Could someone in the Cloudflare community who is able please make sure that the maintainers of Cloudflare Warp receive the following bug report? I reported this via Warp’s in-app “report a bug” function a couple weeks ago, but never received a reply from a human.
I am testing Cloudflare Warp version 220.127.116.11 (20211004.9) on macOS.
When Cloudflare Warp is running and in the “connected” state, it incorrectly handles other programs trying to bind to a server socket.
This bug can be reproduced with a very simple (and commonly-needed) command:
python3 -m http.server
When Cloudflare Warp is enabled, this command hangs forever, never starting a local HTTP server.
After disabling or quitting Cloudflare Warp, it works.
I spent some time debugging this before I narrowed it down to Cloudflare Warp.
Eventually I figured out that it’s possible to work around this by explicitly passing an address via the “-b” flag, e.g.:
python3 -m http.server -b localhost
python3 -m http.server -b 0.0.0.0
Stepping through the path that the code in the Python standard library’s http/server.py is taking right before the hang occurs, this looks related to dual stack, which I think explains why passing an explicit
-b argument works around the bug:
Please let me know if any of the Cloudlfare Warp maintainers receive this bug report and are interested in fixing the bug.