Use join path, remove unused method

Author: gregberge

packages/gitbook/src/lib/pages.ts

@@ -185,13 +185,3 @@ function flattenPages(
 
     return result;
 }
-
-/**
- * Returns a page not found if the request is not from the middleware.
- * Some pages can be
- */
-export async function checkIsFromMiddleware() {
-    const headerList = await headers();
-    // To check if the request is from the middleware, we check if the x-gitbook-token is set in the headers.
-    return Boolean(headerList.get('x-gitbook-token'));
-}

packages/gitbook/src/middleware.ts

@@ -277,7 +277,7 @@ export async function middleware(request: NextRequest) {
         headers.set('x-gitbook-visitor-token', resolved.visitorToken);
     }
 
-    const target = new URL('/middleware' + rewritePathname, request.nextUrl.toString());
+    const target = new URL(joinPath('/middleware', rewritePathname), request.nextUrl.toString());
     target.search = url.search;
 
     const response = writeCookies(