Ensure a new entry data fields are empty

Fixes #795

hook_test.go

@@ -1,10 +1,13 @@
 package logrus
 
 import (
+	"bytes"
+	"encoding/json"
 	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 type TestHook struct {
@@ -85,6 +88,46 @@ func TestCanFireMultipleHooks(t *testing.T) {
 	})
 }
 
+type SingleLevelModifyHook struct {
+	ModifyHook
+}
+
+func (h *SingleLevelModifyHook) Levels() []Level {
+	return []Level{InfoLevel}
+}
+
+func TestHookEntryIsPristine(t *testing.T) {
+	l := New()
+	b := &bytes.Buffer{}
+	l.Formatter = &JSONFormatter{}
+	l.Out = b
+	l.AddHook(&SingleLevelModifyHook{})
+
+	l.Error("error message")
+	data := map[string]string{}
+	err := json.Unmarshal(b.Bytes(), &data)
+	require.NoError(t, err)
+	_, ok := data["wow"]
+	require.False(t, ok)
+	b.Reset()
+
+	l.Info("error message")
+	data = map[string]string{}
+	err = json.Unmarshal(b.Bytes(), &data)
+	require.NoError(t, err)
+	_, ok = data["wow"]
+	require.True(t, ok)
+	b.Reset()
+
+	l.Error("error message")
+	data = map[string]string{}
+	err = json.Unmarshal(b.Bytes(), &data)
+	require.NoError(t, err)
+	_, ok = data["wow"]
+	require.False(t, ok)
+	b.Reset()
+}
+
 type ErrorHook struct {
 	Fired bool
 }

logger.go

@@ -85,6 +85,7 @@ func (logger *Logger) newEntry() *Entry {
 }
 
 func (logger *Logger) releaseEntry(entry *Entry) {
+	entry.Data = map[string]interface{}{}
 	logger.entryPool.Put(entry)
 }