Work around gateway's trailing-slash redirects

[flyingzumwalt]

Background

@Gozala (2017-02-01):

IPFS node automatically redirects if path is for the directory but without / at the end. As a side effect following redirect happens:

fs://ipfs/${cid}/dir -> localhost:8080/ipfs/${cid_v1_base16}/dir/

While it would make more sense to either redirect as

fs://ipfs/${cid}/dir -> ipfs://${cid_v1_base16}/dir/

or redirect and 404 here

fs://ipfs/${cid}/dir -> ipfs://${cid_v1_base16}/dir

Obviously former would be more preferable, but somewhat unclear how to do that given that protocol handler has no knowledge of what’s actually under the requested URL

[ghost]

Example: https://ipfs.io/ipns/ipfs.io redirects to https://ipfs.io/ipns/ipfs.io/ -- this also breaks the "fake fs: path" in the address bar with the firefox addon.

We need this behaviour so that relative links in e.g. HTML documents always work.

One way around this issue is to set a special header in gateway requests from browser addons, and adjust the redirects in the gateway accordingly:

GET /ipns/ipfs.io HTTP/1.1
X-Redirect-Proto: dweb:

HTTP/1.1 301 Moved Permanently
Location: dweb:/ipns/ipfs.io/

[lidel]

I believe this old enough to be closed.
Addressing nuances will be tackled in https://github.com/ipfs/in-web-browsers/issues/147
(linking so we can refer back to this issue)