log output appears to include terminal escape sequences even when stdout is not a tty

[jclulow]

I am running the syncv3 binary with both stdout and stderr redirected to a file, and that file appears to contain colour escape sequences meant for a terminal:

synapse0 # cat -vet /var/svc/log/*ssproxy*
[ Oct  8 08:51:27 Disabled. ]$
[ Oct  8 08:51:27 Rereading configuration. ]$
[ Oct  8 08:51:37 Enabled. ]$
[ Oct  8 08:51:37 Executing start method ("/data/ssproxy/start"). ]$
Sync v3 [0.99.10] (d214047)$
Debug=false LogLevel= MaxConns=0$
2023/10/08 08:51:37 goose: no migrations to run. current version: 20230822180807$
^[[90m08:51:37^[[0m ^[[32mINF^[[0m creating handler$
^[[90m08:51:37^[[0m ^[[32mINF^[[0m retrieved global snapshot from database$
^[[90m08:51:37^[[0m ^[[32mINF^[[0m listening on 0.0.0.0:8009$
^[[90m08:51:37^[[0m ^[[32mINF^[[0m StartV2Pollers ^[[36mnum_devices=^[[0m1 ^[[36mnum_fail_decrypt=^[[0m0$

When stdout is not a tty, it would be good if the log output could just be plain text.

[dougluce]

#420 should address this via env var setting.

[jclulow]

@dougluce An environment variable override doesn't fix this bug. The program needs to check if it's being run interactively, or is redirected to something that isn't a tty; e.g., a file or a pipe. In the case that it's not interactive, it must not emit any terminal control sequences by default.

One would use isatty(3C) for this check, or whatever the Go wrapper around that call is called, on whichever of stdout or stderr is the target of the logging stream.