpack_decoder_write_decoder` writes decoder stream into
 * |dbuf|.
 *
 * The caller must ensure that `nghttp3_buf_left(dbuf)
 * <nghttp3_buf_left>` >=
 * `nghttp3_qpack_decoder_get_decoder_streamlen(decoder)
 * <nghttp3_qpack_decoder_get_decoder_streamlen>`.
 */
NGHTTP3_EXTERN void
nghttp3_qpack_decoder_write_decoder(nghttp3_qpack_decoder *decoder,
                                    nghttp3_buf *dbuf);

/**
 * @function
 *
 * `nghttp3_qpack_decoder_get_decoder_streamlen` returns the length of
 * decoder stream that is currently pending.
 */
NGHTTP3_EXTERN size_t
nghttp3_qpack_decoder_get_decoder_streamlen(nghttp3_qpack_decoder *decoder);

/**
 * @function
 *
 * `nghttp3_qpack_decoder_cancel_stream` cancels HTTP field section
 * decoding for stream denoted by |stream_id|.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 * :macro:`NGHTTP3_ERR_QPACK_FATAL`
 *     Decoder stream overflow.
 */
NGHTTP3_EXTERN int
nghttp3_qpack_decoder_cancel_stream(nghttp3_qpack_decoder *decoder,
                                    int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_qpack_decoder_set_max_dtable_capacity` sets
 * |max_dtable_capacity| as maximum dynamic table size.
 * |max_dtable_capacity| must be equal to, or smaller than
 * ``hard_max_dtable_capacity`` parameter of
 * `nghttp3_qpack_decoder_new`.  Normally, the maximum capacity is
 * communicated in encoder stream.  This function is provided for
 * debugging and testing purpose.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_INVALID_ARGUMENT`
 *     |max_dtable_capacity| exceeds the upper bound of the dynamic
 *     table capacity.
 */
NGHTTP3_EXTERN int
nghttp3_qpack_decoder_set_max_dtable_capacity(nghttp3_qpack_decoder *decoder,
                                              size_t max_dtable_capacity);

/**
 * @function
 *
 * `nghttp3_qpack_decoder_set_max_concurrent_streams` tells |decoder|
 * the maximum number of concurrent streams that a remote endpoint can
 * open, including both bidirectional and unidirectional streams which
 * potentially receive QPACK encoded HEADERS frame.  This value is
 * used as a hint to limit the length of decoder stream.
 */
NGHTTP3_EXTERN void
nghttp3_qpack_decoder_set_max_concurrent_streams(nghttp3_qpack_decoder *decoder,
                                                 size_t max_concurrent_streams);

/**
 * @function
 *
 * `nghttp3_strerror` returns textual representation of |liberr|.
 */
NGHTTP3_EXTERN const char *nghttp3_strerror(int liberr);

/**
 * @function
 *
 * `nghttp3_err_infer_quic_app_error_code` returns a QUIC application
 * error code which corresponds to |liberr|.
 */
NGHTTP3_EXTERN uint64_t nghttp3_err_infer_quic_app_error_code(int liberr);

/**
 * @functypedef
 *
 * :type:`nghttp3_debug_vprintf_callback` is a callback function
 * invoked when the library outputs debug logging.  The function is
 * called with arguments suitable for :manpage:`vfprintf(3)`.
 *
 * The debug output is only enabled if the library is built with
 * :macro:`DEBUGBUILD` macro defined.
 */
typedef void (*nghttp3_debug_vprintf_callback)(const char *format,
                                               va_list args);

/**
 * @function
 *
 * `nghttp3_set_debug_vprintf_callback` sets a debug output callback
 * called by the library when built with :macro:`DEBUGBUILD` macro
 * defined.  If a callback function is not set by this function, debug
 * log is written into standard error output.
 *
 * For builds without :macro:`DEBUGBUILD` macro defined, this function
 * is noop.
 *
 * Note that building with :macro:`DEBUGBUILD` may cause significant
 * performance penalty to libnghttp3 because of extra processing.  It
 * should be used for debugging purpose only.
 *
 * .. Warning::
 *
 *   Building with :macro:`DEBUGBUILD` may cause significant
 *   performance penalty to libnghttp3 because of extra processing.
 *   It should be used for debugging purpose only.  We write this two
 *   times because this is important.
 */
NGHTTP3_EXTERN void nghttp3_set_debug_vprintf_callback(
  nghttp3_debug_vprintf_callback debug_vprintf_callback);

/**
 * @macrosection
 *
 * Shutdown related constants
 */

/**
 * @macro
 *
 * :macro:`NGHTTP3_SHUTDOWN_NOTICE_STREAM_ID` specifies stream ID sent
 * by a server when it initiates graceful shutdown of the connection
 * via `nghttp3_conn_submit_shutdown_notice`.
 */
#define NGHTTP3_SHUTDOWN_NOTICE_STREAM_ID ((1ull << 62) - 4)

/**
 * @macro
 *
 * :macro:`NGHTTP3_SHUTDOWN_NOTICE_PUSH_ID` specifies push ID sent by
 * a client when it initiates graceful shutdown of the connection via
 * `nghttp3_conn_submit_shutdown_notice`.  Note that libnghttp3 does
 * not implement HTTP/3 Server Push.
 */
#define NGHTTP3_SHUTDOWN_NOTICE_PUSH_ID ((1ull << 62) - 1)

/**
 * @struct
 *
 * :type:`nghttp3_conn` represents a single HTTP/3 connection.  The
 * details of this structure are intentionally hidden from the public
 * API.
 */
typedef struct nghttp3_conn nghttp3_conn;

#define NGHTTP3_SETTINGS_V1 1
#define NGHTTP3_SETTINGS_V2 2
#define NGHTTP3_SETTINGS_V3 3
#define NGHTTP3_SETTINGS_VERSION NGHTTP3_SETTINGS_V3

