# Types (structs, unions and typedefs)

type nghttp2_session

  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.

type nghttp2_info

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

  int age

    Age of this struct. This instance of nghttp2 sets it to `NGHTTP2_VERSION_AGE` but a future version may bump it and add more struct fields at the bottom

  int version_num

    the `NGHTTP2_VERSION_NUM` number (since age ==1)

  const char *version_str

    points to the `NGHTTP2_VERSION` string (since age ==1)

  const char *proto_str

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

type nghttp2_vec

  The object representing single contiguous buffer.

  uint8_t *base

    The pointer to the buffer.

  size_t len

    The length of the buffer.

type nghttp2_rcbuf

  The object representing reference counted buffer. The details of this structure are intentionally hidden from the public API.

type nghttp2_nv

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

  uint8_t *name

    The name byte string. If this struct is presented from library (e.g., `nghttp2_on_frame_recv_callback`), name is guaranteed to be NULL-terminated. For some callbacks (`nghttp2_before_frame_send_callback`, `nghttp2_on_frame_send_callback`, and `nghttp2_on_frame_not_send_callback`), it may not be NULL-terminated if header field is passed from application with the flag `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 *value

    The value byte string. If this struct is presented from library (e.g., `nghttp2_on_frame_recv_callback`), value is guaranteed to be NULL-terminated. For some callbacks (`nghttp2_before_frame_send_callback`, `nghttp2_on_frame_send_callback`, and `nghttp2_on_frame_not_send_callback`), it may not be NULL-terminated if header field is passed from application with the flag `nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_VALUE`). When application is constructing this struct, value is not required to be NULL-terminated.

  size_t namelen

    The length of the name, excluding terminating NULL.

  size_t valuelen

    The length of the value, excluding terminating NULL.

  uint8_t flags

    Bitwise OR of one or more of `nghttp2_nv_flag`.

type nghttp2_frame_hd

  The frame header.

  size_t length

    The length field of this frame, excluding frame header.

  int32_t stream_id

    The stream identifier (aka, stream ID)

  uint8_t type

    The type of this frame. See `nghttp2_frame_type()`.

  uint8_t flags

    The flags.

  uint8_t reserved

    Reserved bit in frame header. Currently, this is always set to 0 and application should not expect something useful in here.

type nghttp2_data_source

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

  int fd

    The integer field, suitable for a file descriptor.

  void *ptr

    The pointer to an arbitrary object.

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)

  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 `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 `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 `nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_COPY`, will invoke `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 `nghttp2_flag.NGHTTP2_FLAG_END_STREAM` set, and `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 `nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_END_STREAM` along with `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 `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 `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 `nghttp2_error.NGHTTP2_ERR_PAUSE`.

  In case of error, there are 2 choices. Returning `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` will close the stream by issuing RST_STREAM with `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 `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`. Returning `nghttp2_error.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.

  nghttp2_data_source source

    The data source.

  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 `nghttp2_on_data_chunk_recv_callback`.

  size_t padlen

    The length of the padding in this frame. This includes PAD_HIGH and PAD_LOW.

type nghttp2_priority_spec

  The structure to specify stream dependency.

  int32_t stream_id

    The stream ID of the stream to depend on. Specifying 0 makes stream not depend any other stream.

  int32_t weight

    The weight of this dependency.

  uint8_t exclusive

    nonzero means exclusive dependency

type nghttp2_headers

  The HEADERS frame. It has the following members:

  nghttp2_frame_hd hd

    The frame header.

  size_t padlen

    The length of the padding in this frame. This includes PAD_HIGH and PAD_LOW.

  nghttp2_priority_spec pri_spec

    The priority specification

  nghttp2_nv *nva

    The name/value pairs.

  size_t nvlen

    The number of name/value pairs in nva.

  nghttp2_headers_category cat

    The category of this HEADERS frame.

type nghttp2_priority

  The PRIORITY frame. It has the following members:

  nghttp2_frame_hd hd

    The frame header.

  nghttp2_priority_spec pri_spec

    The priority specification.

type nghttp2_rst_stream

  The RST_STREAM frame. It has the following members:

  nghttp2_frame_hd hd

    The frame header.

  uint32_t error_code

    The error code. See `nghttp2_error_code`.

type nghttp2_settings_entry

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

  int32_t settings_id

    The SETTINGS ID. See `nghttp2_settings_id`.

  uint32_t value

    The value of this entry.

type nghttp2_settings

  The SETTINGS frame. It has the following members:

  nghttp2_frame_hd hd

    The frame header.

  size_t niv

    The number of SETTINGS ID/Value pairs in iv.

