fixes a bug caused by an observer removing a field from an event

pkg/log/log.go

@@ -91,9 +91,19 @@ func (l *logger) log(typ int, fields []interface{}) {
 	for _, field := range fields {
 		e = l.processField(e, field)
 	}
+
 	for o, _ := range l.observers {
-		o.Log(e)
+		o.Log(clone(e))
+	}
+}
+
+func clone(e Event) Event {
+	c := Event{e.Type, e.Time, Fields{}, []string{}}
+	copy(c.Index, e.Index)
+	for k := range e.Fields {
+		c.Fields[k] = e.Fields[k]
 	}
+	return c
 }
 
 func (l *logger) processField(e Event, field interface{}) Event {

pkg/log/log_test.go

@@ -67,6 +67,32 @@ func TestBuiltinFieldProcessing(t *testing.T) {
 	}
 }
 
+type removePkg struct{}
+
+func (l *removePkg) Log(e Event) {
+	e.Remove("pkg")
+}
+
+func TestRemoveField(t *testing.T) {
+	t.Parallel()
+	for _, test := range []struct {
+		in   args
+		want Fields
+	}{
+		{in: args{"hello"}, want: Fields{"msg": "hello", "pkg": "testing"}},
+	} {
+		log := newLogger()
+		buffer := &logBuffer{}
+		buffer2 := &removePkg{}
+		log.RegisterObserver(buffer)
+		log.RegisterObserver(buffer2)
+		log.Info(test.in...)
+		if got := (*buffer)[0].Fields; !reflect.DeepEqual(got, test.want) {
+			t.Fatalf("Info(%#v) => %#v; want %#v", test.in, got, test.want)
+		}
+	}
+}
+
 func TestExtendedFieldProcessing(t *testing.T) {
 	t.Parallel()
 	fieldProcessor := func(e Event, field interface{}) (Event, bool) {