levellog: dirt-simple leveled text logger

Signed-off-by: Chris Koch <[email protected]>

llog/levellog.go

@@ -0,0 +1,92 @@
+// Copyright 2024 the u-root Authors. All rights reserved
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// llog is a dirt-simple leveled text logger.
+package llog
+
+import (
+	"log"
+	"log/slog"
+	"math"
+	"testing"
+)
+
+// Log is the stdlib default log sink.
+var Default *Logger = &Logger{Sink: log.Printf}
+
+// Null is a logger that prints nothing.
+var Null *Logger = &Logger{Sink: nil}
+
+// Test is a logger that prints every level to t.Logf.
+func Test(t testing.TB) *Logger {
+	return &Logger{Sink: t.Logf, Level: slog.Level(math.MinInt32)}
+}
+
+// Debug prints to log.Printf at the debug level.
+var Debug *Logger = &Logger{Sink: log.Printf, Level: slog.LevelDebug}
+
+// Printf is a logger printf function.
+type Printf func(format string, v ...any)
+
+// Logger is a dirt-simple leveled logger.
+//
+// If the log level is >= Level, it logs to the given Sink.
+//
+// Logger and Sink may be nil in order to log nothing.
+type Logger struct {
+	Sink  Printf
+	Level slog.Level
+}
+
+// Printf returns a Printf that can be passed around to log at the given level.
+func (l *Logger) Printf(level slog.Level) Printf {
+	return func(fmt string, args ...any) {
+		if l == nil {
+			return
+		}
+		l.Logf(level, fmt, args...)
+	}
+}
+
+// Debugf is a printf function that logs at the Debug level.
+func (l *Logger) Debugf(fmt string, args ...any) {
+	if l == nil {
+		return
+	}
+	l.Logf(slog.LevelDebug, fmt, args...)
+}
+
+// Infof is a printf function that logs at the Info level.
+func (l *Logger) Infof(fmt string, args ...any) {
+	if l == nil {
+		return
+	}
+	l.Logf(slog.LevelInfo, fmt, args...)
+}
+
+// Warnf is a printf function that logs at the Warn level.
+func (l *Logger) Warnf(fmt string, args ...any) {
+	if l == nil {
+		return
+	}
+	l.Logf(slog.LevelWarn, fmt, args...)
+}
+
+// Errorf is a printf function that logs at the Error level.
+func (l *Logger) Errorf(fmt string, args ...any) {
+	if l == nil {
+		return
+	}
+	l.Logf(slog.LevelError, fmt, args...)
+}
+
+// Logf logs at the given level.
+func (l *Logger) Logf(level slog.Level, fmt string, args ...any) {
+	if l == nil || l.Sink == nil {
+		return
+	}
+	if level >= l.Level {
+		l.Sink(fmt, args...)
+	}
+}