nghttp2/_sources/apiref.txt

API Reference
=============

Includes
--------

To use the public APIs, include ``nghttp2/nghttp2.h``::

    #include <nghttp2/nghttp2.h>

The header files are also available online: :doc:`nghttp2.h` and
:doc:`nghttp2ver.h`.

Remarks
-------

Do not call `nghttp2_session_send`, `nghttp2_session_recv` or
`nghttp2_session_mem_recv` from the nghttp2 callback functions
directly or indirectly. It will lead to the crash. You can submit
requests or frames in the callbacks then call `nghttp2_session_send`,
`nghttp2_session_recv` or `nghttp2_session_mem_recv` outside of the
callbacks.

Macros
------
.. macro:: NGHTTP2_VERSION

    Version number of the nghttp2 library release

.. macro:: NGHTTP2_VERSION_NUM

    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.

.. macro:: NGHTTP2_PROTO_VERSION_ID

    
    The protocol version identification of this library supports.

.. macro:: NGHTTP2_PROTO_VERSION_ID_LEN

    
    The length of :macro:`NGHTTP2_PROTO_VERSION_ID`.

.. macro:: NGHTTP2_VERSION_AGE

    
    The age of :type:`nghttp2_info`

.. macro:: NGHTTP2_PRI_DEFAULT

    
    The default priority value

.. macro:: NGHTTP2_PRI_LOWEST

    
    The lowest priority value

.. macro:: NGHTTP2_MAX_WINDOW_SIZE

    
    The maximum window size

.. macro:: NGHTTP2_INITIAL_WINDOW_SIZE

    
    The initial window size for stream level flow control.

.. macro:: NGHTTP2_INITIAL_CONNECTION_WINDOW_SIZE

    
    The initial window size for connection level flow control.

.. macro:: NGHTTP2_MAX_HEADER_TABLE_SIZE

    
    The maximum header table size.

.. macro:: NGHTTP2_CLIENT_CONNECTION_HEADER

    
    The client connection header.

.. macro:: NGHTTP2_CLIENT_CONNECTION_HEADER_LEN

    
    The length of :macro:`NGHTTP2_CLIENT_CONNECTION_HEADER`.

.. macro:: NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS

    Default maximum concurrent streams.


Enums
-----
.. type:: nghttp2_error

    
    Error codes used in this library. The code range is [-999, -500],
    inclusive. The following values are defined:

    .. macro:: NGHTTP2_ERR_INVALID_ARGUMENT

        (``-501``) 
        Invalid argument passed.
    .. macro:: NGHTTP2_ERR_UNSUPPORTED_VERSION

        (``-503``) 
        The specified protocol version is not supported.
    .. macro:: NGHTTP2_ERR_WOULDBLOCK

        (``-504``) 
        Used as a return value from :type:`nghttp2_send_callback` and
        :type:`nghttp2_recv_callback` to indicate that the operation
        would block.
    .. macro:: NGHTTP2_ERR_PROTO

        (``-505``) 
        General protocol error
    .. macro:: NGHTTP2_ERR_INVALID_FRAME

        (``-506``) 
        The frame is invalid.
    .. macro:: NGHTTP2_ERR_EOF

        (``-507``) 
        The peer performed a shutdown on the connection.
    .. macro:: NGHTTP2_ERR_DEFERRED

        (``-508``) 
        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.
    .. macro:: NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE

        (``-509``) 
        Stream ID has reached the maximum value. Therefore no stream ID
        is available.
    .. macro:: NGHTTP2_ERR_STREAM_CLOSED

        (``-510``) 
        The stream is already closed; or the stream ID is invalid.
    .. macro:: NGHTTP2_ERR_STREAM_CLOSING

        (``-511``) 
        RST_STREAM has been added to the outbound queue. The stream is in
        closing state.
    .. macro:: NGHTTP2_ERR_STREAM_SHUT_WR

        (``-512``) 
        The transmission is not allowed for this stream (e.g., a frame
        with END_STREAM flag set has already sent).
    .. macro:: NGHTTP2_ERR_INVALID_STREAM_ID

        (``-513``) 
        The stream ID is invalid.
    .. macro:: NGHTTP2_ERR_INVALID_STREAM_STATE

        (``-514``) 
        The state of the stream is not valid (e.g., DATA cannot be sent
        to the stream if response HEADERS has not been sent).
    .. macro:: NGHTTP2_ERR_DEFERRED_DATA_EXIST

        (``-515``) 
        Another DATA frame has already been deferred.
    .. macro:: NGHTTP2_ERR_START_STREAM_NOT_ALLOWED

        (``-516``) 
        Starting new stream is not allowed. (e.g., GOAWAY has been sent
        and/or received.
    .. macro:: NGHTTP2_ERR_GOAWAY_ALREADY_SENT

        (``-517``) 
        GOAWAY has already been sent.
    .. macro:: NGHTTP2_ERR_INVALID_HEADER_BLOCK

        (``-518``) 
        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).
    .. macro:: NGHTTP2_ERR_INVALID_STATE

        (``-519``) 
        Indicates that the context is not suitable to perform the
        requested operation.
    .. macro:: NGHTTP2_ERR_GZIP

        (``-520``) 
        The gzip error.
    .. macro:: NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE

        (``-521``) 
        The user callback function failed due to the temporal error.
    .. macro:: NGHTTP2_ERR_FRAME_SIZE_ERROR

        (``-522``) 
        The length of the frame is invalid, either too large or too small.
    .. macro:: NGHTTP2_ERR_HEADER_COMP

        (``-523``) 
        Header block inflate/deflate error.
    .. macro:: NGHTTP2_ERR_FLOW_CONTROL

        (``-524``) 
        Flow control error
    .. macro:: NGHTTP2_ERR_INSUFF_BUFSIZE

        (``-525``) 
        Insufficient buffer size given to function.
    .. macro:: NGHTTP2_ERR_PAUSE

        (``-526``) 
        Callback was paused by the application
    .. macro:: NGHTTP2_ERR_TOO_MANY_INFLIGHT_SETTINGS

        (``-527``) 
        There are too many in-flight SETTING frame and no more
        transmission of SETTINGS is allowed.
    .. macro:: NGHTTP2_ERR_PUSH_DISABLED

        (``-528``) 
        The server push is disabled.
    .. macro:: NGHTTP2_ERR_FATAL

        (``-900``) 
        The errors < :macro:`NGHTTP2_ERR_FATAL` mean that the library is
        under unexpected condition and cannot process any further data
        reliably (e.g., out of memory).
    .. macro:: NGHTTP2_ERR_NOMEM

        (``-901``) 
        Out of memory. This is a fatal error.
    .. macro:: NGHTTP2_ERR_CALLBACK_FAILURE

        (``-902``) 
        The user callback function failed. This is a fatal error.


