Adding upstream version 1.59.0.upstream/1.59.0

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

4 files changed, 6013 insertions, 0 deletions

diff --git a/lib/includes/CMakeLists.txt b/lib/includes/CMakeLists.txt
new file mode 100644
index 0000000..17de2ec
--- /dev/null
+++ b/lib/includes/CMakeLists.txt
@@ -0,0 +1,4 @@
+install(FILES
+    nghttp2/nghttp2.h
+    "${CMAKE_CURRENT_BINARY_DIR}/nghttp2/nghttp2ver.h"
+  DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/nghttp2")
diff --git a/lib/includes/Makefile.am b/lib/includes/Makefile.am
new file mode 100644
index 0000000..c07cb4d
--- /dev/null
+++ b/lib/includes/Makefile.am
@@ -0,0 +1,26 @@
+# nghttp2 - HTTP/2 C Library
+
+# Copyright (c) 2012 Tatsuhiro Tsujikawa
+
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+EXTRA_DIST = CMakeLists.txt
+
+nobase_include_HEADERS = nghttp2/nghttp2.h nghttp2/nghttp2ver.h
diff --git a/lib/includes/nghttp2/nghttp2.h b/lib/includes/nghttp2/nghttp2.h
new file mode 100644
index 0000000..7910db2
--- /dev/null
+++ b/lib/includes/nghttp2/nghttp2.h
@@ -0,0 +1,5941 @@
+/*
+ * nghttp2 - HTTP/2 C Library
+ *
+ * Copyright (c) 2013, 2014 Tatsuhiro Tsujikawa
+ *
+ * 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 NGHTTP2_H
+#define NGHTTP2_H
+
+/* Define WIN32 when build target is Win32 API (borrowed from
+   libcurl) */
+#if (defined(_WIN32) || defined(__WIN32__)) && !defined(WIN32)
+#  define WIN32
+#endif
+
+/* Compatibility for non-Clang compilers */
+#ifndef __has_declspec_attribute
+#  define __has_declspec_attribute(x) 0
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdlib.h>
+#if defined(_MSC_VER) && (_MSC_VER < 1800)
+/* MSVC < 2013 does not have inttypes.h because it is not C99
+   compliant.  See compiler macros and version number in
+   https://sourceforge.net/p/predef/wiki/Compilers/ */
+#  include <stdint.h>
+#else /* !defined(_MSC_VER) || (_MSC_VER >= 1800) */
+#  include <inttypes.h>
+#endif /* !defined(_MSC_VER) || (_MSC_VER >= 1800) */
+#include <sys/types.h>
+#include <stdarg.h>
+
+#include <nghttp2/nghttp2ver.h>
+
+#ifdef NGHTTP2_STATICLIB
+#  define NGHTTP2_EXTERN
+#elif defined(WIN32) || (__has_declspec_attribute(dllexport) &&                \
+                         __has_declspec_attribute(dllimport))
+#  ifdef BUILDING_NGHTTP2
+#    define NGHTTP2_EXTERN __declspec(dllexport)
+#  else /* !BUILDING_NGHTTP2 */
+#    define NGHTTP2_EXTERN __declspec(dllimport)
+#  endif /* !BUILDING_NGHTTP2 */
+#else    /* !defined(WIN32) */
+#  ifdef BUILDING_NGHTTP2
+#    define NGHTTP2_EXTERN __attribute__((visibility("default")))
+#  else /* !BUILDING_NGHTTP2 */
+#    define NGHTTP2_EXTERN
+#  endif /* !BUILDING_NGHTTP2 */
+#endif   /* !defined(WIN32) */
+
+/**
+ * @macro
+ *
+ * The protocol version identification string of this library
+ * supports.  This identifier is used if HTTP/2 is used over TLS.
+ */
+#define NGHTTP2_PROTO_VERSION_ID "h2"
+/**
+ * @macro
+ *
+ * The length of :macro:`NGHTTP2_PROTO_VERSION_ID`.
+ */
+#define NGHTTP2_PROTO_VERSION_ID_LEN 2
+
+/**
+ * @macro
+ *
+ * The serialized form of ALPN protocol identifier this library
+ * supports.  Notice that first byte is the length of following
+ * protocol identifier.  This is the same wire format of `TLS ALPN
+ * extension <https://tools.ietf.org/html/rfc7301>`_.  This is useful
+ * to process incoming ALPN tokens in wire format.
+ */
+#define NGHTTP2_PROTO_ALPN "\x2h2"
+
+/**
+ * @macro
+ *
+ * The length of :macro:`NGHTTP2_PROTO_ALPN`.
+ */
+#define NGHTTP2_PROTO_ALPN_LEN (sizeof(NGHTTP2_PROTO_ALPN) - 1)
+
+/**
+ * @macro
+ *
+ * The protocol version identification string of this library
+ * supports.  This identifier is used if HTTP/2 is used over cleartext
+ * TCP.
+ */
+#define NGHTTP2_CLEARTEXT_PROTO_VERSION_ID "h2c"
+
+/**
+ * @macro
+ *
+ * The length of :macro:`NGHTTP2_CLEARTEXT_PROTO_VERSION_ID`.
+ */
+#define NGHTTP2_CLEARTEXT_PROTO_VERSION_ID_LEN 3
+
+struct nghttp2_session;
+/**
+ * @struct
+ *
+ * The primary structure to hold the resources needed for a HTTP/2
+ * session.  The details of this structure are intentionally hidden
+ * from the public API.
+ */
+typedef struct nghttp2_session nghttp2_session;
+
+/**
+ * @macro
+ *
+ * The age of :type:`nghttp2_info`
+ */
+#define NGHTTP2_VERSION_AGE 1
+
+/**
+ * @struct
+ *
+ * This struct is what `nghttp2_version()` returns.  It holds
+ * information about the particular nghttp2 version.
+ */
+typedef struct {
+  /**
+   * Age of this struct.  This instance of nghttp2 sets it to
+   * :macro:`NGHTTP2_VERSION_AGE` but a future version may bump it and
+   * add more struct fields at the bottom
+   */
+  int age;
+  /**
+   * the :macro:`NGHTTP2_VERSION_NUM` number (since age ==1)
+   */
+  int version_num;
+  /**
+   * points to the :macro:`NGHTTP2_VERSION` string (since age ==1)
+   */
+  const char *version_str;
+  /**
+   * points to the :macro:`NGHTTP2_PROTO_VERSION_ID` string this
+   * instance implements (since age ==1)
+   */
+  const char *proto_str;
+  /* -------- the above fields all exist when age == 1 */
+} nghttp2_info;
+
+/**
+ * @macro
+ *
+ * The default weight of stream dependency.
+ */
+#define NGHTTP2_DEFAULT_WEIGHT 16
+
+/**
+ * @macro
+ *
+ * The maximum weight of stream dependency.
+ */
+#define NGHTTP2_MAX_WEIGHT 256
+
+/**
+ * @macro
+ *
+ * The minimum weight of stream dependency.
+ */
+#define NGHTTP2_MIN_WEIGHT 1
+
+/**
+ * @macro
+ *
+ * The maximum window size
+ */
+#define NGHTTP2_MAX_WINDOW_SIZE ((int32_t)((1U << 31) - 1))
+
+/**
+ * @macro
+ *
+ * The initial window size for stream level flow control.
+ */
+#define NGHTTP2_INITIAL_WINDOW_SIZE ((1 << 16) - 1)
+/**
+ * @macro
+ *
+ * The initial window size for connection level flow control.
+ */
+#define NGHTTP2_INITIAL_CONNECTION_WINDOW_SIZE ((1 << 16) - 1)
+
+/**
+ * @macro
+ *
+ * The default header table size.
+ */
+#define NGHTTP2_DEFAULT_HEADER_TABLE_SIZE (1 << 12)
+
+/**
+ * @macro
+ *
+ * The client magic string, which is the first 24 bytes byte string of
+ * client connection preface.
+ */
+#define NGHTTP2_CLIENT_MAGIC "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"
+
+/**
+ * @macro
+ *
+ * The length of :macro:`NGHTTP2_CLIENT_MAGIC`.
+ */
+#define NGHTTP2_CLIENT_MAGIC_LEN 24
+
+/**
+ * @macro
+ *
+ * The default max number of settings per SETTINGS frame
+ */
+#define NGHTTP2_DEFAULT_MAX_SETTINGS 32
+
+/**
+ * @enum
+ *
+ * Error codes used in this library.  The code range is [-999, -500],
+ * inclusive. The following values are defined:
+ */
+typedef enum {
+  /**
+   * Invalid argument passed.
+   */
+  NGHTTP2_ERR_INVALID_ARGUMENT = -501,
+  /**
+   * Out of buffer space.
+   */
+  NGHTTP2_ERR_BUFFER_ERROR = -502,
+  /**
+   * The specified protocol version is not supported.
+   */
+  NGHTTP2_ERR_UNSUPPORTED_VERSION = -503,
+  /**
+   * Used as a return value from :type:`nghttp2_send_callback`,
+   * :type:`nghttp2_recv_callback` and
+   * :type:`nghttp2_send_data_callback` to indicate that the operation
+   * would block.
+   */
+  NGHTTP2_ERR_WOULDBLOCK = -504,
+  /**
+   * General protocol error
+   */
+  NGHTTP2_ERR_PROTO = -505,
+  /**
+   * The frame is invalid.
+   */
+  NGHTTP2_ERR_INVALID_FRAME = -506,
+  /**
+   * The peer performed a shutdown on the connection.
+   */
+  NGHTTP2_ERR_EOF = -507,
+  /**
+   * Used as a return value from
+   * :func:`nghttp2_data_source_read_callback` to indicate that data
+   * transfer is postponed.  See
+   * :func:`nghttp2_data_source_read_callback` for details.
+   */
+  NGHTTP2_ERR_DEFERRED = -508,
+  /**
+   * Stream ID has reached the maximum value.  Therefore no stream ID
+   * is available.
+   */
+  NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE = -509,
+  /**
+   * The stream is already closed; or the stream ID is invalid.
+   */
+  NGHTTP2_ERR_STREAM_CLOSED = -510,
+  /**
+   * RST_STREAM has been added to the outbound queue.  The stream is
+   * in closing state.
+   */
+  NGHTTP2_ERR_STREAM_CLOSING = -511,
+  /**
+   * The transmission is not allowed for this stream (e.g., a frame
+   * with END_STREAM flag set has already sent).
+   */
+  NGHTTP2_ERR_STREAM_SHUT_WR = -512,
+  /**
+   * The stream ID is invalid.
+   */
+  NGHTTP2_ERR_INVALID_STREAM_ID = -513,
+  /**
+   * The state of the stream is not valid (e.g., DATA cannot be sent
+   * to the stream if response HEADERS has not been sent).
+   */
+  NGHTTP2_ERR_INVALID_STREAM_STATE = -514,
+  /**
+   * Another DATA frame has already been deferred.
+   */
+  NGHTTP2_ERR_DEFERRED_DATA_EXIST = -515,
+  /**
+   * Starting new stream is not allowed (e.g., GOAWAY has been sent
+   * and/or received).
+   */
+  NGHTTP2_ERR_START_STREAM_NOT_ALLOWED = -516,
+  /**
+   * GOAWAY has already been sent.
+   */
+  NGHTTP2_ERR_GOAWAY_ALREADY_SENT = -517,
+  /**
+   * The received frame contains the invalid header block (e.g., There
+   * are duplicate header names; or the header names are not encoded
+   * in US-ASCII character set and not lower cased; or the header name
+   * is zero-length string; or the header value contains multiple
+   * in-sequence NUL bytes).
+   */
+  NGHTTP2_ERR_INVALID_HEADER_BLOCK = -518,
+  /**
+   * Indicates that the context is not suitable to perform the
+   * requested operation.
+   */
+  NGHTTP2_ERR_INVALID_STATE = -519,
+  /**
+   * The user callback function failed due to the temporal error.
+   */
+  NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE = -521,
+  /**
+   * The length of the frame is invalid, either too large or too small.
+   */
+  NGHTTP2_ERR_FRAME_SIZE_ERROR = -522,
+  /**
+   * Header block inflate/deflate error.
+   */
+  NGHTTP2_ERR_HEADER_COMP = -523,
+  /**
+   * Flow control error
+   */
+  NGHTTP2_ERR_FLOW_CONTROL = -524,
+  /**
+   * Insufficient buffer size given to function.
+   */
+  NGHTTP2_ERR_INSUFF_BUFSIZE = -525,
+  /**
+   * Callback was paused by the application
+   */
+  NGHTTP2_ERR_PAUSE = -526,
+  /**
+   * There are too many in-flight SETTING frame and no more
+   * transmission of SETTINGS is allowed.
+   */
+  NGHTTP2_ERR_TOO_MANY_INFLIGHT_SETTINGS = -527,
+  /**
+   * The server push is disabled.
+   */
+  NGHTTP2_ERR_PUSH_DISABLED = -528,
+  /**
+   * DATA or HEADERS frame for a given stream has been already
+   * submitted and has not been fully processed yet.  Application
+   * should wait for the transmission of the previously submitted
+   * frame before submitting another.
+   */
+  NGHTTP2_ERR_DATA_EXIST = -529,
+  /**
+   * The current session is closing due to a connection error or
+   * `nghttp2_session_terminate_session()` is called.
+   */
+  NGHTTP2_ERR_SESSION_CLOSING = -530,
+  /**
+   * Invalid HTTP header field was received and stream is going to be
+   * closed.
+   */
+  NGHTTP2_ERR_HTTP_HEADER = -531,
+  /**
+   * Violation in HTTP messaging rule.
+   */
+  NGHTTP2_ERR_HTTP_MESSAGING = -532,
+  /**
+   * Stream was refused.
+   */
+  NGHTTP2_ERR_REFUSED_STREAM = -533,
+  /**
+   * Unexpected internal error, but recovered.
+   */
+  NGHTTP2_ERR_INTERNAL = -534,
+  /**
+   * Indicates that a processing was canceled.
+   */
+  NGHTTP2_ERR_CANCEL = -535,
+  /**
+   * When a local endpoint expects to receive SETTINGS frame, it
+   * receives an other type of frame.
+   */
+  NGHTTP2_ERR_SETTINGS_EXPECTED = -536,
+  /**
+   * When a local endpoint receives too many settings entries
+   * in a single SETTINGS frame.
+   */
+  NGHTTP2_ERR_TOO_MANY_SETTINGS = -537,
+  /**
+   * The errors < :enum:`nghttp2_error.NGHTTP2_ERR_FATAL` mean that
+   * the library is under unexpected condition and processing was
+   * terminated (e.g., out of memory).  If application receives this
+   * error code, it must stop using that :type:`nghttp2_session`
+   * object and only allowed operation for that object is deallocate
+   * it using `nghttp2_session_del()`.
+   */
+  NGHTTP2_ERR_FATAL = -900,
+  /**
+   * Out of memory.  This is a fatal error.
+   */
+  NGHTTP2_ERR_NOMEM = -901,
+  /**
+   * The user callback function failed.  This is a fatal error.
+   */
+  NGHTTP2_ERR_CALLBACK_FAILURE = -902,
+  /**
+   * Invalid client magic (see :macro:`NGHTTP2_CLIENT_MAGIC`) was
+   * received and further processing is not possible.
+   */
+  NGHTTP2_ERR_BAD_CLIENT_MAGIC = -903,
+  /**
+   * Possible flooding by peer was detected in this HTTP/2 session.
+   * Flooding is measured by how many PING and SETTINGS frames with
+   * ACK flag set are queued for transmission.  These frames are
+   * response for the peer initiated frames, and peer can cause memory
+   * exhaustion on server side to send these frames forever and does
+   * not read network.
+   */
+  NGHTTP2_ERR_FLOODED = -904
+} nghttp2_error;
+
+/**
+ * @struct
+ *
+ * The object representing single contiguous buffer.
+ */
+typedef struct {
+  /**
+   * The pointer to the buffer.
+   */
+  uint8_t *base;
+  /**
+   * The length of the buffer.
+   */
+  size_t len;
+} nghttp2_vec;
+
+struct nghttp2_rcbuf;
+
+/**
+ * @struct
+ *
+ * The object representing reference counted buffer.  The details of
+ * this structure are intentionally hidden from the public API.
+ */
+typedef struct nghttp2_rcbuf nghttp2_rcbuf;
+
+/**
+ * @function
+ *
+ * Increments the reference count of |rcbuf| by 1.
+ */
+NGHTTP2_EXTERN void nghttp2_rcbuf_incref(nghttp2_rcbuf *rcbuf);
+
+/**
+ * @function
+ *
+ * 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.
+ */
+NGHTTP2_EXTERN void nghttp2_rcbuf_decref(nghttp2_rcbuf *rcbuf);
+
+/**
+ * @function
+ *
+ * Returns the underlying buffer managed by |rcbuf|.
+ */
+NGHTTP2_EXTERN nghttp2_vec nghttp2_rcbuf_get_buf(nghttp2_rcbuf *rcbuf);
+
+/**
+ * @function
+ *
+ * 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.
+ */
+NGHTTP2_EXTERN int nghttp2_rcbuf_is_static(const nghttp2_rcbuf *rcbuf);
+
+/**
+ * @enum
+ *
+ * The flags for header field name/value pair.
+ */
+typedef enum {
+  /**
+   * No flag set.
+   */
+  NGHTTP2_NV_FLAG_NONE = 0,
+  /**
+   * Indicates that this name/value pair must not be indexed ("Literal
+   * Header Field never Indexed" representation must be used in HPACK
+   * encoding).  Other implementation calls this bit as "sensitive".
+   */
+  NGHTTP2_NV_FLAG_NO_INDEX = 0x01,
+  /**
+   * This flag is set solely by application.  If this flag is set, the
+   * library does not make a copy of header field name.  This could
+   * improve performance.
+   */
+  NGHTTP2_NV_FLAG_NO_COPY_NAME = 0x02,
+  /**
+   * This flag is set solely by application.  If this flag is set, the
+   * library does not make a copy of header field value.  This could
+   * improve performance.
+   */
+  NGHTTP2_NV_FLAG_NO_COPY_VALUE = 0x04
+} nghttp2_nv_flag;
+
+/**
+ * @struct
+ *
+ * The name/value pair, which mainly used to represent header fields.
+ */
+typedef struct {
+  /**
+   * The |name| byte string.  If this struct is presented from library
+   * (e.g., :type:`nghttp2_on_frame_recv_callback`), |name| is
+   * guaranteed to be NULL-terminated.  For some callbacks
+   * (:type:`nghttp2_before_frame_send_callback`,
+   * :type:`nghttp2_on_frame_send_callback`, and
+   * :type:`nghttp2_on_frame_not_send_callback`), it may not be
+   * NULL-terminated if header field is passed from application with
+   * the flag :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME`).
+   * When application is constructing this struct, |name| is not
+   * required to be NULL-terminated.
+   */
+  uint8_t *name;
+  /**
+   * The |value| byte string.  If this struct is presented from
+   * library (e.g., :type:`nghttp2_on_frame_recv_callback`), |value|
+   * is guaranteed to be NULL-terminated.  For some callbacks
+   * (:type:`nghttp2_before_frame_send_callback`,
+   * :type:`nghttp2_on_frame_send_callback`, and
+   * :type:`nghttp2_on_frame_not_send_callback`), it may not be
+   * NULL-terminated if header field is passed from application with
+   * the flag :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_VALUE`).
+   * When application is constructing this struct, |value| is not
+   * required to be NULL-terminated.
+   */
+  uint8_t *value;
+  /**
+   * The length of the |name|, excluding terminating NULL.
+   */
+  size_t namelen;
+  /**
+   * The length of the |value|, excluding terminating NULL.
+   */
+  size_t valuelen;
+  /**
+   * Bitwise OR of one or more of :type:`nghttp2_nv_flag`.
+   */
+  uint8_t flags;
+} nghttp2_nv;
+
+/**
+ * @enum
+ *
+ * The frame types in HTTP/2 specification.
+ */
+typedef enum {
+  /**
+   * The DATA frame.
+   */
+  NGHTTP2_DATA = 0,
+  /**
+   * The HEADERS frame.
+   */
+  NGHTTP2_HEADERS = 0x01,
+  /**
+   * The PRIORITY frame.
+   */
+  NGHTTP2_PRIORITY = 0x02,
+  /**
+   * The RST_STREAM frame.
+   */
+  NGHTTP2_RST_STREAM = 0x03,
+  /**
+   * The SETTINGS frame.
+   */
+  NGHTTP2_SETTINGS = 0x04,
+  /**
+   * The PUSH_PROMISE frame.
+   */
+  NGHTTP2_PUSH_PROMISE = 0x05,
+  /**
+   * The PING frame.
+   */
+  NGHTTP2_PING = 0x06,
+  /**
+   * The GOAWAY frame.
+   */
+  NGHTTP2_GOAWAY = 0x07,
+  /**
+   * The WINDOW_UPDATE frame.
+   */
+  NGHTTP2_WINDOW_UPDATE = 0x08,
+  /**
+   * The CONTINUATION frame.  This frame type won't be passed to any
+   * callbacks because the library processes this frame type and its
+   * preceding HEADERS/PUSH_PROMISE as a single frame.
+   */
+  NGHTTP2_CONTINUATION = 0x09,
+  /**
+   * The ALTSVC frame, which is defined in `RFC 7383
+   * <https://tools.ietf.org/html/rfc7838#section-4>`_.
+   */
+  NGHTTP2_ALTSVC = 0x0a,
+  /**
+   * The ORIGIN frame, which is defined by `RFC 8336
+   * <https://tools.ietf.org/html/rfc8336>`_.
+   */
+  NGHTTP2_ORIGIN = 0x0c,
+  /**
+   * The PRIORITY_UPDATE frame, which is defined by :rfc:`9218`.
+   */
+  NGHTTP2_PRIORITY_UPDATE = 0x10
+} nghttp2_frame_type;
+
+/**
+ * @enum
+ *
+ * The flags for HTTP/2 frames.  This enum defines all flags for all
+ * frames.
+ */
+typedef enum {
+  /**
+   * No flag set.
+   */
+  NGHTTP2_FLAG_NONE = 0,
+  /**
+   * The END_STREAM flag.
+   */
+  NGHTTP2_FLAG_END_STREAM = 0x01,
+  /**
+   * The END_HEADERS flag.
+   */
+  NGHTTP2_FLAG_END_HEADERS = 0x04,
+  /**
+   * The ACK flag.
+   */
+  NGHTTP2_FLAG_ACK = 0x01,
+  /**
+   * The PADDED flag.
+   */
+  NGHTTP2_FLAG_PADDED = 0x08,
+  /**
+   * The PRIORITY flag.
+   */
+  NGHTTP2_FLAG_PRIORITY = 0x20
+} nghttp2_flag;
+
+/**
+ * @enum
+ * The SETTINGS ID.
+ */
+typedef enum {
+  /**
+   * SETTINGS_HEADER_TABLE_SIZE
+   */
+  NGHTTP2_SETTINGS_HEADER_TABLE_SIZE = 0x01,
+  /**
+   * SETTINGS_ENABLE_PUSH
+   */
+  NGHTTP2_SETTINGS_ENABLE_PUSH = 0x02,
+  /**
+   * SETTINGS_MAX_CONCURRENT_STREAMS
+   */
+  NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS = 0x03,
+  /**
+   * SETTINGS_INITIAL_WINDOW_SIZE
+   */
+  NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE = 0x04,
+  /**
+   * SETTINGS_MAX_FRAME_SIZE
+   */
+  NGHTTP2_SETTINGS_MAX_FRAME_SIZE = 0x05,
+  /**
+   * SETTINGS_MAX_HEADER_LIST_SIZE
+   */
+  NGHTTP2_SETTINGS_MAX_HEADER_LIST_SIZE = 0x06,
+  /**
+   * SETTINGS_ENABLE_CONNECT_PROTOCOL
+   * (`RFC 8441 <https://tools.ietf.org/html/rfc8441>`_)
+   */
+  NGHTTP2_SETTINGS_ENABLE_CONNECT_PROTOCOL = 0x08,
+  /**
+   * SETTINGS_NO_RFC7540_PRIORITIES (:rfc:`9218`)
+   */
+  NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES = 0x09
+} nghttp2_settings_id;
+/* Note: If we add SETTINGS, update the capacity of
+   NGHTTP2_INBOUND_NUM_IV as well */
+
+/**
+ * @macro
+ *
+ * .. warning::
+ *
+ *   Deprecated.  The initial max concurrent streams is 0xffffffffu.
