The main point is to clearly recomend using req.grace for the most
common use case - using different grace time when the backend is
healthy.

Right now there are use cases that cannot be solved without req.ttl,
so we undeprecate it.

The req.grace variable can be set in vcl_recv to cap the grace
of objects in the cache, in the same way as in 3.0.x

The "keep" behavior changes with this patch. We now always go
to vcl_miss when the expired object is out of grace, or we go
to the waiting list. The result is that it is no longer
possible to deliver a "keep" object in vcl_hit.

Note that when we get to vcl_miss, we will still have the 304
candidate, but without the detour by vcl_hit.

This commit changes VCL, but only slightly, so we aim to back
port this to earlier versions of Varnish Cache.

Refs: #1799 and #2519

address family is neither of AF_INET or AF_INET6.

This means that UNKNOWN is sent in probes to UDS backends when
.proxy_header=1 is set.

Also verify that a UDS backend receives PROXY LOCAL in a probe when
.proxy_header=2 is set.

Fixes #2702
Closes #2726

Since we verify that header blocks are not interleaved, and we zero the
struct h2h_decode on every new header block, there is no need to malloc
a separate struct h2h_decode per stream.

... not in the caller

Future-proofing to avoid mistakenly introducing another race down the
line.

The current flow control code's use of h2->cond is racy.

h2->cond is already used for handing over a DATA frame to a stream
thread. In the event that we have both streams waiting on this condvar
for window updates and at the same time the rxthread gets signaled for a
DATA frame, we could end up waking up the wrong thread and the rxthread
gets stuck forever.

This commit addresses this by using a separate condvar for window
updates.

An alternative would be to always issue a broadcast on h2->cond instead
of signal, but I found this approach much cleaner.

Probably fixes: #2623

For ban statistics, we updated VSC_C_main directly, so if we raced
Pool_Sumstat(), that could undo our changes.

This patch fixes statistics by using the per-worker statistics
cache except for the following remaining corner cases:

* bans_persisted_* counters receive absolut updates, which does
  not seem to fit the incremental updates via the per-worker stats.

  I've kept these cases untouched and marked with comments. Worst
  that should happen here are temporary inconsistencies until the
  next absolute update.

* For BAN_Reload(), my understanding is that it should only
  happen during init, so we continue to update VSC_C_main
  directly.

* For bans via the cli, we would need to grab the wstat lock,
  which, at the moment, is private to the worker implementation.

  Until we make a change here, we could miss a ban increment
  from the cli.

* for VCL bans from vcl_init / fini, we do not have access
  to the worker struct at the moment, so for now we also
  accept an inconsistency here.

Fixes #2716 for relevant cases

A bound socket will timeout instead of refusing the connection.
Should fix b00015.vtc under macos.

The previous commit made the assumption that END_STREAM is in the last
of the frames in a header block. This is not necessarily the case.

Previously we've been incorrectly transtitioning to CLOS_REM on
END_HEADERS, which prevents us from seeing if a client incorrectly
transmitted a DATA frame on a closed stream.

This slightly complicates things in that we can now be in state OPEN
with an inactive hpack decoding state, and we need to make sure on
cleanup if that has already been finalized.

This would be simpler if the h/2 spec had split the OPEN state in two
parts, with an extra state transition on END_HEADERS.

Again big thanks to @xcir for his help in diagnosing this.

Fixes: #2623

Should help with the ASAN builds in travis.

Should address #2666 and #2711.

Tune down h2_rx_window_low_water to make sure we don't get a
window_update racing against the response frames.

Fixes: #2709

If we failed to schedule a thread for a stream and it's not cleaned up
prior to handling a request body, the rxthread would sit around waiting
in h2_rx_data indefinitely.

the backend might be going away, and since we cannot afford to hold
the lock over VTP_Open(), we have to pull the VBE_vsc knowledge
one level back up.

Overlooked by:	slink, phk
Spotted by:	Coverity

Conflicts:
	bin/varnishd/cache/cache_backend.c
	bin/varnishd/cache/cache_backend.h

termination of the rxbuf.

Found by:	fgs

This adds -j support to the command

varnishadm ping -j

Tested on RFC4627/RFC7159/ECMA404 standards (all valid JSON)

Conflicts:
	bin/varnishtest/tests/b00008.vtc

Found by:	fgs & ASAN

Previous fix for #2285 (and the duplicate #2624) was missdiagnosed. The
problem stems from a wrong assumption that the number of bytes already
pipelined will be less than maxbytes, with maxbytes beeing the maximum
number of bytes the HTC_RxStuff may need to get a full work unit. That
assumption may fail during the H/1 to H/2 upgrade path where maxbytes
change with the context, or during runtime changing of parameters.

This patch makes HTC_RxStuff not assert if the pipelined data turned out
to exceed maxbytes, but return overflow if we run out of workspace.

(#2624 has received a workaround in the H/2 code that perhaps should be
reverted).

Remove old and now invalid assert.

Change order of evaluation in if-statement to make sure we don't step
outside rxbuf_e.

Previously, tracing the root cause of probe failures was unnecessarily
complicated by the fact that the probe window bits and timing
information were the only source of information when no HTTP status
line was logged and for the case of all the bits being zero, almost
impossible (e.g. differentiating between a local and remote connection
open failure).

We now re-use the response field for failing probes also.

Conflicts:
	bin/varnishd/cache/cache_backend.c

This is similar to the vca pace: Depending on the backend connection
error, it does not make sense to re-try in rapid succession, instead
not attempting the failed connection again for some time will save
resources both locally and remotely, where applicable, and should
thus help improve the overall situation.

Fixes #2622

Previously, we had zero stats on the cause of backend connection
errors, which made it close to impossible to diagnose such issues in
retrospect (only via log mining).

We now pass an optional backend vsc to vcp and record errors per
backend.

Open errors are really per vcp entry (ip + port or udc path), which
can be shared amongst backends (and even vcls), but we maintain the
counters per backend (and, consequently, per vcl) for simplicity.  It
should be noted though that errors for shared endpoints affect all
backends using them.

Ref #2622

Conflicts:
	bin/varnishd/cache/cache_backend.c

... and introduce request functions for this purpose (for busy
objects, there is only one use case yet, so we don't).

Before we reset the workspace, we must ensure that there are no active
references to objects on it. As PRIV_TASK and PRIV_TOP have the same
lifetime as the respective workspace, they need to be destroyed. vmods
must not use workspaces for storing information referenced via any of
the other PRIVs unless the rollback case is considered.

Note that while this bug was exposed by
beeaa19c, it existed all along for any
vmod priv state stored on the workspace, so if a vmod happened to
access a TASK_PRIV stored on the workspace, it would likely have
triggered a magic check assertion as well.

I got plans for making std.rollback() more useful. While this change
is required to do so, it only partly covers the planned changes.

Fixes #2706