/**
 * @struct
 *
 * :type:`nghttp3_settings` defines HTTP/3 settings.
 */
typedef struct nghttp3_settings {
  /**
   * :member:`max_field_section_size` specifies the maximum header
   * section (block) size.
   */
  uint64_t max_field_section_size;
  /**
   * :member:`qpack_max_dtable_capacity` is the maximum size of QPACK
   * dynamic table.
   */
  size_t qpack_max_dtable_capacity;
  /**
   * :member:`qpack_encoder_max_dtable_capacity` is the upper bound of
   * QPACK dynamic table capacity that the QPACK encoder is willing to
   * use.  The effective maximum dynamic table capacity is the minimum
   * of this field and the value of the received
   * SETTINGS_QPACK_MAX_TABLE_CAPACITY.  If this field is set to 0,
   * the encoder does not use the dynamic table.
   *
   * When :type:`nghttp3_settings` is passed to
   * :member:`nghttp3_callbacks.recv_settings` callback, this field
   * should be ignored.
   */
  size_t qpack_encoder_max_dtable_capacity;
  /**
   * :member:`qpack_blocked_streams` is the maximum number of streams
   * which can be blocked while they are being decoded.
   */
  size_t qpack_blocked_streams;
  /**
   * :member:`enable_connect_protocol`, if set to nonzero, enables
   * Extended CONNECT Method (see :rfc:`9220`).  Client ignores this
   * field.
   */
  uint8_t enable_connect_protocol;
  /**
   * :member:`h3_datagram`, if set to nonzero, enables HTTP/3
   * Datagrams (see :rfc:`9297`).
   */
  uint8_t h3_datagram;
  /* The following fields have been added since NGHTTP3_SETTINGS_V2. */
  /**
   * :member:`origin_list`, if set, must contain a serialized HTTP/3
   * ORIGIN frame (see :rfc:`9412`) payload.  The ORIGIN frame payload
   * is a sequence of zero or more of a length prefixed byte string.
   * The length is encoded in 2 bytes in network byte order.  If
   * :member:`origin_list->len <nghttp3_vec.len>` is zero, an empty
   * ORIGIN frame is sent.  An application must keep the buffer
   * pointed by :member:`origin_list->base <nghttp3_vec.base>` alive
   * until the :type:`nghttp3_conn` to which this field was passed is
   * freed by `nghttp3_conn_del`.  The object pointed to by this field
   * is copied internally, and does not need to be kept alive.  Only
   * server uses this field.  This field is available since v1.11.0.
   */
  const nghttp3_vec *origin_list;
  /* The following fields have been added since NGHTTP3_SETTINGS_V3. */
  /**
   * :member:`glitch_ratelim_burst` is the maximum number of tokens
   * available to "glitch" rate limiter.  "glitch" is a suspicious
   * activity from a remote endpoint.  If detected, certain amount of
   * tokens are consumed.  If no tokens are available to consume, the
   * connection is closed.  The rate of token generation is specified
   * by :member:`glitch_ratelim_rate`.  This feature is enabled only
   * when `nghttp3_conn_read_stream2` is used.  This field has been
   * available since v1.12.0.
   */
  uint64_t glitch_ratelim_burst;
  /**
   * :member:`glitch_ratelim_rate` is the number of tokens generated
   * per second.  See :member:`glitch_ratelim_burst` for "glitch" rate
   * limiter.  This field has been available since v1.12.0.
   */
  uint64_t glitch_ratelim_rate;
} nghttp3_settings;

/**
 * @functypedef
 *
 * :type:`nghttp3_acked_stream_data` is a callback function which is
 * invoked when data sent on stream denoted by |stream_id| supplied
 * from application is acknowledged by remote endpoint.  The number of
 * bytes acknowledged is given in |datalen|.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_acked_stream_data)(nghttp3_conn *conn, int64_t stream_id,
                                         uint64_t datalen, void *conn_user_data,
                                         void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_conn_stream_close` is a callback function which is
 * invoked when a stream identified by |stream_id| is closed.  QUIC
 * application error code |app_error_code| indicates the reason of
 * this closure.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_stream_close)(nghttp3_conn *conn, int64_t stream_id,
                                    uint64_t app_error_code,
                                    void *conn_user_data,
                                    void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_recv_data` is a callback function which is invoked
 * when a part of request or response body on stream identified by
 * |stream_id| is received.  |data| points to the received data, and
 * its length is |datalen|.
 *
 * The application is responsible for increasing flow control credit
 * (say, increasing by |datalen| bytes).
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_recv_data)(nghttp3_conn *conn, int64_t stream_id,
                                 const uint8_t *data, size_t datalen,
                                 void *conn_user_data, void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_deferred_consume` is a callback function which is
 * invoked when the library consumed |consumed| bytes for a stream
 * identified by |stream_id|.  This callback is used to notify the
 * consumed bytes for stream blocked due to synchronization between
 * streams.  The application is responsible for increasing flow
 * control credit by |consumed| bytes.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_deferred_consume)(nghttp3_conn *conn, int64_t stream_id,
                                        size_t consumed, void *conn_user_data,
                                        void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_begin_headers` is a callback function which is
 * invoked when an incoming HTTP field section is started on a stream
 * denoted by |stream_id|.  Each HTTP field is passed to application
 * by :type:`nghttp3_recv_header` callback.  And then
 * :type:`nghttp3_end_headers` is called when a whole HTTP field
 * section is processed.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_begin_headers)(nghttp3_conn *conn, int64_t stream_id,
                                     void *conn_user_data,
                                     void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_recv_header` is a callback function which is invoked
 * when an HTTP field is received on a stream denoted by |stream_id|.
 * |name| contains a field name, and |value| contains a field value.
 * |token| is one of token defined in :type:`nghttp3_qpack_token` or
 * -1 if no token is defined for |name|.  |flags| is bitwise OR of
 * zero or more of :macro:`NGHTTP3_NV_FLAG_* <NGHTTP3_NV_FLAG_NONE>`.
 *
 * The buffers for |name| and |value| are reference counted. If
 * application needs to keep them, increment the reference count with
 * `nghttp3_rcbuf_incref`.  When they are no longer used, call
 * `nghttp3_rcbuf_decref`.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_recv_header)(nghttp3_conn *conn, int64_t stream_id,
                                   int32_t token, nghttp3_rcbuf *name,
                                   nghttp3_rcbuf *value, uint8_t flags,
                                   void *conn_user_data,
                                   void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_end_headers` is a callback function which is invoked
 * when an incoming HTTP field section has ended.
 *
 * If the stream ends with this HTTP field section, |fin| is set to
 * nonzero.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_end_headers)(nghttp3_conn *conn, int64_t stream_id,
                                   int fin, void *conn_user_data,
                                   void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_end_stream` is a callback function which is invoked
 * when the receiving side of stream is closed.  For server, this
 * callback function is invoked when HTTP request is received
 * completely.  For client, this callback function is invoked when
 * HTTP response is received completely.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_end_stream)(nghttp3_conn *conn, int64_t stream_id,
                                  void *conn_user_data, void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_stop_sending` is a callback function which is
 * invoked when the library asks application to send STOP_SENDING to
 * the stream identified by |stream_id|.  QUIC application error code
 * |app_error_code| indicates the reason for this action.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_stop_sending)(nghttp3_conn *conn, int64_t stream_id,
                                    uint64_t app_error_code,
                                    void *conn_user_data,
                                    void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_reset_stream` is a callback function which is
 * invoked when the library asks application to reset stream
 * identified by |stream_id|.  QUIC application error code
 * |app_error_code| indicates the reason for this action.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_reset_stream)(nghttp3_conn *conn, int64_t stream_id,
                                    uint64_t app_error_code,
                                    void *conn_user_data,
                                    void *stream_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_shutdown` is a callback function which is invoked
 * when a shutdown is initiated by the remote endpoint. For client,
 * |id| contains a stream ID of a client initiated stream, for server,
 * it contains a push ID. All client streams with stream ID, or pushes
 * with push ID equal to, or larger than |ID| are guaranteed to not be
 * processed by the remote endpoint.  Note that libnghttp3 does not
 * implement Server Push.
 *
 * Parameter |id| for client can contain a special value
 * :macro:`NGHTTP3_SHUTDOWN_NOTICE_STREAM_ID`, and for server it can
 * contain special value
 * :macro:`NGHTTP3_SHUTDOWN_NOTICE_PUSH_ID`. These values signal
 * request for graceful shutdown of the connection, triggered by
 * remote endpoint's invocation of
 * `nghttp3_conn_submit_shutdown_notice`.
 *
 * It is possible that this callback is invoked multiple times on a
 * single connection, however the |id| can only stay the same or
 * decrease, never increase.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_shutdown)(nghttp3_conn *conn, int64_t id,
                                void *conn_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_recv_settings` is a callback function which is
 * invoked when SETTINGS frame is received.  |settings| is a received
 * remote HTTP/3 settings.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_recv_settings)(nghttp3_conn *conn,
                                     const nghttp3_settings *settings,
                                     void *conn_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_recv_origin` is a callback function which is invoked
 * when a single origin in ORIGIN frame is received.  |origin| is a
 * received origin of length |originlen|.  |originlen| never be 0.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_recv_origin)(nghttp3_conn *conn, const uint8_t *origin,
                                   size_t originlen, void *conn_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_end_origin` is a callback function which is invoked
 * when an ORIGIN frame has been completely processed.
 *
 * The implementation of this callback must return 0 if it succeeds.
 * Returning :macro:`NGHTTP3_ERR_CALLBACK_FAILURE` will return to the
 * caller immediately.  Any values other than 0 is treated as
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 */
typedef int (*nghttp3_end_origin)(nghttp3_conn *conn, void *conn_user_data);

