Receives frames from the remote peer.

This function receives as many frames as possible until the user
callback :type:`nghttp2_recv_callback` returns
:enum:`nghttp2_error.NGHTTP2_ERR_WOULDBLOCK`.  This function calls
several callback functions which are passed when initializing the
*session*.  Here is the simple time chart which tells when each
callback is invoked:

1. :type:`nghttp2_recv_callback` is invoked one or more times to
   receive frame header.

2. When frame header is received,
   :type:`nghttp2_on_begin_frame_callback` is invoked.

3. If the frame is DATA frame:

   1. :type:`nghttp2_recv_callback` is invoked to receive DATA
      payload. For each chunk of data,
      :type:`nghttp2_on_data_chunk_recv_callback` is invoked.

   2. If one DATA frame is completely received,
      :type:`nghttp2_on_frame_recv_callback` is invoked.  If the
      reception of the frame triggers the closure of the stream,
      :type:`nghttp2_on_stream_close_callback` is invoked.

4. If the frame is the control frame:

   1. :type:`nghttp2_recv_callback` is invoked one or more times to
      receive whole frame.

   2. If the received frame is valid, then following actions are
      taken.  If the frame is either HEADERS or PUSH_PROMISE,
      :type:`nghttp2_on_begin_headers_callback` is invoked.  Then
      :type:`nghttp2_on_header_callback` is invoked for each header
      name/value pair.  For invalid header field,
      :type:`nghttp2_on_invalid_header_callback` is called.  After
      all name/value pairs are emitted successfully,
      :type:`nghttp2_on_frame_recv_callback` is invoked.  For other
      frames, :type:`nghttp2_on_frame_recv_callback` is invoked.
      If the reception of the frame triggers the closure of the
      stream, :type:`nghttp2_on_stream_close_callback` is invoked.

   3. If the received frame is unpacked but is interpreted as
      invalid, :type:`nghttp2_on_invalid_frame_recv_callback` is
      invoked.

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

:enum:`nghttp2_error.NGHTTP2_ERR_EOF`
    The remote peer did shutdown on the connection.
:enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
    Out of memory.
:enum:`nghttp2_error.NGHTTP2_ERR_CALLBACK_FAILURE`
    The callback function failed.
:enum:`nghttp2_error.NGHTTP2_ERR_BAD_CLIENT_MAGIC`
    Invalid client magic was detected.  This error only returns
    when *session* was configured as server and
    `nghttp2_option_set_no_recv_client_magic()` is not used with
    nonzero value.
:enum:`nghttp2_error.NGHTTP2_ERR_FLOODED`
    Flooding was detected in this HTTP/2 session, and it must be
    closed.  This is most likely caused by misbehaviour of peer.