fix: CORS error in the proxy command due to missing request headers (#176)

* fix: Preserve all client HTTP request headers

* fix: minor reformat

* fix: Exclude "Host" header to prevent CORS error due to proxying

* docs: Add news fragment

* fix: Better host header control

* refactor: Extract header translation and reuse it in websocket handler

Author: achimnol

changes/176.fix

@@ -0,0 +1 @@
+Fix CORS errors when running `backend.ai proxy` in a non-localhost IP address due to missing HTTP headers in the upstream API requests

src/ai/backend/client/cli/proxy.py

@@ -107,19 +107,29 @@ async def close_upstream(self):
             await self.up_conn.close()
 
 
+def _translate_headers(upstream_request: Request, client_request: Request) -> None:
+    for k, v in client_request.headers.items():
+        upstream_request.headers[k] = v
+    api_endpoint = upstream_request.config.endpoint
+    assert api_endpoint.host is not None
+    if api_endpoint.is_default_port():
+        upstream_request.headers['Host'] = api_endpoint.host
+    else:
+        upstream_request.headers['Host'] = f"{api_endpoint.host}:{api_endpoint.port}"
+
+
 async def web_handler(request):
     path = re.sub(r'^/?v(\d+)/', '/', request.path)
     try:
         # We treat all requests and responses as streaming universally
         # to be a transparent proxy.
         api_rqst = Request(
             request.method, path, request.content,
-            params=request.query)
+            params=request.query,
+        )
+        _translate_headers(api_rqst, request)
         if 'Content-Type' in request.headers:
-            api_rqst.content_type = request.content_type                        # set for signing
-            api_rqst.headers['Content-Type'] = request.headers['Content-Type']  # preserve raw value
-        if 'Content-Length' in request.headers:
-            api_rqst.headers['Content-Length'] = request.headers['Content-Length']
+            api_rqst.content_type = request.content_type  # set for signing
         # Uploading request body happens at the entering of the block,
         # and downloading response body happens in the read loop inside.
         async with api_rqst.fetch() as up_resp:
@@ -161,7 +171,9 @@ async def websocket_handler(request):
         api_rqst = Request(
             request.method, path, request.content,
             params=request.query,
-            content_type=request.content_type)
+            content_type=request.content_type,
+        )
+        _translate_headers(api_rqst, request)
         async with api_rqst.connect_websocket() as up_conn:
             down_conn = web.WebSocketResponse()
             await down_conn.prepare(request)