net/http: Client and Transport don't support RFC 6874

[mikioh]

On all released versions, Get with a literal IPv6 address with a zone identifier fails. For example,

u := &url.URL{Scheme: "http", Host: "[::1%lo0]:8080"}
resp, err := http.DefaultClient.Get(u.String())

and

resp, err := http.Get("http://[::1%lo0]:8080")

return parse http://[::1%lo0]:8080: hexadecimal escape in host or parse [::1%lo0]:8080: invalid URL escape "%lo" error. After the fix of #6530, the former works well but the latter still fails.

[mikioh]

In the latter case with the fix of #6530, the Host line of request headers is wrong.

Host: [::1%en0]:8080

On the wire, the line must be

Host: [::1%25en0]:8080

[mikioh]

A correction. As per RFC 6874, the line must be

Host: [::1]:8080

The RFC says that an HTTP client, proxy, or other intermediary MUST remove any ZoneID attached to an outgoing URI, as it has only local significance at the sending host.

[gopherbot]

CL https://golang.org/cl/13296 mentions this issue.