# nghttp2_submit_trailer

## Synopsis

#include <nghttp2/nghttp2.h>

int nghttp2_submit_trailer(nghttp2_session *session, int32_t stream_id, const nghttp2_nv *nva, size_t nvlen)

  Submits trailer fields HEADERS against the stream stream_id.

  The nva is an array of name/value pair `nghttp2_nv` with nvlen elements. The application must not include pseudo-header fields (headers whose names starts with ":") in nva.

  This function creates copies of all name/value pairs in nva. It also lower-cases all names in nva. The order of elements in nva is preserved. For header fields with `nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME` and `nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_VALUE` are set, header field name and value are not copied respectively. With `nghttp2_nv_flag.NGHTTP2_NV_FLAG_NO_COPY_NAME`, application is responsible to pass header field name in lowercase. The application should maintain the references to them until `nghttp2_on_frame_send_callback` or `nghttp2_on_frame_not_send_callback` is called.

  For server, trailer fields must follow response HEADERS or response DATA without END_STREAM flat set. The library does not enforce this requirement, and applications should do this for themselves. If `nghttp2_submit_trailer()` is called before any response HEADERS submission (usually by `nghttp2_submit_response()`), the content of nva will be sent as response headers, which will result in error.

  This function has the same effect with `nghttp2_submit_headers()`, with flags = `nghttp2_flag.NGHTTP2_FLAG_END_STREAM` and both pri_spec and stream_user_data to NULL.

  To submit trailer fields after `nghttp2_submit_response()` is called, the application has to specify `nghttp2_data_provider` to `nghttp2_submit_response()`. Inside of `nghttp2_data_source_read_callback`, when setting `nghttp2_data_flag.NGHTTP2_DATA_FLAG_EOF`, also set `nghttp2_data_flag.NGHTTP2_DATA_FLAG_NO_END_STREAM`. After that, the application can send trailer fields using `nghttp2_submit_trailer()`. `nghttp2_submit_trailer()` can be used inside `nghttp2_data_source_read_callback`.

  This function returns 0 if it succeeds and stream_id is -1. Otherwise, this function returns 0 if it succeeds, or one of the following negative error codes:

  `nghttp2_error.NGHTTP2_ERR_NOMEM`

    Out of memory.

  `nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`

    The stream_id is 0.