refactor(api): 将请求验证逻辑提取到独立函数中

将handleDoH函数中的请求验证逻辑提取到独立的validateRequest函数中，提高代码可读性和可维护性

Author: RATING3PRO

src/app/api/doh/[provider]/route.ts

@@ -49,6 +49,31 @@ function logRequest(entry: LogEntry) {
 
 // --- Main Handler ---
 
+function validateRequest(url: URL): NextResponse | null {
+  // Validate Query String Length
+  if (url.search.length > MAX_QUERY_STRING_LENGTH) {
+    return new NextResponse('Query string too long', { status: 414 });
+  }
+
+  // Validate Domain Name (if present in 'name' param for JSON API)
+  const nameParam = url.searchParams.get('name');
+  
+  // Strict Validation for 'name' param
+  // If name parameter exists (even if empty), it must be valid and non-empty
+  if (url.searchParams.has('name')) {
+    if (!nameParam || nameParam.length === 0) {
+      return new NextResponse('Invalid domain: empty', { status: 400 });
+    }
+    if (nameParam.length > 253) {
+      return new NextResponse('Invalid domain: too long', { status: 400 });
+    }
+    if (!ALLOWED_DOMAIN_REGEX.test(nameParam)) {
+      return new NextResponse('Invalid domain: invalid characters', { status: 400 });
+    }
+  }
+  return null;
+}
+
 async function handleDoH(request: NextRequest, providerId: string) {
   const startTime = Date.now();
   let upstreamEndpoint = '';
@@ -57,31 +82,10 @@ async function handleDoH(request: NextRequest, providerId: string) {
   try {
     // 1. Input Validation
     const url = new URL(request.url);
-    
-    // Validate Query String Length
-    if (url.search.length > MAX_QUERY_STRING_LENGTH) {
-      responseStatus = 414;
-      return new NextResponse('Query string too long', { status: 414 });
-    }
-
-    // Validate Domain Name (if present in 'name' param for JSON API)
-    const nameParam = url.searchParams.get('name');
-    
-    // Strict Validation for 'name' param
-    // If name parameter exists (even if empty), it must be valid and non-empty
-    if (url.searchParams.has('name')) {
-      if (!nameParam || nameParam.length === 0) {
-        responseStatus = 400;
-        return new NextResponse('Invalid domain: empty', { status: 400 });
-      }
-      if (nameParam.length > 253) {
-        responseStatus = 400;
-        return new NextResponse('Invalid domain: too long', { status: 400 });
-      }
-      if (!ALLOWED_DOMAIN_REGEX.test(nameParam)) {
-        responseStatus = 400;
-        return new NextResponse('Invalid domain: invalid characters', { status: 400 });
-      }
+    const validationError = validateRequest(url);
+    if (validationError) {
+      responseStatus = validationError.status;
+      return validationError;
     }
 
     // 2. Provider Logic