/**
 * @functypedef
 *
 * :type:`nghttp3_rand` is a callback function which is invoked when
 * unpredictable data of |destlen| bytes are needed.  The
 * implementation must write unpredictable data of |destlen| bytes
 * into the buffer pointed by |dest|.
 */
typedef void (*nghttp3_rand)(uint8_t *dest, size_t destlen);

#define NGHTTP3_CALLBACKS_V1 1
#define NGHTTP3_CALLBACKS_V2 2
#define NGHTTP3_CALLBACKS_VERSION NGHTTP3_CALLBACKS_V2

/**
 * @struct
 *
 * :type:`nghttp3_callbacks` holds a set of callback functions.
 */
typedef struct nghttp3_callbacks {
  /**
   * :member:`acked_stream_data` is a callback function which is
   * invoked when data sent on a particular stream have been
   * acknowledged by a remote endpoint.
   */
  nghttp3_acked_stream_data acked_stream_data;
  /**
   * :member:`stream_close` is a callback function which is invoked
   * when a particular stream has closed.
   */
  nghttp3_stream_close stream_close;
  /**
   * :member:`recv_data` is a callback function which is invoked when
   * stream data is received.
   */
  nghttp3_recv_data recv_data;
  /**
   * :member:`deferred_consume` is a callback function which is
   * invoked when the library consumed data for a particular stream
   * which had been blocked for synchronization between streams.
   */
  nghttp3_deferred_consume deferred_consume;
  /**
   * :member:`begin_headers` is a callback function which is invoked
   * when an HTTP header field section has started on a particular
   * stream.
   */
  nghttp3_begin_headers begin_headers;
  /**
   * :member:`recv_header` is a callback function which is invoked
   * when a single HTTP header field is received on a particular
   * stream.
   */
  nghttp3_recv_header recv_header;
  /**
   * :member:`end_headers` is a callback function which is invoked
   * when an HTTP header field section has ended on a particular
   * stream.
   */
  nghttp3_end_headers end_headers;
  /**
   * :member:`begin_trailers` is a callback function which is invoked
   * when an HTTP trailer field section has started on a particular
   * stream.
   */
  nghttp3_begin_headers begin_trailers;
  /**
   * :member:`recv_trailer` is a callback function which is invoked
   * when a single HTTP trailer field is received on a particular
   * stream.
   */
  nghttp3_recv_header recv_trailer;
  /**
   * :member:`end_trailers` is a callback function which is invoked
   * when an HTTP trailer field section has ended on a particular
   * stream.
   */
  nghttp3_end_headers end_trailers;
  /**
   * :member:`stop_sending` is a callback function which is invoked
   * when the library asks application to send STOP_SENDING to a
   * particular stream.
   */
  nghttp3_stop_sending stop_sending;
  /**
   * :member:`end_stream` is a callback function which is invoked when
   * a receiving side of stream has been closed.
   */
  nghttp3_end_stream end_stream;
  /**
   * :member:`reset_stream` is a callback function which is invoked
   * when the library asks application to reset stream (by sending
   * RESET_STREAM).
   */
  nghttp3_reset_stream reset_stream;
  /**
   * :member:`shutdown` is a callback function which is invoked when
   * the remote endpoint has signalled initiation of connection
   * shutdown.
   */
  nghttp3_shutdown shutdown;
  /**
   * :member:`recv_settings` is a callback function which is invoked
   * when SETTINGS frame is received.
   */
  nghttp3_recv_settings recv_settings;
  /* The following fields have been added since NGHTTP3_CALLBACKS_V2. */
  /**
   * :member:`recv_origin` is a callback function which is invoked
   * when a single origin in an ORIGIN frame is received.  This field
   * is available since v1.11.0.
   */
  nghttp3_recv_origin recv_origin;
  /**
   * :member:`end_origin` is a callback function which is invoked when
   * an ORIGIN frame has been completely processed.  This field is
   * available since v1.11.0.
   */
  nghttp3_end_origin end_origin;
  /**
   * :member:`rand` is a callback function which is invoked when
   * unpredictable data are needed.  Although this field is optional
   * due to the backward compatibility, it is recommended to specify
   * this field to harden the runtime behavior against suspicious
   * activities of a remote endpoint.  This field is available since
   * v1.11.0.
   */
  nghttp3_rand rand;
} nghttp3_callbacks;