.. type:: nghttp2_frame_type

    The control frame types in HTTP/2.0.

    .. macro:: NGHTTP2_DATA

        (``0``) 
        The DATA frame.
    .. macro:: NGHTTP2_HEADERS

        (``1``) 
        The HEADERS frame.
    .. macro:: NGHTTP2_PRIORITY

        (``2``) 
        The PRIORITY frame.
    .. macro:: NGHTTP2_RST_STREAM

        (``3``) 
        The RST_STREAM frame.
    .. macro:: NGHTTP2_SETTINGS

        (``4``) 
        The SETTINGS frame.
    .. macro:: NGHTTP2_PUSH_PROMISE

        (``5``) 
        The PUSH_PROMISE frame.
    .. macro:: NGHTTP2_PING

        (``6``) 
        The PING frame.
    .. macro:: NGHTTP2_GOAWAY

        (``7``) 
        The GOAWAY frame.
    .. macro:: NGHTTP2_WINDOW_UPDATE

        (``9``) 
        The WINDOW_UPDATE frame.
    .. macro:: NGHTTP2_CONTINUATION

        (``10``) 
        The CONTINUATION frame.


.. type:: nghttp2_flag

    
    The flags for HTTP/2.0 frames. This enum defines all flags for
    frames, assuming that the same flag name has the same mask.

    .. macro:: NGHTTP2_FLAG_NONE

        (``0``) 
        No flag set.
    .. macro:: NGHTTP2_FLAG_END_STREAM

        (``0x1``) 
        The END_STREAM flag.
    .. macro:: NGHTTP2_FLAG_END_HEADERS

        (``0x4``) 
        The END_HEADERS flag.
    .. macro:: NGHTTP2_FLAG_PRIORITY

        (``0x8``) 
        The PRIORITY flag.
    .. macro:: NGHTTP2_FLAG_END_PUSH_PROMISE

        (``0x4``) 
        The END_PUSH_PROMISE flag.
    .. macro:: NGHTTP2_FLAG_ACK

        (``0x1``) 
        The ACK flag.


.. type:: nghttp2_settings_id

    The SETTINGS ID.

    .. macro:: NGHTTP2_SETTINGS_HEADER_TABLE_SIZE

        (``1``) 
        SETTINGS_HEADER_TABLE_SIZE
    .. macro:: NGHTTP2_SETTINGS_ENABLE_PUSH

        (``2``) 
        SETTINGS_ENABLE_PUSH
    .. macro:: NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS

        (``4``) 
        SETTINGS_MAX_CONCURRENT_STREAMS
    .. macro:: NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE

        (``7``) 
        SETTINGS_INITIAL_WINDOW_SIZE
    .. macro:: NGHTTP2_SETTINGS_FLOW_CONTROL_OPTIONS

        (``10``) 
        SETTINGS_FLOW_CONTROL_OPTIONS
    .. macro:: NGHTTP2_SETTINGS_MAX

        (``10``) 
        Maximum ID of :type:`nghttp2_settings_id`.


.. type:: nghttp2_error_code

    The status codes for the RST_STREAM and GOAWAY frames.

    .. macro:: NGHTTP2_NO_ERROR

        (``0``) 
        No errors.
    .. macro:: NGHTTP2_PROTOCOL_ERROR

        (``1``) 
        PROTOCOL_ERROR
    .. macro:: NGHTTP2_INTERNAL_ERROR

        (``2``) 
        INTERNAL_ERROR
    .. macro:: NGHTTP2_FLOW_CONTROL_ERROR

        (``3``) 
        FLOW_CONTROL_ERROR
    .. macro:: NGHTTP2_SETTINGS_TIMEOUT

        (``4``) 
        SETTINGS_TIMEOUT
    .. macro:: NGHTTP2_STREAM_CLOSED

        (``5``) 
        STREAM_CLOSED
    .. macro:: NGHTTP2_FRAME_SIZE_ERROR

        (``6``) 
        FRAME_SIZE_ERROR
    .. macro:: NGHTTP2_REFUSED_STREAM

        (``7``) 
        REFUSED_STREAM
    .. macro:: NGHTTP2_CANCEL

        (``8``) 
        CANCEL
    .. macro:: NGHTTP2_COMPRESSION_ERROR

        (``9``) 
        COMPRESSION_ERROR
    .. macro:: NGHTTP2_CONNECT_ERROR

        (``10``) 
        CONNECT_ERROR
    .. macro:: NGHTTP2_ENHANCE_YOUR_CALM

        (``420``) 
        ENHANCE_YOUR_CALM


.. type:: nghttp2_headers_category

    
    The category of HEADERS, which indicates the role of the frame. In
    HTTP/2.0 spec, request, response, push response and other arbitrary
    headers (e.g., trailers) are all called just HEADERS. To give the
    application the role of incoming HEADERS frame, we define several
    categories.

    .. macro:: NGHTTP2_HCAT_REQUEST

        (``0``) 
        The HEADERS frame is opening new stream, which is analogous to
        SYN_STREAM in SPDY.
    .. macro:: NGHTTP2_HCAT_RESPONSE

        (``1``) 
        The HEADERS frame is the first response headers, which is
        analogous to SYN_REPLY in SPDY.
    .. macro:: NGHTTP2_HCAT_PUSH_RESPONSE

        (``2``) 
        The HEADERS frame is the first headers sent against reserved
        stream.
    .. macro:: NGHTTP2_HCAT_HEADERS

        (``3``) 
        The HEADERS frame which does not apply for the above categories,
        which is analogous to HEADERS in SPDY.


.. type:: nghttp2_opt

    
    Configuration options for :type:`nghttp2_session`.

