nghttp2_submit_extension
========================
Synopsis
--------
*#include <nghttp2/nghttp2.h>*
.. function:: int nghttp2_submit_extension(nghttp2_session *session, uint8_t type, uint8_t flags, int32_t stream_id, void *payload)
Submits extension frame.
Application can pass arbitrary frame flags and stream ID in *flags*
and *stream_id* respectively. The *payload* is opaque pointer, and
it can be accessible though ``frame->ext.payload`` in
:type:`nghttp2_pack_extension_callback`. The library will not own
passed *payload* pointer.
The application must set :type:`nghttp2_pack_extension_callback`
using `nghttp2_session_callbacks_set_pack_extension_callback()`.
The application should retain the memory pointed by *payload* until
the transmission of extension frame is done (which is indicated by
:type:`nghttp2_on_frame_send_callback`), or transmission fails
(which is indicated by :type:`nghttp2_on_frame_not_send_callback`).
If application does not touch this memory region after packing it
into a wire format, application can free it inside
:type:`nghttp2_pack_extension_callback`.
The standard HTTP/2 frame cannot be sent with this function, so
*type* must be strictly grater than 0x9. Otherwise, this function
will fail with error code :macro:`NGHTTP2_ERR_INVALID_ARGUMENT`.
This function returns 0 if it succeeds, or one of the following
negative error codes:
:macro:`NGHTTP2_ERR_INVALID_STATE`
If :type:`nghttp2_pack_extension_callback` is not set.
:macro:`NGHTTP2_ERR_INVALID_ARGUMENT`
If *type* specifies standard HTTP/2 frame type. The frame
types in the rage [0x0, 0x9], both inclusive, are standard
HTTP/2 frame type, and cannot be sent using this function.
:macro:`NGHTTP2_ERR_NOMEM`
Out of memory