out_forward: release buf when no connection available and time_as_integer is true(#6082)

[nokute78]

Fixes #6082

This patch is to free memory when time_as_integer is true and no connection is available.

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Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• [N/A] Attached local packaging test output showing all targets (including any new ones) build.

Documentation

• [N/A] Documentation required for this feature

Backporting

• [N/A] Backport to latest stable release.

Configuration

fluent-bit -i dummy -o forward -p time_as_integer=on

Debug/Valgrind output

$ valgrind --leak-check=full bin/fluent-bit -i dummy -o forward -p time_as_integer=on
==43252== Memcheck, a memory error detector
==43252== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==43252== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==43252== Command: bin/fluent-bit -i dummy -o forward -p time_as_integer=on
==43252== 
[error] setting up section 'output' plugin property 'time_as_integer'
Fluent Bit v2.0.0
* Copyright (C) 2015-2022 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2022/10/15 07:58:02] [ info] [fluent bit] version=2.0.0, commit=095d090aeb, pid=43252
[2022/10/15 07:58:02] [ info] [storage] ver=1.2.0, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2022/10/15 07:58:02] [ info] [cmetrics] version=0.5.2
[2022/10/15 07:58:02] [ info] [input:dummy:dummy.0] initializing
[2022/10/15 07:58:02] [ info] [input:dummy:dummy.0] storage_strategy='memory' (memory only)
[2022/10/15 07:58:02] [ info] [output:forward:forward.0] worker #0 started
[2022/10/15 07:58:02] [ info] [output:forward:forward.0] worker #1 started
[2022/10/15 07:58:02] [ info] [sp] stream processor started
==43252== Warning: client switching stacks?  SP change: 0x6ffb8b8 --> 0x549e9b0
==43252==          to suppress, use: --max-stackframe=28692232 or greater
==43252== Warning: client switching stacks?  SP change: 0x549e908 --> 0x6ffb8b8
==43252==          to suppress, use: --max-stackframe=28692400 or greater
==43252== Warning: client switching stacks?  SP change: 0x6ffb8b8 --> 0x549e908
==43252==          to suppress, use: --max-stackframe=28692400 or greater
==43252==          further instances of this message will not be shown.
[2022/10/15 07:58:04] [error] [output:forward:forward.0] no upstream connections available
[2022/10/15 07:58:04] [ warn] [engine] failed to flush chunk '43252-1665788283.181337898.flb', retry in 11 seconds: task_id=0, input=dummy.0 > output=forward.0 (out_id=0)
[2022/10/15 07:58:05] [error] [output:forward:forward.0] no upstream connections available
[2022/10/15 07:58:05] [ warn] [engine] failed to flush chunk '43252-1665788284.197366321.flb', retry in 7 seconds: task_id=1, input=dummy.0 > output=forward.0 (out_id=0)
^C[2022/10/15 07:58:05] [engine] caught signal (SIGINT)
[2022/10/15 07:58:05] [ warn] [engine] service will shutdown in max 5 seconds
[2022/10/15 07:58:05] [error] [output:forward:forward.0] no upstream connections available
[2022/10/15 07:58:05] [ info] [input] pausing dummy.0
[2022/10/15 07:58:05] [error] [output:forward:forward.0] no upstream connections available
[2022/10/15 07:58:05] [error] [output:forward:forward.0] no upstream connections available
[2022/10/15 07:58:05] [ warn] [engine] failed to flush chunk '43252-1665788285.138903169.flb', retry in 1 seconds: task_id=2, input=dummy.0 > output=forward.0 (out_id=0)
[2022/10/15 07:58:05] [ warn] [engine] chunk '43252-1665788283.181337898.flb' cannot be retried: task_id=0, input=dummy.0 > output=forward.0
[2022/10/15 07:58:05] [ warn] [engine] chunk '43252-1665788284.197366321.flb' cannot be retried: task_id=1, input=dummy.0 > output=forward.0
[2022/10/15 07:58:06] [ info] [task] dummy/dummy.0 has 1 pending task(s):
[2022/10/15 07:58:06] [ info] [task]   task_id=2 still running on route(s): forward/forward.0 
[2022/10/15 07:58:06] [error] [output:forward:forward.0] no upstream connections available
[2022/10/15 07:58:06] [ info] [input] pausing dummy.0
[2022/10/15 07:58:06] [ warn] [engine] chunk '43252-1665788285.138903169.flb' cannot be retried: task_id=2, input=dummy.0 > output=forward.0
[2022/10/15 07:58:07] [ info] [engine] service has stopped (0 pending tasks)
[2022/10/15 07:58:07] [ info] [input] pausing dummy.0
[2022/10/15 07:58:07] [ info] [output:forward:forward.0] thread worker #0 stopping...
[2022/10/15 07:58:07] [ info] [output:forward:forward.0] thread worker #0 stopped
[2022/10/15 07:58:07] [ info] [output:forward:forward.0] thread worker #1 stopping...
[2022/10/15 07:58:07] [ info] [output:forward:forward.0] thread worker #1 stopped
==43252== 
==43252== HEAP SUMMARY:
==43252==     in use at exit: 0 bytes in 0 blocks
==43252==   total heap usage: 1,713 allocs, 1,713 frees, 1,988,031 bytes allocated
==43252== 
==43252== All heap blocks were freed -- no leaks are possible
==43252== 
==43252== For lists of detected and suppressed errors, rerun with: -s
==43252== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[edsiper]

cc: @lecaros

[nokute78]

I sent a patch #6212 for 1.9 branch.