feat: improve get post data. (#1920)

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

context.go

@@ -63,6 +63,10 @@ type Context struct {
 
 	// queryCache use url.ParseQuery cached the param query result from c.Request.URL.Query()
 	queryCache url.Values
+
+	// formCache use url.ParseQuery cached PostForm contains the parsed form data from POST, PATCH,
+	// or PUT body parameters.
+	formCache url.Values
 }
 
 /************************************/
@@ -454,16 +458,24 @@ func (c *Context) PostFormArray(key string) []string {
 	return values
 }
 
-// GetPostFormArray returns a slice of strings for a given form key, plus
-// a boolean value whether at least one value exists for the given key.
-func (c *Context) GetPostFormArray(key string) ([]string, bool) {
+func (c *Context) getFormCache() {
+	if c.formCache == nil {
+		c.formCache = make(url.Values)
 		req := c.Request
 		if err := req.ParseMultipartForm(c.engine.MaxMultipartMemory); err != nil {
 			if err != http.ErrNotMultipart {
 				debugPrint("error on parse multipart form array: %v", err)
 			}
 		}
-	if values := req.PostForm[key]; len(values) > 0 {
+		c.formCache = req.PostForm
+	}
+}
+
+// GetPostFormArray returns a slice of strings for a given form key, plus
+// a boolean value whether at least one value exists for the given key.
+func (c *Context) GetPostFormArray(key string) ([]string, bool) {
+	c.getFormCache()
+	if values := c.formCache[key]; len(values) > 0 {
 		return values, true
 	}
 	return []string{}, false