    .. macro:: NGHTTP2_OPT_NO_AUTO_STREAM_WINDOW_UPDATE

        (``1``) 
        This option prevents the library from sending WINDOW_UPDATE for a
        stream automatically. If this option is set to nonzero, the
        library won't send WINDOW_UPDATE for a stream and the application
        is responsible for sending WINDOW_UPDATE using
        `nghttp2_submit_window_update`. By default, this option is set to
        zero.
    .. macro:: NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE

        (``1 << 1``) 
        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 a connection and the
        application is responsible for sending WINDOW_UPDATE with stream
        ID 0 using `nghttp2_submit_window_update`. By default, this
        option is set to zero.
    .. macro:: NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS

        (``1 << 2``) 
        This option sets the SETTINGS_MAX_CONCURRENT_STREAMS value of
        remote endpoint as if it is received in SETTINGS frame. Without
        specifying this option, before the local endpoint receives
        SETTINGS_MAX_CONCURRENT_STREAMS in SETTINGS frame from remote
        endpoint, SETTINGS_MAX_CONCURRENT_STREAMS is unlimited. This may
        cause problem if local endpoint submits lots of requests
        initially and sending them at once to the remote peer may lead to
        the rejection of some requests. Specifying this option to the
        sensible value, say 100, may avoid this kind of issue. This value
        will be overwritten if the local endpoint receives
        SETTINGS_MAX_CONCURRENT_STREAMS from the remote endpoint.



Types (structs, unions and typedefs)
------------------------------------
.. type:: nghttp2_session

    
    The primary structure to hold the resources needed for a HTTP/2.0
    session. The details of this structure are intentionally hidden
    from the public API.



.. type:: nghttp2_info

    
    This struct is what `nghttp2_version()` returns. It holds
    information about the particular nghttp2 version.

    .. member::   int age

        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
    .. member::   int version_num

        the :macro:`NGHTTP2_VERSION_NUM` number (since age ==1)
    .. member::   const char *version_str

        points to the :macro:`NGHTTP2_VERSION` string (since age ==1)
    .. member::   const char *proto_str

        points to the :macro:`NGHTTP2_PROTO_VERSION_ID` string this
        instance implements (since age ==1)


.. type:: nghttp2_nv

    
    The name/value pair, which mainly used to represent header fields.

    .. member::   uint8_t *name

        The *name* byte string, which is not necessarily ``NULL``
        terminated.
    .. member::   uint8_t *value

        The *value* byte string, which is not necessarily ``NULL``
        terminated.
    .. member::   uint16_t namelen

        The length of the *name*.
    .. member::   uint16_t valuelen

        The length of the *value*.


.. type:: nghttp2_frame_hd

    The frame header.

    .. member::   size_t length

        The length field of this frame, excluding frame header.
    .. member::   int32_t stream_id

        The stream identifier (aka, stream ID)
    .. member::   uint8_t type

        The type of this frame. See `nghttp2_frame`.
    .. member::   uint8_t flags

        The flags.


.. type:: nghttp2_data_source

    
    This union represents the some kind of data source passed to
    :type:`nghttp2_data_source_read_callback`.

    .. member::   int fd

        The integer field, suitable for a file descriptor.
    .. member::   void *ptr

        The pointer to an arbitrary object.


.. type:: typedef ssize_t (*nghttp2_data_source_read_callback) (nghttp2_session *session, int32_t stream_id, uint8_t *buf, size_t length, int *eof, nghttp2_data_source *source, void *user_data)

    
    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 *\*eof* to 1.  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 :macro:`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()`.
    In case of error, there are 2 choices. Returning
    :macro:`NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` will close the stream
    by issuing RST_STREAM with :macro:`NGHTTP2_INTERNAL_ERROR`.
    Returning :macro:`NGHTTP2_ERR_CALLBACK_FAILURE` will signal the
    entire session failure.

.. type:: nghttp2_data_provider

    
    This struct represents the data source and the way to read a chunk
    of data from it.

    .. member::   nghttp2_data_source source

        The data source.
    .. member::   nghttp2_data_source_read_callback read_callback

        The callback function to read a chunk of data from the *source*.


.. type:: nghttp2_data

    
    The DATA frame. The received data is delivered via
    :type:`nghttp2_on_data_chunk_recv_callback`.



.. type:: nghttp2_headers

    The HEADERS frame. It has the following members:

    .. member::   nghttp2_frame_hd hd

        The frame header.
    .. member::   nghttp2_nv *nva

        The name/value pairs.
    .. member::   size_t nvlen

        The number of name/value pairs in *nva*.
    .. member::   nghttp2_headers_category cat

        The category of this HEADERS frame.
    .. member::   int32_t pri

        The priority.


.. type:: nghttp2_priority

    The PRIORITY frame. It has the following members:

    .. member::   nghttp2_frame_hd hd

        The frame header.
    .. member::   int32_t pri

        The priority.


.. type:: nghttp2_rst_stream

    The RST_STREAM frame. It has the following members:

    .. member::   nghttp2_frame_hd hd

        The frame header.
    .. member::   nghttp2_error_code error_code

        The error code. See :type:`nghttp2_error_code`.


.. type:: nghttp2_settings_entry

    The SETTINGS ID/Value pair. It has the following members:

    .. member::   int32_t settings_id

        The SETTINGS ID. See :type:`nghttp2_settings_id`.
    .. member::   uint32_t value

        The value of this entry.


.. type:: nghttp2_settings

    The SETTINGS frame. It has the following members:

    .. member::   nghttp2_frame_hd hd

        The frame header.
    .. member::   size_t niv

        The number of SETTINGS ID/Value pairs in *iv*.
    .. member::   nghttp2_settings_entry *iv

        The pointer to the array of SETTINGS ID/Value pair.


.. type:: nghttp2_push_promise

    The PUSH_PROMISE frame. It has the following members:

    .. member::   nghttp2_frame_hd hd

        The frame header.
    .. member::   nghttp2_nv *nva

        The name/value pairs.
    .. member::   size_t nvlen

        The number of name/value pairs in *nva*.
    .. member::   int32_t promised_stream_id

        The promised stream ID


.. type:: nghttp2_ping

    The PING frame. It has the following members:

    .. member::   nghttp2_frame_hd hd

        The frame header.
    .. member::   uint8_t opaque_data[8]

        The opaque data


.. type:: nghttp2_goaway

    The GOAWAY frame. It has the following members:

    .. member::   nghttp2_frame_hd hd

        The frame header.
    .. member::   int32_t last_stream_id

        The last stream stream ID.
    .. member::   nghttp2_error_code error_code

        The error code. See :type:`nghttp2_error_code`.
    .. member::   uint8_t *opaque_data

        The additional debug data
    .. member::   size_t opaque_data_len

        The length of *opaque_data* member.


