tree 0663d4518f41bbf400d03379f801cac8580f359a
parent fba74ea7b0bc55dfd8a84ba5ecb78ff363e61bc4
author Willy Tarreau <w@1wt.eu> 1545554944 +0100
committer Willy Tarreau <w@1wt.eu> 1545554944 +0100
encoding latin1

MINOR: mux-h2: only increase the connection window with the first update

Commit dc57236 ("BUG/MINOR: mux-h2: advertise a larger connection window
size") caused a WINDOW_UPDATE message to be sent early with the connection
to increase the connection's window size. It turns out that it causes some
minor trouble that need to be worked around :
  - varnishtest cannot transparently cope with the WU frames during the
    handshake, forcing all tests to explicitly declare the handshake
    sequence ;
  - some vtc scripts randomly fail if the WU frame is sent after another
    expected response frame, adding uncertainty to some tests ;
  - h2spec doesn't correctly identify these WU at the connection level
    that it believes are the responses to some purposely erroneous frames
    it sends, resulting in some errors being reported

None of these are a problem with real clients but they add some confusion
during troubleshooting.

Since the fix above was intended to increase the upload bandwidth, we
have another option which is to increase the window size with the first
WU frame sent for the connection. This way, no WU frame is sent until
one is really needed, and this first frame will adjust the window to
the maximum value. It will make the window increase slightly later, so
the client will experience the first round trip when uploading data,
but this should not be perceptible, and is not worth the extra hassle
needed to maintain our debugging abilities. As an extra bonus, a few
extra bytes are saved for each connection until the first attempt to
upload data.

This should possibly be backported to 1.9 and 1.8.