Add ErrorHandler global to allow handling of write errors

README.md

@@ -479,6 +479,7 @@ Some settings can be changed and will by applied to all loggers:
     // using the Dur method.
 * `DurationFieldUnit`: Sets the unit of the fields added by `Dur` (default: `time.Millisecond`).
 * `DurationFieldInteger`: If set to true, `Dur` fields are formatted as integers instead of floats.
+* `ErrorHandler`: Called whenever zerolog fails to write an event on its output. If not set, an error is printed on the stderr. This handler must be thread safe and non-blocking.
 
 ## Field Types
 

event.go

@@ -137,9 +137,13 @@ func (e *Event) msg(msg string) {
 		defer e.done(msg)
 	}
 	if err := e.write(); err != nil {
+		if ErrorHandler != nil {
+			ErrorHandler(err)
+		} else {
 			fmt.Fprintf(os.Stderr, "zerolog: could not write event: %v\n", err)
 		}
 	}
+}
 
 // Fields is a helper function to use a map to set fields using type assertion.
 func (e *Event) Fields(fields map[string]interface{}) *Event {

globals.go

@@ -37,6 +37,11 @@ var (
 	// DurationFieldInteger renders Dur fields as integer instead of float if
 	// set to true.
 	DurationFieldInteger = false
+
+	// ErrorHandler is called whenever zerolog fails to write an event on its
+	// output. If not set, an error is printed on the stderr. This handler must
+	// be thread safe and non-blocking.
+	ErrorHandler func(err error)
 )
 
 var (

log_test.go

@@ -640,3 +640,24 @@ func TestErrorMarshalFunc(t *testing.T) {
 		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 	}
 }
+
+type errWriter struct {
+	error
+}
+
+func (w errWriter) Write(p []byte) (n int, err error) {
+	return 0, w.error
+}
+
+func TestErrorHandler(t *testing.T) {
+	var got error
+	want := errors.New("write error")
+	ErrorHandler = func(err error) {
+		got = err
+	}
+	log := New(errWriter{want})
+	log.Log().Msg("test")
+	if got != want {
+		t.Errorf("ErrorHandler err = %#v, want %#v", got, want)
+	}
+}