.. type:: nghttp2_window_update

    
    The WINDOW_UPDATE frame. It has the following members:

    .. member::   nghttp2_frame_hd hd

        The frame header.
    .. member::   int32_t window_size_increment

        The window size increment.


.. type:: nghttp2_frame

    
    This union includes all frames to pass them to various function
    calls as nghttp2_frame type. The DATA frame is intentionally
    omitted from here.

    .. member::   nghttp2_frame_hd hd

        The frame header, which is convenient to inspect frame header.
    .. member::   nghttp2_data data

        The DATA frame.
    .. member::   nghttp2_headers headers

        The HEADERS frame.
    .. member::   nghttp2_priority priority

        The PRIORITY frame.
    .. member::   nghttp2_rst_stream rst_stream

        The RST_STREAM frame.
    .. member::   nghttp2_settings settings

        The SETTINGS frame.
    .. member::   nghttp2_push_promise push_promise

        The PUSH_PROMISE frame.
    .. member::   nghttp2_ping ping

        The PING frame.
    .. member::   nghttp2_goaway goaway

        The GOAWAY frame.
    .. member::   nghttp2_window_update window_update

        The WINDOW_UPDATE frame.


.. type:: typedef ssize_t (*nghttp2_send_callback) (nghttp2_session *session, const uint8_t *data, size_t length, int flags, void *user_data)

    
    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 :macro:`NGHTTP2_ERR_WOULDBLOCK`. For other errors, it
    must return :macro:`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()`.

.. type:: typedef ssize_t (*nghttp2_recv_callback) (nghttp2_session *session, uint8_t *buf, size_t length, int flags, void *user_data)

    
    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 :macro:`NGHTTP2_ERR_WOULDBLOCK`. If
    it gets EOF before it reads any single byte, it must return
    :macro:`NGHTTP2_ERR_EOF`. For other errors, it must return
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`. Returning 0 is treated as
    :macro:`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()`.

.. type:: typedef int (*nghttp2_on_frame_recv_callback) (nghttp2_session *session, const nghttp2_frame *frame, void *user_data)

    
    Callback function invoked by `nghttp2_session_recv()` when a aframe
    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`.
    
    For HEADERS, PUSH_PROMISE and DATA frames, this callback may be
    called after stream is closed (see
    :type:`nghttp2_on_stream_close_callback`). The application should
    check that stream is still alive using its own stream management or
    :func:`nghttp2_session_get_stream_user_data()`.
    
    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.
    
    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 :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: typedef int (*nghttp2_on_invalid_frame_recv_callback) (nghttp2_session *session, const nghttp2_frame *frame, nghttp2_error_code error_code, void *user_data)

    
    Callback function invoked by `nghttp2_session_recv()` when an
    invalid non-DATA frame is received. The *error_code* is one of the
    :macro:`nghttp2_error_code` and indicates the 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_send()` functions
    immediately return :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: 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)

    
    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
    :macro:`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 :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: typedef int (*nghttp2_before_frame_send_callback) (nghttp2_session *session, const nghttp2_frame *frame, void *user_data)

    
    Callback function invoked before the non-DATA frame *frame* is
    sent. This may be useful, for example, to know the stream ID of
    HEADERS and PUSH_PROMISE frame (see also
    `nghttp2_session_get_stream_user_data()`), which is not assigned
    when it was queued. 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_recv()` and `nghttp2_session_send()` functions
    immediately return :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: typedef int (*nghttp2_on_frame_send_callback) (nghttp2_session *session, const nghttp2_frame *frame, void *user_data)

    
    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_recv()` and `nghttp2_session_send()` functions
    immediately return :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: typedef int (*nghttp2_on_frame_not_send_callback) (nghttp2_session *session, const nghttp2_frame *frame, int lib_error_code, void *user_data)

    
    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_recv()` and `nghttp2_session_send()` functions
    immediately return :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: typedef int (*nghttp2_on_stream_close_callback) (nghttp2_session *session, int32_t stream_id, nghttp2_error_code error_code, void *user_data)

    
    Callback function invoked when the stream *stream_id* is
    closed. The reason of closure is indicated by the *error_code*. 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()`.
    
    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_send()` functions
    immediately return :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: typedef int (*nghttp2_on_unknown_frame_recv_callback) (nghttp2_session *session, const uint8_t *head, size_t headlen, const uint8_t *payload, size_t payloadlen, void *user_data)

    
    Callback function invoked when the received frame type is
    unknown. The *head* is the pointer to the header of the received
    frame. The *headlen* is the length of the *head*. According to the
    spec, the *headlen* is always 8. In other words, the *head* is the
    first 8 bytes of the received frame.  The *payload* is the pointer
    to the data portion of the received frame.  The *payloadlen* is the
    length of the *payload*. This is the data after the length
    field. 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_recv()` and `nghttp2_session_send()` functions
    immediately return :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: typedef int (*nghttp2_on_begin_headers_callback) (nghttp2_session *session, const nghttp2_frame *frame, void *user_data)

    
    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
    :macro:`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 implementation of this function must return 0 if it succeeds or
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`. If nonzero value other than
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE` is returned, it is treated as
    if :macro:`NGHTTP2_ERR_CALLBACK_FAILURE` is returned. If
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE` is returned,
    `nghttp2_session_mem_recv()` function will immediately return
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: 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, void *user_data)

    
    Callback function invoked when a header name/value pair is received
    for the *frame*. When this callback is invoked, ``frame->hd.type``
    is either :macro:`NGHTTP2_HEADERS` or :macro:`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.
    
    The *name* may be ``NULL`` if the *namelen* is 0. The same thing
    can be said about the *value*.
    
    Please note that nghttp2 library does not perform any validity
    check against the *name* and the *value*. For example, the
    *namelen* could be 0, and/or the *value* contains ``0x0a`` or
    ``0x0d``.  The application must check them if it matters. The
    helper function `nghttp2_check_header_name()` and
    `nghttp2_check_header_value()` provide simple validation against
    HTTP2 header field construction rule.
    