  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:

  nghttp2_frame_hd hd

    The frame header.

  size_t padlen

    The length of the padding in this frame. This includes PAD_HIGH and PAD_LOW.

  nghttp2_nv *nva

    The name/value pairs.

  size_t nvlen

    The number of name/value pairs in nva.

  int32_t promised_stream_id

    The promised stream ID

  uint8_t reserved

    Reserved bit. Currently this is always set to 0 and application should not expect something useful in here.

type nghttp2_ping

  The PING frame. It has the following members:

  nghttp2_frame_hd hd

    The frame header.

  uint8_t opaque_data[8]

    The opaque data

type nghttp2_goaway

  The GOAWAY frame. It has the following members:

  nghttp2_frame_hd hd

    The frame header.

  int32_t last_stream_id

    The last stream stream ID.

  uint32_t error_code

    The error code. See `nghttp2_error_code`.

  uint8_t *opaque_data

    The additional debug data

  size_t opaque_data_len

    The length of opaque_data member.

  uint8_t reserved

    Reserved bit. Currently this is always set to 0 and application should not expect something useful in here.

type nghttp2_window_update

  The WINDOW_UPDATE frame. It has the following members:

  nghttp2_frame_hd hd

    The frame header.

  int32_t window_size_increment

    The window size increment.

  uint8_t reserved

    Reserved bit. Currently this is always set to 0 and application should not expect something useful in here.

type nghttp2_extension

  The extension frame. It has following members:

  nghttp2_frame_hd hd

    The frame header.

  void *payload

    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.

type nghttp2_frame

  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.

  nghttp2_frame_hd hd

    The frame header, which is convenient to inspect frame header.

  nghttp2_data data

    The DATA frame.

  nghttp2_headers headers

    The HEADERS frame.

  nghttp2_priority priority

    The PRIORITY frame.

  nghttp2_rst_stream rst_stream

    The RST_STREAM frame.

  nghttp2_settings settings

    The SETTINGS frame.

  nghttp2_push_promise push_promise

    The PUSH_PROMISE frame.

  nghttp2_ping ping

    The PING frame.

  nghttp2_goaway goaway

    The GOAWAY frame.

  nghttp2_window_update window_update

    The WINDOW_UPDATE frame.

  nghttp2_extension ext

    The extension frame.

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 `nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`. For other errors, it must return `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 `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 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)

  Callback function invoked when `nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_COPY` is used in `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 `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 `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 `nghttp2_error.NGHTTP2_ERR_PAUSE`. If application decided to reset this stream, return `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`, which will result in connection closure. Returning any other value is treated as `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned.

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 `nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`. If it gets EOF before it reads any single byte, it must return `nghttp2_error.NGHTTP2_ERR_EOF`. For other errors, it must return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. Returning 0 is treated as `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 `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_recv_callback()`.

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

  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 `nghttp2_on_header_callback`.

  For HEADERS, PUSH_PROMISE and DATA frames, this callback may be called after stream is closed (see `nghttp2_on_stream_close_callback`). The application should check that stream is still alive using its own stream management or `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.

  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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_on_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)

  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 `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_on_invalid_frame_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)

  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 `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 `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_on_data_chunk_recv_callback()`.

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

  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 `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`, which makes `nghttp2_session_send()` and `nghttp2_session_mem_send()` functions immediately return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  If the other value is returned, it is treated as if `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 `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_before_frame_send_callback()`.

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_send()` and `nghttp2_session_mem_send()` functions immediately return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_on_frame_send_callback()`.

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 `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  `nghttp2_session_get_stream_user_data()` can be used to get associated data.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_on_frame_not_send_callback()`.

typedef int (*nghttp2_on_stream_close_callback)(nghttp2_session *session, int32_t stream_id, uint32_t 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 error_code is usually one of `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_on_stream_close_callback()`.