+ *
+ * Default maximum number of incoming concurrent streams.  Use
+ * `nghttp2_submit_settings()` with
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS`
+ * to change the maximum number of incoming concurrent streams.
+ *
+ * .. note::
+ *
+ *   The maximum number of outgoing concurrent streams is 100 by
+ *   default.
+ */
+#define NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS ((1U << 31) - 1)
+
+/**
+ * @enum
+ * The status codes for the RST_STREAM and GOAWAY frames.
+ */
+typedef enum {
+  /**
+   * No errors.
+   */
+  NGHTTP2_NO_ERROR = 0x00,
+  /**
+   * PROTOCOL_ERROR
+   */
+  NGHTTP2_PROTOCOL_ERROR = 0x01,
+  /**
+   * INTERNAL_ERROR
+   */
+  NGHTTP2_INTERNAL_ERROR = 0x02,
+  /**
+   * FLOW_CONTROL_ERROR
+   */
+  NGHTTP2_FLOW_CONTROL_ERROR = 0x03,
+  /**
+   * SETTINGS_TIMEOUT
+   */
+  NGHTTP2_SETTINGS_TIMEOUT = 0x04,
+  /**
+   * STREAM_CLOSED
+   */
+  NGHTTP2_STREAM_CLOSED = 0x05,
+  /**
+   * FRAME_SIZE_ERROR
+   */
+  NGHTTP2_FRAME_SIZE_ERROR = 0x06,
+  /**
+   * REFUSED_STREAM
+   */
+  NGHTTP2_REFUSED_STREAM = 0x07,
+  /**
+   * CANCEL
+   */
+  NGHTTP2_CANCEL = 0x08,
+  /**
+   * COMPRESSION_ERROR
+   */
+  NGHTTP2_COMPRESSION_ERROR = 0x09,
+  /**
+   * CONNECT_ERROR
+   */
+  NGHTTP2_CONNECT_ERROR = 0x0a,
+  /**
+   * ENHANCE_YOUR_CALM
+   */
+  NGHTTP2_ENHANCE_YOUR_CALM = 0x0b,
+  /**
+   * INADEQUATE_SECURITY
+   */
+  NGHTTP2_INADEQUATE_SECURITY = 0x0c,
+  /**
+   * HTTP_1_1_REQUIRED
+   */
+  NGHTTP2_HTTP_1_1_REQUIRED = 0x0d
+} nghttp2_error_code;
+
+/**
+ * @struct
+ * The frame header.
+ */
+typedef struct {
+  /**
+   * The length field of this frame, excluding frame header.
+   */
+  size_t length;
+  /**
+   * The stream identifier (aka, stream ID)
+   */
+  int32_t stream_id;
+  /**
+   * The type of this frame.  See `nghttp2_frame_type`.
+   */
+  uint8_t type;
+  /**
+   * The flags.
+   */
+  uint8_t flags;
+  /**
+   * Reserved bit in frame header.  Currently, this is always set to 0
+   * and application should not expect something useful in here.
+   */
+  uint8_t reserved;
+} nghttp2_frame_hd;
+
+/**
+ * @union
+ *
+ * This union represents the some kind of data source passed to
+ * :type:`nghttp2_data_source_read_callback`.
+ */
+typedef union {
+  /**
+   * The integer field, suitable for a file descriptor.
+   */
+  int fd;
+  /**
+   * The pointer to an arbitrary object.
+   */
+  void *ptr;
+} nghttp2_data_source;
+
+/**
+ * @enum
+ *
+ * The flags used to set in |data_flags| output parameter in
+ * :type:`nghttp2_data_source_read_callback`.
+ */
+typedef enum {
+  /**
+   * No flag set.
+   */
+  NGHTTP2_DATA_FLAG_NONE = 0,
+  /**
+   * Indicates EOF was sensed.
+   */
+  NGHTTP2_DATA_FLAG_EOF = 0x01,
+  /**
+   * Indicates that END_STREAM flag must not be set even if
+   * NGHTTP2_DATA_FLAG_EOF is set.  Usually this flag is used to send
+   * trailer fields with `nghttp2_submit_request()` or
+   * `nghttp2_submit_response()`.
+   */
+  NGHTTP2_DATA_FLAG_NO_END_STREAM = 0x02,
+  /**
+   * Indicates that application will send complete DATA frame in
+   * :type:`nghttp2_send_data_callback`.
+   */
+  NGHTTP2_DATA_FLAG_NO_COPY = 0x04
+} nghttp2_data_flag;
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when the library wants to read data from
+ * the |source|.  The read data is sent in the stream |stream_id|.
+ * The implementation of this function must read at most |length|
+ * bytes of data from |source| (or possibly other places) and store
+ * them in |buf| and return number of data stored in |buf|.  If EOF is
+ * reached, set :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_EOF` flag
+ * in |*data_flags|.
+ *
+ * Sometime it is desirable to avoid copying data into |buf| and let
+ * application to send data directly.  To achieve this, set
+ * :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_COPY` to
+ * |*data_flags| (and possibly other flags, just like when we do
+ * copy), and return the number of bytes to send without copying data
+ * into |buf|.  The library, seeing
+ * :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_COPY`, will invoke
+ * :type:`nghttp2_send_data_callback`.  The application must send
+ * complete DATA frame in that callback.
+ *
+ * If this callback is set by `nghttp2_submit_request()`,
+ * `nghttp2_submit_response()` or `nghttp2_submit_headers()` and
+ * `nghttp2_submit_data()` with flag parameter
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_END_STREAM` set, and
+ * :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_EOF` flag is set to
+ * |*data_flags|, DATA frame will have END_STREAM flag set.  Usually,
+ * this is expected behaviour and all are fine.  One exception is send
+ * trailer fields.  You cannot send trailer fields after sending frame
+ * with END_STREAM set.  To avoid this problem, one can set
+ * :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_END_STREAM` along
+ * with :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_EOF` to signal the
+ * library not to set END_STREAM in DATA frame.  Then application can
+ * use `nghttp2_submit_trailer()` to send trailer fields.
+ * `nghttp2_submit_trailer()` can be called inside this callback.
+ *
+ * If the application wants to postpone DATA frames (e.g.,
+ * asynchronous I/O, or reading data blocks for long time), it is
+ * achieved by returning :enum:`nghttp2_error.NGHTTP2_ERR_DEFERRED`
+ * without reading any data in this invocation.  The library removes
+ * DATA frame from the outgoing queue temporarily.  To move back
+ * deferred DATA frame to outgoing queue, call
+ * `nghttp2_session_resume_data()`.
+ *
+ * By default, |length| is limited to 16KiB at maximum.  If peer
+ * allows larger frames, application can enlarge transmission buffer
+ * size.  See :type:`nghttp2_data_source_read_length_callback` for
+ * more details.
+ *
+ * If the application just wants to return from
+ * `nghttp2_session_send()` or `nghttp2_session_mem_send()` without
+ * sending anything, return :enum:`nghttp2_error.NGHTTP2_ERR_PAUSE`.
+ *
+ * In case of error, there are 2 choices. Returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` will
+ * close the stream by issuing RST_STREAM with
+ * :enum:`nghttp2_error_code.NGHTTP2_INTERNAL_ERROR`.  If a different
+ * error code is desirable, use `nghttp2_submit_rst_stream()` with a
+ * desired error code and then return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.
+ * Returning :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` will
+ * signal the entire session failure.
+ */
+typedef ssize_t (*nghttp2_data_source_read_callback)(
+    nghttp2_session *session, int32_t stream_id, uint8_t *buf, size_t length,
+    uint32_t *data_flags, nghttp2_data_source *source, void *user_data);
+
+/**
+ * @struct
+ *
+ * This struct represents the data source and the way to read a chunk
+ * of data from it.
+ */
+typedef struct {
+  /**
+   * The data source.
+   */
+  nghttp2_data_source source;
+  /**
+   * The callback function to read a chunk of data from the |source|.
+   */
+  nghttp2_data_source_read_callback read_callback;
+} nghttp2_data_provider;
+
+/**
+ * @struct
+ *
+ * The DATA frame.  The received data is delivered via
+ * :type:`nghttp2_on_data_chunk_recv_callback`.
+ */
+typedef struct {
+  nghttp2_frame_hd hd;
+  /**
+   * The length of the padding in this frame.  This includes PAD_HIGH
+   * and PAD_LOW.
+   */
+  size_t padlen;
+} nghttp2_data;
+
+/**
+ * @enum
+ *
+ * The category of HEADERS, which indicates the role of the frame.  In
+ * HTTP/2 spec, request, response, push response and other arbitrary
+ * headers (e.g., trailer fields) are all called just HEADERS.  To
+ * give the application the role of incoming HEADERS frame, we define
+ * several categories.
+ */
+typedef enum {
+  /**
+   * The HEADERS frame is opening new stream, which is analogous to
+   * SYN_STREAM in SPDY.
+   */
+  NGHTTP2_HCAT_REQUEST = 0,
+  /**
+   * The HEADERS frame is the first response headers, which is
+   * analogous to SYN_REPLY in SPDY.
+   */
+  NGHTTP2_HCAT_RESPONSE = 1,
+  /**
+   * The HEADERS frame is the first headers sent against reserved
+   * stream.
+   */
+  NGHTTP2_HCAT_PUSH_RESPONSE = 2,
+  /**
+   * The HEADERS frame which does not apply for the above categories,
+   * which is analogous to HEADERS in SPDY.  If non-final response
+   * (e.g., status 1xx) is used, final response HEADERS frame will be
+   * categorized here.
+   */
+  NGHTTP2_HCAT_HEADERS = 3
+} nghttp2_headers_category;
+
+/**
+ * @struct
+ *
+ * The structure to specify stream dependency.
+ */
+typedef struct {
+  /**
+   * The stream ID of the stream to depend on.  Specifying 0 makes
+   * stream not depend any other stream.
+   */
+  int32_t stream_id;
+  /**
+   * The weight of this dependency.
+   */
+  int32_t weight;
+  /**
+   * nonzero means exclusive dependency
+   */
+  uint8_t exclusive;
+} nghttp2_priority_spec;
+
+/**
+ * @struct
+ *
+ * The HEADERS frame.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The length of the padding in this frame.  This includes PAD_HIGH
+   * and PAD_LOW.
+   */
+  size_t padlen;
+  /**
+   * The priority specification
+   */
+  nghttp2_priority_spec pri_spec;
+  /**
+   * The name/value pairs.
+   */
+  nghttp2_nv *nva;
+  /**
+   * The number of name/value pairs in |nva|.
+   */
+  size_t nvlen;
+  /**
+   * The category of this HEADERS frame.
+   */
+  nghttp2_headers_category cat;
+} nghttp2_headers;
+
+/**
+ * @struct
+ *
+ * The PRIORITY frame.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The priority specification.
+   */
+  nghttp2_priority_spec pri_spec;
+} nghttp2_priority;
+
+/**
+ * @struct
+ *
+ * The RST_STREAM frame.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The error code.  See :type:`nghttp2_error_code`.
+   */
+  uint32_t error_code;
+} nghttp2_rst_stream;
+
+/**
+ * @struct
+ *
+ * The SETTINGS ID/Value pair.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The SETTINGS ID.  See :type:`nghttp2_settings_id`.
+   */
+  int32_t settings_id;
+  /**
+   * The value of this entry.
+   */
+  uint32_t value;
+} nghttp2_settings_entry;
+
+/**
+ * @struct
+ *
+ * The SETTINGS frame.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The number of SETTINGS ID/Value pairs in |iv|.
+   */
+  size_t niv;
+  /**
+   * The pointer to the array of SETTINGS ID/Value pair.
+   */
+  nghttp2_settings_entry *iv;
+} nghttp2_settings;
+
+/**
+ * @struct
+ *
+ * The PUSH_PROMISE frame.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The length of the padding in this frame.  This includes PAD_HIGH
+   * and PAD_LOW.
+   */
+  size_t padlen;
+  /**
+   * The name/value pairs.
+   */
+  nghttp2_nv *nva;
+  /**
+   * The number of name/value pairs in |nva|.
+   */
+  size_t nvlen;
+  /**
+   * The promised stream ID
+   */
+  int32_t promised_stream_id;
+  /**
+   * Reserved bit.  Currently this is always set to 0 and application
+   * should not expect something useful in here.
+   */
+  uint8_t reserved;
+} nghttp2_push_promise;
+
+/**
+ * @struct
+ *
+ * The PING frame.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The opaque data
+   */
+  uint8_t opaque_data[8];
+} nghttp2_ping;
+
+/**
+ * @struct
+ *
+ * The GOAWAY frame.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The last stream stream ID.
+   */
+  int32_t last_stream_id;
+  /**
+   * The error code.  See :type:`nghttp2_error_code`.
+   */
+  uint32_t error_code;
+  /**
+   * The additional debug data
+   */
+  uint8_t *opaque_data;
+  /**
+   * The length of |opaque_data| member.
+   */
+  size_t opaque_data_len;
+  /**
+   * Reserved bit.  Currently this is always set to 0 and application
+   * should not expect something useful in here.
+   */
+  uint8_t reserved;
+} nghttp2_goaway;
+
+/**
+ * @struct
+ *
+ * The WINDOW_UPDATE frame.  It has the following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The window size increment.
+   */
+  int32_t window_size_increment;
+  /**
+   * Reserved bit.  Currently this is always set to 0 and application
+   * should not expect something useful in here.
+   */
+  uint8_t reserved;
+} nghttp2_window_update;
+
+/**
+ * @struct
+ *
+ * The extension frame.  It has following members:
+ */
+typedef struct {
+  /**
+   * The frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The pointer to extension payload.  The exact pointer type is
+   * determined by hd.type.
+   *
+   * Currently, no extension is supported.  This is a place holder for
+   * the future extensions.
+   */
+  void *payload;
+} nghttp2_extension;
+
+/**
+ * @union
+ *
+ * This union includes all frames to pass them to various function
+ * calls as nghttp2_frame type.  The CONTINUATION frame is omitted
+ * from here because the library deals with it internally.
+ */
+typedef union {
+  /**
+   * The frame header, which is convenient to inspect frame header.
+   */
+  nghttp2_frame_hd hd;
+  /**
+   * The DATA frame.
+   */
+  nghttp2_data data;
+  /**
+   * The HEADERS frame.
+   */
+  nghttp2_headers headers;
+  /**
+   * The PRIORITY frame.
+   */
+  nghttp2_priority priority;
+  /**
+   * The RST_STREAM frame.
+   */
+  nghttp2_rst_stream rst_stream;
+  /**
+   * The SETTINGS frame.
+   */
+  nghttp2_settings settings;
+  /**
+   * The PUSH_PROMISE frame.
+   */
+  nghttp2_push_promise push_promise;
+  /**
+   * The PING frame.
+   */
+  nghttp2_ping ping;
+  /**
+   * The GOAWAY frame.
+   */
+  nghttp2_goaway goaway;
+  /**
+   * The WINDOW_UPDATE frame.
+   */
+  nghttp2_window_update window_update;
+  /**
+   * The extension frame.
+   */
+  nghttp2_extension ext;
+} nghttp2_frame;
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when |session| wants to send data to the
+ * remote peer.  The implementation of this function must send at most
+ * |length| bytes of data stored in |data|.  The |flags| is currently
+ * not used and always 0. It must return the number of bytes sent if
+ * it succeeds.  If it cannot send any single byte without blocking,
+ * it must return :enum:`nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`.  For
+ * other errors, it must return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  The
+ * |user_data| pointer is the third argument passed in to the call to
+ * `nghttp2_session_client_new()` or `nghttp2_session_server_new()`.
+ *
+ * This callback is required if the application uses
+ * `nghttp2_session_send()` to send data to the remote endpoint.  If
+ * the application uses solely `nghttp2_session_mem_send()` instead,
+ * this callback function is unnecessary.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_send_callback()`.
+ *
+ * .. note::
+ *
+ *   The |length| may be very small.  If that is the case, and
+ *   application disables Nagle algorithm (``TCP_NODELAY``), then just
+ *   writing |data| to the network stack leads to very small packet,
+ *   and it is very inefficient.  An application should be responsible
+ *   to buffer up small chunks of data as necessary to avoid this
+ *   situation.
+ */
+typedef ssize_t (*nghttp2_send_callback)(nghttp2_session *session,
+                                         const uint8_t *data, size_t length,
+                                         int flags, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when
+ * :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_COPY` is used in
+ * :type:`nghttp2_data_source_read_callback` to send complete DATA
+ * frame.
+ *
+ * The |frame| is a DATA frame to send.  The |framehd| is the
+ * serialized frame header (9 bytes). The |length| is the length of
+ * application data to send (this does not include padding).  The
+ * |source| is the same pointer passed to
+ * :type:`nghttp2_data_source_read_callback`.
+ *
+ * The application first must send frame header |framehd| of length 9
+ * bytes.  If ``frame->data.padlen > 0``, send 1 byte of value
+ * ``frame->data.padlen - 1``.  Then send exactly |length| bytes of
+ * application data.  Finally, if ``frame->data.padlen > 1``, send
+ * ``frame->data.padlen - 1`` bytes of zero as padding.
+ *
+ * The application has to send complete DATA frame in this callback.
+ * If all data were written successfully, return 0.
+ *
+ * If it cannot send any data at all, just return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`; the library will call
+ * this callback with the same parameters later (It is recommended to
+ * send complete DATA frame at once in this function to deal with
+ * error; if partial frame data has already sent, it is impossible to
+ * send another data in that state, and all we can do is tear down
+ * connection).  When data is fully processed, but application wants
+ * to make `nghttp2_session_mem_send()` or `nghttp2_session_send()`
+ * return immediately without processing next frames, return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PAUSE`.  If application decided to
+ * reset this stream, return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`, then
+ * the library will send RST_STREAM with INTERNAL_ERROR as error code.
+ * The application can also return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`, which will
+ * result in connection closure.  Returning any other value is treated
+ * as :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned.
+ */
+typedef int (*nghttp2_send_data_callback)(nghttp2_session *session,
+                                          nghttp2_frame *frame,
+                                          const uint8_t *framehd, size_t length,
+                                          nghttp2_data_source *source,
+                                          void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when |session| wants to receive data from
+ * the remote peer.  The implementation of this function must read at
+ * most |length| bytes of data and store it in |buf|.  The |flags| is
+ * currently not used and always 0.  It must return the number of
+ * bytes written in |buf| if it succeeds.  If it cannot read any
+ * single byte without blocking, it must return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`.  If it gets EOF
+ * before it reads any single byte, it must return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_EOF`.  For other errors, it must
+ * return :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ * Returning 0 is treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`.  The |user_data|
+ * pointer is the third argument passed in to the call to
+ * `nghttp2_session_client_new()` or `nghttp2_session_server_new()`.
+ *
+ * This callback is required if the application uses
+ * `nghttp2_session_recv()` to receive data from the remote endpoint.
+ * If the application uses solely `nghttp2_session_mem_recv()`
+ * instead, this callback function is unnecessary.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_recv_callback()`.
+ */
+typedef ssize_t (*nghttp2_recv_callback)(nghttp2_session *session, uint8_t *buf,
+                                         size_t length, int flags,
+                                         void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked by `nghttp2_session_recv()` and
+ * `nghttp2_session_mem_recv()` when a frame is received.  The
+ * |user_data| pointer is the third argument passed in to the call to
+ * `nghttp2_session_client_new()` or `nghttp2_session_server_new()`.
+ *
+ * If frame is HEADERS or PUSH_PROMISE, the ``nva`` and ``nvlen``
+ * member of their data structure are always ``NULL`` and 0
+ * respectively.  The header name/value pairs are emitted via
+ * :type:`nghttp2_on_header_callback`.
+ *
+ * Only HEADERS and DATA frame can signal the end of incoming data.
+ * If ``frame->hd.flags & NGHTTP2_FLAG_END_STREAM`` is nonzero, the
+ * |frame| is the last frame from the remote peer in this stream.
+ *
+ * This callback won't be called for CONTINUATION frames.
+ * HEADERS/PUSH_PROMISE + CONTINUATIONs are treated as single frame.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * If nonzero value is returned, it is treated as fatal error and
+ * `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_frame_recv_callback()`.
+ */
+typedef int (*nghttp2_on_frame_recv_callback)(nghttp2_session *session,
+                                              const nghttp2_frame *frame,
+                                              void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked by `nghttp2_session_recv()` and
+ * `nghttp2_session_mem_recv()` when an invalid non-DATA frame is
+ * received.  The error is indicated by the |lib_error_code|, which is
+ * one of the values defined in :type:`nghttp2_error`.  When this
+ * callback function is invoked, the library automatically submits
+ * either RST_STREAM or GOAWAY frame.  The |user_data| pointer is the
+ * third argument passed in to the call to
+ * `nghttp2_session_client_new()` or `nghttp2_session_server_new()`.
+ *
+ * If frame is HEADERS or PUSH_PROMISE, the ``nva`` and ``nvlen``
+ * member of their data structure are always ``NULL`` and 0
+ * respectively.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * If nonzero is returned, it is treated as fatal error and
+ * `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_invalid_frame_recv_callback()`.
+ */
+typedef int (*nghttp2_on_invalid_frame_recv_callback)(
+    nghttp2_session *session, const nghttp2_frame *frame, int lib_error_code,
+    void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when a chunk of data in DATA frame is
+ * received.  The |stream_id| is the stream ID this DATA frame belongs
+ * to.  The |flags| is the flags of DATA frame which this data chunk
+ * is contained.  ``(flags & NGHTTP2_FLAG_END_STREAM) != 0`` does not
+ * necessarily mean this chunk of data is the last one in the stream.
+ * You should use :type:`nghttp2_on_frame_recv_callback` to know all
+ * data frames are received.  The |user_data| pointer is the third
+ * argument passed in to the call to `nghttp2_session_client_new()` or
+ * `nghttp2_session_server_new()`.
+ *
+ * If the application uses `nghttp2_session_mem_recv()`, it can return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PAUSE` to make
+ * `nghttp2_session_mem_recv()` return without processing further
+ * input bytes.  The memory by pointed by the |data| is retained until
+ * `nghttp2_session_mem_recv()` or `nghttp2_session_recv()` is called.
+ * The application must retain the input bytes which was used to
+ * produce the |data| parameter, because it may refer to the memory
+ * region included in the input bytes.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * If nonzero is returned, it is treated as fatal error, and
+ * `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_data_chunk_recv_callback()`.
+ */
+typedef int (*nghttp2_on_data_chunk_recv_callback)(nghttp2_session *session,
+                                                   uint8_t flags,
+                                                   int32_t stream_id,
+                                                   const uint8_t *data,
+                                                   size_t len, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked just before the non-DATA frame |frame| is
+ * sent.  The |user_data| pointer is the third argument passed in to
+ * the call to `nghttp2_session_client_new()` or
+ * `nghttp2_session_server_new()`.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * It can also return :enum:`nghttp2_error.NGHTTP2_ERR_CANCEL` to
+ * cancel the transmission of the given frame.
+ *
+ * If there is a fatal error while executing this callback, the
+ * implementation should return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`, which makes
+ * `nghttp2_session_send()` and `nghttp2_session_mem_send()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * If the other value is returned, it is treated as if
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned.
+ * But the implementation should not rely on this since the library
+ * may define new return value to extend its capability.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_before_frame_send_callback()`.
+ */
+typedef int (*nghttp2_before_frame_send_callback)(nghttp2_session *session,
+                                                  const nghttp2_frame *frame,
+                                                  void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked after the frame |frame| is sent.  The
+ * |user_data| pointer is the third argument passed in to the call to
+ * `nghttp2_session_client_new()` or `nghttp2_session_server_new()`.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * If nonzero is returned, it is treated as fatal error and
+ * `nghttp2_session_send()` and `nghttp2_session_mem_send()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_frame_send_callback()`.