/**
 * @function
 *
 * `nghttp3_settings_default` fills |settings| with the default
 * values.
 *
 * - :member:`max_field_section_size
 *   <nghttp3_settings.max_field_section_size>` = :expr:`((1ull << 62) - 1)`
 * - :member:`qpack_max_dtable_capacity
 *   <nghttp3_settings.qpack_max_dtable_capacity>` = 0
 * - :member:`qpack_encoder_max_dtable_capacity
 *   <nghttp3_settings.qpack_encoder_max_dtable_capacity>` = 4096
 * - :member:`qpack_blocked_streams
 *   <nghttp3_settings.qpack_blocked_streams>` = 0
 * - :member:`enable_connect_protocol
 *   <nghttp3_settings.enable_connect_protocol>` = 0
 * - :member:`glitch_ratelim_burst
 *   <nghttp3_settings.glitch_ratelim_burst>` = 1000
 * - :member:`glitch_ratelim_rate
 *   <nghttp3_settings.glitch_ratelim_rate>` = 33
 */
NGHTTP3_EXTERN void
nghttp3_settings_default_versioned(int settings_version,
                                   nghttp3_settings *settings);

/**
 * @function
 *
 * `nghttp3_conn_client_new` creates :type:`nghttp3_conn`, and
 * initializes it for client use.  The pointer to the object is stored
 * in |*pconn|.  If |mem| is ``NULL``, the memory allocator returned
 * by `nghttp3_mem_default` is used.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int
nghttp3_conn_client_new_versioned(nghttp3_conn **pconn, int callbacks_version,
                                  const nghttp3_callbacks *callbacks,
                                  int settings_version,
                                  const nghttp3_settings *settings,
                                  const nghttp3_mem *mem, void *conn_user_data);

/**
 * @function
 *
 * `nghttp3_conn_server_new` creates :type:`nghttp3_conn`, and
 * initializes it for server use.  The pointer to the object is stored
 * in |*pconn|.  If |mem| is ``NULL``, the memory allocator returned
 * by `nghttp3_mem_default` is used.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int
nghttp3_conn_server_new_versioned(nghttp3_conn **pconn, int callbacks_version,
                                  const nghttp3_callbacks *callbacks,
                                  int settings_version,
                                  const nghttp3_settings *settings,
                                  const nghttp3_mem *mem, void *conn_user_data);

/**
 * @function
 *
 * `nghttp3_conn_del` frees resources allocated for |conn|.  This
 * function also frees memory pointed by |conn| itself.  This function
 * does nothing if |conn| is NULL.
 */
NGHTTP3_EXTERN void nghttp3_conn_del(nghttp3_conn *conn);

/**
 * @function
 *
 * `nghttp3_conn_bind_control_stream` binds stream denoted by
 * |stream_id| to outgoing unidirectional control stream.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_INVALID_STATE`
 *     Control stream has already corresponding stream ID.
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_bind_control_stream(nghttp3_conn *conn,
                                                    int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_conn_bind_qpack_streams` binds stream denoted by
 * |qenc_stream_id| to outgoing QPACK encoder stream, and stream
 * denoted by |qdec_stream_id| to outgoing QPACK encoder stream.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_INVALID_STATE`
 *     QPACK encoder/decoder stream have already corresponding stream
 *     IDs.
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_bind_qpack_streams(nghttp3_conn *conn,
                                                   int64_t qenc_stream_id,
                                                   int64_t qdec_stream_id);

/**
 * @function
 *
 * .. warning::
 *
 *   Deprecated since v1.12.0.  Use `nghttp3_conn_read_stream2`
 *   instead.
 *
 * `nghttp3_conn_read_stream` reads data |src| of length |srclen| on
 * stream identified by |stream_id|.  It returns the number of bytes
 * consumed.  The "consumed" means that application can increase flow
 * control credit (both stream and connection) of underlying QUIC
 * connection by that amount.  It does not include the amount of data
 * carried by DATA frame which contains application data (excluding
 * any control or QPACK unidirectional streams).  See
 * :type:`nghttp3_recv_data` to handle those bytes.  If |fin| is
 * nonzero, this is the last data from remote endpoint in this stream.
 *
 * This function returns the number of bytes consumed, or one of the
 * following negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`
 *     User callback failed.
 *
 * It may return the other error codes.  The negative error code means
 * that |conn| encountered a connection error, and the connection must
 * be closed.  Calling nghttp3 API other than `nghttp3_conn_del`
 * causes undefined behavior.
 */
NGHTTP3_EXTERN nghttp3_ssize nghttp3_conn_read_stream(nghttp3_conn *conn,
                                                      int64_t stream_id,
                                                      const uint8_t *src,
                                                      size_t srclen, int fin);

/**
 * @function
 *
 * `nghttp3_conn_read_stream2` reads data |src| of length |srclen| on
 * stream identified by |stream_id|.  It returns the number of bytes
 * consumed.  The "consumed" means that application can increase flow
 * control credit (both stream and connection) of underlying QUIC
 * connection by that amount.  It does not include the amount of data
 * carried by DATA frame which contains application data (excluding
 * any control or QPACK unidirectional streams).  See
 * :type:`nghttp3_recv_data` to handle those bytes.  If |fin| is
 * nonzero, this is the last data from remote endpoint in this stream.
 * |ts| is the current timestamp, and must be non-decreasing.  It
 * should be obtained from the clock that is steadily increasing.
 *
 * This function returns the number of bytes consumed, or one of the
 * following negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`
 *     User callback failed.
 *
 * It may return the other error codes.  The negative error code means
 * that |conn| encountered a connection error, and the connection must
 * be closed.  Calling nghttp3 API other than `nghttp3_conn_del`
 * causes undefined behavior.
 *
 * This function is available since v1.12.0.
 */
NGHTTP3_EXTERN nghttp3_ssize nghttp3_conn_read_stream2(nghttp3_conn *conn,
                                                       int64_t stream_id,
                                                       const uint8_t *src,
                                                       size_t srclen, int fin,
                                                       nghttp3_tstamp ts);

