.. warning::

  This function is deprecated in favor of
  `nghttp2_session_upgrade2()`, because this function lacks the
  parameter to tell the library the request method used in the
  original HTTP request.  This information is required for client
  to validate actual response body length against content-length
  header field (see `nghttp2_option_set_no_http_messaging()`).  If
  HEAD is used in request, the length of response body must be 0
  regardless of value included in content-length header field.

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:

:enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
    Out of memory.
:enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
    The *settings_payload* is badly formed.
:enum:`nghttp2_error.NGHTTP2_ERR_PROTO`
    The stream ID 1 is already used or closed; or is not available.