2 files changed, 47 insertions, 30 deletions

diff --git a/src/log/log.go b/src/log/log.go
index 9e38b6ed69..78458c19f3 100644
--- a/src/log/log.go
+++ b/src/log/log.go
@@ -190,6 +190,17 @@ func putBuffer(p *[]byte) {
 // provided for generality, although at the moment on all pre-defined
 // paths it will be 2.
 func (l *Logger) Output(calldepth int, s string) error {
+	calldepth++ // +1 for this frame.
+	return l.output(calldepth, func(b []byte) []byte {
+		return append(b, s...)
+	})
+}
+
+func (l *Logger) output(calldepth int, appendOutput func([]byte) []byte) error {
+	if l.isDiscard.Load() {
+		return nil
+	}
+
 	now := time.Now() // get this early.
 
 	// Load prefix and flag once so that their value is consistent within
@@ -211,7 +222,9 @@ func (l *Logger) Output(calldepth int, s string) error {
 	buf := getBuffer()
 	defer putBuffer(buf)
 	formatHeader(buf, now, prefix, flag, file, line)
-	*buf = append(*buf, s...)
+	headerLen := len(*buf)
+	*buf = appendOutput(*buf)
+	s := (*buf)[headerLen:]
 	if len(s) == 0 || s[len(s)-1] != '\n' {
 		*buf = append(*buf, '\n')
 	}
@@ -222,31 +235,28 @@ func (l *Logger) Output(calldepth int, s string) error {
 	return err
 }
 
-// Printf calls l.Output to print to the logger.
-// Arguments are handled in the manner of fmt.Printf.
-func (l *Logger) Printf(format string, v ...any) {
-	if l.isDiscard.Load() {
-		return
-	}
-	l.Output(2, fmt.Sprintf(format, v...))
-}
-
 // Print calls l.Output to print to the logger.
 // Arguments are handled in the manner of fmt.Print.
 func (l *Logger) Print(v ...any) {
-	if l.isDiscard.Load() {
-		return
-	}
-	l.Output(2, fmt.Sprint(v...))
+	l.output(2, func(b []byte) []byte {
+		return fmt.Append(b, v...)
+	})
+}
+
+// Printf calls l.Output to print to the logger.
+// Arguments are handled in the manner of fmt.Printf.
+func (l *Logger) Printf(format string, v ...any) {
+	l.output(2, func(b []byte) []byte {
+		return fmt.Appendf(b, format, v...)
+	})
 }
 
 // Println calls l.Output to print to the logger.
 // Arguments are handled in the manner of fmt.Println.
 func (l *Logger) Println(v ...any) {
-	if l.isDiscard.Load() {
-		return
-	}
-	l.Output(2, fmt.Sprintln(v...))
+	l.output(2, func(b []byte) []byte {
+		return fmt.Appendln(b, v...)
+	})
 }
 
 // Fatal is equivalent to l.Print() followed by a call to os.Exit(1).
@@ -357,28 +367,25 @@ func Writer() io.Writer {
 // Print calls Output to print to the standard logger.
 // Arguments are handled in the manner of fmt.Print.
 func Print(v ...any) {
-	if std.isDiscard.Load() {
-		return
-	}
-	std.Output(2, fmt.Sprint(v...))
+	std.output(2, func(b []byte) []byte {
+		return fmt.Append(b, v...)
+	})
 }
 
 // Printf calls Output to print to the standard logger.
 // Arguments are handled in the manner of fmt.Printf.
 func Printf(format string, v ...any) {
-	if std.isDiscard.Load() {
-		return
-	}
-	std.Output(2, fmt.Sprintf(format, v...))
+	std.output(2, func(b []byte) []byte {
+		return fmt.Appendf(b, format, v...)
+	})
 }
 
 // Println calls Output to print to the standard logger.
 // Arguments are handled in the manner of fmt.Println.
 func Println(v ...any) {
-	if std.isDiscard.Load() {
-		return
-	}
-	std.Output(2, fmt.Sprintln(v...))
+	std.output(2, func(b []byte) []byte {
+		return fmt.Appendln(b, v...)
+	})
 }
 
 // Fatal is equivalent to Print() followed by a call to os.Exit(1).
diff --git a/src/log/log_test.go b/src/log/log_test.go
index c212b60554..ea7e7917b8 100644
--- a/src/log/log_test.go
+++ b/src/log/log_test.go
@@ -217,6 +217,7 @@ func BenchmarkPrintln(b *testing.B) {
 	const testString = "test"
 	var buf bytes.Buffer
 	l := New(&buf, "", LstdFlags)
+	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {
 		buf.Reset()
 		l.Println(testString)
@@ -227,6 +228,7 @@ func BenchmarkPrintlnNoFlags(b *testing.B) {
 	const testString = "test"
 	var buf bytes.Buffer
 	l := New(&buf, "", 0)
+	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {
 		buf.Reset()
 		l.Println(testString)
@@ -255,3 +257,11 @@ func BenchmarkConcurrent(b *testing.B) {
 	}
 	group.Wait()
 }
+
+func BenchmarkDiscard(b *testing.B) {
+	l := New(io.Discard, "", LstdFlags|Lshortfile)
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		l.Printf("processing %d objects from bucket %q", 1234, "fizzbuzz")
+	}
+}