/**
 * @function
 *
 * `nghttp3_conn_writev_stream` stores stream data to send to |vec| of
 * length |veccnt|, and returns the number of nghttp3_vec object in
 * which it stored data.  It stores stream ID to |*pstream_id|.  An
 * application has to call `nghttp3_conn_add_write_offset` to inform
 * |conn| of the actual number of bytes that underlying QUIC stack
 * accepted.  |*pfin| will be nonzero if this is the last data to
 * send.  If there is no stream to write data or send fin, this
 * function returns 0, and -1 is assigned to |*pstream_id|.  This
 * function may return 0, and |*pstream_id| is not -1, and |*pfin| is
 * nonzero.  It means 0 length data to |*pstream_id|, and it is the
 * last data to the stream.  They must be passed to QUIC stack, and
 * they are accepted, the application has to call
 * `nghttp3_conn_add_write_offset` with 0 byte.
 *
 * This function returns the number of bytes consumed, or one of the
 * following negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`
 *     User callback failed.
 *
 * It may return the other error codes.  The negative error code means
 * that |conn| encountered a connection error, and the connection must
 * be closed.  Calling nghttp3 API other than `nghttp3_conn_del`
 * causes undefined behavior.
 */
NGHTTP3_EXTERN nghttp3_ssize nghttp3_conn_writev_stream(nghttp3_conn *conn,
                                                        int64_t *pstream_id,
                                                        int *pfin,
                                                        nghttp3_vec *vec,
                                                        size_t veccnt);

/**
 * @function
 *
 * `nghttp3_conn_add_write_offset` tells |conn| the number of bytes
 * |n| for stream denoted by |stream_id| QUIC stack accepted.
 *
 * If stream has no data to send but just sends fin (closing the write
 * side of a stream), the number of bytes sent is 0.  It is important
 * to call this function even if |n| is 0 in this case.  It is safe to
 * call this function if |n| is 0.
 *
 * `nghttp3_conn_writev_stream` must be called before calling this
 * function to get data to send, and those data must be fed into QUIC
 * stack.
 *
 * If a stream denoted by |stream_id| is not found, this function
 * returns 0.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_add_write_offset(nghttp3_conn *conn,
                                                 int64_t stream_id, size_t n);

/**
 * @function
 *
 * `nghttp3_conn_add_ack_offset` tells |conn| the number of bytes |n|
 * for stream denoted by |stream_id| QUIC stack has acknowledged.
 *
 * If a stream denoted by |stream_id| is not found, this function
 * returns 0.
 *
 * Alternatively, `nghttp3_conn_update_ack_offset` can be used to
 * accomplish the same thing.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`
 *     User callback failed.
 */
NGHTTP3_EXTERN int nghttp3_conn_add_ack_offset(nghttp3_conn *conn,
                                               int64_t stream_id, uint64_t n);

/**
 * @function
 *
 * `nghttp3_conn_update_ack_offset` tells |conn| that QUIC stack has
 * acknowledged the stream data up to |offset| for a stream denoted by
 * |stream_id|.
 *
 * If a stream denoted by |stream_id| is not found, this function
 * returns 0.
 *
 * Alternatively, `nghttp3_conn_add_ack_offset` can be used to
 * accomplish the same thing.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_INVALID_ARGUMENT`
 *     |offset| is less than the number of bytes acknowledged so far.
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`
 *     User callback failed.
 */
NGHTTP3_EXTERN int nghttp3_conn_update_ack_offset(nghttp3_conn *conn,
                                                  int64_t stream_id,
                                                  uint64_t offset);

/**
 * @function
 *
 * `nghttp3_conn_block_stream` tells the library that stream
 * identified by |stream_id| is blocked due to QUIC flow control.
 */
NGHTTP3_EXTERN void nghttp3_conn_block_stream(nghttp3_conn *conn,
                                              int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_conn_unblock_stream` tells the library that stream
 * identified by |stream_id| which was blocked by QUIC flow control
 * (see `nghttp3_conn_block_stream`) is unblocked.
 *
 * If a stream denoted by |stream_id| is not found, this function
 * returns 0.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_unblock_stream(nghttp3_conn *conn,
                                               int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_conn_is_stream_writable` returns nonzero if a stream
 * identified by |stream_id| is writable.  It is not writable if:
 *
 * - the stream does not exist; or,
 * - the stream is closed (e.g., `nghttp3_conn_close_stream` is
 *   called); or,
 * - the stream is QUIC flow control blocked (e.g.,
 *   `nghttp3_conn_block_stream` is called); or,
 * - the stream is input data blocked (e.g.,
 *   :macro:`NGHTTP3_ERR_WOULDBLOCK` is returned from
 *   :type:`nghttp3_read_data_callback`); or,
 * - the stream is half-closed local (e.g.,
 *   `nghttp3_conn_shutdown_stream_write` is called).
 */
NGHTTP3_EXTERN int nghttp3_conn_is_stream_writable(nghttp3_conn *conn,
                                                   int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_conn_shutdown_stream_write` tells the library that any
 * further write operation to stream identified by |stream_id| is
 * prohibited.  This works like `nghttp3_conn_block_stream`, but it
 * cannot be unblocked by `nghttp3_conn_unblock_stream`.
 */
NGHTTP3_EXTERN void nghttp3_conn_shutdown_stream_write(nghttp3_conn *conn,
                                                       int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_conn_shutdown_stream_read` tells the library that
 * read-side of stream denoted by |stream_id| is abruptly closed, and
 * any further incoming data and pending stream data should be
 * discarded.
 *
 * If a stream denoted by |stream_id| is not client bidirectional
 * stream, this function returns 0.  If the stream has already
 * shutdown read-side stream, this function returns 0.
 *
 * This function does not fail if a stream denoted by |stream_id| is
 * not found, although it may fail with the other reasons.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 * :macro:`NGHTTP3_ERR_QPACK_FATAL`
 *     QPACK decoder stream overflow.
 */
NGHTTP3_EXTERN int nghttp3_conn_shutdown_stream_read(nghttp3_conn *conn,
                                                     int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_conn_resume_stream` resumes stream identified by
 * |stream_id| which was previously unable to provide data.  See
 * :type:`nghttp3_read_data_callback`.
 *
 * If a stream denoted by |stream_id| is not found, this function
 * returns 0.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_resume_stream(nghttp3_conn *conn,
                                              int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_conn_close_stream` tells the library that a stream
 * identified by |stream_id| has been closed.  QUIC application error
 * code |app_error_code| is the reason of the closure.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_STREAM_NOT_FOUND`
 *     Stream not found.
 * :macro:`NGHTTP3_ERR_H3_CLOSED_CRITICAL_STREAM`
 *     A critical stream is closed.
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`
 *     User callback failed
 */
NGHTTP3_EXTERN int nghttp3_conn_close_stream(nghttp3_conn *conn,
                                             int64_t stream_id,
                                             uint64_t app_error_code);

