log: make NewBufferLogger safe to read/write across goroutines

log/logger_impl.go

@@ -6,6 +6,7 @@ import (
 	"runtime"
 	"sort"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -44,11 +45,39 @@ func NewTestLogger() Logger {
 	return NewNopLogger()
 }
 
-func NewBufferLogger() (*strings.Builder, Logger) {
-	buffer := strings.Builder{}
-	writer := log.NewLogfmtLogger(log.NewSyncWriter(&buffer))
+func NewBufferLogger() (*BufferedLogger, Logger) {
+	buffer := &BufferedLogger{
+		buf: &strings.Builder{},
+	}
+	writer := log.NewLogfmtLogger(log.NewSyncWriter(buffer))
 	log := NewLogger(writer)
-	return &buffer, log
+	return buffer, log
+}
+
+type BufferedLogger struct {
+	mu  sync.RWMutex
+	buf *strings.Builder
+}
+
+func (bl *BufferedLogger) Write(p []byte) (n int, err error) {
+	bl.mu.Lock()
+	defer bl.mu.Unlock()
+
+	return bl.buf.Write(p)
+}
+
+func (bl *BufferedLogger) Reset() {
+	bl.mu.Lock()
+	defer bl.mu.Unlock()
+
+	bl.buf.Reset()
+}
+
+func (bl *BufferedLogger) String() string {
+	bl.mu.RLock()
+	defer bl.mu.RUnlock()
+
+	return bl.buf.String()
 }
 
 func NewLogger(writer log.Logger) Logger {

log/logger_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"regexp"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -297,7 +298,27 @@ func Test_Caller(t *testing.T) {
 	a.Regexp(regexp.MustCompile(`caller_0=(.*?)(\/log\/logger_test\.go)`), buffer.String())
 }
 
-func Setup(t *testing.T) (*assert.Assertions, *strings.Builder, lib.Logger) {
+func Test_BufferedLogger_Concurrent(t *testing.T) {
+	_, buffer, log := Setup(t)
+
+	var wg sync.WaitGroup
+	wg.Add(1000)
+	for i := 0; i < 1000; i++ {
+		go func(idx int) {
+			defer wg.Done()
+
+			if idx%3 == 0 {
+				t.Log(buffer.String()) // read
+			} else {
+				log.Info().Logf("idx %d", idx)
+			}
+		}(i)
+	}
+
+	wg.Wait()
+}
+
+func Setup(t *testing.T) (*assert.Assertions, *lib.BufferedLogger, lib.Logger) {
 	a := assert.New(t)
 	buffer, log := lib.NewBufferLogger()
 	return a, buffer, log