1 files changed, 80 insertions, 11 deletions

diff --git a/sd_daemon/log.go b/sd_daemon/log.go
index df82d4b..806f248 100644
--- a/sd_daemon/log.go
+++ b/sd_daemon/log.go
@@ -17,7 +17,7 @@
 package sd_daemon
 
 import (
-	"fmt"
+	"bytes"
 	"io"
 	"log/syslog"
 	"os"
@@ -36,6 +36,7 @@ import (
 type Logger struct {
 	mu  sync.Mutex
 	out io.Writer
+	buf []byte
 }
 
 func NewLogger(w io.Writer) Logger {
@@ -50,25 +51,93 @@ func NewLogger(w io.Writer) Logger {
 // talk to syslog or journald directly.
 var Log = Logger{out: os.Stderr}
 
+// Cheap version of
+//
+//     *buf = append(*buf, fmt.Sprintf("<%d>", n)...)
+func appendPrefix(buf []byte, n syslog.Priority) []byte {
+	var b [22]byte // 21 = ceil(log_10(2^64))+len("<>")
+	b[len(b)-1] = '>'
+	i := len(b) - 2
+	for n >= 10 {
+		b[i] = byte('0' + n%10)
+		n = n / 10
+		i--
+	}
+	b[i] = byte('0' + n)
+	i--
+	b[i] = '<'
+	return append(buf, b[i:]...)
+}
+
 // WriteString writes a message with the specified priority to the
 // log.
-func (l Logger) WriteBytes(level syslog.Priority, msg []byte) (n int, err error) {
-	return l.WriteString(level, string(msg))
+func (l Logger) WriteString(level syslog.Priority, msg string) (n int, err error) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+
+	msg = strings.TrimSuffix(msg, "\n")
+
+	// The following is a cheap version of:
+	//
+	//    prefix := fmt.Sprintf("<%d>", level)
+	//    buf := prefix + strings.Replace(msg, "\n", "\n"+prefix, -1)
+	//    return io.WriteString(l.out, buf)
+
+	l.buf = l.buf[:0]
+	l.buf = appendPrefix(l.buf, level) // possible allocation
+	prefix := l.buf
+	nlines := strings.Count(msg, "\n") + 1
+	n = len(msg) + len(prefix)*nlines + 1
+	if cap(l.buf) < n {
+		l.buf = make([]byte, len(l.buf), n) // allocation
+		copy(l.buf, prefix)
+	}
+
+	for nlines > 1 {
+		nl := strings.IndexByte(msg, '\n')
+		l.buf = append(l.buf, msg[:nl+1]...)
+		l.buf = append(l.buf, prefix...)
+		msg = msg[nl+1:]
+		nlines--
+	}
+	l.buf = append(l.buf, msg...)
+	l.buf = append(l.buf, '\n')
+
+	return l.out.Write(l.buf)
 }
 
 // WriteString writes a message with the specified priority to the
 // log.
-func (l Logger) WriteString(level syslog.Priority, msg string) (n int, err error) {
+func (l Logger) WriteBytes(level syslog.Priority, msg []byte) (n int, err error) {
+	// Copy/pasted from WriteString and
+	//  * `strings.` -> `bytes.`
+	//  * `"\n"` -> `[]byte{'\n'}`
 	l.mu.Lock()
 	defer l.mu.Unlock()
 
-	// BUG(lukeshu): Logger uses high-level string functions that
-	// do many small allocations, making it insuitable for in
-	// tight loops; it should use a buffer property to be
-	// essentially zero-allocation.
-	prefix := fmt.Sprintf("<%d>", level)
-	buf := prefix + strings.Replace(strings.TrimSuffix(msg, "\n"), "\n", "\n"+prefix, -1)
-	return io.WriteString(l.out, buf)
+	msg = bytes.TrimSuffix(msg, []byte{'\n'})
+
+	l.buf = l.buf[:0]
+	l.buf = appendPrefix(l.buf, level) // possible allocation
+	prefix := l.buf
+	nlines := bytes.Count(msg, []byte{'\n'}) + 1
+	n = len(msg) + len(prefix)*nlines + 1
+	if cap(l.buf) < n {
+		l.buf = make([]byte, len(l.buf), n) // allocation
+		copy(l.buf, prefix)
+	}
+
+	for nlines > 1 {
+		nl := bytes.IndexByte(msg, '\n')
+		l.buf = append(l.buf, msg[:nl+1]...)
+		l.buf = append(l.buf, prefix...)
+		msg = msg[nl+1:]
+		nlines--
+	}
+	l.buf = append(l.buf, msg...)
+	l.buf = append(l.buf, '\n')
+
+	return l.out.Write(l.buf)
 }
 
 type loggerWriter struct {