net/http: doFollowingRedirects changes URL on redirect

[mattdr]

When following a redirect (e.g. 302), doFollowingRedirects will call URL.Parse() on the
value of the Location header, then use URL.String() from the resulting object as the new
URL. URL.String(URL.Parse(x)) doesn't round-trip. In particular, %2F gets flattened to
"/" but never converted back. This caveat is noted here:
http://golang.org/pkg/net/url/#URL.

As a result, a server can't actually redirect a Go client to a URL with %2F in it. This
disagrees with the behavior of at least Chrome and curl.

I expect the best option here is to make URL.Parse / URL.String round-trip, since the
%2F exception is weird and surprising. At the very least, net/http should keep the
verbatim URL when redirecting.

[ianlancetaylor]

Comment 1:

Labels changed: added repo-main, release-none.

[mattdr]

Comment 2:

Comments on this page suggest that developers trying to use Go to consume Google Cloud
APIs using Google-provided libraries are hitting similar problems with '/' not
round-tripping.
https://code.google.com/p/google-api-go-client/wiki/GettingStarted