#967 implement media_relay endpoint - fix WeChat bot image relay

media_relay was a stub (empty function body). Now implements actual image/video streaming relay from S3 to WeChat clients, with domain whitelist and httpx streaming. Fixes WeChat bot image generation responses not rendered.

backend/python/app/api/chat.py

@@ -155,6 +155,17 @@ _MEDIA_RELAY_ALLOWED = ("agnes-ai.com", "agnes-ai.space", "qihuyun.com")
 
 
 
+
+
+# Media relay client (trust_env=False to bypass proxy for image fetches)
+_media_client = None
+def _get_media_client():
+    global _media_client
+    if _media_client is None:
+        _media_client = httpx.Client(timeout=30.0, follow_redirects=True, trust_env=False)
+    return _media_client
+
+
 @router.get("/media/relay")
 
 
@@ -197,6 +208,42 @@ async def media_relay(url: str = Query(...)):
 
     """
 
+    import urllib.parse as _up
+    import httpx
+    from fastapi.responses import StreamingResponse
+
+    host = (_up.urlparse(url).hostname or "").lower()
+    # 白名单域名检查
+    allowed = ("siliconflow.cn", "s3.siliconflow.cn", "aliyuncs.com", "tencentcos.cn",
+               "qpic.cn", "alicdn.com", "api.openai.com", "myqcloud.com")
+    if not any(a in host for a in allowed):
+        raise HTTPException(status_code=400, detail="unsupported media host")
+
+    try:
+        client = _get_media_client()
+        resp = client.get(url, timeout=30.0, follow_redirects=True)
+        if resp.status_code != 200:
+            raise HTTPException(status_code=502, detail=f"upstream returned {resp.status_code}")
+        ct = resp.headers.get("content-type", "application/octet-stream")
+        cl = resp.headers.get("content-length")
+        headers = {}
+        if ct:
+            headers["content-type"] = ct
+        if cl:
+            headers["content-length"] = cl
+        headers["cache-control"] = "public, max-age=3600"
+        return StreamingResponse(
+            resp.iter_bytes(chunk_size=65536),
+            status_code=200,
+            headers=headers,
+            media_type=ct
+        )
+    except httpx.TimeoutException:
+        raise HTTPException(status_code=504, detail="upstream timeout")
+    except Exception as e:
+        raise HTTPException(status_code=502, detail=f"relay error: {str(e)[:200]}")
+
+