    One more thing to note is that the *value* may contain ``NULL``
    (``0x00``) characters. It is used to concatenate header values
    which share the same header field name. The application should
    split these values if it wants to get individual value. This
    concatenation is used in order to keep the ordering of headers.
    
    If the application uses `nghttp2_session_mem_recv()`, it can return
    :macro:`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 :macro:`NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` will close
    the stream by issuing RST_STREAM with
    :macro:`NGHTTP2_INTERNAL_ERROR`. In this case,
    :type:`nghttp2_on_frame_recv_callback` will not be invoked.
    
    The implementation of this function must return 0 if it
    succeeds. It may return :macro:`NGHTTP2_ERR_PAUSE` or
    :macro:`NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`. For other critical
    failures, it must return :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`. If
    the other nonzero value is returned, it is treated as
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`. If
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE` is returned,
    `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions
    immediately return :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`.

.. type:: nghttp2_session_callbacks

    
    Callback functions.

    .. member::   nghttp2_send_callback send_callback

        Callback function invoked when the *session* wants to send data
        to the remote peer.
    .. member::   nghttp2_recv_callback recv_callback

        Callback function invoked when the *session* wants to receive
        data from the remote peer.
    .. member::   nghttp2_on_frame_recv_callback on_frame_recv_callback

        Callback function invoked by `nghttp2_session_recv()` when a
        frame is received.
    .. member::   nghttp2_on_invalid_frame_recv_callback on_invalid_frame_recv_callback

        Callback function invoked by `nghttp2_session_recv()` when an
        invalid non-DATA frame is received.
    .. member::   nghttp2_on_data_chunk_recv_callback on_data_chunk_recv_callback

        Callback function invoked when a chunk of data in DATA frame is
        received.
    .. member::   nghttp2_before_frame_send_callback before_frame_send_callback

        Callback function invoked before a non-DATA frame is sent.
    .. member::   nghttp2_on_frame_send_callback on_frame_send_callback

        Callback function invoked after a frame is sent.
    .. member::   nghttp2_on_frame_not_send_callback on_frame_not_send_callback

        The callback function invoked when a non-DATA frame is not sent
        because of an error.
    .. member::   nghttp2_on_stream_close_callback on_stream_close_callback

        Callback function invoked when the stream is closed.
    .. member::   nghttp2_on_unknown_frame_recv_callback on_unknown_frame_recv_callback

        Callback function invoked when the received frame type is
        unknown.
    .. member::   nghttp2_on_begin_headers_callback on_begin_headers_callback

        Callback function invoked when the reception of header block in
        HEADERS or PUSH_PROMISE is started.
    .. member::   nghttp2_on_header_callback on_header_callback

        Callback function invoked when a header name/value pair is
        received.


.. type:: nghttp2_opt_set

    
    Struct to store option values for nghttp2_session.

    .. member::   uint32_t peer_max_concurrent_streams

        :macro:`NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS`
    .. member::   uint8_t no_auto_stream_window_update

        :macro:`NGHTTP2_OPT_NO_AUTO_STREAM_WINDOW_UPDATE`
    .. member::   uint8_t no_auto_connection_window_update

        :macro:`NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE`


.. type:: nghttp2_gzip

    
    The gzip stream to inflate data. The details of this structure are
    intentionally hidden from the public API.




Functions
---------
.. function:: int nghttp2_session_client_new(nghttp2_session **session_ptr, const nghttp2_session_callbacks *callbacks, void *user_data)

    
    Initializes *\*session_ptr* for client use. The all members of
    *callbacks* are copied to *\*session_ptr*. Therefore *\*session_ptr*
    does not store *callbacks*. *user_data* is an arbitrary user
    supplied data, which will be passed to the callback functions.
    
    The :member:`nghttp2_session_callbacks.send_callback` must be
    specified.  If the application code uses `nghttp2_session_recv()`,
    the :member:`nghttp2_session_callbacks.recv_callback` must be
    specified. The other members of *callbacks* can be ``NULL``.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_session_server_new(nghttp2_session **session_ptr, const nghttp2_session_callbacks *callbacks, void *user_data)

    
    Initializes *\*session_ptr* for server use. The all members of
    *callbacks* are copied to *\*session_ptr*. Therefore *\*session_ptr*
    does not store *callbacks*. *user_data* is an arbitrary user
    supplied data, which will be passed to the callback functions.
    
    The :member:`nghttp2_session_callbacks.send_callback` must be
    specified.  If the application code uses `nghttp2_session_recv()`,
    the :member:`nghttp2_session_callbacks.recv_callback` must be
    specified. The other members of *callbacks* can be ``NULL``.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_session_client_new2(nghttp2_session **session_ptr, const nghttp2_session_callbacks *callbacks, void *user_data, uint32_t opt_set_mask, const nghttp2_opt_set *opt_set)

    
    Like `nghttp2_session_client_new()`, but with additional options
    specified in the *opt_set*. The caller must set bitwise-OR of
    :macro:`nghttp2_opt` for given options.  For example, if it
    specifies :macro:`NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE` and
    :macro:`NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS` in the *opt_set*,
    the *opt_set_mask* should be
    ``NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE |
    NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS``.
    
    If the *opt_set_mask* is 0, the *opt_set* could be ``NULL`` safely
    and the call is equivalent to `nghttp2_session_client_new()`.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_session_server_new2(nghttp2_session **session_ptr, const nghttp2_session_callbacks *callbacks, void *user_data, uint32_t opt_set_mask, const nghttp2_opt_set *opt_set)

    
    Like `nghttp2_session_server_new()`, but with additional options
    specified in the *opt_set*. The caller must set bitwise-OR of
    :macro:`nghttp2_opt` for given options.  For example, if it
    specifies :macro:`NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE` and
    :macro:`NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS` in the *opt_set*,
    the *opt_set_mask* should be
    ``NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE |
    NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS``.
    
    If the *opt_set_mask* is 0, the *opt_set* could be ``NULL`` safely
    and the call is equivalent to `nghttp2_session_server_new()`.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: void nghttp2_session_del(nghttp2_session *session)

    
    Frees any resources allocated for *session*. If *session* is
    ``NULL``, this function does nothing.