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 `nghttp2_on_header_callback`.

  The `frame->hd.flags` may not have `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 `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` will close the stream (promised stream if frame is PUSH_PROMISE) by issuing RST_STREAM with `nghttp2_error_code.NGHTTP2_INTERNAL_ERROR`. In this case, `nghttp2_on_header_callback` and `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 `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 `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` to reset the stream (promised stream if frame is PUSH_PROMISE). For critical errors, it must return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. If the other value is returned, it is treated as if `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned. If `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned, `nghttp2_session_mem_recv()` function will immediately return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_on_begin_headers_callback()`.

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)

  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 `nghttp2_nv_flag`.

  If `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 `nghttp2_frame_type.NGHTTP2_HEADERS` or `nghttp2_frame_type.NGHTTP2_PUSH_PROMISE`. After all header name/value pairs are processed with this callback, and no error has been detected, `nghttp2_on_frame_recv_callback` will be invoked. If there is an error in decompression, `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 HTTP Messaging section.

  If the application uses `nghttp2_session_mem_recv()`, it can return `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 `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE` will close the stream (promised stream if frame is PUSH_PROMISE) by issuing RST_STREAM with `nghttp2_error_code.NGHTTP2_INTERNAL_ERROR`. In this case, `nghttp2_on_header_callback` and `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 `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 `nghttp2_error.NGHTTP2_ERR_PAUSE` or `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`. For other critical failures, it must return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. If the other nonzero value is returned, it is treated as `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. If `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` is returned, `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions immediately return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `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_callback2)(nghttp2_session *session, const nghttp2_frame *frame, nghttp2_rcbuf *name, nghttp2_rcbuf *value, uint8_t flags, void *user_data)

  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 `nghttp2_nv_flag`.

  This callback behaves like `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_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)

  Callback function invoked when a invalid header name/value pair is received for the frame.

  The parameter and behaviour are similar to `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 `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`. By default, the error code is `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 `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_callback2)(nghttp2_session *session, const nghttp2_frame *frame, nghttp2_rcbuf *name, nghttp2_rcbuf *value, uint8_t flags, void *user_data)

  Callback function invoked when a invalid header name/value pair is received for the frame.

  The parameter and behaviour are similar to `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 `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`. By default, the error code is `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 `nghttp2_error.NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE`.

typedef ssize_t (*nghttp2_select_padding_callback)(nghttp2_session *session, const nghttp2_frame *frame, size_t max_payloadlen, void *user_data)

  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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. Returning `frame->hd.length` means no padding is added. Returning `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` will make `nghttp2_session_send()` and `nghttp2_session_mem_send()` functions immediately return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_select_padding_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)

  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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. The frame_type is provided for future extensibility and identifies the type of frame (see `nghttp2_frame_type`) for which to get the length for. Currently supported frame types are: `nghttp2_frame_type.NGHTTP2_DATA`.

  This callback can be used to control the length in bytes for which `nghttp2_data_source_read_callback` is allowed to send to the remote endpoint. This callback is optional. Returning `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE` will signal the entire session failure.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_data_source_read_length_callback()`.

typedef int (*nghttp2_on_begin_frame_callback)(nghttp2_session *session, const nghttp2_frame_hd *hd, void *user_data)

  Callback function invoked when a frame header is received. The hd points to received frame header.

  Unlike `nghttp2_on_frame_recv_callback`, this callback will also be called when frame header of CONTINUATION frame is received.

  If both `nghttp2_on_begin_frame_callback` and `nghttp2_on_begin_headers_callback` are set and HEADERS or PUSH_PROMISE is received, `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

  To set this callback to `nghttp2_session_callbacks`, use `nghttp2_session_callbacks_set_on_begin_frame_callback()`.

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)

  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 `nghttp2_error.NGHTTP2_ERR_CANCEL`.

  If fatal error occurred, application should return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. In this case, `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions immediately return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. If the other values are returned, currently they are treated as `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)

  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 `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 `nghttp2_on_frame_recv_callback`. Therefore if application can free that memory inside `nghttp2_on_frame_recv_callback` callback. Of course, application has a liberty not ot use *payload, and do its own mechanism to process extension frames.

