http2,doc: minor fixes

Some small fixes on HTTP/2 and its documentation:

 - Add a note that, on server streams, it's not necessary
   to start data flow.

 - Set EOF flag if we have marked all data for sending:
   there's no need to wait until the queue is
   actually empty (and send a separate, empty DATA).

   (Note that, even with this change, a separate DATA
   frame will always be sent, because the streams
   layer waits until data has been flushed before
   dispatching EOF)

Backport-PR-URL: #34845
PR-URL: #28044
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/http2.md

@@ -927,8 +927,9 @@ the value is `undefined`, the stream is not yet ready for use.
 All [`Http2Stream`][] instances are destroyed either when:
 
 * An `RST_STREAM` frame for the stream is received by the connected peer,
-  and pending data has been read.
-* The `http2stream.close()` method is called, and pending data has been read.
+  and (for client streams only) pending data has been read.
+* The `http2stream.close()` method is called, and (for client streams only)
+  pending data has been read.
 * The `http2stream.destroy()` or `http2session.destroy()` methods are called.
 
 When an `Http2Stream` instance is destroyed, an attempt will be made to send an

src/node_http2.cc

@@ -2367,7 +2367,7 @@ ssize_t Http2Stream::Provider::Stream::OnRead(nghttp2_session* handle,
     return NGHTTP2_ERR_DEFERRED;
   }
 
-  if (stream->queue_.empty() && !stream->IsWritable()) {
+  if (stream->available_outbound_length_ == 0 && !stream->IsWritable()) {
     Debug(session, "no more data for stream %d", id);
     *flags |= NGHTTP2_DATA_FLAG_EOF;
     if (stream->HasTrailers()) {