feat: add stdlog writer

logger.go

@@ -77,6 +77,8 @@ type Logger interface {
  // Error logs an error message.
  Error(msg interface{}, keyval ...interface{})
 
+ // StandardLoggerWriter returns a io.Writer that can be used along with the
+ StandardLoggerWriter(...StandardLoggerOption) io.Writer
  // StandardLogger returns a standard logger from this logger.
  StandardLogger(...StandardLoggerOption) *log.Logger
 }

stdlog.go

@@ -1,16 +1,17 @@
 package log
 
 import (
+ "io"
  "log"
  "strings"
 )
 
-type stdLogger struct {
+type stdLoggerWriter struct {
  l *logger
  opt *StandardLoggerOption
 }
 
-func (l *stdLogger) Write(p []byte) (n int, err error) {
+func (l *stdLoggerWriter) Write(p []byte) (n int, err error) {
  str := strings.TrimSuffix(string(p), "\n")
 
  if l.opt != nil {
@@ -44,24 +45,31 @@ func (l *stdLogger) Write(p []byte) (n int, err error) {
  return len(p), nil
 }
 
-// StandardLoggerOption can be used to configure the standard log addapter.
+// StandardLoggerOption can be used to configure the standard log adapter.
 type StandardLoggerOption struct {
  ForceLevel Level
 }
 
-// StandardLogger returns a standard logger from Logger. The returned logger
-// can infer log levels from message prefix. Expected prefixes are DEBUG, INFO,
-// WARN, ERROR, and ERR.
-func (l *logger) StandardLogger(opts ...StandardLoggerOption) *log.Logger {
+// StandardLoggerWriter is a io.Writer that can be used along with the standard
+// log library. The writer can infer log levels from message prefix. Expected
+// prefixes are DEBUG, INFO, WARN, ERROR, and ERR.
+func (l *logger) StandardLoggerWriter(opts ...StandardLoggerOption) io.Writer {
  nl := *l
  // The caller stack is
  // log.Printf() -> l.Output() -> l.out.Write(stdLogger.Write)
  nl.callerOffset += 3
- sl := &stdLogger{
+ sl := &stdLoggerWriter{
  l: &nl,
  }
  if len(opts) > 0 {
  sl.opt = &opts[0]
  }
- return log.New(sl, "", 0)
+ return sl
+}
+
+// StandardLogger returns a standard logger from Logger. The returned logger
+// can infer log levels from message prefix. Expected prefixes are DEBUG, INFO,
+// WARN, ERROR, and ERR.
+func (l *logger) StandardLogger(opts ...StandardLoggerOption) *log.Logger {
+ return log.New(l.StandardLoggerWriter(opts...), "", 0)
 }

stdlog_test.go

@@ -80,3 +80,37 @@ func TestStdLog_forceLevel(t *testing.T) {
  })
  }
 }
+
+func TestStdLog_writer(t *testing.T) {
+ var buf bytes.Buffer
+ logger := New(WithOutput(&buf), WithCaller(), WithNoStyles())
+ cases := []struct {
+ name string
+ expected string
+ level Level
+ }{
+ {
+ name: "debug",
+ expected: "",
+ level: DebugLevel,
+ },
+ {
+ name: "info",
+ expected: "INFO <log/stdlog_test.go:112> coffee\n",
+ level: InfoLevel,
+ },
+ {
+ name: "error",
+ expected: "ERROR <log/stdlog_test.go:112> coffee\n",
+ level: ErrorLevel,
+ },
+ }
+ for _, c := range cases {
+ buf.Reset()
+ t.Run(c.name, func(t *testing.T) {
+ l := log.New(logger.StandardLoggerWriter(StandardLoggerOption{ForceLevel: c.level}), "", 0)
+ l.Print("coffee")
+ assert.Equal(t, c.expected, buf.String())
+ })
+ }
+}