Submits one or more DATA frames to the stream *stream_id*.  The
data to be sent are provided by *data_prd*.  If *flags* contains
:enum:`nghttp2_flag.NGHTTP2_FLAG_END_STREAM`, the last DATA frame
has END_STREAM flag set.

This function does not take ownership of the *data_prd*.  The
function copies the members of the *data_prd*.

This function returns 0 if it succeeds, or one of the following
negative error codes:

:enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
    Out of memory.
:enum:`nghttp2_error.NGHTTP2_ERR_DATA_EXIST`
    DATA or HEADERS has been already submitted and not fully
    processed yet.
:enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
    The *stream_id* is 0.
:enum:`nghttp2_error.NGHTTP2_ERR_STREAM_CLOSED`
    The stream was already closed; or the *stream_id* is invalid.

.. note::

  Currently, only one DATA or HEADERS is allowed for a stream at a
  time.  Submitting these frames more than once before first DATA
  or HEADERS is finished results in
  :enum:`nghttp2_error.NGHTTP2_ERR_DATA_EXIST` error code.  The
  earliest callback which tells that previous frame is done is
  :type:`nghttp2_on_frame_send_callback`.  In side that callback,
  new data can be submitted using `nghttp2_submit_data2()`.  Of
  course, all data except for last one must not have
  :enum:`nghttp2_flag.NGHTTP2_FLAG_END_STREAM` flag set in *flags*.
  This sounds a bit complicated, and we recommend to use
  `nghttp2_submit_request2()` and `nghttp2_submit_response2()` to
  avoid this cascading issue.  The experience shows that for HTTP
  use, these two functions are enough to implement both client and
  server.