net/http: make Client follow redirects even if Request.Method is empty

Fixes #12705

Change-Id: I69639d2b03777835b2697ff349a00ccab410aa49
Reviewed-on: https://go-review.googlesource.com/17318Reviewed-by: Burcu Dogan <jbd@google.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/client.go

@@ -172,7 +172,7 @@ func (c *Client) send(req *Request) (*Response, error) {
 //
 // Generally Get, Post, or PostForm will be used instead of Do.
 func (c *Client) Do(req *Request) (resp *Response, err error) {
-	if req.Method == "GET" || req.Method == "HEAD" {
+	if req.Method == "" || req.Method == "GET" || req.Method == "HEAD" {
 		return c.doFollowingRedirects(req, shouldRedirectGet)
 	}
 	if req.Method == "POST" || req.Method == "PUT" {
@@ -423,6 +423,9 @@ func (c *Client) doFollowingRedirects(ireq *Request, shouldRedirect func(int) bo
 	}
 
 	method := ireq.Method
+	if method == "" {
+		method = "GET"
+	}
 	urlErr := &url.Error{
 		Op:  method[0:1] + strings.ToLower(method[1:]),
 		URL: urlStr,

src/net/http/client_test.go

@@ -230,6 +230,13 @@ func TestClientRedirects(t *testing.T) {
 		t.Errorf("with default client Do, expected error %q, got %q", e, g)
 	}
 
+	// Requests with an empty Method should also redirect (Issue 12705)
+	greq.Method = ""
+	_, err = c.Do(greq)
+	if e, g := "Get /?n=10: stopped after 10 redirects", fmt.Sprintf("%v", err); e != g {
+		t.Errorf("with default client Do and empty Method, expected error %q, got %q", e, g)
+	}
+
 	var checkErr error
 	var lastVia []*Request
 	c = &Client{CheckRedirect: func(_ *Request, via []*Request) error {