BUG/MAJOR: tcp: fix a possible busy spinning loop in content track-sc*

As a consequence of various recent changes on the sample conversion,
a corner case has emerged where it is possible to wait forever for a
sample in track-sc*.

The issue is caused by the fact that functions relying on sample_process()
don't all exactly work the same regarding the SMP_F_MAY_CHANGE flag and
the output result. Here it was possible to wait forever for an output
sample from stktable_fetch_key() without checking the SMP_OPT_FINAL flag.
As a result, if the client connects and closes without sending the data
and haproxy expects a sample which is capable of coming, it will ignore
this impossible case and will continue to wait.

This change adds control for SMP_OPT_FINAL before waiting for extra data.
The various relevant functions have been better documented regarding their
output values.

This fix must be backported to 1.5 since it appeared there.
(cherry picked from commit 6bcb0a84e7256f00793fa8ec8a0d6c19c3b22935)
3 files changed