fix(context): prevent PostForm panic when Request is nil

initFormCache called ParseMultipartForm without checking c.Request,
so PostForm getters panicked on contexts from CreateTestContext.
Match initQueryCache by initializing an empty form cache when there
is no request.

Fixes #4772

Signed-off-by: elix3r <157088510+22elix3r@users.noreply.github.com>

context.go

@@ -647,14 +647,18 @@ func (c *Context) PostFormArray(key string) (values []string) {
 
 func (c *Context) initFormCache() {
 	if c.formCache == nil {
-		c.formCache = make(url.Values)
-		req := c.Request
-		if err := req.ParseMultipartForm(c.engine.MaxMultipartMemory); err != nil {
-			if !errors.Is(err, http.ErrNotMultipart) {
-				debugPrint("error on parse multipart form array: %v", err)
+		if c.Request != nil {
+			c.formCache = make(url.Values)
+			req := c.Request
+			if err := req.ParseMultipartForm(c.engine.MaxMultipartMemory); err != nil {
+				if !errors.Is(err, http.ErrNotMultipart) {
+					debugPrint("error on parse multipart form array: %v", err)
+				}
 			}
+			c.formCache = req.PostForm
+		} else {
+			c.formCache = url.Values{}
 		}
-		c.formCache = req.PostForm
 	}
 }
 

context_test.go

@@ -903,6 +903,33 @@ func TestContextDefaultQueryOnEmptyRequest(t *testing.T) {
 	})
 }
 
+func TestContextPostFormOnEmptyRequest(t *testing.T) {
+	c, _ := CreateTestContext(httptest.NewRecorder()) // here c.Request == nil
+	assert.NotPanics(t, func() {
+		value, ok := c.GetPostForm("key")
+		assert.False(t, ok)
+		assert.Empty(t, value)
+	})
+	assert.NotPanics(t, func() {
+		assert.Empty(t, c.PostForm("key"))
+	})
+	assert.NotPanics(t, func() {
+		assert.Equal(t, "fallback", c.DefaultPostForm("key", "fallback"))
+	})
+	assert.NotPanics(t, func() {
+		values, ok := c.GetPostFormArray("key")
+		assert.False(t, ok)
+		assert.Empty(t, values)
+		assert.Empty(t, c.PostFormArray("key"))
+	})
+	assert.NotPanics(t, func() {
+		dicts, ok := c.GetPostFormMap("key")
+		assert.False(t, ok)
+		assert.Empty(t, dicts)
+		assert.Empty(t, c.PostFormMap("key"))
+	})
+}
+
 func TestContextQueryAndPostForm(t *testing.T) {
 	c, _ := CreateTestContext(httptest.NewRecorder())
 	body := strings.NewReader("foo=bar&page=11&both=&foo=second")