in_forward: clear out_tag before using(#4670)

[nokute78]

Fixes #4670

out_tag is not clear and re-used.
It causes out_tag is increasing for each loop.

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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

• Backport to latest stable release.

Configuration

[INPUT]
     Name forward
     Listen 0.0.0.0
     Port 24224
     Tag *

[OUTPUT]
     name                  stdout
     match                 *
     json_date_key         false

Debug output

$ ../bin/fluent-bit -c a.conf 
Fluent Bit v1.9.0
* Copyright (C) 2019-2021 The Fluent Bit Authors
* Copyright (C) 2015-2018 Treasure Data
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2022/01/23 14:56:11] [ info] [engine] started (pid=19874)
[2022/01/23 14:56:11] [ info] [storage] version=1.1.5, initializing...
[2022/01/23 14:56:11] [ info] [storage] in-memory
[2022/01/23 14:56:11] [ info] [storage] normal synchronization mode, checksum disabled, max_chunks_up=128
[2022/01/23 14:56:11] [ info] [cmetrics] version=0.2.2
[2022/01/23 14:56:11] [ info] [input:forward:forward.0] listening on 0.0.0.0:24224
[2022/01/23 14:56:11] [ info] [sp] stream processor started
[0] 2cbb69924a23: [1642917374.000000000, {"container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]"source"=>"stdout", "log"=>"/
[0] 2cbb69924a23: [1642917376.000000000, {"container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]"source"=>"stdout", "log"=>"root@2cbb69924a23:/# pwd
", "container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]
[0] 2cbb69924a23: [1642917384.000000000, {"container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]"source"=>"stdout", "log"=>"root@2cbb69924a23:/# lspwd
[1] 2cbb69924a23: [1642917384.000000000, {"container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]"source"=>"stdout", "log"=>"bash: lspwd: command not found
^C[2022/01/23 14:56:32] [engine] caught signal (SIGINT)
[2022/01/23 14:56:32] [ info] [input] pausing forward.0
[2022/01/23 14:56:32] [ warn] [engine] service will shutdown in max 5 seconds
[2022/01/23 14:56:32] [ info] [engine] service has stopped (0 pending tasks)

Valgrind output

$ valgrind --leak-check=full ../bin/fluent-bit -c a.conf 
==19871== Memcheck, a memory error detector
==19871== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==19871== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==19871== Command: ../bin/fluent-bit -c a.conf
==19871== 
Fluent Bit v1.9.0
* Copyright (C) 2019-2021 The Fluent Bit Authors
* Copyright (C) 2015-2018 Treasure Data
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2022/01/23 14:55:27] [ info] [engine] started (pid=19871)
[2022/01/23 14:55:27] [ info] [storage] version=1.1.5, initializing...
[2022/01/23 14:55:27] [ info] [storage] in-memory
[2022/01/23 14:55:27] [ info] [storage] normal synchronization mode, checksum disabled, max_chunks_up=128
[2022/01/23 14:55:27] [ info] [cmetrics] version=0.2.2
[2022/01/23 14:55:27] [ info] [input:forward:forward.0] listening on 0.0.0.0:24224
[2022/01/23 14:55:27] [ info] [sp] stream processor started
==19871== Warning: client switching stacks?  SP change: 0x57e59f8 --> 0x4d84fd0
==19871==          to suppress, use: --max-stackframe=10881576 or greater
==19871== Warning: client switching stacks?  SP change: 0x4d84f78 --> 0x57e59f8
==19871==          to suppress, use: --max-stackframe=10881664 or greater
==19871== Warning: client switching stacks?  SP change: 0x57e59f8 --> 0x4d84f78
==19871==          to suppress, use: --max-stackframe=10881664 or greater
==19871==          further instances of this message will not be shown.
", "container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]
[0] 2cbb69924a23: [1642917333.000000000, {"container_name"=>"/pedantic_rubin", "", "container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884"}]
[1] 2cbb69924a23: [1642917333.000000000, {"container_name"=>"/pedantic_rubin", "", "container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884"}]
[0] 2cbb69924a23: [1642917338.000000000, {"container_name"=>"/pedantic_rubin", "", "container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884"}]
[1] 2cbb69924a23: [1642917338.000000000, {"container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]"source"=>"stdout", "log"=>"/
[2] 2cbb69924a23: [1642917340.000000000, {"container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]"source"=>"stdout", "log"=>"root@2cbb69924a23:/# pwd
[3] 2cbb69924a23: [1642917340.000000000, {"container_id"=>"2cbb69924a2349c23280f1ef413c1128f4f9d6d5019c382babb8926a5fa39884", "container_name"=>"/pedantic_rubin"}]"source"=>"stdout", "log"=>"/
^C[2022/01/23 14:55:43] [engine] caught signal (SIGINT)
[2022/01/23 14:55:43] [ info] [input] pausing forward.0
[2022/01/23 14:55:43] [ warn] [engine] service will shutdown in max 5 seconds
[2022/01/23 14:55:44] [ info] [engine] service has stopped (0 pending tasks)
==19871== 
==19871== HEAP SUMMARY:
==19871==     in use at exit: 0 bytes in 0 blocks
==19871==   total heap usage: 1,202 allocs, 1,202 frees, 2,658,677 bytes allocated
==19871== 
==19871== All heap blocks were freed -- no leaks are possible
==19871== 
==19871== For lists of detected and suppressed errors, rerun with: -s
==19871== 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.

[nokute78]

CI failed.
It should be fixed by #4673 .

[edsiper]

thank you!, is 1.8 affected too ?