logtail,logpolicy: tweak minor cosmetic things

Just reading the code again in prep for some alloc reductions.

Change-Id: I065226ea794b7ec7144c2b15942d35131c9313a8
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

logpolicy/logpolicy.go

@@ -520,7 +520,7 @@ func New(collection string) *Policy {
 		}
 	}
 
-	c := logtail.Config{
+	conf := logtail.Config{
 		Collection: newc.Collection,
 		PrivateID:  newc.PrivateID,
 		Stderr:     logWriter{console},
@@ -534,16 +534,16 @@ func New(collection string) *Policy {
 		HTTPC: &http.Client{Transport: NewLogtailTransport(logtail.DefaultHost)},
 	}
 	if collection == logtail.CollectionNode {
-		c.MetricsDelta = clientmetric.EncodeLogTailMetricsDelta
-		c.IncludeProcID = true
-		c.IncludeProcSequence = true
+		conf.MetricsDelta = clientmetric.EncodeLogTailMetricsDelta
+		conf.IncludeProcID = true
+		conf.IncludeProcSequence = true
 	}
 
 	if val := getLogTarget(); val != "" {
 		log.Println("You have enabled a non-default log target. Doing without being told to by Tailscale staff or your network administrator will make getting support difficult.")
-		c.BaseURL = val
+		conf.BaseURL = val
 		u, _ := url.Parse(val)
-		c.HTTPC = &http.Client{Transport: NewLogtailTransport(u.Host)}
+		conf.HTTPC = &http.Client{Transport: NewLogtailTransport(u.Host)}
 	}
 
 	filchOptions := filch.Options{
@@ -566,16 +566,16 @@ func New(collection string) *Policy {
 
 	filchBuf, filchErr := filch.New(filchPrefix, filchOptions)
 	if filchBuf != nil {
-		c.Buffer = filchBuf
+		conf.Buffer = filchBuf
 		if filchBuf.OrigStderr != nil {
-			c.Stderr = filchBuf.OrigStderr
+			conf.Stderr = filchBuf.OrigStderr
 		}
 	}
-	lw := logtail.NewLogger(c, log.Printf)
+	lw := logtail.NewLogger(conf, log.Printf)
 
 	var logOutput io.Writer = lw
 
-	if runtime.GOOS == "windows" && c.Collection == logtail.CollectionNode {
+	if runtime.GOOS == "windows" && conf.Collection == logtail.CollectionNode {
 		logID := newc.PublicID.String()
 		exe, _ := os.Executable()
 		if strings.EqualFold(filepath.Base(exe), "tailscaled.exe") {

logtail/buffer.go

@@ -21,6 +21,8 @@ type Buffer interface {
 	TryReadLine() ([]byte, error)
 
 	// Write writes a log line into the ring buffer.
+	//
+	// Write takes ownership of the provided slice.
 	Write([]byte) (int, error)
 }
 

logtail/logtail.go

@@ -167,8 +167,9 @@ type Logger struct {
 
 	procID              uint32
 	includeProcSequence bool
-	writeLock           sync.Mutex // guards increments of procSequence
-	procSequence        uint64
+
+	writeLock    sync.Mutex // guards increments of procSequence
+	procSequence uint64
 
 	shutdownStart chan struct{} // closed when shutdown begins
 	shutdownDone  chan struct{} // closed when shutdown complete
@@ -454,7 +455,7 @@ func Disable() {
 	logtailDisabled.Set(true)
 }
 
-func (l *Logger) send(jsonBlob []byte) (int, error) {
+func (l *Logger) sendLocked(jsonBlob []byte) (int, error) {
 	if logtailDisabled.Get() {
 		return len(jsonBlob), nil
 	}
@@ -578,7 +579,7 @@ func (l *Logger) encodeText(buf []byte, skipClientTime bool, procID uint32, proc
 	return b
 }
 
-func (l *Logger) encode(buf []byte, level int) []byte {
+func (l *Logger) encodeLocked(buf []byte, level int) []byte {
 	if l.includeProcSequence {
 		l.procSequence++
 	}
@@ -659,10 +660,12 @@ func (l *Logger) Write(buf []byte) (int, error) {
 			l.stderr.Write(withNL)
 		}
 	}
+
 	l.writeLock.Lock()
-	b := l.encode(buf, level)
-	_, err := l.send(b)
-	l.writeLock.Unlock()
+	defer l.writeLock.Unlock()
+
+	b := l.encodeLocked(buf, level)
+	_, err := l.sendLocked(b)
 	return len(buf), err
 }