refactor(handlers): extract request validation logic to new function

Extract the request validation logic from ValidateRequest into a new ValidateRequestWithBody function to allow passing pre-read request bodies. Update all handler functions to use the new validation function for consistency and to avoid duplicate body reading.

frpc.go

@@ -108,7 +108,7 @@ func CreateInstanceHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	userID, _, err := ValidateRequest(w, r)
+	userID, _, err := ValidateRequestWithBody(w, r, body)
 	if err != nil {
 		SendErrorResponse(w, http.StatusUnauthorized, err.Error())
 		return
@@ -185,7 +185,14 @@ func DeleteInstanceHandler(w http.ResponseWriter, r *http.Request, instanceName
 		return
 	}
 
-	userID, _, err := ValidateRequest(w, r)
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		SendErrorResponse(w, http.StatusBadRequest, "failed to read request body")
+		return
+	}
+	defer r.Body.Close()
+
+	userID, _, err := ValidateRequestWithBody(w, r, body)
 	if err != nil {
 		SendErrorResponse(w, http.StatusUnauthorized, err.Error())
 		return
@@ -263,7 +270,7 @@ func ModifyInstanceHandler(w http.ResponseWriter, r *http.Request, instanceName
 		return
 	}
 
-	userID, _, err := ValidateRequest(w, r)
+	userID, _, err := ValidateRequestWithBody(w, r, body)
 	if err != nil {
 		SendErrorResponse(w, http.StatusUnauthorized, err.Error())
 		return
@@ -393,7 +400,14 @@ func ListInstancesHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	userID, _, err := ValidateRequest(w, r)
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		SendErrorResponse(w, http.StatusBadRequest, "failed to read request body")
+		return
+	}
+	defer r.Body.Close()
+
+	userID, _, err := ValidateRequestWithBody(w, r, body)
 	if err != nil {
 		SendErrorResponse(w, http.StatusUnauthorized, err.Error())
 		return

handlers.go

@@ -202,6 +202,10 @@ func ValidateRequest(w http.ResponseWriter, r *http.Request, requiredFields ...s
 	}
 	defer r.Body.Close()
 
+	return ValidateRequestWithBody(w, r, body, requiredFields...)
+}
+
+func ValidateRequestWithBody(w http.ResponseWriter, r *http.Request, body []byte, requiredFields ...string) (int, string, error) {
 	var reqMap map[string]interface{}
 	if err := json.Unmarshal(body, &reqMap); err != nil {
 		return 0, "", errors.New("invalid request format")