gateway: handle non-JSON upstream responses with 502 and upstream text

gateway/main.py

@@ -61,16 +61,23 @@ async def _get_health(client: httpx.AsyncClient, base: str) -> Dict[str, Any]:
 async def _post_json(client: httpx.AsyncClient, url: str, payload: Dict[str, Any]) -> Dict[str, Any]:
     r = await client.post(url, json=payload)
     if r.status_code >= 400:
-        raise HTTPException(status_code=502, detail=f"Upstream error {url}: {r.status_code} {r.text[:200]}")
+        raise HTTPException(status_code=502, detail=f"Upstream error {url}: {r.status_code} {r.text[:1000]}")
-    return r.json()
+    try:
+        return r.json()
+    except Exception:
+        # upstream returned non-JSON (HTML error page or empty body)
+        raise HTTPException(status_code=502, detail=f"Upstream returned non-JSON at {url}: {r.status_code} {r.text[:1000]}")
 
 
 async def _post_file(client: httpx.AsyncClient, url: str, data: bytes, fields: Dict[str, Any]) -> Dict[str, Any]:
     files = {"file": ("image", data, "application/octet-stream")}
     r = await client.post(url, data={k: str(v) for k, v in fields.items()}, files=files)
     if r.status_code >= 400:
-        raise HTTPException(status_code=502, detail=f"Upstream error {url}: {r.status_code} {r.text[:200]}")
+        raise HTTPException(status_code=502, detail=f"Upstream error {url}: {r.status_code} {r.text[:1000]}")
-    return r.json()
+    try:
+        return r.json()
+    except Exception:
+        raise HTTPException(status_code=502, detail=f"Upstream returned non-JSON at {url}: {r.status_code} {r.text[:1000]}")
 
 
 @app.get("/health")