/**
 * @macrosection
 *
 * Data flags
 */

/**
 * @macro
 *
 * :macro:`NGHTTP3_DATA_FLAG_NONE` indicates no flag set.
 */
#define NGHTTP3_DATA_FLAG_NONE 0x00u

/**
 * @macro
 *
 * :macro:`NGHTTP3_DATA_FLAG_EOF` indicates that all request or
 * response body has been provided to the library.  It also indicates
 * that sending side of stream is closed unless
 * :macro:`NGHTTP3_DATA_FLAG_NO_END_STREAM` is given at the same time.
 */
#define NGHTTP3_DATA_FLAG_EOF 0x01u

/**
 * @macro
 *
 * :macro:`NGHTTP3_DATA_FLAG_NO_END_STREAM` indicates that sending
 * side of stream is not closed even if :macro:`NGHTTP3_DATA_FLAG_EOF`
 * is set.  Usually this flag is used to send trailer fields with
 * `nghttp3_conn_submit_trailers`.  If `nghttp3_conn_submit_trailers`
 * has been called, regardless of this flag, the submitted trailer
 * fields are sent.
 */
#define NGHTTP3_DATA_FLAG_NO_END_STREAM 0x02u

/**
 * @function
 *
 * `nghttp3_conn_set_max_client_streams_bidi` tells |conn| the
 * cumulative number of bidirectional streams that client can open.
 */
NGHTTP3_EXTERN void
nghttp3_conn_set_max_client_streams_bidi(nghttp3_conn *conn,
                                         uint64_t max_streams);

/**
 * @function
 *
 * `nghttp3_conn_set_max_concurrent_streams` tells |conn| the maximum
 * number of concurrent streams that a remote endpoint can open,
 * including both bidirectional and unidirectional streams which
 * potentially receive QPACK encoded HEADERS frame.  This value is
 * used as a hint to limit the internal resource consumption.
 */
NGHTTP3_EXTERN void
nghttp3_conn_set_max_concurrent_streams(nghttp3_conn *conn,
                                        size_t max_concurrent_streams);

/**
 * @functypedef
 *
 * :type:`nghttp3_read_data_callback` is a callback function invoked
 * when the library asks an application to provide stream data for a
 * stream denoted by |stream_id|.
 *
 * The library provides |vec| of length |veccnt| to the application.
 * The application should fill data and its length to |vec|.  It has
 * to return the number of the filled objects.  The application must
 * retain data until they are safe to free.  It is notified by
 * :type:`nghttp3_acked_stream_data` callback.
 *
 * If this is the last data to send (or there is no data to send
 * because all data have been sent already), set
 * :macro:`NGHTTP3_DATA_FLAG_EOF` to |*pflags|.
 *
 * If the application is unable to provide data temporarily, return
 * :macro:`NGHTTP3_ERR_WOULDBLOCK`.  When it is ready to provide data,
 * call `nghttp3_conn_resume_stream`.
 *
 * The callback should return the number of objects in |vec| that the
 * application filled if it succeeds, or
 * :macro:`NGHTTP3_ERR_CALLBACK_FAILURE`.
 *
 * TODO Add NGHTTP3_ERR_TEMPORAL_CALLBACK_FAILURE to reset just this
 * stream.
 */
typedef nghttp3_ssize (*nghttp3_read_data_callback)(
  nghttp3_conn *conn, int64_t stream_id, nghttp3_vec *vec, size_t veccnt,
  uint32_t *pflags, void *conn_user_data, void *stream_user_data);

/**
 * @struct
 *
 * :type:`nghttp3_data_reader` specifies the way how to generate
 * request or response body.
 */
typedef struct nghttp3_data_reader {
  /**
   * :member:`read_data` is a callback function to generate body.
   */
  nghttp3_read_data_callback read_data;
} nghttp3_data_reader;

/**
 * @function
 *
 * `nghttp3_conn_submit_request` submits HTTP request header fields
 * and body on the stream identified by |stream_id|.  |stream_id| must
 * be a client initiated bidirectional stream.  Only client can submit
 * HTTP request.  |nva| of length |nvlen| specifies HTTP request
 * header fields.  |dr| specifies a request body.  If there is no
 * request body, specify NULL.  If |dr| is NULL, it implies the end of
 * stream.  |stream_user_data| is an opaque pointer attached to the
 * stream.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_CONN_CLOSING`
 *     Connection is shutting down, and no new stream is allowed.
 * :macro:`NGHTTP3_ERR_STREAM_IN_USE`
 *     Stream has already been opened.
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_submit_request(
  nghttp3_conn *conn, int64_t stream_id, const nghttp3_nv *nva, size_t nvlen,
  const nghttp3_data_reader *dr, void *stream_user_data);

/**
 * @function
 *
 * `nghttp3_conn_submit_info` submits HTTP non-final response header
 * fields on the stream identified by |stream_id|.  |nva| of length
 * |nvlen| specifies HTTP response header fields.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_STREAM_NOT_FOUND`
 *     Stream not found
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_submit_info(nghttp3_conn *conn,
                                            int64_t stream_id,
                                            const nghttp3_nv *nva,
                                            size_t nvlen);

/**
 * @function
 *
 * `nghttp3_conn_submit_response` submits HTTP response header fields
 * and body on the stream identified by |stream_id|.  |nva| of length
 * |nvlen| specifies HTTP response header fields.  |dr| specifies a
 * response body.  If there is no response body, specify NULL.  If
 * |dr| is NULL, it implies the end of stream.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_STREAM_NOT_FOUND`
 *     Stream not found
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_submit_response(nghttp3_conn *conn,
                                                int64_t stream_id,
                                                const nghttp3_nv *nva,
                                                size_t nvlen,
                                                const nghttp3_data_reader *dr);

