net/http: move extra redirect logic for 307/308 into redirectBehavior

Follow up of CL https://go-review.googlesource.com/32595.

Change-Id: I2b3ff7e6b2c764bb6bc5e9aa692d0aed79eb5626
Reviewed-on: https://go-review.googlesource.com/32750Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/client.go

@@ -388,17 +388,38 @@ func (c *Client) checkRedirect(req *Request, via []*Request) error {
 
 // redirectBehavior describes what should happen when the
 // client encounters a 3xx status code from the server
-func redirectBehavior(reqMethod string, serverStatus int) (redirectMethod string, canRedirect bool) {
-	switch serverStatus {
+func redirectBehavior(reqMethod string, resp *Response, via []*Request) (redirectMethod string, shouldRedirect bool) {
+	switch resp.StatusCode {
 	case 301, 302, 303:
 		redirectMethod = "GET"
-		canRedirect = true
+		shouldRedirect = true
 	case 307, 308:
 		redirectMethod = reqMethod
-		canRedirect = true
+		shouldRedirect = true
+
+		// Treat 307 and 308 specially, since they're new in
+		// Go 1.8, and they also require re-sending the request body.
+		loc := resp.Header.Get("Location")
+		if loc == "" {
+			// 308s have been observed in the wild being served
+			// without Location headers. Since Go 1.7 and earlier
+			// didn't follow these codes, just stop here instead
+			// of returning an error.
+			// See Issue 17773.
+			shouldRedirect = false
+			break
+		}
+		ireq := via[0]
+		if ireq.GetBody == nil && ireq.outgoingLength() != 0 {
+			// We had a request body, and 307/308 require
+			// re-sending it, but GetBody is not defined. So just
+			// return this response to the user instead of an
+			// error, like we did in Go 1.7 and earlier.
+			shouldRedirect = false
+		}
 	}
 
-	return redirectMethod, canRedirect
+	return redirectMethod, shouldRedirect
 }
 
 // Do sends an HTTP request and returns an HTTP response, following
@@ -536,35 +557,7 @@ func (c *Client) Do(req *Request) (*Response, error) {
 		}
 
 		var shouldRedirect bool
-		redirectMethod, shouldRedirect = redirectBehavior(req.Method, resp.StatusCode)
-
-		// Treat 307 and 308 specially, since they're new in
-		// Go 1.8, and they also require re-sending the
-		// request body.
-		//
-		// TODO: move this logic into func redirectBehavior?
-		// It would need to take a bunch more things then.
-		switch resp.StatusCode {
-		case 307, 308:
-			loc := resp.Header.Get("Location")
-			if loc == "" {
-				// 308s have been observed in the wild being served
-				// without Location headers. Since Go 1.7 and earlier
-				// didn't follow these codes, just stop here instead
-				// of returning an error.
-				shouldRedirect = false
-				break
-			}
-			ireq := reqs[0]
-			if ireq.GetBody == nil && ireq.outgoingLength() != 0 {
-				// We had a request body, and 307/308 require
-				// re-sending it, but GetBody is not defined. So just
-				// return this response to the user instead of an
-				// error, like we did in Go 1.7 and earlier.
-				shouldRedirect = false
-			}
-		}
-
+		redirectMethod, shouldRedirect = redirectBehavior(req.Method, resp, reqs)
 		if !shouldRedirect {
 			return resp, nil
 		}