fix safeError & safeString for json format (#20)

json_logger.go

@@ -68,7 +68,7 @@ func safeString(str fmt.Stringer) (s string) {
 			if v := reflect.ValueOf(str); v.Kind() == reflect.Ptr && v.IsNil() {
 				s = "NULL"
 			} else {
-				panic(panicVal)
+				s = fmt.Sprintf("PANIC in String method: %v", panicVal)
 			}
 		}
 	}()
@@ -82,7 +82,7 @@ func safeError(err error) (s interface{}) {
 			if v := reflect.ValueOf(err); v.Kind() == reflect.Ptr && v.IsNil() {
 				s = nil
 			} else {
-				panic(panicVal)
+				s = fmt.Sprintf("PANIC in Error method: %v", panicVal)
 			}
 		}
 	}()

json_logger_test.go

@@ -60,6 +60,19 @@ func TestJSONLoggerNilStringerKey(t *testing.T) {
 	}
 }
 
+func TestJSONLoggerPanicStringerValue(t *testing.T) {
+	t.Parallel()
+
+	buf := &bytes.Buffer{}
+	logger := log.NewJSONLogger(buf)
+	if err := logger.Log("k", unsafeStringer{}); err != nil {
+		t.Fatal(err)
+	}
+	if want, have := `{"k":"PANIC in String method: error"}`+"\n", buf.String(); want != have {
+		t.Errorf("\nwant %#v\nhave %#v", want, have)
+	}
+}
+
 func TestJSONLoggerNilErrorValue(t *testing.T) {
 	t.Parallel()
 
@@ -73,6 +86,19 @@ func TestJSONLoggerNilErrorValue(t *testing.T) {
 	}
 }
 
+func TestJSONLoggerPanicErrorValue(t *testing.T) {
+	t.Parallel()
+
+	buf := &bytes.Buffer{}
+	logger := log.NewJSONLogger(buf)
+	if err := logger.Log("err", unsafeError{}); err != nil {
+		t.Fatal(err)
+	}
+	if want, have := `{"err":"PANIC in Error method: error"}`+"\n", buf.String(); want != have {
+		t.Errorf("\nwant %#v\nhave %#v", want, have)
+	}
+}
+
 func TestJSONLoggerNoHTMLEscape(t *testing.T) {
 	t.Parallel()
 	buf := &bytes.Buffer{}
@@ -160,6 +186,18 @@ func (s stringError) Error() string {
 	return string(s)
 }
 
+type unsafeStringer struct{}
+
+func (s unsafeStringer) String() string {
+	panic("error")
+}
+
+type unsafeError struct{}
+
+func (s unsafeError) Error() string {
+	panic("error")
+}
+
 func BenchmarkJSONLoggerSimple(b *testing.B) {
 	benchmarkRunner(b, log.NewJSONLogger(ioutil.Discard), baseMessage)
 }