/**
 * @function
 *
 * `nghttp3_conn_submit_trailers` submits HTTP trailer fields on the
 * stream identified by |stream_id|.  |nva| of length |nvlen|
 * specifies HTTP trailer fields.  Calling this function implies the
 * end of stream.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_STREAM_NOT_FOUND`
 *     Stream not found
 * :macro:`NGHTTP3_ERR_INVALID_STATE`
 *     Application has already submitted fin to stream.
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_submit_trailers(nghttp3_conn *conn,
                                                int64_t stream_id,
                                                const nghttp3_nv *nva,
                                                size_t nvlen);

/**
 * @function
 *
 * `nghttp3_conn_submit_shutdown_notice` notifies the other endpoint
 * to stop creating new stream.  After a couple of RTTs later, call
 * `nghttp3_conn_shutdown` to start graceful shutdown.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_submit_shutdown_notice(nghttp3_conn *conn);

/**
 * @function
 *
 * `nghttp3_conn_shutdown` starts graceful shutdown.  It should be
 * called after `nghttp3_conn_submit_shutdown_notice` and a couple of
 * RTTs.  After calling this function, the local endpoint starts
 * rejecting new incoming streams.  The existing streams are processed
 * normally.  See also `nghttp3_conn_is_drained`.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_shutdown(nghttp3_conn *conn);

/**
 * @function
 *
 * `nghttp3_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:`NGHTTP3_ERR_STREAM_NOT_FOUND`
 *     Stream not found.
 */
NGHTTP3_EXTERN int nghttp3_conn_set_stream_user_data(nghttp3_conn *conn,
                                                     int64_t stream_id,
                                                     void *stream_user_data);

/**
 * @function
 *
 * `nghttp3_conn_get_frame_payload_left` returns the number of bytes
 * left to read current frame payload for a stream denoted by
 * |stream_id|.  If no such stream is found, or |stream_id| identifies
 * neither client bidirectional stream nor remote control stream, it
 * returns 0.
 */
NGHTTP3_EXTERN uint64_t nghttp3_conn_get_frame_payload_left(nghttp3_conn *conn,
                                                            int64_t stream_id);

/**
 * @macrosection
 *
 * HTTP stream priority flags
 */

/**
 * @macro
 *
 * :macro:`NGHTTP3_DEFAULT_URGENCY` is the default urgency level.
 */
#define NGHTTP3_DEFAULT_URGENCY 3

/**
 * @macro
 *
 * :macro:`NGHTTP3_URGENCY_HIGH` is the highest urgency level.
 */
#define NGHTTP3_URGENCY_HIGH 0

/**
 * @macro
 *
 * :macro:`NGHTTP3_URGENCY_LOW` is the lowest urgency level.
 */
#define NGHTTP3_URGENCY_LOW 7

/**
 * @macro
 *
 * :macro:`NGHTTP3_URGENCY_LEVELS` is the number of urgency levels.
 */
#define NGHTTP3_URGENCY_LEVELS (NGHTTP3_URGENCY_LOW + 1)

#define NGHTTP3_PRI_V1 1
#define NGHTTP3_PRI_VERSION NGHTTP3_PRI_V1

/**
 * @struct
 *
 * :type:`nghttp3_pri` represents HTTP priority.
 */
typedef struct NGHTTP3_ALIGN(8) nghttp3_pri {
  /**
   * :member:`urgency` is the urgency of a stream, it must be in
   * [:macro:`NGHTTP3_URGENCY_HIGH`, :macro:`NGHTTP3_URGENCY_LOW`],
   * inclusive, and 0 is the highest urgency.
   */
  uint32_t urgency;
  /**
   * :member:`inc` indicates that a content can be processed
   * incrementally or not.  If it is 0, it cannot be processed
   * incrementally.  If it is 1, it can be processed incrementally.
   * Other value is not permitted.
   */
  uint8_t inc;
} nghttp3_pri;

/**
 * @function
 *
 * `nghttp3_conn_get_stream_priority` stores stream priority of a
 * stream denoted by |stream_id| into |*dest|.  |stream_id| must
 * identify client initiated bidirectional stream.  Only server can
 * use this function.
 *
 * This function must not be called if |conn| is initialized as
 * client.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_INVALID_ARGUMENT`
 *     |stream_id| is not a client initiated bidirectional stream ID.
 * :macro:`NGHTTP3_ERR_STREAM_NOT_FOUND`
 *     Stream not found.
 */
NGHTTP3_EXTERN int nghttp3_conn_get_stream_priority_versioned(
  nghttp3_conn *conn, int pri_version, nghttp3_pri *dest, int64_t stream_id);

/**
 * @function
 *
 * `nghttp3_conn_set_client_stream_priority` updates priority of a
 * stream denoted by |stream_id| with the value pointed by |data| of
 * length |datalen|, which should be a serialized :rfc:`9218` priority
 * field value.  |stream_id| must identify client initiated
 * bidirectional stream.
 *
 * This function must not be called if |conn| is initialized as
 * server.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_INVALID_ARGUMENT`
 *     |stream_id| is not a client initiated bidirectional stream ID.
 * :macro:`NGHTTP3_ERR_STREAM_NOT_FOUND`
 *     Stream not found.
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_set_client_stream_priority(nghttp3_conn *conn,
                                                           int64_t stream_id,
                                                           const uint8_t *data,
                                                           size_t datalen);

/**
 * @function
 *
 * `nghttp3_conn_set_server_stream_priority` updates priority of a
 * stream denoted by |stream_id| with the value pointed by |pri|.
 * |stream_id| must identify client initiated bidirectional stream.
 *
 * This function must not be called if |conn| is initialized as
 * client.
 *
 * This function completely overrides stream priority set by client,
 * and any attempts to update priority by client are ignored.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_INVALID_ARGUMENT`
 *     |stream_id| is not a client initiated bidirectional stream ID.
 * :macro:`NGHTTP3_ERR_STREAM_NOT_FOUND`
 *     Stream not found.
 * :macro:`NGHTTP3_ERR_NOMEM`
 *     Out of memory.
 */
NGHTTP3_EXTERN int nghttp3_conn_set_server_stream_priority_versioned(
  nghttp3_conn *conn, int64_t stream_id, int pri_version,
  const nghttp3_pri *pri);

