Exclude cfg.Stderr if only Stdout is provided in env var

[Bidon15]

Introduction 👋

If I want to change the logging output from Stderr to Stdout, the os env GOLOG_OUTPUT should be changed to stdout
Still, after setting env to only stdout - I still see that the same log is duplicated in both pipelines(StdErr, Stdout)
This behaviour was found during testing in testground and the testable application is using ipfs/go-log/v2 logger

• ERROR logs show the same as OTHER

Example of testground's log

Aug 22 11:38:39.023690	INFO	65.2779s      ERROR << instance[002] (9c984e) >>
Aug 22 11:38:39.023713	INFO	65.2779s      ERROR << instance[002] (9c984e) >> /_____/  /_____/  /_____/  /_____/  /_____/
Aug 22 11:38:39.023753	INFO	65.2780s      ERROR << instance[002] (9c984e) >>
Aug 22 11:38:39.023794	INFO	65.2780s      ERROR << instance[002] (9c984e) >> Started celestia DA node
Aug 22 11:38:39.023826	INFO	65.2780s      ERROR << instance[002] (9c984e) >> node type: 	bridge
Aug 22 11:38:39.023868	INFO	65.2781s      ERROR << instance[002] (9c984e) >> network: 	private
Aug 22 11:38:39.023901	INFO	65.2781s      ERROR << instance[002] (9c984e) >>
Aug 22 11:38:39.023954	INFO	65.2782s      ERROR << instance[002] (9c984e) >> /_____/  /_____/  /_____/  /_____/  /_____/
Aug 22 11:38:39.023989	INFO	65.2782s      OTHER << instance[002] (9c984e) >> 2022-08-22T11:38:39.023Z	INFO	node	node/node.go:104	
Aug 22 11:38:39.024010	INFO	65.2782s      ERROR << instance[002] (9c984e) >>
Aug 22 11:38:39.024025	INFO	65.2782s      OTHER << instance[002] (9c984e) >>
Aug 22 11:38:39.024070	INFO	65.2783s      OTHER << instance[002] (9c984e) >> /_____/  /_____/  /_____/  /_____/  /_____/
Aug 22 11:38:39.024100	INFO	65.2783s      OTHER << instance[002] (9c984e) >>
Aug 22 11:38:39.024126	INFO	65.2783s      OTHER << instance[002] (9c984e) >> Started celestia DA node
Aug 22 11:38:39.024148	INFO	65.2784s      OTHER << instance[002] (9c984e) >> node type: 	bridge
Aug 22 11:38:39.024168	INFO	65.2784s      OTHER << instance[002] (9c984e) >> network: 	private
Aug 22 11:38:39.024206	INFO	65.2784s      OTHER << instance[002] (9c984e) >>
Aug 22 11:38:39.024227	INFO	65.2784s      OTHER << instance[002] (9c984e) >> /_____/  /_____/  /_____/  /_____/  /_____/
Aug 22 11:38:39.024249	INFO	65.2785s      OTHER << instance[002] (9c984e) >>

Solutions 🧐

There are 2 approaches that I've found for myself:

• If we set the env GOLOG_FILE to /dev/null and GOLOG_OUTPUT = stdout , then Stderr (hence, ERROR in testground) won't appear anymore
• If the user is explicitly setting the env to only stdout, the why should we also leave Stderr flag to true? There is already a possibility to add multiple options in the env, so I propose the selection to be more strict. Example: feat: exclude stderr output if only stdout is passed in env #135

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