+ */
+typedef int (*nghttp2_on_frame_send_callback)(nghttp2_session *session,
+                                              const nghttp2_frame *frame,
+                                              void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked after the non-DATA frame |frame| is not
+ * sent because of the error.  The error is indicated by the
+ * |lib_error_code|, which is one of the values defined in
+ * :type:`nghttp2_error`.  The |user_data| pointer is the third
+ * argument passed in to the call to `nghttp2_session_client_new()` or
+ * `nghttp2_session_server_new()`.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * If nonzero is returned, it is treated as fatal error and
+ * `nghttp2_session_send()` and `nghttp2_session_mem_send()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * `nghttp2_session_get_stream_user_data()` can be used to get
+ * associated data.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_frame_not_send_callback()`.
+ */
+typedef int (*nghttp2_on_frame_not_send_callback)(nghttp2_session *session,
+                                                  const nghttp2_frame *frame,
+                                                  int lib_error_code,
+                                                  void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when the stream |stream_id| is closed.
+ * The reason of closure is indicated by the |error_code|.  The
+ * |error_code| is usually one of :enum:`nghttp2_error_code`, but that
+ * is not guaranteed.  The stream_user_data, which was specified in
+ * `nghttp2_submit_request()` or `nghttp2_submit_headers()`, is still
+ * available in this function.  The |user_data| pointer is the third
+ * argument passed in to the call to `nghttp2_session_client_new()` or
+ * `nghttp2_session_server_new()`.
+ *
+ * This function is also called for a stream in reserved state.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * If nonzero is returned, it is treated as fatal error and
+ * `nghttp2_session_recv()`, `nghttp2_session_mem_recv()`,
+ * `nghttp2_session_send()`, and `nghttp2_session_mem_send()`
+ * functions immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_stream_close_callback()`.
+ */
+typedef int (*nghttp2_on_stream_close_callback)(nghttp2_session *session,
+                                                int32_t stream_id,
+                                                uint32_t error_code,
+                                                void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when the reception of header block in
+ * HEADERS or PUSH_PROMISE is started.  Each header name/value pair
+ * will be emitted by :type:`nghttp2_on_header_callback`.
+ *
+ * The ``frame->hd.flags`` may not have
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_END_HEADERS` flag set, which
+ * indicates that one or more CONTINUATION frames are involved.  But
+ * the application does not need to care about that because the header
+ * name/value pairs are emitted transparently regardless of
+ * CONTINUATION frames.
+ *
+ * The server applications probably create an object to store
+ * information about new stream if ``frame->hd.type ==
+ * NGHTTP2_HEADERS`` and ``frame->headers.cat ==
+ * NGHTTP2_HCAT_REQUEST``.  If |session| is configured as server side,
+ * ``frame->headers.cat`` is either ``NGHTTP2_HCAT_REQUEST``
+ * containing request headers or ``NGHTTP2_HCAT_HEADERS`` containing
+ * trailer fields and never get PUSH_PROMISE in this callback.
+ *
+ * For the client applications, ``frame->hd.type`` is either
+ * ``NGHTTP2_HEADERS`` or ``NGHTTP2_PUSH_PROMISE``.  In case of
+ * ``NGHTTP2_HEADERS``, ``frame->headers.cat ==
+ * NGHTTP2_HCAT_RESPONSE`` means that it is the first response
+ * headers, but it may be non-final response which is indicated by 1xx
+ * status code.  In this case, there may be zero or more HEADERS frame
+ * with ``frame->headers.cat == NGHTTP2_HCAT_HEADERS`` which has
+ * non-final response code and finally client gets exactly one HEADERS
+ * frame with ``frame->headers.cat == NGHTTP2_HCAT_HEADERS``
+ * containing final response headers (non-1xx status code).  The
+ * trailer fields also has ``frame->headers.cat ==
+ * NGHTTP2_HCAT_HEADERS`` which does not contain any status code.
+ *
+ * Returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` will
+ * close the stream (promised stream if frame is PUSH_PROMISE) by
+ * issuing RST_STREAM with
+ * :enum:`nghttp2_error_code.NGHTTP2_INTERNAL_ERROR`.  In this case,
+ * :type:`nghttp2_on_header_callback` and
+ * :type:`nghttp2_on_frame_recv_callback` will not be invoked.  If a
+ * different error code is desirable, use
+ * `nghttp2_submit_rst_stream()` with a desired error code and then
+ * return :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.
+ * Again, use ``frame->push_promise.promised_stream_id`` as stream_id
+ * parameter in `nghttp2_submit_rst_stream()` if frame is
+ * PUSH_PROMISE.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * It can return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` to
+ * reset the stream (promised stream if frame is PUSH_PROMISE).  For
+ * critical errors, it must return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  If the other
+ * value is returned, it is treated as if
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned.  If
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned,
+ * `nghttp2_session_mem_recv()` function will immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_begin_headers_callback()`.
+ */
+typedef int (*nghttp2_on_begin_headers_callback)(nghttp2_session *session,
+                                                 const nghttp2_frame *frame,
+                                                 void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when a header name/value pair is received
+ * for the |frame|.  The |name| of length |namelen| is header name.
+ * The |value| of length |valuelen| is header value.  The |flags| is
+ * bitwise OR of one or more of :type:`nghttp2_nv_flag`.
+ *
+ * If :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_INDEX` is set in
+ * |flags|, the receiver must not index this name/value pair when
+ * forwarding it to the next hop.  More specifically, "Literal Header
+ * Field never Indexed" representation must be used in HPACK encoding.
+ *
+ * When this callback is invoked, ``frame->hd.type`` is either
+ * :enum:`nghttp2_frame_type.NGHTTP2_HEADERS` or
+ * :enum:`nghttp2_frame_type.NGHTTP2_PUSH_PROMISE`.  After all header
+ * name/value pairs are processed with this callback, and no error has
+ * been detected, :type:`nghttp2_on_frame_recv_callback` will be
+ * invoked.  If there is an error in decompression,
+ * :type:`nghttp2_on_frame_recv_callback` for the |frame| will not be
+ * invoked.
+ *
+ * Both |name| and |value| are guaranteed to be NULL-terminated.  The
+ * |namelen| and |valuelen| do not include terminal NULL.  If
+ * `nghttp2_option_set_no_http_messaging()` is used with nonzero
+ * value, NULL character may be included in |name| or |value| before
+ * terminating NULL.
+ *
+ * Please note that unless `nghttp2_option_set_no_http_messaging()` is
+ * used, nghttp2 library does perform validation against the |name|
+ * and the |value| using `nghttp2_check_header_name()` and
+ * `nghttp2_check_header_value()`.  In addition to this, nghttp2
+ * performs validation based on HTTP Messaging rule, which is briefly
+ * explained in :ref:`http-messaging` section.
+ *
+ * If the application uses `nghttp2_session_mem_recv()`, it can return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PAUSE` to make
+ * `nghttp2_session_mem_recv()` return without processing further
+ * input bytes.  The memory pointed by |frame|, |name| and |value|
+ * parameters are retained until `nghttp2_session_mem_recv()` or
+ * `nghttp2_session_recv()` is called.  The application must retain
+ * the input bytes which was used to produce these parameters, because
+ * it may refer to the memory region included in the input bytes.
+ *
+ * Returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` will
+ * close the stream (promised stream if frame is PUSH_PROMISE) by
+ * issuing RST_STREAM with
+ * :enum:`nghttp2_error_code.NGHTTP2_INTERNAL_ERROR`.  In this case,
+ * :type:`nghttp2_on_header_callback` and
+ * :type:`nghttp2_on_frame_recv_callback` will not be invoked.  If a
+ * different error code is desirable, use
+ * `nghttp2_submit_rst_stream()` with a desired error code and then
+ * return :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.
+ * Again, use ``frame->push_promise.promised_stream_id`` as stream_id
+ * parameter in `nghttp2_submit_rst_stream()` if frame is
+ * PUSH_PROMISE.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * It may return :enum:`nghttp2_error.NGHTTP2_ERR_PAUSE` or
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.  For
+ * other critical failures, it must return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  If the other
+ * nonzero value is returned, it is treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  If
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned,
+ * `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_header_callback()`.
+ *
+ * .. warning::
+ *
+ *   Application should properly limit the total buffer size to store
+ *   incoming header fields.  Without it, peer may send large number
+ *   of header fields or large header fields to cause out of memory in
+ *   local endpoint.  Due to how HPACK works, peer can do this
+ *   effectively without using much memory on their own.
+ */
+typedef int (*nghttp2_on_header_callback)(nghttp2_session *session,
+                                          const nghttp2_frame *frame,
+                                          const uint8_t *name, size_t namelen,
+                                          const uint8_t *value, size_t valuelen,
+                                          uint8_t flags, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when a header name/value pair is received
+ * for the |frame|.  The |name| is header name.  The |value| is header
+ * value.  The |flags| is bitwise OR of one or more of
+ * :type:`nghttp2_nv_flag`.
+ *
+ * This callback behaves like :type:`nghttp2_on_header_callback`,
+ * except that |name| and |value| are stored in reference counted
+ * buffer.  If application wishes to keep these references without
+ * copying them, use `nghttp2_rcbuf_incref()` to increment their
+ * reference count.  It is the application's responsibility to call
+ * `nghttp2_rcbuf_decref()` if they called `nghttp2_rcbuf_incref()` so
+ * as not to leak memory.  If the |session| is created by
+ * `nghttp2_session_server_new3()` or `nghttp2_session_client_new3()`,
+ * the function to free memory is the one belongs to the mem
+ * parameter.  As long as this free function alives, |name| and
+ * |value| can live after |session| was destroyed.
+ */
+typedef int (*nghttp2_on_header_callback2)(nghttp2_session *session,
+                                           const nghttp2_frame *frame,
+                                           nghttp2_rcbuf *name,
+                                           nghttp2_rcbuf *value, uint8_t flags,
+                                           void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when a invalid header name/value pair is
+ * received for the |frame|.
+ *
+ * The parameter and behaviour are similar to
+ * :type:`nghttp2_on_header_callback`.  The difference is that this
+ * callback is only invoked when a invalid header name/value pair is
+ * received which is treated as stream error if this callback is not
+ * set.  Only invalid regular header field are passed to this
+ * callback.  In other words, invalid pseudo header field is not
+ * passed to this callback.  Also header fields which includes upper
+ * cased latter are also treated as error without passing them to this
+ * callback.
+ *
+ * This callback is only considered if HTTP messaging validation is
+ * turned on (which is on by default, see
+ * `nghttp2_option_set_no_http_messaging()`).
+ *
+ * With this callback, application inspects the incoming invalid
+ * field, and it also can reset stream from this callback by returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.  By
+ * default, the error code is
+ * :enum:`nghttp2_error_code.NGHTTP2_PROTOCOL_ERROR`.  To change the
+ * error code, call `nghttp2_submit_rst_stream()` with the error code
+ * of choice in addition to returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.
+ *
+ * If 0 is returned, the header field is ignored, and the stream is
+ * not reset.
+ */
+typedef int (*nghttp2_on_invalid_header_callback)(
+    nghttp2_session *session, const nghttp2_frame *frame, const uint8_t *name,
+    size_t namelen, const uint8_t *value, size_t valuelen, uint8_t flags,
+    void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when a invalid header name/value pair is
+ * received for the |frame|.
+ *
+ * The parameter and behaviour are similar to
+ * :type:`nghttp2_on_header_callback2`.  The difference is that this
+ * callback is only invoked when a invalid header name/value pair is
+ * received which is silently ignored if this callback is not set.
+ * Only invalid regular header field are passed to this callback.  In
+ * other words, invalid pseudo header field is not passed to this
+ * callback.  Also header fields which includes upper cased latter are
+ * also treated as error without passing them to this callback.
+ *
+ * This callback is only considered if HTTP messaging validation is
+ * turned on (which is on by default, see
+ * `nghttp2_option_set_no_http_messaging()`).
+ *
+ * With this callback, application inspects the incoming invalid
+ * field, and it also can reset stream from this callback by returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.  By
+ * default, the error code is
+ * :enum:`nghttp2_error_code.NGHTTP2_INTERNAL_ERROR`.  To change the
+ * error code, call `nghttp2_submit_rst_stream()` with the error code
+ * of choice in addition to returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.
+ */
+typedef int (*nghttp2_on_invalid_header_callback2)(
+    nghttp2_session *session, const nghttp2_frame *frame, nghttp2_rcbuf *name,
+    nghttp2_rcbuf *value, uint8_t flags, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when the library asks application how
+ * many padding bytes are required for the transmission of the
+ * |frame|.  The application must choose the total length of payload
+ * including padded bytes in range [frame->hd.length, max_payloadlen],
+ * inclusive.  Choosing number not in this range will be treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  Returning
+ * ``frame->hd.length`` means no padding is added.  Returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` will make
+ * `nghttp2_session_send()` and `nghttp2_session_mem_send()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_select_padding_callback()`.
+ */
+typedef ssize_t (*nghttp2_select_padding_callback)(nghttp2_session *session,
+                                                   const nghttp2_frame *frame,
+                                                   size_t max_payloadlen,
+                                                   void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when library wants to get max length of
+ * data to send data to the remote peer.  The implementation of this
+ * function should return a value in the following range.  [1,
+ * min(|session_remote_window_size|, |stream_remote_window_size|,
+ * |remote_max_frame_size|)].  If a value greater than this range is
+ * returned than the max allow value will be used.  Returning a value
+ * smaller than this range is treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  The
+ * |frame_type| is provided for future extensibility and identifies
+ * the type of frame (see :type:`nghttp2_frame_type`) for which to get
+ * the length for.  Currently supported frame types are:
+ * :enum:`nghttp2_frame_type.NGHTTP2_DATA`.
+ *
+ * This callback can be used to control the length in bytes for which
+ * :type:`nghttp2_data_source_read_callback` is allowed to send to the
+ * remote endpoint.  This callback is optional.  Returning
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` will signal the
+ * entire session failure.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_data_source_read_length_callback()`.
+ */
+typedef ssize_t (*nghttp2_data_source_read_length_callback)(
+    nghttp2_session *session, uint8_t frame_type, int32_t stream_id,
+    int32_t session_remote_window_size, int32_t stream_remote_window_size,
+    uint32_t remote_max_frame_size, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when a frame header is received.  The
+ * |hd| points to received frame header.
+ *
+ * Unlike :type:`nghttp2_on_frame_recv_callback`, this callback will
+ * also be called when frame header of CONTINUATION frame is received.
+ *
+ * If both :type:`nghttp2_on_begin_frame_callback` and
+ * :type:`nghttp2_on_begin_headers_callback` are set and HEADERS or
+ * PUSH_PROMISE is received, :type:`nghttp2_on_begin_frame_callback`
+ * will be called first.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ * If nonzero value is returned, it is treated as fatal error and
+ * `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ *
+ * To set this callback to :type:`nghttp2_session_callbacks`, use
+ * `nghttp2_session_callbacks_set_on_begin_frame_callback()`.
+ */
+typedef int (*nghttp2_on_begin_frame_callback)(nghttp2_session *session,
+                                               const nghttp2_frame_hd *hd,
+                                               void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when chunk of extension frame payload is
+ * received.  The |hd| points to frame header.  The received
+ * chunk is |data| of length |len|.
+ *
+ * The implementation of this function must return 0 if it succeeds.
+ *
+ * To abort processing this extension frame, return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CANCEL`.
+ *
+ * If fatal error occurred, application should return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  In this case,
+ * `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  If the other
+ * values are returned, currently they are treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ */
+typedef int (*nghttp2_on_extension_chunk_recv_callback)(
+    nghttp2_session *session, const nghttp2_frame_hd *hd, const uint8_t *data,
+    size_t len, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when library asks the application to
+ * unpack extension payload from its wire format.  The extension
+ * payload has been passed to the application using
+ * :type:`nghttp2_on_extension_chunk_recv_callback`.  The frame header
+ * is already unpacked by the library and provided as |hd|.
+ *
+ * To receive extension frames, the application must tell desired
+ * extension frame type to the library using
+ * `nghttp2_option_set_user_recv_extension_type()`.
+ *
+ * The implementation of this function may store the pointer to the
+ * created object as a result of unpacking in |*payload|, and returns
+ * 0.  The pointer stored in |*payload| is opaque to the library, and
+ * the library does not own its pointer.  |*payload| is initialized as
+ * ``NULL``.  The |*payload| is available as ``frame->ext.payload`` in
+ * :type:`nghttp2_on_frame_recv_callback`.  Therefore if application
+ * can free that memory inside :type:`nghttp2_on_frame_recv_callback`
+ * callback.  Of course, application has a liberty not to use
+ * |*payload|, and do its own mechanism to process extension frames.
+ *
+ * To abort processing this extension frame, return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CANCEL`.
+ *
+ * If fatal error occurred, application should return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  In this case,
+ * `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  If the other
+ * values are returned, currently they are treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ */
+typedef int (*nghttp2_unpack_extension_callback)(nghttp2_session *session,
+                                                 void **payload,
+                                                 const nghttp2_frame_hd *hd,
+                                                 void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when library asks the application to pack
+ * extension payload in its wire format.  The frame header will be
+ * packed by library.  Application must pack payload only.
+ * ``frame->ext.payload`` is the object passed to
+ * `nghttp2_submit_extension()` as payload parameter.  Application
+ * must pack extension payload to the |buf| of its capacity |len|
+ * bytes.  The |len| is at least 16KiB.
+ *
+ * The implementation of this function should return the number of
+ * bytes written into |buf| when it succeeds.
+ *
+ * To abort processing this extension frame, return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CANCEL`, and
+ * :type:`nghttp2_on_frame_not_send_callback` will be invoked.
+ *
+ * If fatal error occurred, application should return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  In this case,
+ * `nghttp2_session_send()` and `nghttp2_session_mem_send()` functions
+ * immediately return
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  If the other
+ * values are returned, currently they are treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  If the return
+ * value is strictly larger than |len|, it is treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ */
+typedef ssize_t (*nghttp2_pack_extension_callback)(nghttp2_session *session,
+                                                   uint8_t *buf, size_t len,
+                                                   const nghttp2_frame *frame,
+                                                   void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when library provides the error message
+ * intended for human consumption.  This callback is solely for
+ * debugging purpose.  The |msg| is typically NULL-terminated string
+ * of length |len|.  |len| does not include the sentinel NULL
+ * character.
+ *
+ * This function is deprecated.  The new application should use
+ * :type:`nghttp2_error_callback2`.
+ *
+ * The format of error message may change between nghttp2 library
+ * versions.  The application should not depend on the particular
+ * format.
+ *
+ * Normally, application should return 0 from this callback.  If fatal
+ * error occurred while doing something in this callback, application
+ * should return :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ * In this case, library will return immediately with return value
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  Currently, if
+ * nonzero value is returned from this callback, they are treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`, but application
+ * should not rely on this details.
+ */
+typedef int (*nghttp2_error_callback)(nghttp2_session *session, const char *msg,
+                                      size_t len, void *user_data);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when library provides the error code, and
+ * message.  This callback is solely for debugging purpose.
+ * |lib_error_code| is one of error code defined in
+ * :enum:`nghttp2_error`.  The |msg| is typically NULL-terminated
+ * string of length |len|, and intended for human consumption.  |len|
+ * does not include the sentinel NULL character.
+ *
+ * The format of error message may change between nghttp2 library
+ * versions.  The application should not depend on the particular
+ * format.
+ *
+ * Normally, application should return 0 from this callback.  If fatal
+ * error occurred while doing something in this callback, application
+ * should return :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.
+ * In this case, library will return immediately with return value
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.  Currently, if
+ * nonzero value is returned from this callback, they are treated as
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`, but application
+ * should not rely on this details.
+ */
+typedef int (*nghttp2_error_callback2)(nghttp2_session *session,
+                                       int lib_error_code, const char *msg,
+                                       size_t len, void *user_data);
+
+struct nghttp2_session_callbacks;
+
+/**
+ * @struct
+ *
+ * Callback functions for :type:`nghttp2_session`.  The details of
+ * this structure are intentionally hidden from the public API.
+ */
+typedef struct nghttp2_session_callbacks nghttp2_session_callbacks;
+
+/**
+ * @function
+ *
+ * Initializes |*callbacks_ptr| with NULL values.
+ *
+ * The initialized object can be used when initializing multiple
+ * :type:`nghttp2_session` objects.
+ *
+ * When the application finished using this object, it can use
+ * `nghttp2_session_callbacks_del()` to free its memory.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_callbacks_new(nghttp2_session_callbacks **callbacks_ptr);
+
+/**
+ * @function
+ *
+ * Frees any resources allocated for |callbacks|.  If |callbacks| is
+ * ``NULL``, this function does nothing.
+ */
+NGHTTP2_EXTERN void
+nghttp2_session_callbacks_del(nghttp2_session_callbacks *callbacks);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when a session wants to send data to
+ * the remote peer.  This callback is not necessary if the application
+ * uses solely `nghttp2_session_mem_send()` to serialize data to
+ * transmit.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_send_callback(
+    nghttp2_session_callbacks *cbs, nghttp2_send_callback send_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when the a session wants to receive
+ * data from the remote peer.  This callback is not necessary if the
+ * application uses solely `nghttp2_session_mem_recv()` to process
+ * received data.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_recv_callback(
+    nghttp2_session_callbacks *cbs, nghttp2_recv_callback recv_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked by `nghttp2_session_recv()` and
+ * `nghttp2_session_mem_recv()` when a frame is received.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_frame_recv_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_frame_recv_callback on_frame_recv_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked by `nghttp2_session_recv()` and
+ * `nghttp2_session_mem_recv()` when an invalid non-DATA frame is
+ * received.
+ */
+NGHTTP2_EXTERN void
+nghttp2_session_callbacks_set_on_invalid_frame_recv_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_invalid_frame_recv_callback on_invalid_frame_recv_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when a chunk of data in DATA frame
+ * is received.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_data_chunk_recv_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_data_chunk_recv_callback on_data_chunk_recv_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked before a non-DATA frame is sent.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_before_frame_send_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_before_frame_send_callback before_frame_send_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked after a frame is sent.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_frame_send_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_frame_send_callback on_frame_send_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when a non-DATA frame is not sent
+ * because of an error.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_frame_not_send_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_frame_not_send_callback on_frame_not_send_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when the stream is closed.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_stream_close_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_stream_close_callback on_stream_close_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when the reception of header block
+ * in HEADERS or PUSH_PROMISE is started.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_begin_headers_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_begin_headers_callback on_begin_headers_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when a header name/value pair is
+ * received.  If both
+ * `nghttp2_session_callbacks_set_on_header_callback()` and
+ * `nghttp2_session_callbacks_set_on_header_callback2()` are used to
+ * set callbacks, the latter has the precedence.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_header_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_header_callback on_header_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when a header name/value pair is
+ * received.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_header_callback2(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_header_callback2 on_header_callback2);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when a invalid header name/value
+ * pair is received.  If both
+ * `nghttp2_session_callbacks_set_on_invalid_header_callback()` and
+ * `nghttp2_session_callbacks_set_on_invalid_header_callback2()` are
+ * used to set callbacks, the latter takes the precedence.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_invalid_header_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_invalid_header_callback on_invalid_header_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when a invalid header name/value
+ * pair is received.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_invalid_header_callback2(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_invalid_header_callback2 on_invalid_header_callback2);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when the library asks application
+ * how many padding bytes are required for the transmission of the
+ * given frame.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_select_padding_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_select_padding_callback select_padding_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function determine the length allowed in
+ * :type:`nghttp2_data_source_read_callback`.
+ */
+NGHTTP2_EXTERN void
+nghttp2_session_callbacks_set_data_source_read_length_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_data_source_read_length_callback data_source_read_length_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when a frame header is received.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_on_begin_frame_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_begin_frame_callback on_begin_frame_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when
+ * :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_COPY` is used in
+ * :type:`nghttp2_data_source_read_callback` to avoid data copy.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_send_data_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_send_data_callback send_data_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when the library asks the
+ * application to pack extension frame payload in wire format.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_pack_extension_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_pack_extension_callback pack_extension_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when the library asks the
+ * application to unpack extension frame payload from wire format.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_unpack_extension_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_unpack_extension_callback unpack_extension_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when chunk of extension frame
+ * payload is received.
