[release-branch.go1.14] net/http: make Transport.RoundTrip preserve Requests

Ensure that the exact Request passed to Transport.RoundTrip
is returned in the Response. Do not replace the Request with
a copy when resetting the request body.

Updates #39533.
Fixes #40973.

Change-Id: Ie6fb080c24b0f6625b0761b7aa542af3d2411817
Reviewed-on: https://go-review.googlesource.com/c/go/+/237560
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/249880
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

src/net/http/transport.go

@@ -511,6 +511,7 @@ func (t *Transport) roundTrip(req *Request) (*Response, error) {
 		}
 	}
 
+	origReq := req
 	req = setupRewindBody(req)
 
 	if altRT := t.alternateRoundTripper(req); altRT != nil {
@@ -572,6 +573,7 @@ func (t *Transport) roundTrip(req *Request) (*Response, error) {
 			resp, err = pconn.roundTrip(treq)
 		}
 		if err == nil {
+			resp.Request = origReq
 			return resp, nil
 		}
 

src/net/http/transport_test.go

@@ -3490,7 +3490,8 @@ func TestRetryRequestsOnError(t *testing.T) {
 
 			for i := 0; i < 3; i++ {
 				t0 := time.Now()
-				res, err := c.Do(tc.req())
+				req := tc.req()
+				res, err := c.Do(req)
 				if err != nil {
 					if time.Since(t0) < MaxWriteWaitBeforeConnReuse/2 {
 						mu.Lock()
@@ -3501,6 +3502,9 @@ func TestRetryRequestsOnError(t *testing.T) {
 					t.Skipf("connection likely wasn't recycled within %d, interfering with actual test; skipping", MaxWriteWaitBeforeConnReuse)
 				}
 				res.Body.Close()
+				if res.Request != req {
+					t.Errorf("Response.Request != original request; want identical Request")
+				}
 			}
 
 			mu.Lock()