/**
 * @function
 *
 * `nghttp3_vec_len` returns the sum of length in |vec| of |cnt|
 * elements.
 */
NGHTTP3_EXTERN uint64_t nghttp3_vec_len(const nghttp3_vec *vec, size_t cnt);

/**
 * @function
 *
 * `nghttp3_check_header_name` returns nonzero if HTTP field name
 * |name| of length |len| is valid according to
 * :rfc:`7230#section-3.2`.
 *
 * Because this is an HTTP field name in HTTP/3, the upper cased
 * alphabet is treated as error.
 */
NGHTTP3_EXTERN int nghttp3_check_header_name(const uint8_t *name, size_t len);

/**
 * @function
 *
 * `nghttp3_check_header_value` returns nonzero if HTTP field value
 * |value| of length |len| is valid according to
 * :rfc:`7230#section-3.2`.
 */
NGHTTP3_EXTERN int nghttp3_check_header_value(const uint8_t *value, size_t len);

/**
 * @function
 *
 * `nghttp3_conn_is_drained` returns nonzero if
 * `nghttp3_conn_shutdown` has been called, and there is no active
 * remote streams.  This function is for server use only.
 */
NGHTTP3_EXTERN int nghttp3_conn_is_drained(nghttp3_conn *conn);

/**
 * @function
 *
 * `nghttp3_pri_parse_priority` parses Priority header field value
 * pointed by |value| of length |len|, and stores the result in the
 * object pointed by |dest|.  Priority header field is defined in
 * :rfc:`9218`.
 *
 * This function does not initialize the object pointed by |dest|
 * before storing the result.  It only assigns the values that the
 * parser correctly extracted to fields.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * :macro:`NGHTTP3_ERR_INVALID_ARGUMENT`
 *     Failed to parse the header field value.
 */
NGHTTP3_EXTERN int nghttp3_pri_parse_priority_versioned(int pri_version,
                                                        nghttp3_pri *dest,
                                                        const uint8_t *value,
                                                        size_t len);

/**
 * @macrosection
 *
 * nghttp3_info flags
 */

/**
 * @macro
 *
 * :macro:`NGHTTP3_VERSION_AGE` is the age of :type:`nghttp3_info`.
 */
#define NGHTTP3_VERSION_AGE 1

/**
 * @struct
 *
 * :type:`nghttp3_info` is what `nghttp3_version` returns.  It holds
 * information about the particular nghttp3 version.
 */
typedef struct nghttp3_info {
  /**
   * :member:`age` is the age of this struct.  This instance of
   * nghttp3 sets it to :macro:`NGHTTP3_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:`NGHTTP3_VERSION_NUM` number
   * (since age == 1)
   */
  int version_num;
  /**
   * :member:`version_str` points to the :macro:`NGHTTP3_VERSION`
   * string (since age ==1)
   */
  const char *version_str;
  /* -------- the above fields all exist when age == 1 */
} nghttp3_info;

/**
 * @function
 *
 * `nghttp3_version` returns a pointer to a :type:`nghttp3_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.
 */
NGHTTP3_EXTERN const nghttp3_info *nghttp3_version(int least_version);

/**
 * @function
 *
 * `nghttp3_err_is_fatal` returns nonzero if |liberr| is a fatal
 * error.  |liberr| must be one of nghttp3 library error codes (which
 * is defined as NGHTTP3_ERR_* macro, such as
 * :macro:`NGHTTP3_ERR_NOMEM`).
 */
NGHTTP3_EXTERN int nghttp3_err_is_fatal(int liberr);

/*
 * Versioned function wrappers
 */

/*
 * `nghttp3_settings_default` is a wrapper around
 * `nghttp3_settings_default_versioned` to set the correct struct
 * version.
 */
#define nghttp3_settings_default(SETTINGS)                                     \
  nghttp3_settings_default_versioned(NGHTTP3_SETTINGS_VERSION, (SETTINGS))

/*
 * `nghttp3_conn_client_new` is a wrapper around
 * `nghttp3_conn_client_new_versioned` to set the correct struct
 * version.
 */
#define nghttp3_conn_client_new(PCONN, CALLBACKS, SETTINGS, MEM, USER_DATA)    \
  nghttp3_conn_client_new_versioned((PCONN), NGHTTP3_CALLBACKS_VERSION,        \
                                    (CALLBACKS), NGHTTP3_SETTINGS_VERSION,     \
                                    (SETTINGS), (MEM), (USER_DATA))

/*
 * `nghttp3_conn_server_new` is a wrapper around
 * `nghttp3_conn_server_new_versioned` to set the correct struct
 * version.
 */
#define nghttp3_conn_server_new(PCONN, CALLBACKS, SETTINGS, MEM, USER_DATA)    \
  nghttp3_conn_server_new_versioned((PCONN), NGHTTP3_CALLBACKS_VERSION,        \
                                    (CALLBACKS), NGHTTP3_SETTINGS_VERSION,     \
                                    (SETTINGS), (MEM), (USER_DATA))

/*
 * `nghttp3_conn_set_server_stream_priority` is a wrapper around
 * `nghttp3_conn_set_server_stream_priority_versioned` to set the
 * correct struct version.
 */
#define nghttp3_conn_set_server_stream_priority(CONN, STREAM_ID, PRI)          \
  nghttp3_conn_set_server_stream_priority_versioned(                           \
    (CONN), (STREAM_ID), NGHTTP3_PRI_VERSION, (PRI))

/*
 * `nghttp3_conn_get_stream_priority` is a wrapper around
 * `nghttp3_conn_get_stream_priority_versioned` to set the correct
 * struct version.
 */
#define nghttp3_conn_get_stream_priority(CONN, DEST, STREAM_ID)                \
  nghttp3_conn_get_stream_priority_versioned((CONN), NGHTTP3_PRI_VERSION,      \
                                             (DEST), (STREAM_ID))

/*
 * `nghttp3_pri_parse_priority` is a wrapper around
 * `nghttp3_pri_parse_priority_versioned` to set the correct struct
 * version.
 */
#define nghttp3_pri_parse_priority(DEST, VALUE, LEN)                           \
  nghttp3_pri_parse_priority_versioned(NGHTTP3_PRI_VERSION, (DEST), (VALUE),   \
                                       (LEN))

#ifdef __cplusplus
}
#endif /* defined(__cplusplus) */

#endif /* !defined(NGHTTP3_H) */