+ */
+NGHTTP2_EXTERN void
+nghttp2_session_callbacks_set_on_extension_chunk_recv_callback(
+    nghttp2_session_callbacks *cbs,
+    nghttp2_on_extension_chunk_recv_callback on_extension_chunk_recv_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when library tells error message to
+ * the application.
+ *
+ * This function is deprecated.  The new application should use
+ * `nghttp2_session_callbacks_set_error_callback2()`.
+ *
+ * If both :type:`nghttp2_error_callback` and
+ * :type:`nghttp2_error_callback2` are set, the latter takes
+ * precedence.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_error_callback(
+    nghttp2_session_callbacks *cbs, nghttp2_error_callback error_callback);
+
+/**
+ * @function
+ *
+ * Sets callback function invoked when library tells error code, and
+ * message to the application.
+ *
+ * If both :type:`nghttp2_error_callback` and
+ * :type:`nghttp2_error_callback2` are set, the latter takes
+ * precedence.
+ */
+NGHTTP2_EXTERN void nghttp2_session_callbacks_set_error_callback2(
+    nghttp2_session_callbacks *cbs, nghttp2_error_callback2 error_callback2);
+
+/**
+ * @functypedef
+ *
+ * Custom memory allocator to replace malloc().  The |mem_user_data|
+ * is the mem_user_data member of :type:`nghttp2_mem` structure.
+ */
+typedef void *(*nghttp2_malloc)(size_t size, void *mem_user_data);
+
+/**
+ * @functypedef
+ *
+ * Custom memory allocator to replace free().  The |mem_user_data| is
+ * the mem_user_data member of :type:`nghttp2_mem` structure.
+ */
+typedef void (*nghttp2_free)(void *ptr, void *mem_user_data);
+
+/**
+ * @functypedef
+ *
+ * Custom memory allocator to replace calloc().  The |mem_user_data|
+ * is the mem_user_data member of :type:`nghttp2_mem` structure.
+ */
+typedef void *(*nghttp2_calloc)(size_t nmemb, size_t size, void *mem_user_data);
+
+/**
+ * @functypedef
+ *
+ * Custom memory allocator to replace realloc().  The |mem_user_data|
+ * is the mem_user_data member of :type:`nghttp2_mem` structure.
+ */
+typedef void *(*nghttp2_realloc)(void *ptr, size_t size, void *mem_user_data);
+
+/**
+ * @struct
+ *
+ * Custom memory allocator functions and user defined pointer.  The
+ * |mem_user_data| member 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 ``malloc``, ``free``, ``calloc`` and
+ * ``realloc`` respectively::
+ *
+ *     void *my_malloc_cb(size_t size, void *mem_user_data) {
+ *       return my_malloc(size);
+ *     }
+ *
+ *     void my_free_cb(void *ptr, void *mem_user_data) { my_free(ptr); }
+ *
+ *     void *my_calloc_cb(size_t nmemb, size_t size, void *mem_user_data) {
+ *       return my_calloc(nmemb, size);
+ *     }
+ *
+ *     void *my_realloc_cb(void *ptr, size_t size, void *mem_user_data) {
+ *       return my_realloc(ptr, size);
+ *     }
+ *
+ *     void session_new() {
+ *       nghttp2_session *session;
+ *       nghttp2_session_callbacks *callbacks;
+ *       nghttp2_mem mem = {NULL, my_malloc_cb, my_free_cb, my_calloc_cb,
+ *                          my_realloc_cb};
+ *
+ *       ...
+ *
+ *       nghttp2_session_client_new3(&session, callbacks, NULL, NULL, &mem);
+ *
+ *       ...
+ *     }
+ */
+typedef struct {
+  /**
+   * An arbitrary user supplied data.  This is passed to each
+   * allocator function.
+   */
+  void *mem_user_data;
+  /**
+   * Custom allocator function to replace malloc().
+   */
+  nghttp2_malloc malloc;
+  /**
+   * Custom allocator function to replace free().
+   */
+  nghttp2_free free;
+  /**
+   * Custom allocator function to replace calloc().
+   */
+  nghttp2_calloc calloc;
+  /**
+   * Custom allocator function to replace realloc().
+   */
+  nghttp2_realloc realloc;
+} nghttp2_mem;
+
+struct nghttp2_option;
+
+/**
+ * @struct
+ *
+ * Configuration options for :type:`nghttp2_session`.  The details of
+ * this structure are intentionally hidden from the public API.
+ */
+typedef struct nghttp2_option nghttp2_option;
+
+/**
+ * @function
+ *
+ * Initializes |*option_ptr| with default values.
+ *
+ * When the application finished using this object, it can use
+ * `nghttp2_option_del()` to free its memory.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_option_new(nghttp2_option **option_ptr);
+
+/**
+ * @function
+ *
+ * Frees any resources allocated for |option|.  If |option| is
+ * ``NULL``, this function does nothing.
+ */
+NGHTTP2_EXTERN void nghttp2_option_del(nghttp2_option *option);
+
+/**
+ * @function
+ *
+ * This option prevents the library from sending WINDOW_UPDATE for a
+ * connection automatically.  If this option is set to nonzero, the
+ * library won't send WINDOW_UPDATE for DATA until application calls
+ * `nghttp2_session_consume()` to indicate the consumed amount of
+ * data.  Don't use `nghttp2_submit_window_update()` for this purpose.
+ * By default, this option is set to zero.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_no_auto_window_update(nghttp2_option *option, int val);
+
+/**
+ * @function
+ *
+ * This option sets the SETTINGS_MAX_CONCURRENT_STREAMS value of
+ * remote endpoint as if it is received in SETTINGS frame.  Without
+ * specifying this option, the maximum number of outgoing concurrent
+ * streams is initially limited to 100 to avoid issues when the local
+ * endpoint submits lots of requests before receiving initial SETTINGS
+ * frame from the remote endpoint, since sending them at once to the
+ * remote endpoint could lead to rejection of some of the requests.
+ * This value will be overwritten when the local endpoint receives
+ * initial SETTINGS frame from the remote endpoint, either to the
+ * value advertised in SETTINGS_MAX_CONCURRENT_STREAMS or to the
+ * default value (unlimited) if none was advertised.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_peer_max_concurrent_streams(nghttp2_option *option,
+                                               uint32_t val);
+
+/**
+ * @function
+ *
+ * By default, nghttp2 library, if configured as server, requires
+ * first 24 bytes of client magic byte string (MAGIC).  In most cases,
+ * this will simplify the implementation of server.  But sometimes
+ * server may want to detect the application protocol based on first
+ * few bytes on clear text communication.
+ *
+ * If this option is used with nonzero |val|, nghttp2 library does not
+ * handle MAGIC.  It still checks following SETTINGS frame.  This
+ * means that applications should deal with MAGIC by themselves.
+ *
+ * If this option is not used or used with zero value, if MAGIC does
+ * not match :macro:`NGHTTP2_CLIENT_MAGIC`, `nghttp2_session_recv()`
+ * and `nghttp2_session_mem_recv()` will return error
+ * :enum:`nghttp2_error.NGHTTP2_ERR_BAD_CLIENT_MAGIC`, which is fatal
+ * error.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_no_recv_client_magic(nghttp2_option *option, int val);
+
+/**
+ * @function
+ *
+ * By default, nghttp2 library enforces subset of HTTP Messaging rules
+ * described in `HTTP/2 specification, section 8
+ * <https://tools.ietf.org/html/rfc7540#section-8>`_.  See
+ * :ref:`http-messaging` section for details.  For those applications
+ * who use nghttp2 library as non-HTTP use, give nonzero to |val| to
+ * disable this enforcement.  Please note that disabling this feature
+ * does not change the fundamental client and server model of HTTP.
+ * That is, even if the validation is disabled, only client can send
+ * requests.
+ */
+NGHTTP2_EXTERN void nghttp2_option_set_no_http_messaging(nghttp2_option *option,
+                                                         int val);
+
+/**
+ * @function
+ *
+ * RFC 7540 does not enforce any limit on the number of incoming
+ * reserved streams (in RFC 7540 terms, streams in reserved (remote)
+ * state).  This only affects client side, since only server can push
+ * streams.  Malicious server can push arbitrary number of streams,
+ * and make client's memory exhausted.  This option can set the
+ * maximum number of such incoming streams to avoid possible memory
+ * exhaustion.  If this option is set, and pushed streams are
+ * automatically closed on reception, without calling user provided
+ * callback, if they exceed the given limit.  The default value is
+ * 200.  If session is configured as server side, this option has no
+ * effect.  Server can control the number of streams to push.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_max_reserved_remote_streams(nghttp2_option *option,
+                                               uint32_t val);
+
+/**
+ * @function
+ *
+ * Sets extension frame type the application is willing to handle with
+ * user defined callbacks (see
+ * :type:`nghttp2_on_extension_chunk_recv_callback` and
+ * :type:`nghttp2_unpack_extension_callback`).  The |type| is
+ * extension frame type, and must be strictly greater than 0x9.
+ * Otherwise, this function does nothing.  The application can call
+ * this function multiple times to set more than one frame type to
+ * receive.  The application does not have to call this function if it
+ * just sends extension frames.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_user_recv_extension_type(nghttp2_option *option,
+                                            uint8_t type);
+
+/**
+ * @function
+ *
+ * Sets extension frame type the application is willing to receive
+ * using builtin handler.  The |type| is the extension frame type to
+ * receive, and must be strictly greater than 0x9.  Otherwise, this
+ * function does nothing.  The application can call this function
+ * multiple times to set more than one frame type to receive.  The
+ * application does not have to call this function if it just sends
+ * extension frames.
+ *
+ * If same frame type is passed to both
+ * `nghttp2_option_set_builtin_recv_extension_type()` and
+ * `nghttp2_option_set_user_recv_extension_type()`, the latter takes
+ * precedence.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_builtin_recv_extension_type(nghttp2_option *option,
+                                               uint8_t type);
+
+/**
+ * @function
+ *
+ * This option prevents the library from sending PING frame with ACK
+ * flag set automatically when PING frame without ACK flag set is
+ * received.  If this option is set to nonzero, the library won't send
+ * PING frame with ACK flag set in the response for incoming PING
+ * frame.  The application can send PING frame with ACK flag set using
+ * `nghttp2_submit_ping()` with :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK`
+ * as flags parameter.
+ */
+NGHTTP2_EXTERN void nghttp2_option_set_no_auto_ping_ack(nghttp2_option *option,
+                                                        int val);
+
+/**
+ * @function
+ *
+ * This option sets the maximum length of header block (a set of
+ * header fields per one HEADERS frame) to send.  The length of a
+ * given set of header fields is calculated using
+ * `nghttp2_hd_deflate_bound()`.  The default value is 64KiB.  If
+ * application attempts to send header fields larger than this limit,
+ * the transmission of the frame fails with error code
+ * :enum:`nghttp2_error.NGHTTP2_ERR_FRAME_SIZE_ERROR`.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_max_send_header_block_length(nghttp2_option *option,
+                                                size_t val);
+
+/**
+ * @function
+ *
+ * This option sets the maximum dynamic table size for deflating
+ * header fields.  The default value is 4KiB.  In HTTP/2, receiver of
+ * deflated header block can specify maximum dynamic table size.  The
+ * actual maximum size is the minimum of the size receiver specified
+ * and this option value.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_max_deflate_dynamic_table_size(nghttp2_option *option,
+                                                  size_t val);
+
+/**
+ * @function
+ *
+ * This option prevents the library from retaining closed streams to
+ * maintain the priority tree.  If this option is set to nonzero,
+ * applications can discard closed stream completely to save memory.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 1 is submitted via `nghttp2_submit_settings()`, any
+ * closed streams are not retained regardless of this option.
+ */
+NGHTTP2_EXTERN void nghttp2_option_set_no_closed_streams(nghttp2_option *option,
+                                                         int val);
+
+/**
+ * @function
+ *
+ * This function sets the maximum number of outgoing SETTINGS ACK and
+ * PING ACK frames retained in :type:`nghttp2_session` object.  If
+ * more than those frames are retained, the peer is considered to be
+ * misbehaving and session will be closed.  The default value is 1000.
+ */
+NGHTTP2_EXTERN void nghttp2_option_set_max_outbound_ack(nghttp2_option *option,
+                                                        size_t val);
+
+/**
+ * @function
+ *
+ * This function sets the maximum number of SETTINGS entries per
+ * SETTINGS frame that will be accepted. If more than those entries
+ * are received, the peer is considered to be misbehaving and session
+ * will be closed. The default value is 32.
+ */
+NGHTTP2_EXTERN void nghttp2_option_set_max_settings(nghttp2_option *option,
+                                                    size_t val);
+
+/**
+ * @function
+ *
+ * This option, if set to nonzero, allows server to fallback to
+ * :rfc:`7540` priorities if SETTINGS_NO_RFC7540_PRIORITIES was not
+ * received from client, and server submitted
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * = 1 via `nghttp2_submit_settings()`.  Most of the advanced
+ * functionality for RFC 7540 priorities are still disabled.  This
+ * fallback only enables the minimal feature set of RFC 7540
+ * priorities to deal with priority signaling from client.
+ *
+ * Client session ignores this option.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_server_fallback_rfc7540_priorities(nghttp2_option *option,
+                                                      int val);
+
+/**
+ * @function
+ *
+ * This option, if set to nonzero, turns off RFC 9113 leading and
+ * trailing white spaces validation against HTTP field value.  Some
+ * important fields, such as HTTP/2 pseudo header fields, are
+ * validated more strictly and this option does not apply to them.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_no_rfc9113_leading_and_trailing_ws_validation(
+    nghttp2_option *option, int val);
+
+/**
+ * @function
+ *
+ * This function sets the rate limit for the incoming stream reset
+ * (RST_STREAM frame).  It is server use only.  It is a token-bucket
+ * based rate limiter.  |burst| specifies the number of tokens that is
+ * initially available.  The maximum number of tokens is capped to
+ * this value.  |rate| specifies the number of tokens that are
+ * regenerated per second.  An incoming RST_STREAM consumes one token.
+ * If there is no token available, GOAWAY is sent to tear down the
+ * connection.  |burst| and |rate| default to 1000 and 33
+ * respectively.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_stream_reset_rate_limit(nghttp2_option *option,
+                                           uint64_t burst, uint64_t rate);
+
+/**
+ * @function
+ *
+ * Initializes |*session_ptr| for client use.  The all members of
+ * |callbacks| are copied to |*session_ptr|.  Therefore |*session_ptr|
+ * does not store |callbacks|.  The |user_data| is an arbitrary user
+ * supplied data, which will be passed to the callback functions.
+ *
+ * The :type:`nghttp2_send_callback` must be specified.  If the
+ * application code uses `nghttp2_session_recv()`, the
+ * :type:`nghttp2_recv_callback` must be specified.  The other members
+ * of |callbacks| can be ``NULL``.
+ *
+ * If this function fails, |*session_ptr| is left untouched.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_client_new(nghttp2_session **session_ptr,
+                           const nghttp2_session_callbacks *callbacks,
+                           void *user_data);
+
+/**
+ * @function
+ *
+ * Initializes |*session_ptr| for server use.  The all members of
+ * |callbacks| are copied to |*session_ptr|. Therefore |*session_ptr|
+ * does not store |callbacks|.  The |user_data| is an arbitrary user
+ * supplied data, which will be passed to the callback functions.
+ *
+ * The :type:`nghttp2_send_callback` must be specified.  If the
+ * application code uses `nghttp2_session_recv()`, the
+ * :type:`nghttp2_recv_callback` must be specified.  The other members
+ * of |callbacks| can be ``NULL``.
+ *
+ * If this function fails, |*session_ptr| is left untouched.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_server_new(nghttp2_session **session_ptr,
+                           const nghttp2_session_callbacks *callbacks,
+                           void *user_data);
+
+/**
+ * @function
+ *
+ * Like `nghttp2_session_client_new()`, but with additional options
+ * specified in the |option|.
+ *
+ * The |option| can be ``NULL`` and the call is equivalent to
+ * `nghttp2_session_client_new()`.
+ *
+ * This function does not take ownership |option|.  The application is
+ * responsible for freeing |option| if it finishes using the object.
+ *
+ * The library code does not refer to |option| after this function
+ * returns.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_client_new2(nghttp2_session **session_ptr,
+                            const nghttp2_session_callbacks *callbacks,
+                            void *user_data, const nghttp2_option *option);
+
+/**
+ * @function
+ *
+ * Like `nghttp2_session_server_new()`, but with additional options
+ * specified in the |option|.
+ *
+ * The |option| can be ``NULL`` and the call is equivalent to
+ * `nghttp2_session_server_new()`.
+ *
+ * This function does not take ownership |option|.  The application is
+ * responsible for freeing |option| if it finishes using the object.
+ *
+ * The library code does not refer to |option| after this function
+ * returns.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_server_new2(nghttp2_session **session_ptr,
+                            const nghttp2_session_callbacks *callbacks,
+                            void *user_data, const nghttp2_option *option);
+
+/**
+ * @function
+ *
+ * Like `nghttp2_session_client_new2()`, but with additional custom
+ * memory allocator specified in the |mem|.
+ *
+ * The |mem| can be ``NULL`` and the call is equivalent to
+ * `nghttp2_session_client_new2()`.
+ *
+ * This function does not take ownership |mem|.  The application is
+ * responsible for freeing |mem|.
+ *
+ * The library code does not refer to |mem| pointer after this
+ * function returns, so the application can safely free it.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_session_client_new3(
+    nghttp2_session **session_ptr, const nghttp2_session_callbacks *callbacks,
+    void *user_data, const nghttp2_option *option, nghttp2_mem *mem);
+
+/**
+ * @function
+ *
+ * Like `nghttp2_session_server_new2()`, but with additional custom
+ * memory allocator specified in the |mem|.
+ *
+ * The |mem| can be ``NULL`` and the call is equivalent to
+ * `nghttp2_session_server_new2()`.
+ *
+ * This function does not take ownership |mem|.  The application is
+ * responsible for freeing |mem|.
+ *
+ * The library code does not refer to |mem| pointer after this
+ * function returns, so the application can safely free it.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_session_server_new3(
+    nghttp2_session **session_ptr, const nghttp2_session_callbacks *callbacks,
+    void *user_data, const nghttp2_option *option, nghttp2_mem *mem);
+
+/**
+ * @function
+ *
+ * Frees any resources allocated for |session|.  If |session| is
+ * ``NULL``, this function does nothing.
+ */
+NGHTTP2_EXTERN void nghttp2_session_del(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Sends pending frames to the remote peer.
+ *
+ * This function retrieves the highest prioritized frame from the
+ * outbound queue and sends it to the remote peer.  It does this as
+ * many times as possible until the user callback
+ * :type:`nghttp2_send_callback` returns
+ * :enum:`nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`, the outbound queue
+ * becomes empty or flow control is triggered (remote window size
+ * becomes depleted or maximum number of concurrent streams is
+ * reached).  This function calls several callback functions which are
+ * passed when initializing the |session|.  Here is the simple time
+ * chart which tells when each callback is invoked:
+ *
+ * 1. Get the next frame to send from outbound queue.
+ *
+ * 2. Prepare transmission of the frame.
+ *
+ * 3. If the control frame cannot be sent because some preconditions
+ *    are not met (e.g., request HEADERS cannot be sent after GOAWAY),
+ *    :type:`nghttp2_on_frame_not_send_callback` is invoked.  Abort
+ *    the following steps.
+ *
+ * 4. If the frame is HEADERS, PUSH_PROMISE or DATA,
+ *    :type:`nghttp2_select_padding_callback` is invoked.
+ *
+ * 5. If the frame is request HEADERS, the stream is opened here.
+ *
+ * 6. :type:`nghttp2_before_frame_send_callback` is invoked.
+ *
+ * 7. If :enum:`nghttp2_error.NGHTTP2_ERR_CANCEL` is returned from
+ *    :type:`nghttp2_before_frame_send_callback`, the current frame
+ *    transmission is canceled, and
+ *    :type:`nghttp2_on_frame_not_send_callback` is invoked.  Abort
+ *    the following steps.
+ *
+ * 8. :type:`nghttp2_send_callback` is invoked one or more times to
+ *    send the frame.
+ *
+ * 9. :type:`nghttp2_on_frame_send_callback` is invoked.
+ *
+ * 10. If the transmission of the frame triggers closure of the
+ *     stream, the stream is closed and
+ *     :type:`nghttp2_on_stream_close_callback` is invoked.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`
+ *     The callback function failed.
+ */
+NGHTTP2_EXTERN int nghttp2_session_send(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns the serialized data to send.
+ *
+ * This function behaves like `nghttp2_session_send()` except that it
+ * does not use :type:`nghttp2_send_callback` to transmit data.
+ * Instead, it assigns the pointer to the serialized data to the
+ * |*data_ptr| and returns its length.  The other callbacks are called
+ * in the same way as they are in `nghttp2_session_send()`.
+ *
+ * If no data is available to send, this function returns 0.
+ *
+ * This function may not return all serialized data in one invocation.
+ * To get all data, call this function repeatedly until it returns 0
+ * or one of negative error codes.
+ *
+ * The assigned |*data_ptr| is valid until the next call of
+ * `nghttp2_session_mem_send()` or `nghttp2_session_send()`.
+ *
+ * The caller must send all data before sending the next chunk of
+ * data.
+ *
+ * This function returns the length of the data pointed by the
+ * |*data_ptr| if it succeeds, or one of the following negative error
+ * codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ *
+ * .. note::
+ *
+ *   This function may produce very small byte string.  If that is the
+ *   case, and application disables Nagle algorithm (``TCP_NODELAY``),
+ *   then writing this small chunk leads to very small packet, and it
+ *   is very inefficient.  An application should be responsible to
+ *   buffer up small chunks of data as necessary to avoid this
+ *   situation.
+ */
+NGHTTP2_EXTERN ssize_t nghttp2_session_mem_send(nghttp2_session *session,
+                                                const uint8_t **data_ptr);
+
+/**
+ * @function
+ *
+ * Receives frames from the remote peer.
+ *
+ * This function receives as many frames as possible until the user
+ * callback :type:`nghttp2_recv_callback` returns
+ * :enum:`nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`.  This function calls
+ * several callback functions which are passed when initializing the
+ * |session|.  Here is the simple time chart which tells when each
+ * callback is invoked:
+ *
+ * 1. :type:`nghttp2_recv_callback` is invoked one or more times to
+ *    receive frame header.
+ *
+ * 2. When frame header is received,
+ *    :type:`nghttp2_on_begin_frame_callback` is invoked.
+ *
+ * 3. If the frame is DATA frame:
+ *
+ *    1. :type:`nghttp2_recv_callback` is invoked to receive DATA
+ *       payload. For each chunk of data,
+ *       :type:`nghttp2_on_data_chunk_recv_callback` is invoked.
+ *
+ *    2. If one DATA frame is completely received,
+ *       :type:`nghttp2_on_frame_recv_callback` is invoked.  If the
+ *       reception of the frame triggers the closure of the stream,
+ *       :type:`nghttp2_on_stream_close_callback` is invoked.
+ *
+ * 4. If the frame is the control frame:
+ *
+ *    1. :type:`nghttp2_recv_callback` is invoked one or more times to
+ *       receive whole frame.
+ *
+ *    2. If the received frame is valid, then following actions are
+ *       taken.  If the frame is either HEADERS or PUSH_PROMISE,
+ *       :type:`nghttp2_on_begin_headers_callback` is invoked.  Then
+ *       :type:`nghttp2_on_header_callback` is invoked for each header
+ *       name/value pair.  For invalid header field,
+ *       :type:`nghttp2_on_invalid_header_callback` is called.  After
+ *       all name/value pairs are emitted successfully,
+ *       :type:`nghttp2_on_frame_recv_callback` is invoked.  For other
+ *       frames, :type:`nghttp2_on_frame_recv_callback` is invoked.
+ *       If the reception of the frame triggers the closure of the
+ *       stream, :type:`nghttp2_on_stream_close_callback` is invoked.
