Debugging shows file/lineno.

logging/example/example.go

@@ -8,13 +8,17 @@ import (
 )
 
 var log = logging.Init()
-var olog = logging.New("subsystem #42", logging.LevelNotice)
+var olog, _ = logging.New("subsystem #42", logging.LevelNotice)
 
 func main() {
 	exampleNewWriters()
 	log.Notice("Hello, world.")
 	log.Warning("this program is about to end")
 
+	log.SetLevel(logging.LevelDebug)
+	log.Debug("hello world")
+	log.SetLevel(logging.LevelNotice)
+
 	olog.Print("now online")
 	logging.Suppress("olog")
 	olog.Print("extraneous information")
@@ -41,7 +45,7 @@ func exampleNewWriters() {
 	o := testio.NewBufCloser(nil)
 	e := testio.NewBufCloser(nil)
 
-	wlog := logging.NewFromWriters("writers", logging.DefaultLevel, o, e)
+	wlog, _ := logging.NewFromWriters("writers", logging.DefaultLevel, o, e)
 	wlog.Notice("hello, world")
 	wlog.Notice("some more things happening")
 	wlog.Warning("something suspicious has happened")

logging/levels.go

@@ -3,6 +3,7 @@ package logging
 import (
 	"fmt"
 	"os"
+	"runtime"
 	"time"
 )
 
@@ -43,6 +44,24 @@ const (
 	LevelFatal
 )
 
+// Cheap integer to fixed-width decimal ASCII.  Give a negative width
+// to avoid zero-padding. (From log/log.go in the standard library).
+func itoa(i int, wid int) string {
+	// Assemble decimal in reverse order.
+	var b [20]byte
+	bp := len(b) - 1
+	for i >= 10 || wid > 1 {
+		wid--
+		q := i / 10
+		b[bp] = byte('0' + i - q*10)
+		bp--
+		i = q
+	}
+	// i < 10
+	b[bp] = byte('0' + i)
+	return string(b[bp:])
+}
+
 func writeToOut(level Level) bool {
 	if level < LevelWarning {
 		return true
@@ -69,9 +88,17 @@ func (l *Logger) outputf(level Level, format string, v []interface{}) {
 	}
 
 	if level >= l.level {
+		domain := l.domain
+		if level == LevelDebug {
+			_, file, line, ok := runtime.Caller(2)
+			if ok {
+				domain += " " + file + ":" + itoa(line, -1)
+			}
+		}
+
 		format = fmt.Sprintf("%s %s: %s%s\n",
 			time.Now().Format(DateFormat),
-			l.domain, levelPrefix[level], format)
+			domain, levelPrefix[level], format)
 		if writeToOut(level) {
 			fmt.Fprintf(l.out, format, v...)
 		} else {
@@ -86,9 +113,17 @@ func (l *Logger) output(level Level, v []interface{}) {
 	}
 
 	if level >= l.level {
+		domain := l.domain
+		if level == LevelDebug {
+			_, file, line, ok := runtime.Caller(2)
+			if ok {
+				domain += " " + file + ":" + itoa(line, -1)
+			}
+		}
+
 		format := fmt.Sprintf("%s %s: %s",
 			time.Now().Format(DateFormat),
-			l.domain, levelPrefix[level])
+			domain, levelPrefix[level])
 		if writeToOut(level) {
 			fmt.Fprintf(l.out, format)
 			fmt.Fprintln(l.out, v...)
@@ -179,7 +214,8 @@ func (l *Logger) Info(v ...interface{}) {
 }
 
 // Debugf logs a formatted message at the "debug" level. The arguments
-// are handled in the same manner as fmt.Printf.
+// are handled in the same manner as fmt.Printf. Note that debug
+// logging will print the current
 func (l *Logger) Debugf(format string, v ...interface{}) {
 	l.outputf(LevelDebug, format, v)
 }

logging/log.go

@@ -1,8 +1,15 @@
-// Package logging is an adaptation of the CFSSL logging library. It
-// operates on domains, which are components for which logging can be
-// selectively enabled or disabled. It also differentiates between
-// normal messages (which are sent to standard output) and errors,
-// which are sent to standard error.
+// Package logging provides domain-based logging in the same style as
+// sylog. Domains are some name for which logging can be selectively
+// enabled or disabled. Logging also differentiates between normal
+// messages (which are sent to standard output) and errors, which are
+// sent to standard error; debug messages will also include the file
+// and line number.
+//
+// Domains are intended for identifying logging subystems. A domain
+// can be suppressed with Suppress, and re-enabled with Enable. There
+// are prefixed versions of these as well.
+//
+// This package was adapted from the CFSSL logging code.
 package logging
 
 import (
@@ -159,6 +166,10 @@ func NewFromWriters(domain string, level Level, w, e io.WriteCloser) (l *Logger,
 		return l, true
 	}
 
+	if w == nil {
+		w = os.Stdout
+	}
+
 	if e == nil {
 		e = w
 	}
@@ -179,19 +190,19 @@ func NewFromWriters(domain string, level Level, w, e io.WriteCloser) (l *Logger,
 // NewFile returns a new logger that opens the files for writing. If
 // multiplex is true, output will be multiplexed to standard output
 // and standard error as well.
-func NewFromFile(domain string, level Level, outFile, errFile string, multiplex bool) (*Logger, error) {
+func NewFromFile(domain string, level Level, outFile, errFile string, multiplex bool, flags int) (*Logger, error) {
 	l := &Logger{
 		domain: domain,
 		level:  level,
 		lock:   new(sync.Mutex),
 	}
 
-	outf, err := os.OpenFile(outFile, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	outf, err := os.OpenFile(outFile, os.O_APPEND|os.O_CREATE|os.O_WRONLY|flags, 0644)
 	if err != nil {
 		return nil, err
 	}
 
-	errf, err := os.OpenFile(errFile, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	errf, err := os.OpenFile(errFile, os.O_APPEND|os.O_CREATE|os.O_WRONLY|flags, 0644)
 	if err != nil {
 		return nil, err
 	}