tree 97a09ccd58f0729664a200566e4e7a258979a96c
parent d057960769f284e2e4ee9b38d3c99f28f656c71d
author Christopher Faulet <cfaulet@haproxy.com> 1649316313 +0200
committer Christopher Faulet <cfaulet@haproxy.com> 1649322247 +0200

BUG/MEDIUM: stats: Be sure to never set EOM flag on an empty HTX message

During the last call to the stats I/O handle, it is possible to have nothing
to dump. It may happen for many reasons. For instance, all remaining proxies
are disabled or they don't match the specified scope. In HTML or in JSON, it
is not really an issue because there is a footer. So there are still some
data to push in the response channel buffer. In CSV, it is a problem because
there is no footer. It means it is possible to finish the response with no
payload at all in the HTX message. Thus, the EOM flag may be added on an
empty message. When this happens, a shutdown is performed on an empty HTX
message. Because there is nothing to send, the mux on the client side is not
notified that the message was properly finished and interprets the shutdown
as an abort.

The response is chunked. So an abort at this stage means the last CRLF is
never sent to the client. All data were sent but the message is invalid
because the response chunking is not finished. If the reponse is compressed,
because of a similar bug in the comppression filter, the compression is also
aborted and the content is truncated because some data a lost in the
compression filter.

It is design issue with the HTX. It must be addressed. And there is an
opportunity to do so with the recent conn-stream refactoring. It must be
carefully evaluated first. But it is possible. In the means time and to also
fix stable versions, to workaround the bug, a end-of-trailer HTX block is
systematically added at the end of the message when the EOM flag is set if
the HTX message is empty. This way, there are always some data to send when
the EOM flag is set.

Note that with a H2 client, it is only a problem when the response is
compressed.

This patch should fix the issue #1478. It must be backported as far as
2.4. On previous versions there is still the EOM block.