Added backend formatter

Makes it possible to have different formatters for different backends.

Fixes #25 and #31.

Author: op

format.go

@@ -345,3 +345,24 @@ func formatFuncName(v fmtVerb, f string) string {
 	}
 	panic("unexpected func formatter")
 }
+
+// backendFormatter combines a backend with a specific formatter making it
+// possible to have different log formats for different backends.
+type backendFormatter struct {
+	b Backend
+	f Formatter
+}
+
+// NewBackendFormatter creates a new backend which makes all records that
+// passes through it beeing formatted by the specific formatter.
+func NewBackendFormatter(b Backend, f Formatter) *backendFormatter {
+	return &backendFormatter{b, f}
+}
+
+// Log implements the Log function required by the Backend interface.
+func (bf *backendFormatter) Log(level Level, calldepth int, r *Record) error {
+	// Make a shallow copy of the record and replace any formatter
+	r2 := *r
+	r2.formatter = bf.f
+	return bf.b.Log(level, calldepth+1, &r2)
+}

format_test.go

@@ -32,6 +32,10 @@ func logAndGetLine(backend *MemoryBackend) string {
 	return MemoryRecordN(backend, 0).Formatted(1)
 }
 
+func getLastLine(backend *MemoryBackend) string {
+	return MemoryRecordN(backend, 0).Formatted(1)
+}
+
 func realFunc(backend *MemoryBackend) string {
 	return logAndGetLine(backend)
 }
@@ -138,6 +142,28 @@ func TestFormatFuncName(t *testing.T) {
 	}
 }
 
+func TestBackendFormatter(t *testing.T) {
+	InitForTesting(DEBUG)
+
+	// Create two backends and wrap one of the with a backend formatter
+	b1 := NewMemoryBackend(1)
+	b2 := NewMemoryBackend(1)
+
+	f := MustStringFormatter("%{level} %{message}")
+	bf := NewBackendFormatter(b2, f)
+
+	SetBackend(b1, bf)
+
+	log := MustGetLogger("module")
+	log.Info("foo")
+	if "foo" != getLastLine(b1) {
+		t.Errorf("Unexpected line: %s", getLastLine(b1))
+	}
+	if "INFO foo" != getLastLine(b2) {
+		t.Errorf("Unexpected line: %s", getLastLine(b2))
+	}
+}
+
 func BenchmarkStringFormatter(b *testing.B) {
 	fmt := "%{time:2006-01-02T15:04:05} %{level:.1s} %{id:04d} %{module} %{message}"
 	f := MustStringFormatter(fmt)

level.go

@@ -107,6 +107,7 @@ func (l *moduleLeveled) IsEnabledFor(level Level, module string) bool {
 
 func (l *moduleLeveled) Log(level Level, calldepth int, rec *Record) (err error) {
 	if l.IsEnabledFor(level, rec.Module) {
+		// TODO get rid of traces of formatter here. BackendFormatter should be used.
 		rec.formatter = l.getFormatterAndCacheCurrent()
 		err = l.backend.Log(level, calldepth+1, rec)
 	}

multi.go

@@ -4,6 +4,8 @@
 
 package logging
 
+// TODO remove Level stuff from the multi logger. Do one thing.
+
 // multiLogger is a log multiplexer which can be used to utilize multiple log
 // backends at once.
 type multiLogger struct {