Smart API detection when loaded from non-standard API port in go-ipfs

[lidel]

This is something came to me when I was looking at ipfs/js-ipfs#1595 and #785.

If go-ipfs runs API on a different port than :5001, then webui will not be able to connect to it, even tho it was loaded from the API port 🙃

Instead, it will display error page where user needs to manually provide the port.

Its not bad, and may be enough for now, however I feel we could make it work automatically:

• (A) by appending parameter with custom API port to the webui URL printed to the console (see feat: show Web UI url in daemon output js-ipfs#1595 and discussion in Permalinks with API Address #785)
• (B) by adding a simple fallback to webui: if default port fails, check the same hostname but under the port from window.location.port ("" means 80/443)

I think (B) makes more sense, it would fix the issue for both go-ipfs and js-ipfs without adding any cruft to URL.

@olizilla thoughts?

[olizilla]

@lidel oh my yes! B is a very good idea.

[olizilla]

First pass of this is in ipfs-inactive/ipfs-redux-bundle#15