Send standard logger's output to logrus

[mikesep]

What is the problem I am trying to address?

Some packages like httputil's ReverseProxy use the standard log.Logger to emit log traces. This means that their output won't match the format of Athens's logrus output.

How is the fix applied?

logrus.Logger.Writer's documentation states that it "can be used to override the standard library logger easily." It spawns a go routine, so instead of doing that each time we need to make logrus look like a (standard) log.Logger (and then remembering to Close() it right away), this calls logrus.Writer() once in main, defers the Close(), and sets it into the global log.Logger.

What GitHub issue(s) does this PR fix or close?

Related to the work done in #1819 to unify logging.

[mikesep]

If maintainers would rather I figure out how to pass this down through the call chain to the sumdb ReverseProxy, I can try that approach, but it occurred to me that this global approach would catch anything else using the standard log too, and I wanted to avoid repeatedly spawning and closing the pipe-reading goroutine.

[nrwiersma]

IMO, global loggers are not great, but given the cost (A go routine to mimic an io.Writer seems a little insane), this might be OK in this case.

[nrwiersma]

LGTM

[Ullaakut]

Scoping the variables here seems unnecessary, unless I am missing something that isn't described by the comment.

Suggested change

	{
	logrusWriter := logger.WriterLevel(logrus.ErrorLevel)
	defer func() {
	if err := logrusWriter.Close(); err != nil {
	logger.WithError(err).Warn("Could not close logrus writer pipe")
	}
	}()
	stdlog.SetOutput(logrusWriter)
	stdlog.SetFlags(stdlog.Flags() &^ (stdlog.Ldate | stdlog.Ltime))
	}
	logrusWriter := logger.WriterLevel(logrus.ErrorLevel)
	defer func() {
	if err := logrusWriter.Close(); err != nil {
	logger.WithError(err).Warn("Could not close logrus writer pipe")
	}
	}()
	stdlog.SetOutput(logrusWriter)
	stdlog.SetFlags(stdlog.Flags() &^ (stdlog.Ldate | stdlog.Ltime))

WDYT of simply removing the scope?

[mikesep]

I did it just to logically group things together, and also to discourage/prevent using logrusWriter later on. I'm fine removing it if this feels too awkward/unusual to others.

[mikesep]

Removed scope in 6eea0a6.

[Ullaakut]

Suggested change

	// logrus.Writer() spawns a go routine, so instead of doing that each time
	// we need to make logrus look like a (standard) log.Logger (and then Close()ing it),
	// we can do it once in main and have the global log.Logger use it.
	// Use the logrus writer as the standard logger's output in order to avoid starting goroutines whenever logrus.Writer() is called.

WDYT of this simplification of the comment?

[mikesep]

I think it's fair to say that this was too long a comment for code and better off in the PR/commit explanation. I went with something even shorter in 6eea0a6.

[Ullaakut]

LGTM, thanks!