Proxying relative URLs in redirects

In gitter I was chatting with @yuvipanda about the possibility of proxying one version of JupyterLab (specifically using --dev-mode) underneath the main one running in binder. https://gitter.im/jupyterhub/binder?at=5c42411983189945240fa7af

In trying this I ran into an issue with redirects. The proxied notebook server returns several redirects towards the default page, but when these redirects (e.g., to /lab), are received by the outer notebook server, they are then used to proxy to a page there rather than a page on the proxied server. This is not the effect I was looking for, and it seems to make pages in the proxied server entirely inaccessible if there is a redirect in the way.

This can be tested locally in this branch by running jupyter notebook --config=binder/config.py. Any thoughts on how to move forward?

I don’t know a ton about the right language around proxies, so apologies if this is using the wrong language or is easily fixable 😃

[manics]

• /proxy/12345/sub/path will rewrite the proxied URL so the application see /sub/path, but with HTTP headers to indicate it’s running under /proxy/12345
• /proxy/absolute/12345/sub/path passes the full URL directly so the application sees /proxy/absolute/12345/sub/path and no special headers are set

Also see my reply on https://discourse.jupyter.org/t/pgadmin-in-mybinder/365/6

[ian-r-rose]

@yuvipanda This was fixed by #85, right?