fix call Stream() on copy of *Context (#1763)

context.go

@@ -78,7 +78,6 @@ func (c *Context) reset() {
 // This has to be used when the context has to be passed to a goroutine.
 func (c *Context) Copy() *Context {
 	var cp = *c
-	cp.writermem.ResponseWriter = nil
 	cp.Writer = &cp.writermem
 	cp.index = abortIndex
 	cp.handlers = nil

context_test.go

@@ -324,7 +324,6 @@ func TestContextCopy(t *testing.T) {
 
 	cp := c.Copy()
 	assert.Nil(t, cp.handlers)
-	assert.Nil(t, cp.writermem.ResponseWriter)
 	assert.Equal(t, &cp.writermem, cp.Writer.(*responseWriter))
 	assert.Equal(t, cp.Request, c.Request)
 	assert.Equal(t, cp.index, abortIndex)
@@ -1755,3 +1754,29 @@ func TestContextResetInHandler(t *testing.T) {
 		c.Next()
 	})
 }
+
+func TestContextStreamToCopyOfContext(t *testing.T) {
+	w := CreateTestResponseRecorder()
+	c, _ := CreateTestContext(w)
+
+	h := func(c *Context) {
+		nc := c.Copy()
+		nc.Stream(func(w io.Writer) bool {
+			w.Write([]byte("1"))
+			return false
+		})
+		c.String(http.StatusOK, "%s", "2")
+		w.closeClient()
+
+		nc.Stream(func(w io.Writer) bool {
+			w.Write([]byte("3"))
+			return false
+		})
+	}
+
+	assert.NotPanics(t, func() {
+		h(c)
+	})
+
+	assert.Equal(t, "12", w.Body.String())
+}