import template code

app/logger/logger.go

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2026 Oleg Borodin <onborodin@gmail.com>
+ *
+ * This work is published and licensed under a Creative Commons
+ * Attribution-NonCommercial-NoDerivatives 4.0 International License.
+ *
+ * Distribution of this work is permitted, but commercial use and
+ * modifications are strictly prohibited.
+ */
+package logger
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"sync"
+	"time"
+)
+
+var (
+	mtx    sync.Mutex
+	output io.WriteCloser = os.Stderr
+)
+
+type Logger struct {
+	subject string
+	writer  io.WriteCloser
+	mtx     *sync.Mutex
+}
+
+func NewLogger(subj string) *Logger {
+	return &Logger{
+		subject: subj,
+		writer:  output,
+		mtx:     &mtx,
+	}
+}
+
+func xxxNewLogger() *Logger {
+	return &Logger{
+		writer: output,
+		mtx:    &mtx,
+	}
+}
+
+func SetWriter(newOut io.WriteCloser) {
+	mtx.Lock()
+	output = newOut
+	mtx.Unlock()
+}
+
+func (logg *Logger) SetWriter(newOut io.WriteCloser) {
+	mtx.Lock()
+	logg.writer = newOut
+	var newMtx sync.Mutex
+	logg.mtx = &newMtx
+	mtx.Unlock()
+}
+
+func (logg *Logger) Debugf(message string, args ...any) {
+	logg.printf("debug", message, args...)
+}
+
+func (logg *Logger) Infof(message string, args ...any) {
+	logg.printf("info", message, args...)
+}
+
+func (logg *Logger) Warningf(message string, args ...any) {
+	logg.printf("warning", message, args...)
+}
+
+func (logg *Logger) Errorf(message string, args ...any) {
+	logg.printf("error", message, args...)
+}
+
+func (logg *Logger) printf(level, message string, args ...any) {
+	timestamp := time.Now().Format(time.RFC3339)
+	buffer := bytes.NewBuffer([]byte{})
+	if logg.subject != "" {
+		fmt.Fprintf(buffer, "%s %s.%s: ", timestamp, logg.subject, level)
+	} else {
+		fmt.Fprintf(buffer, "%s %s: ", timestamp, level)
+	}
+	fmt.Fprintf(buffer, message, args...)
+	fmt.Fprintf(buffer, "\n")
+	logg.mtx.Lock()
+	fmt.Fprint(output, buffer.String())
+	logg.mtx.Unlock()
+}

app/logger/logger_test.go

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2026 Oleg Borodin <onborodin@gmail.com>
+ *
+ * This work is published and licensed under a Creative Commons
+ * Attribution-NonCommercial-NoDerivatives 4.0 International License.
+ *
+ * Distribution of this work is permitted, but commercial use and
+ * modifications are strictly prohibited.
+ */
+package logger
+
+import (
+	"io/ioutil"
+	"testing"
+)
+
+func TestLogger(t *testing.T) {
+	logg := NewLogger("test")
+	logg.Debugf("foo: %s", "bar")
+}
+
+func BenchmarkLoggerL(b *testing.B) {
+	SetWriter(ioutil.Discard)
+	logg := NewLogger("test")
+	for i := 0; i < b.N; i++ {
+		logg.Debugf("foo: %s", "bar")
+	}
+}
+
+func BenchmarkLoggerP(b *testing.B) {
+	SetWriter(ioutil.Discard)
+	logg := NewLogger("test")
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			logg.Debugf("foo: %s", "bar")
+		}
+	})
+}