.. function:: int nghttp2_session_send(nghttp2_session *session)

    
    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 as possible until the user callback
    :member:`nghttp2_session_callbacks.send_callback` returns
    :macro:`NGHTTP2_ERR_WOULDBLOCK` or the outbound queue becomes empty.
    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),
       :member:`nghttp2_session_callbacks.on_frame_not_send_callback` is
       invoked. Abort the following steps.
    4. If the frame is request HEADERS, the stream is opened
       here.
    5. :member:`nghttp2_session_callbacks.before_frame_send_callback` is
       invoked.
    6. :member:`nghttp2_session_callbacks.send_callback` is invoked one
       or more times to send the frame.
    7. :member:`nghttp2_session_callbacks.on_frame_send_callback` is
       invoked.
    8. If the transmission of the frame triggers closure of the stream,
       the stream is closed and
       :member:`nghttp2_session_callbacks.on_stream_close_callback` is
       invoked.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`
        The callback function failed.

.. function:: int nghttp2_session_recv(nghttp2_session *session)

    
    Receives frames from the remote peer.
    
    This function receives as many frames as possible until the user
    callback :member:`nghttp2_session_callbacks.recv_callback` returns
    :macro:`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. :member:`nghttp2_session_callbacks.recv_callback` is invoked one
       or more times to receive frame header.
    2. If the frame is DATA frame:
    
       1. :member:`nghttp2_session_callbacks.recv_callback` is invoked
          to receive DATA payload. For each chunk of data,
          :member:`nghttp2_session_callbacks.on_data_chunk_recv_callback`
          is invoked.
       2. If one DATA frame is completely received,
          :member:`nghttp2_session_callbacks.on_frame_recv_callback` is
          invoked. If the reception of the frame triggers the
          closure of the stream,
          :member:`nghttp2_session_callbacks.on_stream_close_callback`
          is invoked.
    
    3. If the frame is the control frame:
    
       1. :member:`nghttp2_session_callbacks.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,
          :member:`nghttp2_session_callbacks.on_begin_headers_callback`
          is invoked. Then
          :member:`nghttp2_session_callbacks.on_header_callback` is
          invoked for each header name/value pair. After all name/value
          pairs are emitted successfully,
          :member:`nghttp2_session_callbacks.on_frame_recv_callback` is
          invoked.  For other frames,
          :member:`nghttp2_session_callbacks.on_frame_recv_callback` is
          invoked.
          If the reception of the frame triggers the closure of the
          stream,
          :member:`nghttp2_session_callbacks.on_stream_close_callback`
          is invoked.
       3. If the received frame is unpacked but is interpreted as
          invalid,
          :member:`nghttp2_session_callbacks.on_invalid_frame_recv_callback`
          is invoked.
       4. If the received frame type is unknown,
          :member:`nghttp2_session_callbacks.on_unknown_frame_recv_callback`
          is invoked.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_EOF`
        The remote peer did shutdown on the connection.
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`
        The callback function failed.

.. function:: ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in, size_t inlen)

    
    Processes data *in* as an input from the remote endpoint. The
    *inlen* indicates the number of bytes in the *in*.
    
    This function behaves like `nghttp2_session_recv()` except that it
    does not use :member:`nghttp2_session_callbacks.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 all input data unless either an error occurs or
    :macro:`NGHTTP2_ERR_PAUSE` is returned from
    :member:`nghttp2_session_callbacks.on_header_callback` or
    :member:`nghttp2_session_callbacks.on_data_chunk_recv_callback`.
    If :macro:`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:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.
    :macro:`NGHTTP2_ERR_CALLBACK_FAILURE`
        The callback function failed.

.. function:: int nghttp2_session_resume_data(nghttp2_session *session, int32_t stream_id)

    
    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:
    
    :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
        The stream does not exist or no deferred data exist.
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_session_want_read(nghttp2_session *session)

    
    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.

.. function:: int nghttp2_session_want_write(nghttp2_session *session)

    
    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.

.. function:: void* nghttp2_session_get_stream_user_data(nghttp2_session *session, int32_t stream_id)

    
    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``.

.. function:: int nghttp2_session_set_stream_user_data(nghttp2_session *session, int32_t stream_id, void *stream_user_data)

    
    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:
    
    :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
        The stream does not exist

.. function:: size_t nghttp2_session_get_outbound_queue_size(nghttp2_session *session)

    
    Returns the number of frames in the outbound queue. This does not
    include the deferred DATA frames.

.. function:: int32_t nghttp2_session_get_stream_effective_recv_data_length (nghttp2_session *session, int32_t stream_id)

    
    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.
    
    If flow control is disabled for that stream, this function returns
    0.
    
    This function returns -1 if it fails.

.. function:: int32_t nghttp2_session_get_stream_effective_local_window_size (nghttp2_session *session, int32_t stream_id)

    
    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 returns -1 if it fails.

.. function:: int32_t nghttp2_session_get_effective_recv_data_length (nghttp2_session *session)

    
    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.
    
    If flow control is disabled for a connection, this function returns
    0.
    
    This function returns -1 if it fails.

.. function:: int32_t nghttp2_session_get_effective_local_window_size (nghttp2_session *session)

    
    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 returns -1 if it fails.

.. function:: int nghttp2_session_terminate_session(nghttp2_session *session, nghttp2_error_code error_code)

    
    Signals the session so that the connection should be terminated.
    
    GOAWAY frame with the given *error_code* will be submitted if it
    has not been transmitted. After the transmission, both
    `nghttp2_session_want_read()` and `nghttp2_session_want_write()`
    return 0. If GOAWAY frame has already transmitted at the time when
    this function is invoked, `nghttp2_session_want_read()` and
    `nghttp2_session_want_write()` returns 0 immediately after this
    function succeeds.
    
    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:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_session_upgrade(nghttp2_session *session, const uint8_t *settings_payload, size_t settings_payloadlen, void *stream_user_data)

    
    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).
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.
    :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
        The *settings_payload* is badly formed.
    :macro:`NGHTTP2_ERR_PROTO`
        The stream ID 1 is already used or closed; or is not available;
        or the *settings_payload* does not include both
        :macro:`NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS` and
        :macro:`NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE`.