+ *
+ *    3. If the received frame is unpacked but is interpreted as
+ *       invalid, :type:`nghttp2_on_invalid_frame_recv_callback` is
+ *       invoked.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_EOF`
+ *     The remote peer did shutdown on the connection.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`
+ *     The callback function failed.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_BAD_CLIENT_MAGIC`
+ *     Invalid client magic was detected.  This error only returns
+ *     when |session| was configured as server and
+ *     `nghttp2_option_set_no_recv_client_magic()` is not used with
+ *     nonzero value.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_FLOODED`
+ *     Flooding was detected in this HTTP/2 session, and it must be
+ *     closed.  This is most likely caused by misbehaviour of peer.
+ */
+NGHTTP2_EXTERN int nghttp2_session_recv(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Processes data |in| as an input from the remote endpoint.  The
+ * |inlen| indicates the number of bytes to receive in the |in|.
+ *
+ * This function behaves like `nghttp2_session_recv()` except that it
+ * does not use :type:`nghttp2_recv_callback` to receive data; the
+ * |in| is the only data for the invocation of this function.  If all
+ * bytes are processed, this function returns.  The other callbacks
+ * are called in the same way as they are in `nghttp2_session_recv()`.
+ *
+ * In the current implementation, this function always tries to
+ * processes |inlen| bytes of input data unless either an error occurs or
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PAUSE` is returned from
+ * :type:`nghttp2_on_header_callback` or
+ * :type:`nghttp2_on_data_chunk_recv_callback`.  If
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PAUSE` is used, the return value
+ * includes the number of bytes which was used to produce the data or
+ * frame for the callback.
+ *
+ * This function returns the number of processed bytes, or one of the
+ * following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`
+ *     The callback function failed.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_BAD_CLIENT_MAGIC`
+ *     Invalid client magic was detected.  This error only returns
+ *     when |session| was configured as server and
+ *     `nghttp2_option_set_no_recv_client_magic()` is not used with
+ *     nonzero value.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_FLOODED`
+ *     Flooding was detected in this HTTP/2 session, and it must be
+ *     closed.  This is most likely caused by misbehaviour of peer.
+ */
+NGHTTP2_EXTERN ssize_t nghttp2_session_mem_recv(nghttp2_session *session,
+                                                const uint8_t *in,
+                                                size_t inlen);
+
+/**
+ * @function
+ *
+ * Puts back previously deferred DATA frame in the stream |stream_id|
+ * to the outbound queue.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The stream does not exist; or no deferred data exist.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_session_resume_data(nghttp2_session *session,
+                                               int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Returns nonzero value if |session| wants to receive data from the
+ * remote peer.
+ *
+ * If both `nghttp2_session_want_read()` and
+ * `nghttp2_session_want_write()` return 0, the application should
+ * drop the connection.
+ */
+NGHTTP2_EXTERN int nghttp2_session_want_read(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns nonzero value if |session| wants to send data to the remote
+ * peer.
+ *
+ * If both `nghttp2_session_want_read()` and
+ * `nghttp2_session_want_write()` return 0, the application should
+ * drop the connection.
+ */
+NGHTTP2_EXTERN int nghttp2_session_want_write(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns stream_user_data for the stream |stream_id|.  The
+ * stream_user_data is provided by `nghttp2_submit_request()`,
+ * `nghttp2_submit_headers()` or
+ * `nghttp2_session_set_stream_user_data()`.  Unless it is set using
+ * `nghttp2_session_set_stream_user_data()`, if the stream is
+ * initiated by the remote endpoint, stream_user_data is always
+ * ``NULL``.  If the stream does not exist, this function returns
+ * ``NULL``.
+ */
+NGHTTP2_EXTERN void *
+nghttp2_session_get_stream_user_data(nghttp2_session *session,
+                                     int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Sets the |stream_user_data| to the stream denoted by the
+ * |stream_id|.  If a stream user data is already set to the stream,
+ * it is replaced with the |stream_user_data|.  It is valid to specify
+ * ``NULL`` in the |stream_user_data|, which nullifies the associated
+ * data pointer.
+ *
+ * It is valid to set the |stream_user_data| to the stream reserved by
+ * PUSH_PROMISE frame.
+ *
+ * This function returns 0 if it succeeds, or one of following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The stream does not exist
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_set_stream_user_data(nghttp2_session *session,
+                                     int32_t stream_id, void *stream_user_data);
+
+/**
+ * @function
+ *
+ * Sets |user_data| to |session|, overwriting the existing user data
+ * specified in `nghttp2_session_client_new()`, or
+ * `nghttp2_session_server_new()`.
+ */
+NGHTTP2_EXTERN void nghttp2_session_set_user_data(nghttp2_session *session,
+                                                  void *user_data);
+
+/**
+ * @function
+ *
+ * Returns the number of frames in the outbound queue.  This does not
+ * include the deferred DATA frames.
+ */
+NGHTTP2_EXTERN size_t
+nghttp2_session_get_outbound_queue_size(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns the number of DATA payload in bytes received without
+ * WINDOW_UPDATE transmission for the stream |stream_id|.  The local
+ * (receive) window size can be adjusted by
+ * `nghttp2_submit_window_update()`.  This function takes into account
+ * that and returns effective data length.  In particular, if the
+ * local window size is reduced by submitting negative
+ * window_size_increment with `nghttp2_submit_window_update()`, this
+ * function returns the number of bytes less than actually received.
+ *
+ * This function returns -1 if it fails.
+ */
+NGHTTP2_EXTERN int32_t nghttp2_session_get_stream_effective_recv_data_length(
+    nghttp2_session *session, int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Returns the local (receive) window size for the stream |stream_id|.
+ * The local window size can be adjusted by
+ * `nghttp2_submit_window_update()`.  This function takes into account
+ * that and returns effective window size.
+ *
+ * This function does not take into account the amount of received
+ * data from the remote endpoint.  Use
+ * `nghttp2_session_get_stream_local_window_size()` to know the amount
+ * of data the remote endpoint can send without receiving stream level
+ * WINDOW_UPDATE frame.  Note that each stream is still subject to the
+ * connection level flow control.
+ *
+ * This function returns -1 if it fails.
+ */
+NGHTTP2_EXTERN int32_t nghttp2_session_get_stream_effective_local_window_size(
+    nghttp2_session *session, int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Returns the amount of flow-controlled payload (e.g., DATA) that the
+ * remote endpoint can send without receiving stream level
+ * WINDOW_UPDATE frame.  It is also subject to the connection level
+ * flow control.  So the actual amount of data to send is
+ * min(`nghttp2_session_get_stream_local_window_size()`,
+ * `nghttp2_session_get_local_window_size()`).
+ *
+ * This function returns -1 if it fails.
+ */
+NGHTTP2_EXTERN int32_t nghttp2_session_get_stream_local_window_size(
+    nghttp2_session *session, int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Returns the number of DATA payload in bytes received without
+ * WINDOW_UPDATE transmission for a connection.  The local (receive)
+ * window size can be adjusted by `nghttp2_submit_window_update()`.
+ * This function takes into account that and returns effective data
+ * length.  In particular, if the local window size is reduced by
+ * submitting negative window_size_increment with
+ * `nghttp2_submit_window_update()`, this function returns the number
+ * of bytes less than actually received.
+ *
+ * This function returns -1 if it fails.
+ */
+NGHTTP2_EXTERN int32_t
+nghttp2_session_get_effective_recv_data_length(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns the local (receive) window size for a connection.  The
+ * local window size can be adjusted by
+ * `nghttp2_submit_window_update()`.  This function takes into account
+ * that and returns effective window size.
+ *
+ * This function does not take into account the amount of received
+ * data from the remote endpoint.  Use
+ * `nghttp2_session_get_local_window_size()` to know the amount of
+ * data the remote endpoint can send without receiving
+ * connection-level WINDOW_UPDATE frame.  Note that each stream is
+ * still subject to the stream level flow control.
+ *
+ * This function returns -1 if it fails.
+ */
+NGHTTP2_EXTERN int32_t
+nghttp2_session_get_effective_local_window_size(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns the amount of flow-controlled payload (e.g., DATA) that the
+ * remote endpoint can send without receiving connection level
+ * WINDOW_UPDATE frame.  Note that each stream is still subject to the
+ * stream level flow control (see
+ * `nghttp2_session_get_stream_local_window_size()`).
+ *
+ * This function returns -1 if it fails.
+ */
+NGHTTP2_EXTERN int32_t
+nghttp2_session_get_local_window_size(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns the remote window size for a given stream |stream_id|.
+ *
+ * This is the amount of flow-controlled payload (e.g., DATA) that the
+ * local endpoint can send without stream level WINDOW_UPDATE.  There
+ * is also connection level flow control, so the effective size of
+ * payload that the local endpoint can actually send is
+ * min(`nghttp2_session_get_stream_remote_window_size()`,
+ * `nghttp2_session_get_remote_window_size()`).
+ *
+ * This function returns -1 if it fails.
+ */
+NGHTTP2_EXTERN int32_t nghttp2_session_get_stream_remote_window_size(
+    nghttp2_session *session, int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Returns the remote window size for a connection.
+ *
+ * This function always succeeds.
+ */
+NGHTTP2_EXTERN int32_t
+nghttp2_session_get_remote_window_size(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns 1 if local peer half closed the given stream |stream_id|.
+ * Returns 0 if it did not.  Returns -1 if no such stream exists.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_get_stream_local_close(nghttp2_session *session,
+                                       int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Returns 1 if remote peer half closed the given stream |stream_id|.
+ * Returns 0 if it did not.  Returns -1 if no such stream exists.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_get_stream_remote_close(nghttp2_session *session,
+                                        int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Returns the current dynamic table size of HPACK inflater, including
+ * the overhead 32 bytes per entry described in RFC 7541.
+ */
+NGHTTP2_EXTERN size_t
+nghttp2_session_get_hd_inflate_dynamic_table_size(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns the current dynamic table size of HPACK deflater including
+ * the overhead 32 bytes per entry described in RFC 7541.
+ */
+NGHTTP2_EXTERN size_t
+nghttp2_session_get_hd_deflate_dynamic_table_size(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Signals the session so that the connection should be terminated.
+ *
+ * The last stream ID is the minimum value between the stream ID of a
+ * stream for which :type:`nghttp2_on_frame_recv_callback` was called
+ * most recently and the last stream ID we have sent to the peer
+ * previously.
+ *
+ * The |error_code| is the error code of this GOAWAY frame.  The
+ * pre-defined error code is one of :enum:`nghttp2_error_code`.
+ *
+ * After the transmission, both `nghttp2_session_want_read()` and
+ * `nghttp2_session_want_write()` return 0.
+ *
+ * This function should be called when the connection should be
+ * terminated after sending GOAWAY.  If the remaining streams should
+ * be processed after GOAWAY, use `nghttp2_submit_goaway()` instead.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_session_terminate_session(nghttp2_session *session,
+                                                     uint32_t error_code);
+
+/**
+ * @function
+ *
+ * Signals the session so that the connection should be terminated.
+ *
+ * This function behaves like `nghttp2_session_terminate_session()`,
+ * but the last stream ID can be specified by the application for fine
+ * grained control of stream.  The HTTP/2 specification does not allow
+ * last_stream_id to be increased.  So the actual value sent as
+ * last_stream_id is the minimum value between the given
+ * |last_stream_id| and the last_stream_id we have previously sent to
+ * the peer.
+ *
+ * The |last_stream_id| is peer's stream ID or 0.  So if |session| is
+ * initialized as client, |last_stream_id| must be even or 0.  If
+ * |session| is initialized as server, |last_stream_id| must be odd or
+ * 0.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |last_stream_id| is invalid.
+ */
+NGHTTP2_EXTERN int nghttp2_session_terminate_session2(nghttp2_session *session,
+                                                      int32_t last_stream_id,
+                                                      uint32_t error_code);
+
+/**
+ * @function
+ *
+ * Signals to the client that the server started graceful shutdown
+ * procedure.
+ *
+ * This function is only usable for server.  If this function is
+ * called with client side session, this function returns
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`.
+ *
+ * To gracefully shutdown HTTP/2 session, server should call this
+ * function to send GOAWAY with last_stream_id (1u << 31) - 1.  And
+ * after some delay (e.g., 1 RTT), send another GOAWAY with the stream
+ * ID that the server has some processing using
+ * `nghttp2_submit_goaway()`.  See also
+ * `nghttp2_session_get_last_proc_stream_id()`.
+ *
+ * Unlike `nghttp2_submit_goaway()`, this function just sends GOAWAY
+ * and does nothing more.  This is a mere indication to the client
+ * that session shutdown is imminent.  The application should call
+ * `nghttp2_submit_goaway()` with appropriate last_stream_id after
+ * this call.
+ *
+ * If one or more GOAWAY frame have been already sent by either
+ * `nghttp2_submit_goaway()` or `nghttp2_session_terminate_session()`,
+ * this function has no effect.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     The |session| is initialized as client.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_shutdown_notice(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns the value of SETTINGS |id| notified by a remote endpoint.
+ * The |id| must be one of values defined in
+ * :enum:`nghttp2_settings_id`.
+ */
+NGHTTP2_EXTERN uint32_t nghttp2_session_get_remote_settings(
+    nghttp2_session *session, nghttp2_settings_id id);
+
+/**
+ * @function
+ *
+ * Returns the value of SETTINGS |id| of local endpoint acknowledged
+ * by the remote endpoint.  The |id| must be one of the values defined
+ * in :enum:`nghttp2_settings_id`.
+ */
+NGHTTP2_EXTERN uint32_t nghttp2_session_get_local_settings(
+    nghttp2_session *session, nghttp2_settings_id id);
+
+/**
+ * @function
+ *
+ * Tells the |session| that next stream ID is |next_stream_id|.  The
+ * |next_stream_id| must be equal or greater than the value returned
+ * by `nghttp2_session_get_next_stream_id()`.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |next_stream_id| is strictly less than the value
+ *     `nghttp2_session_get_next_stream_id()` returns; or
+ *     |next_stream_id| is invalid (e.g., even integer for client, or
+ *     odd integer for server).
+ */
+NGHTTP2_EXTERN int nghttp2_session_set_next_stream_id(nghttp2_session *session,
+                                                      int32_t next_stream_id);
+
+/**
+ * @function
+ *
+ * Returns the next outgoing stream ID.  Notice that return type is
+ * uint32_t.  If we run out of stream ID for this session, this
+ * function returns 1 << 31.
+ */
+NGHTTP2_EXTERN uint32_t
+nghttp2_session_get_next_stream_id(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Tells the |session| that |size| bytes for a stream denoted by
+ * |stream_id| were consumed by application and are ready to
+ * WINDOW_UPDATE.  The consumed bytes are counted towards both
+ * connection and stream level WINDOW_UPDATE (see
+ * `nghttp2_session_consume_connection()` and
+ * `nghttp2_session_consume_stream()` to update consumption
+ * independently).  This function is intended to be used without
+ * automatic window update (see
+ * `nghttp2_option_set_no_auto_window_update()`).
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     Automatic WINDOW_UPDATE is not disabled.
+ */
+NGHTTP2_EXTERN int nghttp2_session_consume(nghttp2_session *session,
+                                           int32_t stream_id, size_t size);
+
+/**
+ * @function
+ *
+ * Like `nghttp2_session_consume()`, but this only tells library that
+ * |size| bytes were consumed only for connection level.  Note that
+ * HTTP/2 maintains connection and stream level flow control windows
+ * independently.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     Automatic WINDOW_UPDATE is not disabled.
+ */
+NGHTTP2_EXTERN int nghttp2_session_consume_connection(nghttp2_session *session,
+                                                      size_t size);
+
+/**
+ * @function
+ *
+ * Like `nghttp2_session_consume()`, but this only tells library that
+ * |size| bytes were consumed only for stream denoted by |stream_id|.
+ * Note that HTTP/2 maintains connection and stream level flow control
+ * windows independently.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     Automatic WINDOW_UPDATE is not disabled.
+ */
+NGHTTP2_EXTERN int nghttp2_session_consume_stream(nghttp2_session *session,
+                                                  int32_t stream_id,
+                                                  size_t size);
+
+/**
+ * @function
+ *
+ * Changes priority of existing stream denoted by |stream_id|.  The
+ * new priority specification is |pri_spec|.
+ *
+ * The priority is changed silently and instantly, and no PRIORITY
+ * frame will be sent to notify the peer of this change.  This
+ * function may be useful for server to change the priority of pushed
+ * stream.
+ *
+ * If |session| is initialized as server, and ``pri_spec->stream_id``
+ * points to the idle stream, the idle stream is created if it does
+ * not exist.  The created idle stream will depend on root stream
+ * (stream 0) with weight 16.
+ *
+ * Otherwise, if stream denoted by ``pri_spec->stream_id`` is not
+ * found, we use default priority instead of given |pri_spec|.  That
+ * is make stream depend on root stream with weight 16.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 1 is submitted via `nghttp2_submit_settings()`, this
+ * function does nothing and returns 0.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     Attempted to depend on itself; or no stream exist for the given
+ *     |stream_id|; or |stream_id| is 0
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_change_stream_priority(nghttp2_session *session,
+                                       int32_t stream_id,
+                                       const nghttp2_priority_spec *pri_spec);
+
+/**
+ * @function
+ *
+ * Creates idle stream with the given |stream_id|, and priority
+ * |pri_spec|.
+ *
+ * The stream creation is done without sending PRIORITY frame, which
+ * means that peer does not know about the existence of this idle
+ * stream in the local endpoint.
+ *
+ * RFC 7540 does not disallow the use of creation of idle stream with
+ * odd or even stream ID regardless of client or server.  So this
+ * function can create odd or even stream ID regardless of client or
+ * server.  But probably it is a bit safer to use the stream ID the
+ * local endpoint can initiate (in other words, use odd stream ID for
+ * client, and even stream ID for server), to avoid potential
+ * collision from peer's instruction.  Also we can use
+ * `nghttp2_session_set_next_stream_id()` to avoid to open created
+ * idle streams accidentally if we follow this recommendation.
+ *
+ * If |session| is initialized as server, and ``pri_spec->stream_id``
+ * points to the idle stream, the idle stream is created if it does
+ * not exist.  The created idle stream will depend on root stream
+ * (stream 0) with weight 16.
+ *
+ * Otherwise, if stream denoted by ``pri_spec->stream_id`` is not
+ * found, we use default priority instead of given |pri_spec|.  That
+ * is make stream depend on root stream with weight 16.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 1 is submitted via `nghttp2_submit_settings()`, this
+ * function does nothing and returns 0.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     Attempted to depend on itself; or stream denoted by |stream_id|
+ *     already exists; or |stream_id| cannot be used to create idle
+ *     stream (in other words, local endpoint has already opened
+ *     stream ID greater than or equal to the given stream ID; or
+ *     |stream_id| is 0
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_create_idle_stream(nghttp2_session *session, int32_t stream_id,
+                                   const nghttp2_priority_spec *pri_spec);
+
+/**
+ * @function
+ *
+ * Performs post-process of HTTP Upgrade request.  This function can
+ * be called from both client and server, but the behavior is very
+ * different in each other.
+ *
+ * .. warning::
+ *
+ *   This function is deprecated in favor of
+ *   `nghttp2_session_upgrade2()`, because this function lacks the
+ *   parameter to tell the library the request method used in the
+ *   original HTTP request.  This information is required for client
+ *   to validate actual response body length against content-length
+ *   header field (see `nghttp2_option_set_no_http_messaging()`).  If
+ *   HEAD is used in request, the length of response body must be 0
+ *   regardless of value included in content-length header field.
+ *
+ * If called from client side, the |settings_payload| must be the
+ * value sent in ``HTTP2-Settings`` header field and must be decoded
+ * by base64url decoder.  The |settings_payloadlen| is the length of
+ * |settings_payload|.  The |settings_payload| is unpacked and its
+ * setting values will be submitted using `nghttp2_submit_settings()`.
+ * This means that the client application code does not need to submit
+ * SETTINGS by itself.  The stream with stream ID=1 is opened and the
+ * |stream_user_data| is used for its stream_user_data.  The opened
+ * stream becomes half-closed (local) state.
+ *
+ * If called from server side, the |settings_payload| must be the
+ * value received in ``HTTP2-Settings`` header field and must be
+ * decoded by base64url decoder.  The |settings_payloadlen| is the
+ * length of |settings_payload|.  It is treated as if the SETTINGS
+ * frame with that payload is received.  Thus, callback functions for
+ * the reception of SETTINGS frame will be invoked.  The stream with
+ * stream ID=1 is opened.  The |stream_user_data| is ignored.  The
+ * opened stream becomes half-closed (remote).
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |settings_payload| is badly formed.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PROTO`
+ *     The stream ID 1 is already used or closed; or is not available.
+ */
+NGHTTP2_EXTERN int nghttp2_session_upgrade(nghttp2_session *session,
+                                           const uint8_t *settings_payload,
+                                           size_t settings_payloadlen,
+                                           void *stream_user_data);
+
+/**
+ * @function
+ *
+ * Performs post-process of HTTP Upgrade request.  This function can
+ * be called from both client and server, but the behavior is very
+ * different in each other.
+ *
+ * If called from client side, the |settings_payload| must be the
+ * value sent in ``HTTP2-Settings`` header field and must be decoded
+ * by base64url decoder.  The |settings_payloadlen| is the length of
+ * |settings_payload|.  The |settings_payload| is unpacked and its
+ * setting values will be submitted using `nghttp2_submit_settings()`.
+ * This means that the client application code does not need to submit
+ * SETTINGS by itself.  The stream with stream ID=1 is opened and the
+ * |stream_user_data| is used for its stream_user_data.  The opened
+ * stream becomes half-closed (local) state.
+ *
+ * If called from server side, the |settings_payload| must be the
+ * value received in ``HTTP2-Settings`` header field and must be
+ * decoded by base64url decoder.  The |settings_payloadlen| is the
+ * length of |settings_payload|.  It is treated as if the SETTINGS
+ * frame with that payload is received.  Thus, callback functions for
+ * the reception of SETTINGS frame will be invoked.  The stream with
+ * stream ID=1 is opened.  The |stream_user_data| is ignored.  The
+ * opened stream becomes half-closed (remote).
+ *
+ * If the request method is HEAD, pass nonzero value to
+ * |head_request|.  Otherwise, pass 0.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |settings_payload| is badly formed.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PROTO`
+ *     The stream ID 1 is already used or closed; or is not available.
+ */
+NGHTTP2_EXTERN int nghttp2_session_upgrade2(nghttp2_session *session,
+                                            const uint8_t *settings_payload,
+                                            size_t settings_payloadlen,
+                                            int head_request,
+                                            void *stream_user_data);
+
+/**
+ * @function
+ *
+ * Serializes the SETTINGS values |iv| in the |buf|.  The size of the
+ * |buf| is specified by |buflen|.  The number of entries in the |iv|
+ * array is given by |niv|.  The required space in |buf| for the |niv|
+ * entries is ``6*niv`` bytes and if the given buffer is too small, an
+ * error is returned.  This function is used mainly for creating a
+ * SETTINGS payload to be sent with the ``HTTP2-Settings`` header
+ * field in an HTTP Upgrade request.  The data written in |buf| is NOT
+ * base64url encoded and the application is responsible for encoding.
+ *
+ * This function returns the number of bytes written in |buf|, or one
+ * of the following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |iv| contains duplicate settings ID or invalid value.
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INSUFF_BUFSIZE`
+ *     The provided |buflen| size is too small to hold the output.
+ */
+NGHTTP2_EXTERN ssize_t nghttp2_pack_settings_payload(
+    uint8_t *buf, size_t buflen, const nghttp2_settings_entry *iv, size_t niv);
+
+/**
+ * @function
+ *
+ * Returns string describing the |lib_error_code|.  The
+ * |lib_error_code| must be one of the :enum:`nghttp2_error`.
+ */
+NGHTTP2_EXTERN const char *nghttp2_strerror(int lib_error_code);
+
+/**
+ * @function
+ *
+ * Returns string representation of HTTP/2 error code |error_code|
+ * (e.g., ``PROTOCOL_ERROR`` is returned if ``error_code ==
+ * NGHTTP2_PROTOCOL_ERROR``).  If string representation is unknown for
+ * given |error_code|, this function returns string ``unknown``.
+ */
+NGHTTP2_EXTERN const char *nghttp2_http2_strerror(uint32_t error_code);
+
+/**
+ * @function
+ *
+ * Initializes |pri_spec| with the |stream_id| of the stream to depend
+ * on with |weight| and its exclusive flag.  If |exclusive| is
+ * nonzero, exclusive flag is set.
