Connection reset by peer when using CodeCompanion with Github Copilot, but can still use Copilot.vim

[lebedov]

CodeCompanion (revision e003fac) in Neovim 0.11.6 on MacOS 26.4.1 recently began displaying a curl "Connection reset by peer" error when I try to use it with an enterprise Github Copilot subscription over a corporate VPN (I was able to use it successfully a few days ago). I confirmed that trying to manually access https://api.githubcopilot.com/_ping with curl results in the same message. What is curious, though, is that I can still authenticate and use the copilot.vim plugin (revision a12fd56) successfully on the same system. Any thoughts as to why this is the case and why CodeCompanion might have started being unable to access Copilot? I'm using the default CodeCompanion setup, i.e., require('codecompanion').setup() in a lua block of my init.vim file.

[olimorris]

It can be difficult to keep pace with changes in Copilot especially as it's undocumented. In the past, I have used mitmproxy to investigate what's happeing in Copilot Chat in VS Code. Often it can be a missing header that does the trick.

Copilot.vim is of course the officially supported vim plugin so that might be sending over an identifier which is handled by the server.

[lebedov]

It turns out that the VPN I was using recently started filtering HTTP requests to enforce use of certain browsers, seemingly by user-agent because certain user-agent strings elicited normal HTTP responses while others did not. Once they tweaked that filtering, CodeCompanion was able to communicate with Github's Copilot API normally.

[olimorris]

Fantastic to hear and thanks for sharing that.