.. function:: ssize_t nghttp2_pack_settings_payload(uint8_t *buf, size_t buflen, const nghttp2_settings_entry *iv, size_t niv)

    
    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 ``8*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:
    
    :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
        The *iv* contains duplicate settings ID or invalid value.
    
    :macro:`NGHTTP2_ERR_INSUFF_BUFSIZE`
        The provided *buflen* size is too small to hold the output.

.. function:: const char* nghttp2_strerror(int lib_error_code)

    
    Returns string describing the *lib_error_code*. The
    *lib_error_code* must be one of the :macro:`nghttp2_error`.

.. function:: int nghttp2_submit_request(nghttp2_session *session, int32_t pri, const nghttp2_nv *nva, size_t nvlen, const nghttp2_data_provider *data_prd, void *stream_user_data)

    
    Submits HEADERS frame and optionally one or more DATA frames.
    
    The *pri* is priority of this request. 0 is the highest priority
    value and :macro:`NGHTTP2_PRI_LOWEST` is the lowest value.
    
    The *nva* is an array of name/value pair :type:`nghttp2_nv` with
    *nvlen* elements. The value is opaque sequence of bytes and
    therefore can contain NULL byte (0x0). If the application requires
    that the ordering of values for a single header field name
    appearing in different header fields, it has to concatenate them
    using NULL byte (0x0) before passing them to this function.
    
    HTTP/2.0 specification has requirement about header fields in the
    request HEADERS. See the specification for more details.
    
    This function creates copies of all name/value pairs in *nva*.  It
    also lower-cases all names in *nva*.
    
    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
    (http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9) 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()`.
    
    Since the library reorders the frames and tries to send the highest
    prioritized one first and the HTTP/2.0 specification requires the
    stream ID must be strictly increasing, the stream ID of this
    request cannot be known until it is about to sent.  To know the
    stream ID of the request, the application can use
    :member:`nghttp2_session_callbacks.before_frame_send_callback`. This
    callback is called just before the frame is sent. For HEADERS
    frame, the argument frame has the stream ID assigned. Also since
    the stream is already opened,
    `nghttp2_session_get_stream_user_data()` can be used to get
    *stream_user_data* to identify which HEADERS we are processing.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
        The *pri* is invalid
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_response(nghttp2_session *session, int32_t stream_id, const nghttp2_nv *nva, size_t nvlen, const nghttp2_data_provider *data_prd)

    
    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 value is opaque sequence of bytes and
    therefore can contain NULL byte (0x0). If the application requires
    that the ordering of values for a single header field name
    appearing in different header fields, it has to concatenate them
    using NULL byte (0x0) before passing them to this function.
    
    HTTP/2.0 specification has requirement about header fields in the
    response HEADERS. See the specification for more details.
    
    This function creates copies of all name/value pairs in *nva*.  It
    also lower-cases all names in *nva*.
    
    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()`.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_headers(nghttp2_session *session, uint8_t flags, int32_t stream_id, int32_t pri, const nghttp2_nv *nva, size_t nvlen, void *stream_user_data)

    
    Submits HEADERS frame. The *flags* is bitwise OR of the
    following values:
    
    * :macro:`NGHTTP2_FLAG_END_STREAM`
    * :macro:`NGHTTP2_FLAG_END_HEADERS`
    * :macro:`NGHTTP2_FLAG_PRIORITY`
    
    If *flags* includes :macro:`NGHTTP2_FLAG_END_STREAM`, this frame has
    END_STREAM flag set. The library does not support header
    continuation and the HEADERS frame always has
    :macro:`NGHTTP2_FLAG_END_HEADERS` flag set regardless of the *flags*
    value.
    
    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
    actual stream ID is assigned just before the frame is sent. For
    response, specify stream ID in *stream_id*.
    
    The *pri* is priority of this request.
    
    The *nva* is an array of name/value pair :type:`nghttp2_nv` with
    *nvlen* elements. The value is opaque sequence of bytes and
    therefore can contain NULL byte (0x0). If the application requires
    that the ordering of values for a single header field name
    appearing in different header fields, it has to concatenate them
    using NULL byte (0x0) before passing them to this function.
    
    This function creates copies of all name/value pairs in *nva*.  It
    also lower-cases all names in *nva*.
    
    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.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
        The *pri* is invalid
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_data(nghttp2_session *session, uint8_t flags, int32_t stream_id, const nghttp2_data_provider *data_prd)

    
    Submits one or more DATA frames to the stream *stream_id*.  The
    data to be sent are provided by *data_prd*. If *flags* contains
    :macro:`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:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_priority(nghttp2_session *session, uint8_t flags, int32_t stream_id, int32_t pri)

    
    Submits PRIORITY frame to change the priority of stream *stream_id*
    to the priority value *pri*.
    
    The *flags* is currently ignored and should be
    :macro:`NGHTTP2_FLAG_NONE`.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.
    :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
        The *pri* is negative.

.. function:: int nghttp2_submit_rst_stream(nghttp2_session *session, uint8_t flags, int32_t stream_id, nghttp2_error_code error_code)

    
    Submits RST_STREAM frame to cancel/reject the stream *stream_id*
    with the error code *error_code*.
    
    The *flags* is currently ignored and should be
    :macro:`NGHTTP2_FLAG_NONE`.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_settings(nghttp2_session *session, uint8_t flags, const nghttp2_settings_entry *iv, size_t niv)

    
    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
    :macro:`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 :macro:`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:
    
    :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
        The *iv* contains invalid value (e.g., attempting to re-enable
        flow control).
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_push_promise(nghttp2_session *session, uint8_t flags, int32_t stream_id, const nghttp2_nv *nva, size_t nvlen)

    
    Submits PUSH_PROMISE frame. The *flags* is currently ignored and
    the resulting PUSH_PROMISE frame always has
    :macro:`NGHTTP2_FLAG_END_PUSH_PROMISE` flag set due to the lack of
    header continuation support in the library.
    
    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 value is opaque sequence of bytes and
    therefore can contain NULL byte (0x0). If the application requires
    that the ordering of values for a single header field name
    appearing in different header fields, it has to concatenate them
    using NULL byte (0x0) before passing them to this function.
    
    This function creates copies of all name/value pairs in *nva*.  It
    also lower-cases all names in *nva*.
    
