Add stderr and file log backends

backend.go

@@ -1,40 +1,74 @@
 package logging
 
 import (
+	"errors"
+	"fmt"
 	"io"
 	"os"
 )
 
 type Backend interface {
 	Write(*Record) error
-	SetLevel(Level)
 	SetFormatter(*Formatter)
+	SetLevel(Level)
+	Level() Level
 }
 
-type StdoutBackend struct {
+//
+// Backend to write in file-like objects
+//
+
+type FileBackend struct {
 	l         io.Writer
-	level     Level
 	formatter *Formatter
+	level     Level
 }
 
-func NewStdoutBackend() (b *StdoutBackend) {
+// Creates a new backend to write the logs on the standard output
-	b = &StdoutBackend{
+func NewStdoutBackend() (b *FileBackend) {
+	b = &FileBackend{
 		l:         os.Stdout,
 		formatter: &defaultFormatter,
 	}
 	return
 }
 
-func (b StdoutBackend) Write(r *Record) error {
+// Creates a new backend to write the logs on the error output
+func NewStderrBackend() (b *FileBackend) {
+	b = &FileBackend{
+		l:         os.Stderr,
+		formatter: &defaultFormatter,
+	}
+	return
+}
+
+// Creates a new backend to write the logs in a given file
+func NewFileBackend(filename string) (b *FileBackend, e error) {
+	filename_fd, err := os.OpenFile(filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0644)
+	if err != nil {
+		e = errors.New(fmt.Sprintf("Cannot open log file %s (%s)", filename, err.Error()))
+	}
+	b = &FileBackend{
+		l:         filename_fd,
+		formatter: &defaultFormatter,
+	}
+	return
+}
+
+func (b FileBackend) Write(r *Record) error {
 	text := (*b.formatter)(r)
 	_, err := io.WriteString(b.l, text)
 	return err
 }
 
-func (b *StdoutBackend) SetLevel(l Level) {
+func (b *FileBackend) SetLevel(l Level) {
 	b.level = l
 }
 
-func (b *StdoutBackend) SetFormatter(f *Formatter) {
+func (b *FileBackend) Level() Level {
+	return b.level
+}
+
+func (b *FileBackend) SetFormatter(f *Formatter) {
 	b.formatter = f
 }