server: fix empty response for /cors-proxy (#26656)

tools/server/tests/unit/test_proxy.py

@@ -1,5 +1,7 @@
 import pytest
 from utils import *
+import threading
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 
 server = ServerPreset.tinyllama2()
 
@@ -39,3 +41,31 @@ def test_mcp_proxy_custom_port():
     res = server.make_request("GET", f"/cors-proxy?url=http://{server.server_host}:{server.server_port}/models")
     assert res.status_code == 200
     assert "data" in res.body
+
+
+def test_mcp_proxy_no_content():
+    # note: see issue #26598
+    class NoContentHandler(BaseHTTPRequestHandler):
+        def do_POST(self):
+            self.send_response(204)
+            self.end_headers()
+
+        def log_message(self, format, *args):
+            pass
+
+    target = ThreadingHTTPServer(("127.0.0.1", 0), NoContentHandler)
+    target_thread = threading.Thread(target=target.serve_forever, daemon=True)
+    target_thread.start()
+
+    try:
+        global server
+        server.ui_mcp_proxy = True
+        server.start()
+
+        res = server.make_request("POST", f"/cors-proxy?url=http://127.0.0.1:{target.server_port}/", data={})
+        assert res.status_code == 204
+        assert res.body in (None, b"", "")
+    finally:
+        target.shutdown()
+        target.server_close()
+