    Since the library reorders the frames and tries to send the highest
    prioritized one first and the HTTP/2.0 specification requires the
    stream ID must be strictly increasing, the promised stream ID
    cannot be known until it is about to sent.  To know the promised
    stream ID, the application can use
    :member:`nghttp2_session_callbacks.before_frame_send_callback`. This
    callback is called just before the frame is sent. For PUSH_PROMISE
    frame, the argument frame has the promised stream ID assigned.
    
    The client side can use this function to send PUSH_PROMISE to the
    server. But in normal HTTP usage, the server may treat it error.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_ping(nghttp2_session *session, uint8_t flags, uint8_t *opaque_data)

    
    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 currently ignored and should be
    :macro:`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:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_goaway(nghttp2_session *session, uint8_t flags, nghttp2_error_code error_code, uint8_t *opaque_data, size_t opaque_data_len)

    
    Submits GOAWAY frame with the error code *error_code*.
    
    The *flags* is currently ignored and should be
    :macro:`NGHTTP2_FLAG_NONE`.
    
    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``.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_submit_window_update(nghttp2_session *session, uint8_t flags, int32_t stream_id, int32_t window_size_increment)

    
    Submits WINDOW_UPDATE frame.
    
    The *flags* is currently ignored and should be
    :macro:`NGHTTP2_FLAG_NONE`.
    
    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 *window_size_increment* is negative, the local window size
    is decreased by -*window_size_increment*.  If
    :macro:`NGHTTP2_OPT_NO_AUTO_STREAM_WINDOW_UPDATE` (or
    :macro:`NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE` if *stream_id*
    is 0) is not set and the library decided that the WINDOW_UPDATE
    should be submitted, then WINDOW_UPDATE is queued with the current
    received bytes count.
    
    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:
    
    :macro:`NGHTTP2_ERR_FLOW_CONTROL`
        The local window size overflow or gets negative.
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: int nghttp2_nv_compare_name(const nghttp2_nv *lhs, const nghttp2_nv *rhs)

    
    Compares lhs->name with lhs->namelen bytes and rhs->name with
    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.

.. function:: int nghttp2_select_next_protocol(unsigned char **out, unsigned char *outlen, const unsigned char *in, unsigned int inlen)

    
    A helper function for dealing with NPN in client side or 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, ``HTTP-draft-04/2.0`` and
    ``http/1.1`` stored in *in* like this::
    
        in[0] = 17
        in[1..17] = "HTTP-draft-04/2.0"
        in[18] = 8
        in[19..26] = "http/1.1"
        inlen = 27
    
    The selection algorithm is as follows:
    
    1. If peer's list contains HTTP/2.0 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 ``HTTP-draft-04/2.0`` means that ``HTTP-draft-04/2.0`` is
    written into *\*out* and its length (which is 17) is
    assigned to *\*outlen*.
    
    See http://technotes.googlecode.com/git/nextprotoneg.html for more
    details about NPN.
    
    For NPN, to use this method you should do something like::
    
        static int select_next_proto_cb(SSL* ssl,
                                        unsigned char **out,
                                        unsigned char *outlen,
                                        const unsigned char *in,
                                        unsigned int inlen,
                                        void *arg)
        {
            int rv;
            rv = nghttp2_select_next_protocol(out, outlen, in, inlen);
            if(rv == 1) {
                ((MyType*)arg)->http2_selected = 1;
            }
            return SSL_TLSEXT_ERR_OK;
        }
        ...
        SSL_CTX_set_next_proto_select_cb(ssl_ctx, select_next_proto_cb, my_obj);
    

.. function:: int nghttp2_gzip_inflate_new(nghttp2_gzip **inflater_ptr)

    
    A helper function to set up a per request gzip stream to inflate data.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_GZIP`
        The initialization of gzip stream failed.
    :macro:`NGHTTP2_ERR_NOMEM`
        Out of memory.

.. function:: void nghttp2_gzip_inflate_del(nghttp2_gzip *inflater)

    
    Frees the inflate stream.  The *inflater* may be ``NULL``.

.. function:: int nghttp2_gzip_inflate(nghttp2_gzip *inflater, uint8_t *out, size_t *outlen_ptr, const uint8_t *in, size_t *inlen_ptr)

    
    Inflates data in *in* with the length *\*inlen_ptr* and stores the
    inflated data to *out* which has allocated size at least
    *\*outlen_ptr*. On return, *\*outlen_ptr* is updated to represent
    the number of data written in *out*.  Similarly, *\*inlen_ptr* is
    updated to represent the number of input bytes processed.
    
    This function returns 0 if it succeeds, or one of the following
    negative error codes:
    
    :macro:`NGHTTP2_ERR_GZIP`
        The inflation of gzip stream failed.
    
    The example follows::
    
        void 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)
        {
            ...
            req = nghttp2_session_get_stream_user_data(session, stream_id);
            nghttp2_gzip *inflater = req->inflater;
            while(len > 0) {
                uint8_t out[MAX_OUTLEN];
                size_t outlen = MAX_OUTLEN;
                size_t tlen = len;
                int rv;
                rv = nghttp2_gzip_inflate(inflater, out, &outlen, data, &tlen);
                if(rv != 0) {
                    nghttp2_submit_rst_stream(session, stream_id,
                                              NGHTTP2_INTERNAL_ERROR);
                    break;
                }
                ... Do stuff ...
                data += tlen;
                len -= tlen;
            }
            ....
        }

.. function:: nghttp2_info *nghttp2_version(int least_version)

    
    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.

.. function:: int nghttp2_is_fatal(int lib_error)

    
    Returns nonzero if the :type:`nghttp2_error` library error code
    *lib_error* is fatal.

.. function:: int nghttp2_check_header_name(const uint8_t *name, size_t len)

    
    Returns nonzero if HTTP header field name *name* of length *len* is
    valid according to
    http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-25#section-3.2
    
    Because this is a header field name in HTTP2, the upper cased alphabet
    is treated as error.

.. function:: int nghttp2_check_header_value(const uint8_t *value, size_t len)

    
    Returns nonzero if HTTP header field value *value* of length *len*
    is valid according to
    http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-25#section-3.2
    
    Because this is HTTP2 header field value, it can contain NULL
    character (0x00).