  To abort processing this extension frame, return `nghttp2_error.NGHTTP2_ERR_CANCEL`.

  If fatal error occurred, application should return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. In this case, `nghttp2_session_recv()` and `nghttp2_session_mem_recv()` functions immediately return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. If the other values are returned, currently they are treated as `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)

  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 `nghttp2_error.NGHTTP2_ERR_CANCEL`, and `nghttp2_on_frame_not_send_callback` will be invoked.

  If fatal error occurred, application should return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. In this case, `nghttp2_session_send()` and `nghttp2_session_mem_send()` functions immediately return `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. If the other values are returned, currently they are treated as `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. If the return value is strictly larger than len, it is treated as `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`.

typedef int (*nghttp2_error_callback)(nghttp2_session *session, const char *msg, size_t len, void *user_data)

  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 `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. In this case, library will return immediately with return value `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. Currently, if nonzero value is returned from this callback, they are treated as `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)

  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 `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 `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. In this case, library will return immediately with return value `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`. Currently, if nonzero value is returned from this callback, they are treated as `nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`, but application should not rely on this details.

type nghttp2_session_callbacks

  Callback functions for `nghttp2_session`. The details of this structure are intentionally hidden from the public API.

typedef void *(*nghttp2_malloc)(size_t size, void *mem_user_data)

  Custom memory allocator to replace malloc(). The mem_user_data is the mem_user_data member of `nghttp2_mem` structure.

typedef void (*nghttp2_free)(void *ptr, void *mem_user_data)

  Custom memory allocator to replace free(). The mem_user_data is the mem_user_data member of `nghttp2_mem` structure.

typedef void *(*nghttp2_calloc)(size_t nmemb, size_t size, void *mem_user_data)

  Custom memory allocator to replace calloc(). The mem_user_data is the mem_user_data member of `nghttp2_mem` structure.

typedef void *(*nghttp2_realloc)(void *ptr, size_t size, void *mem_user_data)

  Custom memory allocator to replace realloc(). The mem_user_data is the mem_user_data member of `nghttp2_mem` structure.

type nghttp2_mem

  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);

        ...
      }

  void *mem_user_data

    An arbitrary user supplied data. This is passed to each allocator function.

  nghttp2_malloc malloc

    Custom allocator function to replace malloc().

  nghttp2_free free

    Custom allocator function to replace free().

  nghttp2_calloc calloc

    Custom allocator function to replace calloc().

  nghttp2_realloc realloc

    Custom allocator function to replace realloc().

type nghttp2_option

  Configuration options for `nghttp2_session`. The details of this structure are intentionally hidden from the public API.

type nghttp2_ext_altsvc

  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 `nghttp2_frame_type.NGHTTP2_ALTSVC`, `nghttp2_extension.payload` will point to this struct.

  It has the following members:

  uint8_t *origin

    The pointer to origin which this alternative service is associated with. This is not necessarily NULL-terminated.

  size_t origin_len

    The length of the origin.

  uint8_t *field_value

    The pointer to Alt-Svc field value contained in ALTSVC frame. This is not necessarily NULL-terminated.

  size_t field_value_len

    The length of the field_value.

type nghttp2_origin_entry

  The single entry of an origin.

  uint8_t *origin

    The pointer to origin. No validation is made against this field by the library. This is not necessarily NULL-terminated.

  size_t origin_len

    The length of the origin.

type nghttp2_ext_origin

  The payload of ORIGIN frame. ORIGIN frame is a non-critical extension to HTTP/2 and defined by RFC 8336.

  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 `nghttp2_frame_type.NGHTTP2_ORIGIN`, `nghttp2_extension.payload` will point to this struct.

  It has the following members:

  size_t nov

    The number of origins contained in ov.

  nghttp2_origin_entry *ov

    The pointer to the array of origins contained in ORIGIN frame.

type nghttp2_hd_deflater

  HPACK deflater object.

type nghttp2_hd_inflater

  HPACK inflater object.

type nghttp2_stream

  The structure to represent HTTP/2 stream. The details of this structure are intentionally hidden from the public API.

typedef void (*nghttp2_debug_vprintf_callback)(const char *format, va_list args)

  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.