From 6bcd15ecf028bbb3e5cc7225f5fd110b06cf58b0 Mon Sep 17 00:00:00 2001
From: Olivier Poitrey <rs@rhapsodyk.net>
Date: Thu, 1 Jun 2017 23:17:28 -0700
Subject: [PATCH] Add support for zerolog as an output for stdlib logger

---
 README.md           | 15 +++++++++++++++
 event.go            | 14 +++++++-------
 log.go              | 12 ++++++++++++
 log_example_test.go | 14 ++++++++++++++
 4 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index a59fb5e..4e18417 100644
--- a/README.md
+++ b/README.md
@@ -154,6 +154,21 @@ log.Ctx(ctx).Info().Msg("hello world")
 // Output: {"component":"module","level":"info","message":"hello world"}
 ```
 
+### Set as standard logger output
+
+```go
+log := zerolog.New(os.Stdout).With().
+    Str("foo", "bar").
+    Logger()
+
+stdlog.SetFlags(0)
+stdlog.SetOutput(log)
+
+stdlog.Print("hello world")
+
+// Output: {"foo":"bar","message":"hello world"}
+```
+
 ### Integration with `net/http`
 
 The `github.com/rs/zerolog/hlog` package provides some helpers to integrate zerolog with `http.Handler`.
diff --git a/event.go b/event.go
index d15dda7..9bb3f56 100644
--- a/event.go
+++ b/event.go
@@ -38,12 +38,12 @@ func newEvent(w LevelWriter, level Level, enabled bool) *Event {
 	return e
 }
 
-func (e *Event) write() (n int, err error) {
+func (e *Event) write() (err error) {
 	if !e.enabled {
-		return 0, nil
+		return nil
 	}
 	e.buf = append(e.buf, '}', '\n')
-	n, err = e.w.WriteLevel(e.level, e.buf)
+	_, err = e.w.WriteLevel(e.level, e.buf)
 	eventPool.Put(e)
 	return
 }
@@ -58,9 +58,9 @@ func (e *Event) Enabled() bool {
 //
 // NOTICE: once this methid is called, the *Event should be disposed.
 // Calling Msg twice can have unexpected result.
-func (e *Event) Msg(msg string) (n int, err error) {
+func (e *Event) Msg(msg string) error {
 	if !e.enabled {
-		return 0, nil
+		return nil
 	}
 	if msg != "" {
 		e.buf = appendString(e.buf, MessageFieldName, msg)
@@ -75,9 +75,9 @@ func (e *Event) Msg(msg string) (n int, err error) {
 //
 // NOTICE: once this methid is called, the *Event should be disposed.
 // Calling Msg twice can have unexpected result.
-func (e *Event) Msgf(format string, v ...interface{}) (n int, err error) {
+func (e *Event) Msgf(format string, v ...interface{}) error {
 	if !e.enabled {
-		return 0, nil
+		return nil
 	}
 	msg := fmt.Sprintf(format, v...)
 	if msg != "" {
diff --git a/log.go b/log.go
index ab50cec..a74b310 100644
--- a/log.go
+++ b/log.go
@@ -249,6 +249,18 @@ func (l Logger) Log() *Event {
 	return l.newEvent(ErrorLevel, false, nil)
 }
 
+// Write implements the io.Writer interface. This is useful to set as a writer
+// for the standard library log.
+func (l Logger) Write(p []byte) (n int, err error) {
+	n = len(p)
+	if n > 0 && p[n-1] == '\n' {
+		// Trim CR added by stdlog.
+		p = p[0 : n-1]
+	}
+	err = l.Log().Msg(string(p))
+	return
+}
+
 func (l Logger) newEvent(level Level, addLevelField bool, done func(string)) *Event {
 	enabled := l.should(level)
 	if !enabled {
diff --git a/log_example_test.go b/log_example_test.go
index 863f3c1..a53d448 100644
--- a/log_example_test.go
+++ b/log_example_test.go
@@ -2,6 +2,7 @@ package zerolog_test
 
 import (
 	"errors"
+	stdlog "log"
 	"os"
 	"time"
 
@@ -90,6 +91,19 @@ func ExampleLogger_Error() {
 	// Output: {"level":"error","error":"some error","message":"error doing something"}
 }
 
+func ExampleLogger_Write() {
+	log := zerolog.New(os.Stdout).With().
+		Str("foo", "bar").
+		Logger()
+
+	stdlog.SetFlags(0)
+	stdlog.SetOutput(log)
+
+	stdlog.Print("hello world")
+
+	// Output: {"foo":"bar","message":"hello world"}
+}
+
 func ExampleLogger_Log() {
 	log := zerolog.New(os.Stdout)