+ *
+ * The |weight| must be in [:macro:`NGHTTP2_MIN_WEIGHT`,
+ * :macro:`NGHTTP2_MAX_WEIGHT`], inclusive.
+ */
+NGHTTP2_EXTERN void nghttp2_priority_spec_init(nghttp2_priority_spec *pri_spec,
+                                               int32_t stream_id,
+                                               int32_t weight, int exclusive);
+
+/**
+ * @function
+ *
+ * Initializes |pri_spec| with the default values.  The default values
+ * are: stream_id = 0, weight = :macro:`NGHTTP2_DEFAULT_WEIGHT` and
+ * exclusive = 0.
+ */
+NGHTTP2_EXTERN void
+nghttp2_priority_spec_default_init(nghttp2_priority_spec *pri_spec);
+
+/**
+ * @function
+ *
+ * Returns nonzero if the |pri_spec| is filled with default values.
+ */
+NGHTTP2_EXTERN int
+nghttp2_priority_spec_check_default(const nghttp2_priority_spec *pri_spec);
+
+/**
+ * @function
+ *
+ * Submits HEADERS frame and optionally one or more DATA frames.
+ *
+ * The |pri_spec| is priority specification of this request.  ``NULL``
+ * means the default priority (see
+ * `nghttp2_priority_spec_default_init()`).  To specify the priority,
+ * use `nghttp2_priority_spec_init()`.  If |pri_spec| is not ``NULL``,
+ * this function will copy its data members.
+ *
+ * The ``pri_spec->weight`` must be in [:macro:`NGHTTP2_MIN_WEIGHT`,
+ * :macro:`NGHTTP2_MAX_WEIGHT`], inclusive.  If ``pri_spec->weight``
+ * is strictly less than :macro:`NGHTTP2_MIN_WEIGHT`, it becomes
+ * :macro:`NGHTTP2_MIN_WEIGHT`.  If it is strictly greater than
+ * :macro:`NGHTTP2_MAX_WEIGHT`, it becomes
+ * :macro:`NGHTTP2_MAX_WEIGHT`.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 1 is received by a remote endpoint, |pri_spec| is
+ * ignored, and treated as if ``NULL`` is specified.
+ *
+ * The |nva| is an array of name/value pair :type:`nghttp2_nv` with
+ * |nvlen| elements.  The application is responsible to include
+ * required pseudo-header fields (header field whose name starts with
+ * ":") in |nva| and must place pseudo-headers before regular header
+ * fields.
+ *
+ * This function creates copies of all name/value pairs in |nva|.  It
+ * also lower-cases all names in |nva|.  The order of elements in
+ * |nva| is preserved.  For header fields with
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME` and
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_VALUE` are set,
+ * header field name and value are not copied respectively.  With
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME`, application
+ * is responsible to pass header field name in lowercase.  The
+ * application should maintain the references to them until
+ * :type:`nghttp2_on_frame_send_callback` or
+ * :type:`nghttp2_on_frame_not_send_callback` is called.
+ *
+ * HTTP/2 specification has requirement about header fields in the
+ * request HEADERS.  See the specification for more details.
+ *
+ * If |data_prd| is not ``NULL``, it provides data which will be sent
+ * in subsequent DATA frames.  In this case, a method that allows
+ * request message bodies
+ * (https://tools.ietf.org/html/rfc7231#section-4) must be specified
+ * with ``:method`` key in |nva| (e.g. ``POST``).  This function does
+ * not take ownership of the |data_prd|.  The function copies the
+ * members of the |data_prd|.  If |data_prd| is ``NULL``, HEADERS have
+ * END_STREAM set.  The |stream_user_data| is data associated to the
+ * stream opened by this request and can be an arbitrary pointer,
+ * which can be retrieved later by
+ * `nghttp2_session_get_stream_user_data()`.
+ *
+ * This function returns assigned stream ID if it succeeds, or one of
+ * the following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE`
+ *     No stream ID is available because maximum stream ID was
+ *     reached.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     Trying to depend on itself (new stream ID equals
+ *     ``pri_spec->stream_id``).
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PROTO`
+ *     The |session| is server session.
+ *
+ * .. warning::
+ *
+ *   This function returns assigned stream ID if it succeeds.  But
+ *   that stream is not created yet.  The application must not submit
+ *   frame to that stream ID before
+ *   :type:`nghttp2_before_frame_send_callback` is called for this
+ *   frame.  This means `nghttp2_session_get_stream_user_data()` does
+ *   not work before the callback.  But
+ *   `nghttp2_session_set_stream_user_data()` handles this situation
+ *   specially, and it can set data to a stream during this period.
+ *
+ */
+NGHTTP2_EXTERN int32_t nghttp2_submit_request(
+    nghttp2_session *session, const nghttp2_priority_spec *pri_spec,
+    const nghttp2_nv *nva, size_t nvlen, const nghttp2_data_provider *data_prd,
+    void *stream_user_data);
+
+/**
+ * @function
+ *
+ * Submits response HEADERS frame and optionally one or more DATA
+ * frames against the stream |stream_id|.
+ *
+ * The |nva| is an array of name/value pair :type:`nghttp2_nv` with
+ * |nvlen| elements.  The application is responsible to include
+ * required pseudo-header fields (header field whose name starts with
+ * ":") in |nva| and must place pseudo-headers before regular header
+ * fields.
+ *
+ * This function creates copies of all name/value pairs in |nva|.  It
+ * also lower-cases all names in |nva|.  The order of elements in
+ * |nva| is preserved.  For header fields with
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME` and
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_VALUE` are set,
+ * header field name and value are not copied respectively.  With
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME`, application
+ * is responsible to pass header field name in lowercase.  The
+ * application should maintain the references to them until
+ * :type:`nghttp2_on_frame_send_callback` or
+ * :type:`nghttp2_on_frame_not_send_callback` is called.
+ *
+ * HTTP/2 specification has requirement about header fields in the
+ * response HEADERS.  See the specification for more details.
+ *
+ * If |data_prd| is not ``NULL``, it provides data which will be sent
+ * in subsequent DATA frames.  This function does not take ownership
+ * of the |data_prd|.  The function copies the members of the
+ * |data_prd|.  If |data_prd| is ``NULL``, HEADERS will have
+ * END_STREAM flag set.
+ *
+ * This method can be used as normal HTTP response and push response.
+ * When pushing a resource using this function, the |session| must be
+ * configured using `nghttp2_session_server_new()` or its variants and
+ * the target stream denoted by the |stream_id| must be reserved using
+ * `nghttp2_submit_push_promise()`.
+ *
+ * To send non-final response headers (e.g., HTTP status 101), don't
+ * use this function because this function half-closes the outbound
+ * stream.  Instead, use `nghttp2_submit_headers()` for this purpose.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_DATA_EXIST`
+ *     DATA or HEADERS has been already submitted and not fully
+ *     processed yet.  Normally, this does not happen, but when
+ *     application wrongly calls `nghttp2_submit_response()` twice,
+ *     this may happen.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PROTO`
+ *     The |session| is client session.
+ *
+ * .. warning::
+ *
+ *   Calling this function twice for the same stream ID may lead to
+ *   program crash.  It is generally considered to a programming error
+ *   to commit response twice.
+ */
+NGHTTP2_EXTERN int
+nghttp2_submit_response(nghttp2_session *session, int32_t stream_id,
+                        const nghttp2_nv *nva, size_t nvlen,
+                        const nghttp2_data_provider *data_prd);
+
+/**
+ * @function
+ *
+ * Submits trailer fields HEADERS against the stream |stream_id|.
+ *
+ * The |nva| is an array of name/value pair :type:`nghttp2_nv` with
+ * |nvlen| elements.  The application must not include pseudo-header
+ * fields (headers whose names starts with ":") in |nva|.
+ *
+ * This function creates copies of all name/value pairs in |nva|.  It
+ * also lower-cases all names in |nva|.  The order of elements in
+ * |nva| is preserved.  For header fields with
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME` and
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_VALUE` are set,
+ * header field name and value are not copied respectively.  With
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME`, application
+ * is responsible to pass header field name in lowercase.  The
+ * application should maintain the references to them until
+ * :type:`nghttp2_on_frame_send_callback` or
+ * :type:`nghttp2_on_frame_not_send_callback` is called.
+ *
+ * For server, trailer fields must follow response HEADERS or response
+ * DATA without END_STREAM flat set.  The library does not enforce
+ * this requirement, and applications should do this for themselves.
+ * If `nghttp2_submit_trailer()` is called before any response HEADERS
+ * submission (usually by `nghttp2_submit_response()`), the content of
+ * |nva| will be sent as response headers, which will result in error.
+ *
+ * This function has the same effect with `nghttp2_submit_headers()`,
+ * with flags = :enum:`nghttp2_flag.NGHTTP2_FLAG_END_STREAM` and both
+ * pri_spec and stream_user_data to NULL.
+ *
+ * To submit trailer fields after `nghttp2_submit_response()` is
+ * called, the application has to specify
+ * :type:`nghttp2_data_provider` to `nghttp2_submit_response()`.
+ * Inside of :type:`nghttp2_data_source_read_callback`, when setting
+ * :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_EOF`, also set
+ * :enum:`nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_END_STREAM`.  After
+ * that, the application can send trailer fields using
+ * `nghttp2_submit_trailer()`.  `nghttp2_submit_trailer()` can be used
+ * inside :type:`nghttp2_data_source_read_callback`.
+ *
+ * This function returns 0 if it succeeds and |stream_id| is -1.
+ * Otherwise, this function returns 0 if it succeeds, or one of the
+ * following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_trailer(nghttp2_session *session,
+                                          int32_t stream_id,
+                                          const nghttp2_nv *nva, size_t nvlen);
+
+/**
+ * @function
+ *
+ * Submits HEADERS frame. The |flags| is bitwise OR of the
+ * following values:
+ *
+ * * :enum:`nghttp2_flag.NGHTTP2_FLAG_END_STREAM`
+ *
+ * If |flags| includes :enum:`nghttp2_flag.NGHTTP2_FLAG_END_STREAM`,
+ * this frame has END_STREAM flag set.
+ *
+ * The library handles the CONTINUATION frame internally and it
+ * correctly sets END_HEADERS to the last sequence of the PUSH_PROMISE
+ * or CONTINUATION frame.
+ *
+ * If the |stream_id| is -1, this frame is assumed as request (i.e.,
+ * request HEADERS frame which opens new stream).  In this case, the
+ * assigned stream ID will be returned.  Otherwise, specify stream ID
+ * in |stream_id|.
+ *
+ * The |pri_spec| is priority specification of this request.  ``NULL``
+ * means the default priority (see
+ * `nghttp2_priority_spec_default_init()`).  To specify the priority,
+ * use `nghttp2_priority_spec_init()`.  If |pri_spec| is not ``NULL``,
+ * this function will copy its data members.
+ *
+ * The ``pri_spec->weight`` must be in [:macro:`NGHTTP2_MIN_WEIGHT`,
+ * :macro:`NGHTTP2_MAX_WEIGHT`], inclusive.  If ``pri_spec->weight``
+ * is strictly less than :macro:`NGHTTP2_MIN_WEIGHT`, it becomes
+ * :macro:`NGHTTP2_MIN_WEIGHT`.  If it is strictly greater than
+ * :macro:`NGHTTP2_MAX_WEIGHT`, it becomes :macro:`NGHTTP2_MAX_WEIGHT`.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 1 is received by a remote endpoint, |pri_spec| is
+ * ignored, and treated as if ``NULL`` is specified.
+ *
+ * The |nva| is an array of name/value pair :type:`nghttp2_nv` with
+ * |nvlen| elements.  The application is responsible to include
+ * required pseudo-header fields (header field whose name starts with
+ * ":") in |nva| and must place pseudo-headers before regular header
+ * fields.
+ *
+ * This function creates copies of all name/value pairs in |nva|.  It
+ * also lower-cases all names in |nva|.  The order of elements in
+ * |nva| is preserved.  For header fields with
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME` and
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_VALUE` are set,
+ * header field name and value are not copied respectively.  With
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME`, application
+ * is responsible to pass header field name in lowercase.  The
+ * application should maintain the references to them until
+ * :type:`nghttp2_on_frame_send_callback` or
+ * :type:`nghttp2_on_frame_not_send_callback` is called.
+ *
+ * The |stream_user_data| is a pointer to an arbitrary data which is
+ * associated to the stream this frame will open.  Therefore it is
+ * only used if this frame opens streams, in other words, it changes
+ * stream state from idle or reserved to open.
+ *
+ * This function is low-level in a sense that the application code can
+ * specify flags directly.  For usual HTTP request,
+ * `nghttp2_submit_request()` is useful.  Likewise, for HTTP response,
+ * prefer `nghttp2_submit_response()`.
+ *
+ * This function returns newly assigned stream ID if it succeeds and
+ * |stream_id| is -1.  Otherwise, this function returns 0 if it
+ * succeeds, or one of the following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE`
+ *     No stream ID is available because maximum stream ID was
+ *     reached.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0; or trying to depend on itself (stream ID
+ *     equals ``pri_spec->stream_id``).
+ * :enum:`nghttp2_error.NGHTTP2_ERR_DATA_EXIST`
+ *     DATA or HEADERS has been already submitted and not fully
+ *     processed yet.  This happens if stream denoted by |stream_id|
+ *     is in reserved state.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PROTO`
+ *     The |stream_id| is -1, and |session| is server session.
+ *
+ * .. warning::
+ *
+ *   This function returns assigned stream ID if it succeeds and
+ *   |stream_id| is -1.  But that stream is not opened yet.  The
+ *   application must not submit frame to that stream ID before
+ *   :type:`nghttp2_before_frame_send_callback` is called for this
+ *   frame.
+ *
+ */
+NGHTTP2_EXTERN int32_t nghttp2_submit_headers(
+    nghttp2_session *session, uint8_t flags, int32_t stream_id,
+    const nghttp2_priority_spec *pri_spec, const nghttp2_nv *nva, size_t nvlen,
+    void *stream_user_data);
+
+/**
+ * @function
+ *
+ * Submits one or more DATA frames to the stream |stream_id|.  The
+ * data to be sent are provided by |data_prd|.  If |flags| contains
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_END_STREAM`, the last DATA frame
+ * has END_STREAM flag set.
+ *
+ * This function does not take ownership of the |data_prd|.  The
+ * function copies the members of the |data_prd|.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_DATA_EXIST`
+ *     DATA or HEADERS has been already submitted and not fully
+ *     processed yet.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_STREAM_CLOSED`
+ *     The stream was already closed; or the |stream_id| is invalid.
+ *
+ * .. note::
+ *
+ *   Currently, only one DATA or HEADERS is allowed for a stream at a
+ *   time.  Submitting these frames more than once before first DATA
+ *   or HEADERS is finished results in
+ *   :enum:`nghttp2_error.NGHTTP2_ERR_DATA_EXIST` error code.  The
+ *   earliest callback which tells that previous frame is done is
+ *   :type:`nghttp2_on_frame_send_callback`.  In side that callback,
+ *   new data can be submitted using `nghttp2_submit_data()`.  Of
+ *   course, all data except for last one must not have
+ *   :enum:`nghttp2_flag.NGHTTP2_FLAG_END_STREAM` flag set in |flags|.
+ *   This sounds a bit complicated, and we recommend to use
+ *   `nghttp2_submit_request()` and `nghttp2_submit_response()` to
+ *   avoid this cascading issue.  The experience shows that for HTTP
+ *   use, these two functions are enough to implement both client and
+ *   server.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_data(nghttp2_session *session, uint8_t flags,
+                                       int32_t stream_id,
+                                       const nghttp2_data_provider *data_prd);
+
+/**
+ * @function
+ *
+ * Submits PRIORITY frame to change the priority of stream |stream_id|
+ * to the priority specification |pri_spec|.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * The |pri_spec| is priority specification of this request.  ``NULL``
+ * is not allowed for this function. To specify the priority, use
+ * `nghttp2_priority_spec_init()`.  This function will copy its data
+ * members.
+ *
+ * The ``pri_spec->weight`` must be in [:macro:`NGHTTP2_MIN_WEIGHT`,
+ * :macro:`NGHTTP2_MAX_WEIGHT`], inclusive.  If ``pri_spec->weight``
+ * is strictly less than :macro:`NGHTTP2_MIN_WEIGHT`, it becomes
+ * :macro:`NGHTTP2_MIN_WEIGHT`.  If it is strictly greater than
+ * :macro:`NGHTTP2_MAX_WEIGHT`, it becomes
+ * :macro:`NGHTTP2_MAX_WEIGHT`.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 1 is received by a remote endpoint, this function does
+ * nothing and returns 0.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0; or the |pri_spec| is NULL; or trying to
+ *     depend on itself.
+ */
+NGHTTP2_EXTERN int
+nghttp2_submit_priority(nghttp2_session *session, uint8_t flags,
+                        int32_t stream_id,
+                        const nghttp2_priority_spec *pri_spec);
+
+/**
+ * @macro
+ *
+ * :macro:`NGHTTP2_EXTPRI_DEFAULT_URGENCY` is the default urgency
+ * level for :rfc:`9218` extensible priorities.
+ */
+#define NGHTTP2_EXTPRI_DEFAULT_URGENCY 3
+
+/**
+ * @macro
+ *
+ * :macro:`NGHTTP2_EXTPRI_URGENCY_HIGH` is the highest urgency level
+ * for :rfc:`9218` extensible priorities.
+ */
+#define NGHTTP2_EXTPRI_URGENCY_HIGH 0
+
+/**
+ * @macro
+ *
+ * :macro:`NGHTTP2_EXTPRI_URGENCY_LOW` is the lowest urgency level for
+ * :rfc:`9218` extensible priorities.
+ */
+#define NGHTTP2_EXTPRI_URGENCY_LOW 7
+
+/**
+ * @macro
+ *
+ * :macro:`NGHTTP2_EXTPRI_URGENCY_LEVELS` is the number of urgency
+ * levels for :rfc:`9218` extensible priorities.
+ */
+#define NGHTTP2_EXTPRI_URGENCY_LEVELS (NGHTTP2_EXTPRI_URGENCY_LOW + 1)
+
+/**
+ * @struct
+ *
+ * :type:`nghttp2_extpri` is :rfc:`9218` extensible priorities
+ * specification for a stream.
+ */
+typedef struct nghttp2_extpri {
+  /**
+   * :member:`urgency` is the urgency of a stream, it must be in
+   * [:macro:`NGHTTP2_EXTPRI_URGENCY_HIGH`,
+   * :macro:`NGHTTP2_EXTPRI_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 inc is 0, it cannot be processed
+   * incrementally.  If inc is 1, it can be processed incrementally.
+   * Other value is not permitted.
+   */
+  int inc;
+} nghttp2_extpri;
+
+/**
+ * @function
+ *
+ * Submits RST_STREAM frame to cancel/reject the stream |stream_id|
+ * with the error code |error_code|.
+ *
+ * The pre-defined error code is one of :enum:`nghttp2_error_code`.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_rst_stream(nghttp2_session *session,
+                                             uint8_t flags, int32_t stream_id,
+                                             uint32_t error_code);
+
+/**
+ * @function
+ *
+ * Stores local settings and submits SETTINGS frame.  The |iv| is the
+ * pointer to the array of :type:`nghttp2_settings_entry`.  The |niv|
+ * indicates the number of :type:`nghttp2_settings_entry`.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * This function does not take ownership of the |iv|.  This function
+ * copies all the elements in the |iv|.
+ *
+ * While updating individual stream's local window size, if the window
+ * size becomes strictly larger than NGHTTP2_MAX_WINDOW_SIZE,
+ * RST_STREAM is issued against such a stream.
+ *
+ * SETTINGS with :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK` is
+ * automatically submitted by the library and application could not
+ * send it at its will.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |iv| contains invalid value (e.g., initial window size
+ *     strictly greater than (1 << 31) - 1.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_settings(nghttp2_session *session,
+                                           uint8_t flags,
+                                           const nghttp2_settings_entry *iv,
+                                           size_t niv);
+
+/**
+ * @function
+ *
+ * Submits PUSH_PROMISE frame.
+ *
+ * The |flags| is currently ignored.  The library handles the
+ * CONTINUATION frame internally and it correctly sets END_HEADERS to
+ * the last sequence of the PUSH_PROMISE or CONTINUATION frame.
+ *
+ * The |stream_id| must be client initiated stream ID.
+ *
+ * The |nva| is an array of name/value pair :type:`nghttp2_nv` with
+ * |nvlen| elements.  The application is responsible to include
+ * required pseudo-header fields (header field whose name starts with
+ * ":") in |nva| and must place pseudo-headers before regular header
+ * fields.
+ *
+ * This function creates copies of all name/value pairs in |nva|.  It
+ * also lower-cases all names in |nva|.  The order of elements in
+ * |nva| is preserved.  For header fields with
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME` and
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_VALUE` are set,
+ * header field name and value are not copied respectively.  With
+ * :enum:`nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME`, application
+ * is responsible to pass header field name in lowercase.  The
+ * application should maintain the references to them until
+ * :type:`nghttp2_on_frame_send_callback` or
+ * :type:`nghttp2_on_frame_not_send_callback` is called.
+ *
+ * The |promised_stream_user_data| is a pointer to an arbitrary data
+ * which is associated to the promised stream this frame will open and
+ * make it in reserved state.  It is available using
+ * `nghttp2_session_get_stream_user_data()`.  The application can
+ * access it in :type:`nghttp2_before_frame_send_callback` and
+ * :type:`nghttp2_on_frame_send_callback` of this frame.
+ *
+ * The client side is not allowed to use this function.
+ *
+ * To submit response headers and data, use
+ * `nghttp2_submit_response()`.
+ *
+ * This function returns assigned promised stream ID if it succeeds,
+ * or one of the following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_PROTO`
+ *     This function was invoked when |session| is initialized as
+ *     client.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE`
+ *     No stream ID is available because maximum stream ID was
+ *     reached.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is 0; The |stream_id| does not designate stream
+ *     that peer initiated.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_STREAM_CLOSED`
+ *     The stream was already closed; or the |stream_id| is invalid.
+ *
+ * .. warning::
+ *
+ *   This function returns assigned promised stream ID if it succeeds.
+ *   As of 1.16.0, stream object for pushed resource is created when
+ *   this function succeeds.  In that case, the application can submit
+ *   push response for the promised frame.
+ *
+ *   In 1.15.0 or prior versions, pushed stream is not opened yet when
+ *   this function succeeds.  The application must not submit frame to
+ *   that stream ID before :type:`nghttp2_before_frame_send_callback`
+ *   is called for this frame.
+ *
+ */
+NGHTTP2_EXTERN int32_t nghttp2_submit_push_promise(
+    nghttp2_session *session, uint8_t flags, int32_t stream_id,
+    const nghttp2_nv *nva, size_t nvlen, void *promised_stream_user_data);
+
+/**
+ * @function
+ *
+ * Submits PING frame.  You don't have to send PING back when you
+ * received PING frame.  The library automatically submits PING frame
+ * in this case.
+ *
+ * The |flags| is bitwise OR of 0 or more of the following value.
+ *
+ * * :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK`
+ *
+ * Unless `nghttp2_option_set_no_auto_ping_ack()` is used, the |flags|
+ * should be :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * If the |opaque_data| is non ``NULL``, then it should point to the 8
+ * bytes array of memory to specify opaque data to send with PING
+ * frame.  If the |opaque_data| is ``NULL``, zero-cleared 8 bytes will
+ * be sent as opaque data.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_ping(nghttp2_session *session, uint8_t flags,
+                                       const uint8_t *opaque_data);
+
+/**
+ * @function
+ *
+ * Submits GOAWAY frame with the last stream ID |last_stream_id| and
+ * the error code |error_code|.
+ *
+ * The pre-defined error code is one of :enum:`nghttp2_error_code`.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * The |last_stream_id| is peer's stream ID or 0.  So if |session| is
+ * initialized as client, |last_stream_id| must be even or 0.  If
+ * |session| is initialized as server, |last_stream_id| must be odd or
+ * 0.
