logging: convert logger package from zap to slog

[miampf]

Context

Proposed change(s)

• rewrite the logger package in internal/logger to use slog instead of zap
• rewrite references to the logger package to be compatible with slog
• add non-formatting functions for similar usage to fmt.Print(a, b)

Additional info

• code in operators/ was not changed and still uses zap since it didn't depend on the logger package

Checklist

• Update docs
• Add labels (e.g., for changelog category)
• Is PR title adequate for changelog?
• Link to Milestone

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[daniel-weisse]

Thanks, looks mostly good.
Just a couple of small things

[daniel-weisse]

Suggested change

	const (
	LevelDebug = slog.LevelDebug
	LevelInfo = slog.LevelInfo
	LevelWarn = slog.LevelWarn
	LevelError = slog.LevelError
	LevelFatal = 12
	)
	// Log levels defined for the logger.
	const (
	LevelDebug = slog.LevelDebug
	LevelInfo = slog.LevelInfo
	LevelWarn = slog.LevelWarn
	LevelError = slog.LevelError
	LevelFatal = 12
	)

Missing doc string.

[daniel-weisse]

Suggested change

	func replaceAttrFunction(groups []string, a slog.Attr) slog.Attr {
	// change the time format to rfc 3339
	func replaceAttrFunction(_ []string, a slog.Attr) slog.Attr {
	// change the time format to rfc 3339

groups is unused

[daniel-weisse]

When we originally designed the package we decided to only provide access to Printf style logging functions to reduce complexity of the package and enforce (mostly) uniform usage.
Log statements that use log.Info(msg, arg1, arg2) should instead use log.With(key1, arg1, key2, arg2).Infof(msg) or log.Infof(formtStr, arg1, arg2)

I think this still hold true, so I don't see a good reason to keep the additional Print style logging functions.

[daniel-weisse]

Suggested change

	func getOriginalCaller() (original [1]uintptr) {
	var pcs [1]uintptr
	runtime.Callers(3, pcs[:]) // skip Callers, getOriginalCaller and the function calling getOriginalCaller
	return pcs
	}
	func createAndLogRecord(logger *slog.Logger, level slog.Level, originalFunction [1]uintptr, args ...any) {
	record := slog.NewRecord(time.Now(), level, fmt.Sprint(args...), originalFunction[0])
	_ = logger.Handler().Handle(context.Background(), record)
	}
	func createAndLogRecordf(logger *slog.Logger, level slog.Level, originalFunction [1]uintptr, format string, args ...any) {
	record := slog.NewRecord(time.Now(), level, fmt.Sprintf(format, args...), originalFunction[0])
	_ = logger.Handler().Handle(context.Background(), record)
	}
	func createAndLogRecordf(logger *slog.Logger, level slog.Level, callerSkip int, format string, args ...any) {
	var originalFunction uintptr[1]
	runtime.Callers(callerSkip, pcs[:])
	record := slog.NewRecord(time.Now(), level, fmt.Sprintf(format, args...), originalFunction[0])
	_ = logger.Handler().Handle(context.Background(), record)
	}

You can add resolving of the original caller to the createAndLogRecord function directly to reduce overhead in the log functions.
The grpc logging adapter also needs a different caller skip depth (7) than our logging (3), so we should make that configurable.

[daniel-weisse]

Since error is probably the most used additional field for log messages, it might be worth to add a wrapper for this to our logging package. This would more easily ensure uniform logging for error.
E.g.

// Err creates an error attribute for structured logging.
func Err(err error) slog.Attr {
	return slog.Attr{
		Key:   "error",
		Value: slog.StringValue(err.Error()),
	}
}

[daniel-weisse]

Suggested change

	u.log.Error("post-cleaning: deleting temporary blob from s3", err)
	u.log.With(slog.Any("error", err)).Error("post-cleaning: deleting temporary blob from s3 failed")

[katexochen]

Wasn't the purpose of the ticket to get rid of the wrapper and use slog directly?

[msanft]

cc @miampf

After internal discussion, we concluded that we rather want to get rid of the wrapper entirely and replace the logging calls we do in our code with using slog directly, feel free to consult me before implementation or if unsure anywhere. This was a misunderstanding and I didn't explain the issue to you properly - sorry for that. However, pivoting here does not mean that the work you did so far is worthless. You should be able to reuse almost everything you have so far.

[miampf]

Since it was decided that the wrapper should be completely removed, I will create a new branch for implementing that.