Improve documentation.

1 files changed, 23 insertions, 16 deletions

diff --git a/sd_daemon/log.go b/sd_daemon/log.go
index 9fa62d4..9b23f31 100644
--- a/sd_daemon/log.go
+++ b/sd_daemon/log.go
@@ -25,14 +25,21 @@ import (
 	"sync"
 )
 
-// Logger writes "<N>"-prefixed lines to an io.Writer, where N is a
+// A Logger writes "<N>"-prefixed lines to an io.Writer, where N is a
 // syslog priority number.  It implements mostly the same interface as
-// "log/syslog".Writer.
+// syslog.Writer.
 //
 // You probably don't need any instance of this other than the
 // constant "Log", which uses os.Stderr as the writer.  It is
 // implemented as a struct rather than a set of functions so that it
 // can be passed around as an implementation of an interface.
+//
+// Each logging operation makes a single call to the underlying
+// Writer's Write method.  A single logging operation may be multiple
+// lines; each line will have the prefix, and they will all be written
+// in the same Write.  A Logger can be used simultaneously from
+// multiple goroutines; it guarantees to serialize access to the
+// Writer.
 type Logger struct {
 	mu  sync.Mutex
 	out io.Writer
@@ -44,9 +51,9 @@ func NewLogger(w io.Writer) *Logger {
 	return &Logger{out: w}
 }
 
-// Log is a Logger that use used very similarly to
-// "log/syslog".Writer, but writes to os.Stderr under the assumption
-// that stderr is forwarded to syslog/journald.
+// Log is a Logger whose interface is very similar to syslog.Writer,
+// but writes to os.Stderr under the assumption that stderr is
+// forwarded to syslog (or journald).
 //
 // You are encouraged to use stderr unless you have a good reason to
 // talk to syslog or journald directly.
@@ -56,7 +63,7 @@ var Log = NewLogger(os.Stderr)
 //
 //     *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("<>")
+	var b [22]byte // 22 = ceil(log_10(2^64))+len("<>")
 	b[len(b)-1] = '>'
 	i := len(b) - 2
 	for n >= 10 {
@@ -72,7 +79,7 @@ func appendPrefix(buf []byte, n syslog.Priority) []byte {
 
 // 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) WriteString(pri syslog.Priority, msg string) (n int, err error) {
 	l.mu.Lock()
 	defer l.mu.Unlock()
 
@@ -80,12 +87,12 @@ func (l *Logger) WriteString(level syslog.Priority, msg string) (n int, err erro
 
 	// The following is a cheap version of:
 	//
-	//    prefix := fmt.Sprintf("<%d>", level)
+	//    prefix := fmt.Sprintf("<%d>", pri)
 	//    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
+	l.buf = appendPrefix(l.buf, pri) // possible allocation
 	prefix := l.buf
 	nlines := strings.Count(msg, "\n") + 1
 	n = len(msg) + len(prefix)*nlines + 1
@@ -109,7 +116,7 @@ func (l *Logger) WriteString(level syslog.Priority, msg string) (n int, err erro
 
 // WriteString writes a message with the specified priority to the
 // log.
-func (l *Logger) WriteBytes(level syslog.Priority, msg []byte) (n int, err error) {
+func (l *Logger) WriteBytes(pri syslog.Priority, msg []byte) (n int, err error) {
 	// Copy/pasted from WriteString and
 	//  * `strings.` -> `bytes.`
 	//  * `"\n"` -> `[]byte{'\n'}`
@@ -119,7 +126,7 @@ func (l *Logger) WriteBytes(level syslog.Priority, msg []byte) (n int, err error
 	msg = bytes.TrimSuffix(msg, []byte{'\n'})
 
 	l.buf = l.buf[:0]
-	l.buf = appendPrefix(l.buf, level) // possible allocation
+	l.buf = appendPrefix(l.buf, pri) // possible allocation
 	prefix := l.buf
 	nlines := bytes.Count(msg, []byte{'\n'}) + 1
 	n = len(msg) + len(prefix)*nlines + 1
@@ -142,16 +149,16 @@ func (l *Logger) WriteBytes(level syslog.Priority, msg []byte) (n int, err error
 }
 
 type loggerWriter struct {
-	log   *Logger
-	level syslog.Priority
+	log *Logger
+	pri syslog.Priority
 }
 
 func (lw loggerWriter) Write(p []byte) (n int, err error) {
-	return lw.log.WriteBytes(lw.level, p)
+	return lw.log.WriteBytes(lw.pri, p)
 }
 
 // Writer returns an io.Writer that writes messages with the specified
 // priority to the log.
-func (l *Logger) Writer(level syslog.Priority) io.Writer {
-	return loggerWriter{log: l, level: level}
+func (l *Logger) Writer(pri syslog.Priority) io.Writer {
+	return loggerWriter{log: l, pri: pri}
 }