+ *
+ * The HTTP/2 specification says last_stream_id must not be increased
+ * from the value previously sent.  So the actual value sent as
+ * last_stream_id is the minimum value between the given
+ * |last_stream_id| and the last_stream_id previously sent to the
+ * peer.
+ *
+ * If the |opaque_data| is not ``NULL`` and |opaque_data_len| is not
+ * zero, those data will be sent as additional debug data.  The
+ * library makes a copy of the memory region pointed by |opaque_data|
+ * with the length |opaque_data_len|, so the caller does not need to
+ * keep this memory after the return of this function.  If the
+ * |opaque_data_len| is 0, the |opaque_data| could be ``NULL``.
+ *
+ * After successful transmission of GOAWAY, following things happen.
+ * All incoming streams having strictly more than |last_stream_id| are
+ * closed.  All incoming HEADERS which starts new stream are simply
+ * ignored.  After all active streams are handled, both
+ * `nghttp2_session_want_read()` and `nghttp2_session_want_write()`
+ * return 0 and the application can close session.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |opaque_data_len| is too large; the |last_stream_id| is
+ *     invalid.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_goaway(nghttp2_session *session,
+                                         uint8_t flags, int32_t last_stream_id,
+                                         uint32_t error_code,
+                                         const uint8_t *opaque_data,
+                                         size_t opaque_data_len);
+
+/**
+ * @function
+ *
+ * Returns the last stream ID of a stream for which
+ * :type:`nghttp2_on_frame_recv_callback` was invoked most recently.
+ * The returned value can be used as last_stream_id parameter for
+ * `nghttp2_submit_goaway()` and
+ * `nghttp2_session_terminate_session2()`.
+ *
+ * This function always succeeds.
+ */
+NGHTTP2_EXTERN int32_t
+nghttp2_session_get_last_proc_stream_id(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns nonzero if new request can be sent from local endpoint.
+ *
+ * This function return 0 if request is not allowed for this session.
+ * There are several reasons why request is not allowed.  Some of the
+ * reasons are: session is server; stream ID has been spent; GOAWAY
+ * has been sent or received.
+ *
+ * The application can call `nghttp2_submit_request()` without
+ * consulting this function.  In that case, `nghttp2_submit_request()`
+ * may return error.  Or, request is failed to sent, and
+ * :type:`nghttp2_on_stream_close_callback` is called.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_check_request_allowed(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns nonzero if |session| is initialized as server side session.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_check_server_session(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Submits WINDOW_UPDATE frame.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * The |stream_id| is the stream ID to send this WINDOW_UPDATE.  To
+ * send connection level WINDOW_UPDATE, specify 0 to |stream_id|.
+ *
+ * If the |window_size_increment| is positive, the WINDOW_UPDATE with
+ * that value as window_size_increment is queued.  If the
+ * |window_size_increment| is larger than the received bytes from the
+ * remote endpoint, the local window size is increased by that
+ * difference.  If the sole purpose is to increase the local window
+ * size, consider to use `nghttp2_session_set_local_window_size()`.
+ *
+ * If the |window_size_increment| is negative, the local window size
+ * is decreased by -|window_size_increment|.  If automatic
+ * WINDOW_UPDATE is enabled
+ * (`nghttp2_option_set_no_auto_window_update()`), and the library
+ * decided that the WINDOW_UPDATE should be submitted, then
+ * WINDOW_UPDATE is queued with the current received bytes count.  If
+ * the sole purpose is to decrease the local window size, consider to
+ * use `nghttp2_session_set_local_window_size()`.
+ *
+ * If the |window_size_increment| is 0, the function does nothing and
+ * returns 0.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_FLOW_CONTROL`
+ *     The local window size overflow or gets negative.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_window_update(nghttp2_session *session,
+                                                uint8_t flags,
+                                                int32_t stream_id,
+                                                int32_t window_size_increment);
+
+/**
+ * @function
+ *
+ * Set local window size (local endpoints's window size) to the given
+ * |window_size| for the given stream denoted by |stream_id|.  To
+ * change connection level window size, specify 0 to |stream_id|.  To
+ * increase window size, this function may submit WINDOW_UPDATE frame
+ * to transmission queue.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * This sounds similar to `nghttp2_submit_window_update()`, but there
+ * are 2 differences.  The first difference is that this function
+ * takes the absolute value of window size to set, rather than the
+ * delta.  To change the window size, this may be easier to use since
+ * the application just declares the intended window size, rather than
+ * calculating delta.  The second difference is that
+ * `nghttp2_submit_window_update()` affects the received bytes count
+ * which has not acked yet.  By the specification of
+ * `nghttp2_submit_window_update()`, to strictly increase the local
+ * window size, we have to submit delta including all received bytes
+ * count, which might not be desirable in some cases.  On the other
+ * hand, this function does not affect the received bytes count.  It
+ * just sets the local window size to the given value.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |stream_id| is negative.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_set_local_window_size(nghttp2_session *session, uint8_t flags,
+                                      int32_t stream_id, int32_t window_size);
+
+/**
+ * @function
+ *
+ * Submits extension frame.
+ *
+ * Application can pass arbitrary frame flags and stream ID in |flags|
+ * and |stream_id| respectively.  The |payload| is opaque pointer, and
+ * it can be accessible though ``frame->ext.payload`` in
+ * :type:`nghttp2_pack_extension_callback`.  The library will not own
+ * passed |payload| pointer.
+ *
+ * The application must set :type:`nghttp2_pack_extension_callback`
+ * using `nghttp2_session_callbacks_set_pack_extension_callback()`.
+ *
+ * The application should retain the memory pointed by |payload| until
+ * the transmission of extension frame is done (which is indicated by
+ * :type:`nghttp2_on_frame_send_callback`), or transmission fails
+ * (which is indicated by :type:`nghttp2_on_frame_not_send_callback`).
+ * If application does not touch this memory region after packing it
+ * into a wire format, application can free it inside
+ * :type:`nghttp2_pack_extension_callback`.
+ *
+ * The standard HTTP/2 frame cannot be sent with this function, so
+ * |type| must be strictly grater than 0x9.  Otherwise, this function
+ * will fail with error code
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     If :type:`nghttp2_pack_extension_callback` is not set.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     If  |type| specifies  standard  HTTP/2 frame  type.  The  frame
+ *     types  in the  rage [0x0,  0x9], both  inclusive, are  standard
+ *     HTTP/2 frame type, and cannot be sent using this function.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory
+ */
+NGHTTP2_EXTERN int nghttp2_submit_extension(nghttp2_session *session,
+                                            uint8_t type, uint8_t flags,
+                                            int32_t stream_id, void *payload);
+
+/**
+ * @struct
+ *
+ * The payload of ALTSVC frame.  ALTSVC frame is a non-critical
+ * extension to HTTP/2.  If this frame is received, and
+ * `nghttp2_option_set_user_recv_extension_type()` is not set, and
+ * `nghttp2_option_set_builtin_recv_extension_type()` is set for
+ * :enum:`nghttp2_frame_type.NGHTTP2_ALTSVC`,
+ * ``nghttp2_extension.payload`` will point to this struct.
+ *
+ * It has the following members:
+ */
+typedef struct {
+  /**
+   * The pointer to origin which this alternative service is
+   * associated with.  This is not necessarily NULL-terminated.
+   */
+  uint8_t *origin;
+  /**
+   * The length of the |origin|.
+   */
+  size_t origin_len;
+  /**
+   * The pointer to Alt-Svc field value contained in ALTSVC frame.
+   * This is not necessarily NULL-terminated.
+   */
+  uint8_t *field_value;
+  /**
+   * The length of the |field_value|.
+   */
+  size_t field_value_len;
+} nghttp2_ext_altsvc;
+
+/**
+ * @function
+ *
+ * Submits ALTSVC frame.
+ *
+ * ALTSVC frame is a non-critical extension to HTTP/2, and defined in
+ * `RFC 7383 <https://tools.ietf.org/html/rfc7838#section-4>`_.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * The |origin| points to the origin this alternative service is
+ * associated with.  The |origin_len| is the length of the origin.  If
+ * |stream_id| is 0, the origin must be specified.  If |stream_id| is
+ * not zero, the origin must be empty (in other words, |origin_len|
+ * must be 0).
+ *
+ * The ALTSVC frame is only usable from server side.  If this function
+ * is invoked with client side session, this function returns
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     The function is called from client side session
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The sum of |origin_len| and |field_value_len| is larger than
+ *     16382; or |origin_len| is 0 while |stream_id| is 0; or
+ *     |origin_len| is not 0 while |stream_id| is not 0.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_altsvc(nghttp2_session *session,
+                                         uint8_t flags, int32_t stream_id,
+                                         const uint8_t *origin,
+                                         size_t origin_len,
+                                         const uint8_t *field_value,
+                                         size_t field_value_len);
+
+/**
+ * @struct
+ *
+ * The single entry of an origin.
+ */
+typedef struct {
+  /**
+   * The pointer to origin.  No validation is made against this field
+   * by the library.  This is not necessarily NULL-terminated.
+   */
+  uint8_t *origin;
+  /**
+   * The length of the |origin|.
+   */
+  size_t origin_len;
+} nghttp2_origin_entry;
+
+/**
+ * @struct
+ *
+ * The payload of ORIGIN frame.  ORIGIN frame is a non-critical
+ * extension to HTTP/2 and defined by `RFC 8336
+ * <https://tools.ietf.org/html/rfc8336>`_.
+ *
+ * If this frame is received, and
+ * `nghttp2_option_set_user_recv_extension_type()` is not set, and
+ * `nghttp2_option_set_builtin_recv_extension_type()` is set for
+ * :enum:`nghttp2_frame_type.NGHTTP2_ORIGIN`,
+ * ``nghttp2_extension.payload`` will point to this struct.
+ *
+ * It has the following members:
+ */
+typedef struct {
+  /**
+   * The number of origins contained in |ov|.
+   */
+  size_t nov;
+  /**
+   * The pointer to the array of origins contained in ORIGIN frame.
+   */
+  nghttp2_origin_entry *ov;
+} nghttp2_ext_origin;
+
+/**
+ * @function
+ *
+ * Submits ORIGIN frame.
+ *
+ * ORIGIN frame is a non-critical extension to HTTP/2 and defined by
+ * `RFC 8336 <https://tools.ietf.org/html/rfc8336>`_.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * The |ov| points to the array of origins.  The |nov| specifies the
+ * number of origins included in |ov|.  This function creates copies
+ * of all elements in |ov|.
+ *
+ * The ORIGIN frame is only usable by a server.  If this function is
+ * invoked with client side session, this function returns
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`.
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     The function is called from client side session.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     There are too many origins, or an origin is too large to fit
+ *     into a default frame payload.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_origin(nghttp2_session *session,
+                                         uint8_t flags,
+                                         const nghttp2_origin_entry *ov,
+                                         size_t nov);
+
+/**
+ * @struct
+ *
+ * The payload of PRIORITY_UPDATE frame.  PRIORITY_UPDATE frame is a
+ * non-critical extension to HTTP/2.  If this frame is received, and
+ * `nghttp2_option_set_user_recv_extension_type()` is not set, and
+ * `nghttp2_option_set_builtin_recv_extension_type()` is set for
+ * :enum:`nghttp2_frame_type.NGHTTP2_PRIORITY_UPDATE`,
+ * ``nghttp2_extension.payload`` will point to this struct.
+ *
+ * It has the following members:
+ */
+typedef struct {
+  /**
+   * The stream ID of the stream whose priority is updated.
+   */
+  int32_t stream_id;
+  /**
+   * The pointer to Priority field value.  It is not necessarily
+   * NULL-terminated.
+   */
+  uint8_t *field_value;
+  /**
+   * The length of the :member:`field_value`.
+   */
+  size_t field_value_len;
+} nghttp2_ext_priority_update;
+
+/**
+ * @function
+ *
+ * Submits PRIORITY_UPDATE frame.
+ *
+ * PRIORITY_UPDATE frame is a non-critical extension to HTTP/2, and
+ * defined in :rfc:`9218#section-7.1`.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ *
+ * The |stream_id| is the ID of stream which is prioritized.  The
+ * |field_value| points to the Priority field value.  The
+ * |field_value_len| is the length of the Priority field value.
+ *
+ * If this function is called by server,
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE` is returned.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 0 is received by a remote endpoint (or it is omitted),
+ * this function does nothing and returns 0.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     The function is called from server side session
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The |field_value_len| is larger than 16380; or |stream_id| is
+ *     0.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_priority_update(nghttp2_session *session,
+                                                  uint8_t flags,
+                                                  int32_t stream_id,
+                                                  const uint8_t *field_value,
+                                                  size_t field_value_len);
+
+/**
+ * @function
+ *
+ * Changes the priority of the existing stream denoted by |stream_id|.
+ * The new priority is |extpri|.  This function is meant to be used by
+ * server for :rfc:`9218` extensible prioritization scheme.
+ *
+ * If |session| is initialized as client, this function returns
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`.  For client, use
+ * `nghttp2_submit_priority_update()` instead.
+ *
+ * If :member:`extpri->urgency <nghttp2_extpri.urgency>` is out of
+ * bound, it is set to :macro:`NGHTTP2_EXTPRI_URGENCY_LOW`.
+ *
+ * If |ignore_client_signal| is nonzero, server starts to ignore
+ * client priority signals for this stream.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 1 is not submitted via `nghttp2_submit_settings()`,
+ * this function does nothing and returns 0.
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     The |session| is initialized as client.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     |stream_id| is zero; or a stream denoted by |stream_id| is not
+ *     found.
+ */
+NGHTTP2_EXTERN int nghttp2_session_change_extpri_stream_priority(
+    nghttp2_session *session, int32_t stream_id, const nghttp2_extpri *extpri,
+    int ignore_client_signal);
+
+/**
+ * @function
+ *
+ * Stores the stream priority of the existing stream denoted by
+ * |stream_id| in the object pointed by |extpri|.  This function is
+ * meant to be used by server for :rfc:`9218` extensible
+ * prioritization scheme.
+ *
+ * If |session| is initialized as client, this function returns
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`.
+ *
+ * If
+ * :enum:`nghttp2_settings_id.NGHTTP2_SETTINGS_NO_RFC7540_PRIORITIES`
+ * of value of 1 is not submitted via `nghttp2_submit_settings()`,
+ * this function does nothing and returns 0.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     The |session| is initialized as client.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     |stream_id| is zero; or a stream denoted by |stream_id| is not
+ *     found.
+ */
+NGHTTP2_EXTERN int nghttp2_session_get_extpri_stream_priority(
+    nghttp2_session *session, nghttp2_extpri *extpri, int32_t stream_id);
+
+/**
+ * @function
+ *
+ * Parses Priority header field value pointed by |value| of length
+ * |len|, and stores the result in the object pointed by |extpri|.
+ * Priority header field is defined in :rfc:`9218`.
+ *
+ * This function does not initialize the object pointed by |extpri|
+ * 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:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     Failed to parse the header field value.
+ */
+NGHTTP2_EXTERN int nghttp2_extpri_parse_priority(nghttp2_extpri *extpri,
+                                                 const uint8_t *value,
+                                                 size_t len);
+
+/**
+ * @function
+ *
+ * Compares ``lhs->name`` of length ``lhs->namelen`` bytes and
+ * ``rhs->name`` of length ``rhs->namelen`` bytes.  Returns negative
+ * integer if ``lhs->name`` is found to be less than ``rhs->name``; or
+ * returns positive integer if ``lhs->name`` is found to be greater
+ * than ``rhs->name``; or returns 0 otherwise.
+ */
+NGHTTP2_EXTERN int nghttp2_nv_compare_name(const nghttp2_nv *lhs,
+                                           const nghttp2_nv *rhs);
+
+/**
+ * @function
+ *
+ * .. warning::
+ *
+ *   Deprecated.  Use `nghttp2_select_alpn` instead.
+ *
+ * A helper function for dealing with ALPN in server side.  The |in|
+ * contains peer's protocol list in preferable order.  The format of
+ * |in| is length-prefixed and not null-terminated.  For example,
+ * ``h2`` and ``http/1.1`` stored in |in| like this::
+ *
+ *     in[0] = 2
+ *     in[1..2] = "h2"
+ *     in[3] = 8
+ *     in[4..11] = "http/1.1"
+ *     inlen = 12
+ *
+ * The selection algorithm is as follows:
+ *
+ * 1. If peer's list contains HTTP/2 protocol the library supports,
+ *    it is selected and returns 1. The following step is not taken.
+ *
+ * 2. If peer's list contains ``http/1.1``, this function selects
+ *    ``http/1.1`` and returns 0.  The following step is not taken.
+ *
+ * 3. This function selects nothing and returns -1 (So called
+ *    non-overlap case).  In this case, |out| and |outlen| are left
+ *    untouched.
+ *
+ * Selecting ``h2`` means that ``h2`` is written into |*out| and its
+ * length (which is 2) is assigned to |*outlen|.
+ *
+ * For ALPN, refer to https://tools.ietf.org/html/rfc7301
+ *
+ * To use this method you should do something like::
+ *
+ *     static int alpn_select_proto_cb(SSL* ssl,
+ *                                     const unsigned char **out,
+ *                                     unsigned char *outlen,
+ *                                     const unsigned char *in,
+ *                                     unsigned int inlen,
+ *                                     void *arg)
+ *     {
+ *         int rv;
+ *         rv = nghttp2_select_next_protocol((unsigned char**)out, outlen,
+ *                                           in, inlen);
+ *         if (rv == -1) {
+ *             return SSL_TLSEXT_ERR_NOACK;
+ *         }
+ *         if (rv == 1) {
+ *             ((MyType*)arg)->http2_selected = 1;
+ *         }
+ *         return SSL_TLSEXT_ERR_OK;
+ *     }
+ *     ...
+ *     SSL_CTX_set_alpn_select_cb(ssl_ctx, alpn_select_proto_cb, my_obj);
+ *
+ */
+NGHTTP2_EXTERN int nghttp2_select_next_protocol(unsigned char **out,
+                                                unsigned char *outlen,
+                                                const unsigned char *in,
+                                                unsigned int inlen);
+
+/**
+ * @function
+ *
+ * A helper function for dealing with ALPN in server side.  The |in|
+ * contains peer's protocol list in preferable order.  The format of
+ * |in| is length-prefixed and not null-terminated.  For example,
+ * ``h2`` and ``http/1.1`` stored in |in| like this::
+ *
+ *     in[0] = 2
+ *     in[1..2] = "h2"
+ *     in[3] = 8
+ *     in[4..11] = "http/1.1"
+ *     inlen = 12
+ *
+ * The selection algorithm is as follows:
+ *
+ * 1. If peer's list contains HTTP/2 protocol the library supports,
+ *    it is selected and returns 1. The following step is not taken.
+ *
+ * 2. If peer's list contains ``http/1.1``, this function selects
+ *    ``http/1.1`` and returns 0.  The following step is not taken.
+ *
+ * 3. This function selects nothing and returns -1 (So called
+ *    non-overlap case).  In this case, |out| and |outlen| are left
+ *    untouched.
+ *
+ * Selecting ``h2`` means that ``h2`` is written into |*out| and its
+ * length (which is 2) is assigned to |*outlen|.
+ *
+ * For ALPN, refer to https://tools.ietf.org/html/rfc7301
+ *
+ * To use this method you should do something like::
+ *
+ *     static int alpn_select_proto_cb(SSL* ssl,
+ *                                     const unsigned char **out,
+ *                                     unsigned char *outlen,
+ *                                     const unsigned char *in,
+ *                                     unsigned int inlen,
+ *                                     void *arg)
+ *     {
+ *         int rv;
+ *         rv = nghttp2_select_alpn(out, outlen, in, inlen);
+ *         if (rv == -1) {
+ *             return SSL_TLSEXT_ERR_NOACK;
+ *         }
+ *         if (rv == 1) {
+ *             ((MyType*)arg)->http2_selected = 1;
+ *         }
+ *         return SSL_TLSEXT_ERR_OK;
+ *     }
+ *     ...
+ *     SSL_CTX_set_alpn_select_cb(ssl_ctx, alpn_select_proto_cb, my_obj);
+ *
+ */
+NGHTTP2_EXTERN int nghttp2_select_alpn(const unsigned char **out,
+                                       unsigned char *outlen,
+                                       const unsigned char *in,
+                                       unsigned int inlen);
+
+/**
+ * @function
+ *
+ * Returns a pointer to a nghttp2_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.
+ */
+NGHTTP2_EXTERN nghttp2_info *nghttp2_version(int least_version);
+
+/**
+ * @function
+ *
+ * Returns nonzero if the :type:`nghttp2_error` library error code
+ * |lib_error| is fatal.
+ */
+NGHTTP2_EXTERN int nghttp2_is_fatal(int lib_error_code);
+
+/**
+ * @function
+ *
+ * Returns nonzero if HTTP header field name |name| of length |len| is
+ * valid according to http://tools.ietf.org/html/rfc7230#section-3.2
+ *
+ * Because this is a header field name in HTTP2, the upper cased alphabet
+ * is treated as error.
+ */
+NGHTTP2_EXTERN int nghttp2_check_header_name(const uint8_t *name, size_t len);
+
+/**
+ * @function
+ *
+ * Returns nonzero if HTTP header field value |value| of length |len|
+ * is valid according to
+ * http://tools.ietf.org/html/rfc7230#section-3.2
+ *
+ * This function is considered obsolete, and application should
+ * consider to use `nghttp2_check_header_value_rfc9113()` instead.
+ */
+NGHTTP2_EXTERN int nghttp2_check_header_value(const uint8_t *value, size_t len);
+
+/**
+ * @function
+ *
+ * Returns nonzero if HTTP header field value |value| of length |len|
+ * is valid according to
+ * http://tools.ietf.org/html/rfc7230#section-3.2, plus
+ * https://datatracker.ietf.org/doc/html/rfc9113#section-8.2.1
+ */
+NGHTTP2_EXTERN int nghttp2_check_header_value_rfc9113(const uint8_t *value,
+                                                      size_t len);
+
+/**
+ * @function
+ *
+ * Returns nonzero if the |value| which is supposed to be the value of
+ * the :method header field is valid according to
+ * https://datatracker.ietf.org/doc/html/rfc7231#section-4 and
+ * https://datatracker.ietf.org/doc/html/rfc7230#section-3.2.6
+ */
+NGHTTP2_EXTERN int nghttp2_check_method(const uint8_t *value, size_t len);
+
+/**
+ * @function
+ *
+ * Returns nonzero if the |value| which is supposed to be the value of
+ * the :path header field is valid according to
+ * https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2.3
+ *
+ * |value| is valid if it merely consists of the allowed characters.
+ * In particular, it does not check whether |value| follows the syntax
+ * of path.  The allowed characters are all characters valid by
+ * `nghttp2_check_header_value` minus SPC and HT.
+ */
+NGHTTP2_EXTERN int nghttp2_check_path(const uint8_t *value, size_t len);
+
+/**
+ * @function
+ *
+ * Returns nonzero if the |value| which is supposed to be the value of the
+ * :authority or host header field is valid according to
+ * https://tools.ietf.org/html/rfc3986#section-3.2
+ *
+ * |value| is valid if it merely consists of the allowed characters.
+ * In particular, it does not check whether |value| follows the syntax
+ * of authority.
+ */
+NGHTTP2_EXTERN int nghttp2_check_authority(const uint8_t *value, size_t len);
+
+/* HPACK API */
+
+struct nghttp2_hd_deflater;
+
+/**
+ * @struct
+ *
+ * HPACK deflater object.
+ */
+typedef struct nghttp2_hd_deflater nghttp2_hd_deflater;
+
+/**
+ * @function
+ *
+ * Initializes |*deflater_ptr| for deflating name/values pairs.
+ *
+ * The |max_deflate_dynamic_table_size| is the upper bound of header
+ * table size the deflater will use.
+ *
+ * If this function fails, |*deflater_ptr| is left untouched.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int
+nghttp2_hd_deflate_new(nghttp2_hd_deflater **deflater_ptr,
+                       size_t max_deflate_dynamic_table_size);
+
+/**
+ * @function
+ *
+ * Like `nghttp2_hd_deflate_new()`, but with additional custom memory
+ * allocator specified in the |mem|.
+ *
+ * The |mem| can be ``NULL`` and the call is equivalent to
+ * `nghttp2_hd_deflate_new()`.
