Handle stringified Gradio JSON bodies

app.py

@@ -2,6 +2,7 @@
 import logging
 import sys
 import os
+import json
 
 from constants import FONT_FAMILY_SHORT
 
@@ -404,6 +405,71 @@ class RootRedirectMiddleware(BaseHTTPMiddleware):
         return await call_next(request)
 
 
+class StringifiedGradioJSONMiddleware:
+    """Normalize JSON bodies double-encoded by the custom-domain proxy.
+
+    Requests sent through index.openhands.dev can arrive at Gradio as a JSON
+    string containing the real request object, which makes FastAPI validation
+    reject interactive callbacks with 422. Direct HF Space traffic already sends
+    proper JSON objects, so this only rewrites bodies that decode to strings.
+    """
+
+    def __init__(self, app):
+        self.app = app
+
+    async def __call__(self, scope, receive, send):
+        if (
+            scope["type"] == "http"
+            and scope.get("method") == "POST"
+            and scope.get("path", "").startswith("/gradio_api/")
+        ):
+            headers = {
+                key.decode("latin-1").lower(): value.decode("latin-1")
+                for key, value in scope.get("headers", [])
+            }
+            content_type = headers.get("content-type", "")
+            if "application/json" not in content_type:
+                return await self.app(scope, receive, send)
+
+            body_parts = []
+            while True:
+                message = await receive()
+                if message["type"] != "http.request":
+                    break
+                body_parts.append(message.get("body", b""))
+                if not message.get("more_body", False):
+                    break
+
+            body = b"".join(body_parts)
+            replacement_body = body
+            try:
+                decoded = json.loads(body)
+            except json.JSONDecodeError:
+                decoded = None
+
+            if isinstance(decoded, str):
+                stripped = decoded.strip()
+                if stripped.startswith(("{", "[")):
+                    replacement_body = stripped.encode("utf-8")
+
+            sent = False
+
+            async def replay_receive():
+                nonlocal sent
+                if sent:
+                    return {"type": "http.request", "body": b"", "more_body": False}
+                sent = True
+                return {
+                    "type": "http.request",
+                    "body": replacement_body,
+                    "more_body": False,
+                }
+
+            return await self.app(scope, replay_receive, send)
+
+        return await self.app(scope, receive, send)
+
+
 # Create a parent FastAPI app with redirect_slashes=False to prevent
 # automatic trailing slash redirects that cause issues with Gradio
 root_app = FastAPI(redirect_slashes=False)
@@ -415,6 +481,7 @@ root_app.mount("/api", api_app)
 
 # Mount Gradio app at root path
 app = gr.mount_gradio_app(root_app, demo, path="/")
+app = StringifiedGradioJSONMiddleware(app)
 logger.info("REST API mounted at /api, Gradio app mounted at /")
 
 
@@ -427,4 +494,3 @@ if __name__ == "__main__":
     logger.info(f"Launching app on {host}:{port}")
     uvicorn.run(app, host=host, port=port)
     logger.info("App launched successfully")
-