feat: libp2phttp /http-path

[MarcoPolo]

Adds support for multiaddr URIs that contain /http-path components. In other words, this works now:

client := http.Client{Transport: &libp2phttp.Host{ options... }}
client.Get("multiaddr:/dns/example.com/tls/http/http-path/some%2fpath")
// equivalent to
client.Get("https://example.com/some/path")
// And of course works with any libp2p stream transport:
client.Get("multiaddr:/dnsaddr/example.com/p2p/QmFoo/http-path/some%2fpath")

[sukunrt]

We need this parsing only if it's a http multiaddr, right? Otherwise we can just use the addr?

I would prefer calling this only when it's an /http multiaddr because parseMultiaddr looks specific to parsing /http multiaddrs. Having said that, I haven't been able to find any multiaddr that would make parseMultiaddr do something funny.

[MarcoPolo]

We need this parsing only if it's a http multiaddr, right?

Both. We use the http-path, host, and port in both code paths.

Would you prefer we name this something else?

[sukunrt]

You only need parsed.peer in that code path so I was wondering if we should just get the peerID from the addr in that code path.

This is fine too though.

[MarcoPolo]

We need http path as well

[sukunrt]

You only need parsed.peer in that code path so I was wondering if we should just get the peerID from the addr in that code path.

This is fine too though.

[sukunrt]

You can reuse this error and avoid allocation for all the calls. This looks like it'll be used often.