fix: use starlette middleware to intercept /backend/ requests before Gradio routing

app.py

@@ -718,46 +718,55 @@ try:
         description="Backend API for Fake News Detection. REST API available at /backend/api/*"
     )
 
-    # ── 3. FastAPI proxy: /backend/{path} → Flask on 127.0.0.1:7861/{path} ──
+    # ── 3. FastAPI middleware proxy: /backend/{path} → Flask on 127.0.0.1:7861/{path} ──
     _SKIP_HEADERS = {'host', 'content-length', 'transfer-encoding', 'content-encoding'}
 
-    @demo.app.api_route(
-        "/backend/{path:path}",
-        methods=["GET", "POST", "PUT", "DELETE", "OPTIONS", "HEAD", "PATCH"]
-    )
-    async def flask_proxy(request: _FastAPIRequest, path: str):
-        """Transparent proxy forwarding /backend/* → internal Flask server."""
-        target_url = f"http://127.0.0.1:{_FLASK_PORT}/{path}"
-        fwd_headers = {
-            k: v for k, v in request.headers.items()
-            if k.lower() not in _SKIP_HEADERS
-        }
-        try:
-            async with httpx.AsyncClient(timeout=60) as client:
-                resp = await client.request(
-                    method=request.method,
-                    url=target_url,
-                    headers=fwd_headers,
-                    content=await request.body(),
-                    params=dict(request.query_params),
-                    follow_redirects=True,
-                )
-            resp_headers = {
-                k: v for k, v in resp.headers.items()
+    @demo.app.middleware("http")
+    async def flask_proxy_middleware(request: _FastAPIRequest, call_next):
+        if request.url.path.startswith("/backend/"):
+            target_path = request.url.path[len("/backend"):]
+            if not target_path.startswith("/"):
+                target_path = "/" + target_path
+                
+            target_url = f"http://127.0.0.1:{_FLASK_PORT}{target_path}"
+            
+            # Read the request body
+            body = await request.body()
+            
+            fwd_headers = {
+                k: v for k, v in request.headers.items()
                 if k.lower() not in _SKIP_HEADERS
             }
-            return _FastAPIResponse(
-                content=resp.content,
-                status_code=resp.status_code,
-                headers=resp_headers,
-            )
-        except Exception as proxy_err:
-            logger.error(f"Proxy error for /{path}: {proxy_err}")
-            return _FastAPIResponse(
-                content=b'{"error":"Backend proxy error","detail":"' + str(proxy_err).encode() + b'"}',
-                status_code=502,
-                headers={"Content-Type": "application/json"},
-            )
+            
+            try:
+                async with httpx.AsyncClient(timeout=60) as client:
+                    resp = await client.request(
+                        method=request.method,
+                        url=target_url,
+                        headers=fwd_headers,
+                        content=body,
+                        params=dict(request.query_params),
+                        follow_redirects=True,
+                    )
+                resp_headers = {
+                    k: v for k, v in resp.headers.items()
+                    if k.lower() not in _SKIP_HEADERS
+                }
+                return _FastAPIResponse(
+                    content=resp.content,
+                    status_code=resp.status_code,
+                    headers=resp_headers,
+                )
+            except Exception as proxy_err:
+                logger.error(f"Proxy error for {request.url.path}: {proxy_err}")
+                return _FastAPIResponse(
+                    content=b'{"error":"Backend proxy error","detail":"' + str(proxy_err).encode() + b'"}',
+                    status_code=502,
+                    headers={"Content-Type": "application/json"},
+                )
+                
+        # If not /backend/*, let Gradio handle it normally
+        return await call_next(request)
 
     _GRADIO_AVAILABLE = True