+ *
+ * This function does not take ownership |mem|.  The application is
+ * responsible for freeing |mem|.
+ *
+ * The library code does not refer to |mem| pointer after this
+ * function returns, so the application can safely free it.
+ */
+NGHTTP2_EXTERN int
+nghttp2_hd_deflate_new2(nghttp2_hd_deflater **deflater_ptr,
+                        size_t max_deflate_dynamic_table_size,
+                        nghttp2_mem *mem);
+
+/**
+ * @function
+ *
+ * Deallocates any resources allocated for |deflater|.
+ */
+NGHTTP2_EXTERN void nghttp2_hd_deflate_del(nghttp2_hd_deflater *deflater);
+
+/**
+ * @function
+ *
+ * Changes header table size of the |deflater| to
+ * |settings_max_dynamic_table_size| bytes.  This may trigger eviction
+ * in the dynamic table.
+ *
+ * The |settings_max_dynamic_table_size| should be the value received
+ * in SETTINGS_HEADER_TABLE_SIZE.
+ *
+ * The deflater never uses more memory than
+ * ``max_deflate_dynamic_table_size`` bytes specified in
+ * `nghttp2_hd_deflate_new()`.  Therefore, if
+ * |settings_max_dynamic_table_size| >
+ * ``max_deflate_dynamic_table_size``, resulting maximum table size
+ * becomes ``max_deflate_dynamic_table_size``.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int
+nghttp2_hd_deflate_change_table_size(nghttp2_hd_deflater *deflater,
+                                     size_t settings_max_dynamic_table_size);
+
+/**
+ * @function
+ *
+ * Deflates the |nva|, which has the |nvlen| name/value pairs, into
+ * the |buf| of length |buflen|.
+ *
+ * If |buf| is not large enough to store the deflated header block,
+ * this function fails with
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INSUFF_BUFSIZE`.  The caller
+ * should use `nghttp2_hd_deflate_bound()` to know the upper bound of
+ * buffer size required to deflate given header name/value pairs.
+ *
+ * Once this function fails, subsequent call of this function always
+ * returns :enum:`nghttp2_error.NGHTTP2_ERR_HEADER_COMP`.
+ *
+ * After this function returns, it is safe to delete the |nva|.
+ *
+ * This function returns the number of bytes written to |buf| if it
+ * succeeds, or one of the following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_HEADER_COMP`
+ *     Deflation process has failed.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INSUFF_BUFSIZE`
+ *     The provided |buflen| size is too small to hold the output.
+ */
+NGHTTP2_EXTERN ssize_t nghttp2_hd_deflate_hd(nghttp2_hd_deflater *deflater,
+                                             uint8_t *buf, size_t buflen,
+                                             const nghttp2_nv *nva,
+                                             size_t nvlen);
+
+/**
+ * @function
+ *
+ * Deflates the |nva|, which has the |nvlen| name/value pairs, into
+ * the |veclen| size of buf vector |vec|.  The each size of buffer
+ * must be set in len field of :type:`nghttp2_vec`.  If and only if
+ * one chunk is filled up completely, next chunk will be used.  If
+ * |vec| is not large enough to store the deflated header block, this
+ * function fails with
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INSUFF_BUFSIZE`.  The caller
+ * should use `nghttp2_hd_deflate_bound()` to know the upper bound of
+ * buffer size required to deflate given header name/value pairs.
+ *
+ * Once this function fails, subsequent call of this function always
+ * returns :enum:`nghttp2_error.NGHTTP2_ERR_HEADER_COMP`.
+ *
+ * After this function returns, it is safe to delete the |nva|.
+ *
+ * This function returns the number of bytes written to |vec| if it
+ * succeeds, or one of the following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_HEADER_COMP`
+ *     Deflation process has failed.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INSUFF_BUFSIZE`
+ *     The provided |buflen| size is too small to hold the output.
+ */
+NGHTTP2_EXTERN ssize_t nghttp2_hd_deflate_hd_vec(nghttp2_hd_deflater *deflater,
+                                                 const nghttp2_vec *vec,
+                                                 size_t veclen,
+                                                 const nghttp2_nv *nva,
+                                                 size_t nvlen);
+
+/**
+ * @function
+ *
+ * Returns an upper bound on the compressed size after deflation of
+ * |nva| of length |nvlen|.
+ */
+NGHTTP2_EXTERN size_t nghttp2_hd_deflate_bound(nghttp2_hd_deflater *deflater,
+                                               const nghttp2_nv *nva,
+                                               size_t nvlen);
+
+/**
+ * @function
+ *
+ * Returns the number of entries that header table of |deflater|
+ * contains.  This is the sum of the number of static table and
+ * dynamic table, so the return value is at least 61.
+ */
+NGHTTP2_EXTERN
+size_t nghttp2_hd_deflate_get_num_table_entries(nghttp2_hd_deflater *deflater);
+
+/**
+ * @function
+ *
+ * Returns the table entry denoted by |idx| from header table of
+ * |deflater|.  The |idx| is 1-based, and idx=1 returns first entry of
+ * static table.  idx=62 returns first entry of dynamic table if it
+ * exists.  Specifying idx=0 is error, and this function returns NULL.
+ * If |idx| is strictly greater than the number of entries the tables
+ * contain, this function returns NULL.
+ */
+NGHTTP2_EXTERN
+const nghttp2_nv *
+nghttp2_hd_deflate_get_table_entry(nghttp2_hd_deflater *deflater, size_t idx);
+
+/**
+ * @function
+ *
+ * Returns the used dynamic table size, including the overhead 32
+ * bytes per entry described in RFC 7541.
+ */
+NGHTTP2_EXTERN
+size_t nghttp2_hd_deflate_get_dynamic_table_size(nghttp2_hd_deflater *deflater);
+
+/**
+ * @function
+ *
+ * Returns the maximum dynamic table size.
+ */
+NGHTTP2_EXTERN
+size_t
+nghttp2_hd_deflate_get_max_dynamic_table_size(nghttp2_hd_deflater *deflater);
+
+struct nghttp2_hd_inflater;
+
+/**
+ * @struct
+ *
+ * HPACK inflater object.
+ */
+typedef struct nghttp2_hd_inflater nghttp2_hd_inflater;
+
+/**
+ * @function
+ *
+ * Initializes |*inflater_ptr| for inflating name/values pairs.
+ *
+ * If this function fails, |*inflater_ptr| is left untouched.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ */
+NGHTTP2_EXTERN int nghttp2_hd_inflate_new(nghttp2_hd_inflater **inflater_ptr);
+
+/**
+ * @function
+ *
+ * Like `nghttp2_hd_inflate_new()`, but with additional custom memory
+ * allocator specified in the |mem|.
+ *
+ * The |mem| can be ``NULL`` and the call is equivalent to
+ * `nghttp2_hd_inflate_new()`.
+ *
+ * This function does not take ownership |mem|.  The application is
+ * responsible for freeing |mem|.
+ *
+ * The library code does not refer to |mem| pointer after this
+ * function returns, so the application can safely free it.
+ */
+NGHTTP2_EXTERN int nghttp2_hd_inflate_new2(nghttp2_hd_inflater **inflater_ptr,
+                                           nghttp2_mem *mem);
+
+/**
+ * @function
+ *
+ * Deallocates any resources allocated for |inflater|.
+ */
+NGHTTP2_EXTERN void nghttp2_hd_inflate_del(nghttp2_hd_inflater *inflater);
+
+/**
+ * @function
+ *
+ * Changes header table size in the |inflater|.  This may trigger
+ * eviction in the dynamic table.
+ *
+ * The |settings_max_dynamic_table_size| should be the value
+ * transmitted in SETTINGS_HEADER_TABLE_SIZE.
+ *
+ * This function must not be called while header block is being
+ * inflated.  In other words, this function must be called after
+ * initialization of |inflater|, but before calling
+ * `nghttp2_hd_inflate_hd2()`, or after
+ * `nghttp2_hd_inflate_end_headers()`.  Otherwise,
+ * `NGHTTP2_ERR_INVALID_STATE` was returned.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_STATE`
+ *     The function is called while header block is being inflated.
+ *     Probably, application missed to call
+ *     `nghttp2_hd_inflate_end_headers()`.
+ */
+NGHTTP2_EXTERN int
+nghttp2_hd_inflate_change_table_size(nghttp2_hd_inflater *inflater,
+                                     size_t settings_max_dynamic_table_size);
+
+/**
+ * @enum
+ *
+ * The flags for header inflation.
+ */
+typedef enum {
+  /**
+   * No flag set.
+   */
+  NGHTTP2_HD_INFLATE_NONE = 0,
+  /**
+   * Indicates all headers were inflated.
+   */
+  NGHTTP2_HD_INFLATE_FINAL = 0x01,
+  /**
+   * Indicates a header was emitted.
+   */
+  NGHTTP2_HD_INFLATE_EMIT = 0x02
+} nghttp2_hd_inflate_flag;
+
+/**
+ * @function
+ *
+ * .. warning::
+ *
+ *   Deprecated.  Use `nghttp2_hd_inflate_hd2()` instead.
+ *
+ * Inflates name/value block stored in |in| with length |inlen|.  This
+ * function performs decompression.  For each successful emission of
+ * header name/value pair,
+ * :enum:`nghttp2_hd_inflate_flag.NGHTTP2_HD_INFLATE_EMIT` is set in
+ * |*inflate_flags| and name/value pair is assigned to the |nv_out|
+ * and the function returns.  The caller must not free the members of
+ * |nv_out|.
+ *
+ * The |nv_out| may include pointers to the memory region in the |in|.
+ * The caller must retain the |in| while the |nv_out| is used.
+ *
+ * The application should call this function repeatedly until the
+ * ``(*inflate_flags) & NGHTTP2_HD_INFLATE_FINAL`` is nonzero and
+ * return value is non-negative.  This means the all input values are
+ * processed successfully.  Then the application must call
+ * `nghttp2_hd_inflate_end_headers()` to prepare for the next header
+ * block input.
+ *
+ * The caller can feed complete compressed header block.  It also can
+ * feed it in several chunks.  The caller must set |in_final| to
+ * nonzero if the given input is the last block of the compressed
+ * header.
+ *
+ * This function returns the number of bytes processed if it succeeds,
+ * or one of the following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_HEADER_COMP`
+ *     Inflation process has failed.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_BUFFER_ERROR`
+ *     The header field name or value is too large.
+ *
+ * Example follows::
+ *
+ *     int inflate_header_block(nghttp2_hd_inflater *hd_inflater,
+ *                              uint8_t *in, size_t inlen, int final)
+ *     {
+ *         ssize_t rv;
+ *
+ *         for(;;) {
+ *             nghttp2_nv nv;
+ *             int inflate_flags = 0;
+ *
+ *             rv = nghttp2_hd_inflate_hd(hd_inflater, &nv, &inflate_flags,
+ *                                        in, inlen, final);
+ *
+ *             if(rv < 0) {
+ *                 fprintf(stderr, "inflate failed with error code %zd", rv);
+ *                 return -1;
+ *             }
+ *
+ *             in += rv;
+ *             inlen -= rv;
+ *
+ *             if(inflate_flags & NGHTTP2_HD_INFLATE_EMIT) {
+ *                 fwrite(nv.name, nv.namelen, 1, stderr);
+ *                 fprintf(stderr, ": ");
+ *                 fwrite(nv.value, nv.valuelen, 1, stderr);
+ *                 fprintf(stderr, "\n");
+ *             }
+ *             if(inflate_flags & NGHTTP2_HD_INFLATE_FINAL) {
+ *                 nghttp2_hd_inflate_end_headers(hd_inflater);
+ *                 break;
+ *             }
+ *             if((inflate_flags & NGHTTP2_HD_INFLATE_EMIT) == 0 &&
+ *                inlen == 0) {
+ *                break;
+ *             }
+ *         }
+ *
+ *         return 0;
+ *     }
+ *
+ */
+NGHTTP2_EXTERN ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_inflater *inflater,
+                                             nghttp2_nv *nv_out,
+                                             int *inflate_flags, uint8_t *in,
+                                             size_t inlen, int in_final);
+
+/**
+ * @function
+ *
+ * Inflates name/value block stored in |in| with length |inlen|.  This
+ * function performs decompression.  For each successful emission of
+ * header name/value pair,
+ * :enum:`nghttp2_hd_inflate_flag.NGHTTP2_HD_INFLATE_EMIT` is set in
+ * |*inflate_flags| and name/value pair is assigned to the |nv_out|
+ * and the function returns.  The caller must not free the members of
+ * |nv_out|.
+ *
+ * The |nv_out| may include pointers to the memory region in the |in|.
+ * The caller must retain the |in| while the |nv_out| is used.
+ *
+ * The application should call this function repeatedly until the
+ * ``(*inflate_flags) & NGHTTP2_HD_INFLATE_FINAL`` is nonzero and
+ * return value is non-negative.  If that happens, all given input
+ * data (|inlen| bytes) are processed successfully.  Then the
+ * application must call `nghttp2_hd_inflate_end_headers()` to prepare
+ * for the next header block input.
+ *
+ * In other words, if |in_final| is nonzero, and this function returns
+ * |inlen|, you can assert that
+ * :enum:`nghttp2_hd_inflate_final.NGHTTP2_HD_INFLATE_FINAL` is set in
+ * |*inflate_flags|.
+ *
+ * The caller can feed complete compressed header block.  It also can
+ * feed it in several chunks.  The caller must set |in_final| to
+ * nonzero if the given input is the last block of the compressed
+ * header.
+ *
+ * This function returns the number of bytes processed if it succeeds,
+ * or one of the following negative error codes:
+ *
+ * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
+ *     Out of memory.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_HEADER_COMP`
+ *     Inflation process has failed.
+ * :enum:`nghttp2_error.NGHTTP2_ERR_BUFFER_ERROR`
+ *     The header field name or value is too large.
+ *
+ * Example follows::
+ *
+ *     int inflate_header_block(nghttp2_hd_inflater *hd_inflater,
+ *                              uint8_t *in, size_t inlen, int final)
+ *     {
+ *         ssize_t rv;
+ *
+ *         for(;;) {
+ *             nghttp2_nv nv;
+ *             int inflate_flags = 0;
+ *
+ *             rv = nghttp2_hd_inflate_hd2(hd_inflater, &nv, &inflate_flags,
+ *                                         in, inlen, final);
+ *
+ *             if(rv < 0) {
+ *                 fprintf(stderr, "inflate failed with error code %zd", rv);
+ *                 return -1;
+ *             }
+ *
+ *             in += rv;
+ *             inlen -= rv;
+ *
+ *             if(inflate_flags & NGHTTP2_HD_INFLATE_EMIT) {
+ *                 fwrite(nv.name, nv.namelen, 1, stderr);
+ *                 fprintf(stderr, ": ");
+ *                 fwrite(nv.value, nv.valuelen, 1, stderr);
+ *                 fprintf(stderr, "\n");
+ *             }
+ *             if(inflate_flags & NGHTTP2_HD_INFLATE_FINAL) {
+ *                 nghttp2_hd_inflate_end_headers(hd_inflater);
+ *                 break;
+ *             }
+ *             if((inflate_flags & NGHTTP2_HD_INFLATE_EMIT) == 0 &&
+ *                inlen == 0) {
+ *                break;
+ *             }
+ *         }
+ *
+ *         return 0;
+ *     }
+ *
+ */
+NGHTTP2_EXTERN ssize_t nghttp2_hd_inflate_hd2(nghttp2_hd_inflater *inflater,
+                                              nghttp2_nv *nv_out,
+                                              int *inflate_flags,
+                                              const uint8_t *in, size_t inlen,
+                                              int in_final);
+
+/**
+ * @function
+ *
+ * Signals the end of decompression for one header block.
+ *
+ * This function returns 0 if it succeeds. Currently this function
+ * always succeeds.
+ */
+NGHTTP2_EXTERN int
+nghttp2_hd_inflate_end_headers(nghttp2_hd_inflater *inflater);
+
+/**
+ * @function
+ *
+ * Returns the number of entries that header table of |inflater|
+ * contains.  This is the sum of the number of static table and
+ * dynamic table, so the return value is at least 61.
+ */
+NGHTTP2_EXTERN
+size_t nghttp2_hd_inflate_get_num_table_entries(nghttp2_hd_inflater *inflater);
+
+/**
+ * @function
+ *
+ * Returns the table entry denoted by |idx| from header table of
+ * |inflater|.  The |idx| is 1-based, and idx=1 returns first entry of
+ * static table.  idx=62 returns first entry of dynamic table if it
+ * exists.  Specifying idx=0 is error, and this function returns NULL.
+ * If |idx| is strictly greater than the number of entries the tables
+ * contain, this function returns NULL.
+ */
+NGHTTP2_EXTERN
+const nghttp2_nv *
+nghttp2_hd_inflate_get_table_entry(nghttp2_hd_inflater *inflater, size_t idx);
+
+/**
+ * @function
+ *
+ * Returns the used dynamic table size, including the overhead 32
+ * bytes per entry described in RFC 7541.
+ */
+NGHTTP2_EXTERN
+size_t nghttp2_hd_inflate_get_dynamic_table_size(nghttp2_hd_inflater *inflater);
+
+/**
+ * @function
+ *
+ * Returns the maximum dynamic table size.
+ */
+NGHTTP2_EXTERN
+size_t
+nghttp2_hd_inflate_get_max_dynamic_table_size(nghttp2_hd_inflater *inflater);
+
+struct nghttp2_stream;
+
+/**
+ * @struct
+ *
+ * The structure to represent HTTP/2 stream.  The details of this
+ * structure are intentionally hidden from the public API.
+ */
+typedef struct nghttp2_stream nghttp2_stream;
+
+/**
+ * @function
+ *
+ * Returns pointer to :type:`nghttp2_stream` object denoted by
+ * |stream_id|.  If stream was not found, returns NULL.
+ *
+ * Returns imaginary root stream (see
+ * `nghttp2_session_get_root_stream()`) if 0 is given in |stream_id|.
+ *
+ * Unless |stream_id| == 0, the returned pointer is valid until next
+ * call of `nghttp2_session_send()`, `nghttp2_session_mem_send()`,
+ * `nghttp2_session_recv()`, and `nghttp2_session_mem_recv()`.
+ */
+NGHTTP2_EXTERN nghttp2_stream *
+nghttp2_session_find_stream(nghttp2_session *session, int32_t stream_id);
+
+/**
+ * @enum
+ *
+ * State of stream as described in RFC 7540.
+ */
+typedef enum {
+  /**
+   * idle state.
+   */
+  NGHTTP2_STREAM_STATE_IDLE = 1,
+  /**
+   * open state.
+   */
+  NGHTTP2_STREAM_STATE_OPEN,
+  /**
+   * reserved (local) state.
+   */
+  NGHTTP2_STREAM_STATE_RESERVED_LOCAL,
+  /**
+   * reserved (remote) state.
+   */
+  NGHTTP2_STREAM_STATE_RESERVED_REMOTE,
+  /**
+   * half closed (local) state.
+   */
+  NGHTTP2_STREAM_STATE_HALF_CLOSED_LOCAL,
+  /**
+   * half closed (remote) state.
+   */
+  NGHTTP2_STREAM_STATE_HALF_CLOSED_REMOTE,
+  /**
+   * closed state.
+   */
+  NGHTTP2_STREAM_STATE_CLOSED
+} nghttp2_stream_proto_state;
+
+/**
+ * @function
+ *
+ * Returns state of |stream|.  The root stream retrieved by
+ * `nghttp2_session_get_root_stream()` will have stream state
+ * :enum:`nghttp2_stream_proto_state.NGHTTP2_STREAM_STATE_IDLE`.
+ */
+NGHTTP2_EXTERN nghttp2_stream_proto_state
+nghttp2_stream_get_state(nghttp2_stream *stream);
+
+/**
+ * @function
+ *
+ * Returns root of dependency tree, which is imaginary stream with
+ * stream ID 0.  The returned pointer is valid until |session| is
+ * freed by `nghttp2_session_del()`.
+ */
+NGHTTP2_EXTERN nghttp2_stream *
+nghttp2_session_get_root_stream(nghttp2_session *session);
+
+/**
+ * @function
+ *
+ * Returns the parent stream of |stream| in dependency tree.  Returns
+ * NULL if there is no such stream.
+ */
+NGHTTP2_EXTERN nghttp2_stream *
+nghttp2_stream_get_parent(nghttp2_stream *stream);
+
+NGHTTP2_EXTERN int32_t nghttp2_stream_get_stream_id(nghttp2_stream *stream);
+
+/**
+ * @function
+ *
+ * Returns the next sibling stream of |stream| in dependency tree.
+ * Returns NULL if there is no such stream.
+ */
+NGHTTP2_EXTERN nghttp2_stream *
+nghttp2_stream_get_next_sibling(nghttp2_stream *stream);
+
+/**
+ * @function
+ *
+ * Returns the previous sibling stream of |stream| in dependency tree.
+ * Returns NULL if there is no such stream.
+ */
+NGHTTP2_EXTERN nghttp2_stream *
+nghttp2_stream_get_previous_sibling(nghttp2_stream *stream);
+
+/**
+ * @function
+ *
+ * Returns the first child stream of |stream| in dependency tree.
+ * Returns NULL if there is no such stream.
+ */
+NGHTTP2_EXTERN nghttp2_stream *
+nghttp2_stream_get_first_child(nghttp2_stream *stream);
+
+/**
+ * @function
+ *
+ * Returns dependency weight to the parent stream of |stream|.
+ */
+NGHTTP2_EXTERN int32_t nghttp2_stream_get_weight(nghttp2_stream *stream);
+
+/**
+ * @function
+ *
+ * Returns the sum of the weight for |stream|'s children.
+ */
+NGHTTP2_EXTERN int32_t
+nghttp2_stream_get_sum_dependency_weight(nghttp2_stream *stream);
+
+/**
+ * @functypedef
+ *
+ * Callback function invoked when the library outputs debug logging.
+ * The function is called with arguments suitable for ``vfprintf(3)``
+ *
+ * The debug output is only enabled if the library is built with
+ * ``DEBUGBUILD`` macro defined.
+ */
+typedef void (*nghttp2_debug_vprintf_callback)(const char *format,
+                                               va_list args);
+
+/**
+ * @function
+ *
+ * Sets a debug output callback called by the library when built with
+ * ``DEBUGBUILD`` macro defined.  If this option is not used, debug
+ * log is written into standard error output.
+ *
+ * For builds without ``DEBUGBUILD`` macro defined, this function is
+ * noop.
+ *
+ * Note that building with ``DEBUGBUILD`` may cause significant
+ * performance penalty to libnghttp2 because of extra processing.  It
+ * should be used for debugging purpose only.
+ *
+ * .. Warning::
+ *
+ *   Building with ``DEBUGBUILD`` may cause significant performance
+ *   penalty to libnghttp2 because of extra processing.  It should be
+ *   used for debugging purpose only.  We write this two times because
+ *   this is important.
+ */
+NGHTTP2_EXTERN void nghttp2_set_debug_vprintf_callback(
+    nghttp2_debug_vprintf_callback debug_vprintf_callback);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* NGHTTP2_H */
diff --git a/lib/includes/nghttp2/nghttp2ver.h.in b/lib/includes/nghttp2/nghttp2ver.h.in
new file mode 100644
index 0000000..7717a64
--- /dev/null
+++ b/lib/includes/nghttp2/nghttp2ver.h.in
@@ -0,0 +1,42 @@
+/*
+ * nghttp2 - HTTP/2 C Library
+ *
+ * Copyright (c) 2012, 2013 Tatsuhiro Tsujikawa
+ *
+ * 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 NGHTTP2VER_H
+#define NGHTTP2VER_H
+
+/**
+ * @macro
+ * Version number of the nghttp2 library release
+ */
+#define NGHTTP2_VERSION "@PACKAGE_VERSION@"
+
+/**
+ * @macro
+ * Numerical representation of the version number of the nghttp2 library
+ * release. This is a 24 bit number with 8 bits for major number, 8 bits
+ * for minor and 8 bits for patch. Version 1.2.3 becomes 0x010203.
+ */
+#define NGHTTP2_VERSION_NUM @PACKAGE_VERSION_NUM@
+
+#endif /* NGHTTP2VER_H */