net/http: API provides no way to follow 307 redirect for PUT or POST

[gopherbot]

by mdriley:

307 means "try the same verb on this new URL".

Client allows callers to define a redirect policy (CheckRedirect) for whether a given
HTTP redirect should or shouldn't be followed. However, Client.Do() passes an additional
policy to doFollowingRedirects() for GET, HEAD, PUT, and POST that is called before
CheckRedirect. For PUT and POST, that policy only redirects on 302 and 303. Further,
doFollowingRedirects() explicitly changes the verb from POST or PUT to GET on redirect.
As a result, the API provides no way for callers to follow a 307 redirect and keep the
verb.

I imagine the code was written not to follow these redirects because the spec for this
case says "the user agent MUST NOT automatically redirect the request unless it can
be confirmed by the user". The API should allow the CheckRedirect policy to say
such redirects are okay.

wget and curl both support these redirects.

[ianlancetaylor]

Comment 1:

Labels changed: added repo-main, release-go1.4.

[gopherbot]

Comment 2 by mdriley:

.Net's HttpWebRequest also supports this behavior if AllowAutoRedirect is set.
http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest.allowautoredirect.aspx

[bradfitz]

Comment 3:

You can do it by hand with by using http.Transport, which doesn't follow redirects.
How would we do this automatically if there's a Request.Body and we get the 307 after
we've written the body?  Or would this only be in the case where the 307 came in
response to a client Expect: 100-continue?

[gopherbot]

Comment 4 by mdriley:

Sure, this is possible with layers under Client -- but it would be a shame to lose the
convenience Client offers.
The current interface (where body is an io.Reader) would require a 100-continue step.
Given the extra round-trip that shouldn't be the default, so whatever option enables
redirecting PUT/POST would also enable 100-continue. Enabling 100-continue independent
of redirects could be a useful optimization for some callers but is probably a separate
feature request.
An optimization where the body is an io.ReadSeeker is also possible, but leads to cases
that can only be tested based on runtime type and server responses, which seems  fragile.

[rsc]

Comment 5:

It doesn't sound like we know how to do this safely.

Labels changed: added release-none, removed release-go1.4.

Status changed to Thinking.

[juliusv]

Is there any intention of fixing this? Go rewriting POST and PUT to GET upon 307 sounds like a clear violation of the HTTP/1.1 RFC: https://tools.ietf.org/html/rfc7231#section-6.4.7

The relevant client.go code that changes the method is here:

go/src/net/http/client.go

Lines 353 to 355 in 339cf98

	if ireq.Method == "POST" || ireq.Method == "PUT" {
	nreq.Method = "GET"
	}

[bradfitz]

@juliusv, I know where the code is but there is no proposal on how to fix this yet. See earlier comments.