When a filter is attached to a stream, the wrong FLT_END analyzer is added
on the request channel. AN_REQ_FLT_END must be added instead of
AN_RES_FLT_END. Because of this bug, the stream may hang on the filter
release stage.
It seems to be ok for HTTP filters (cache & compression) in HTTP mode. But
when enabled on a TCP proxy, the stream is blocked until the client or the
server timeout expire because data forwarding is blocked. The stream is then
prematurely aborted.
This bug was introduced by commit 26eb5ea35 ("BUG/MINOR: filters: Always set
FLT_END analyser when CF_FLT_ANALYZE flag is set"). The patch must be
backported in all stable versions.
It is only a problem on the response path because the request payload length
it always known. But when a filter is registered to analyze the response
payload, the filtering may hang if the server closes just after the headers.
The root cause of the bug comes from an attempt to allow the filters to not
immediately forward the headers if necessary. A filter may choose to hold
the headers by not forwarding any bytes of the payload. For a message with
no payload but a known payload length, there is always a EOM block to
forward. Thus holding the EOM block for bodyless messages is a good way to
also hold the headers. However, messages with an unknown payload length,
there is no EOM block finishing the message, but only a SHUTR flag on the
channel to mark the end of the stream. If there is no payload when it
happens, there is no payload at all to forward. In the filters API, it is
wrongly detected as a condition to not forward the headers.
Because it is not the most used feature and not the obvious one, this patch
introduces another way to hold the message headers at the begining of the
forwarding. A filter flag is added to explicitly says the headers should be
hold. A filter may choose to set the STRM_FLT_FL_HOLD_HTTP_HDRS flag and not
forwad anything to hold the headers. This flag is removed at each call, thus
it must always be explicitly set by filters. This flag is only evaluated if
no byte has ever been forwarded because the headers are forwarded with the
first byte of the payload.
reg-tests/filters/random-forwarding.vtc reg-test is updated to also test
responses with unknown payload length (with and without payload).
This patch must be backported as far as 2.0.
Three filters are used. The compression filter is enclose by two trace filters,
both with the random forwarding enabled. An HTTP test is performed but also a
TCP test using an HTTP tunnel.
Christopher Faulet
Tim Duesterhus