net/http: don't treat an alternate protocol as a known round tripper

As of CL 175857, the client code checks for known round tripper
implementations, and uses simpler cancellation code when it finds one.
However, this code was not considering the case of a request that uses
a user-defined protocol, where the user-defined protocol was
registered with the transport to use a different round tripper.
The effect was that round trippers that worked with earlier
releases would not see the expected cancellation semantics with tip.

Fixes #36820

Change-Id: I60e75b5d0badcfb9fde9d73a966ba1d3f7aa42b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/216618
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go
index 5fc60e1842..3ca7ce93b2 100644
--- a/src/net/http/transport_test.go
+++ b/src/net/http/transport_test.go
@@ -6143,3 +6143,35 @@ func TestTransportDecrementConnWhenIdleConnRemoved(t *testing.T) {
 		t.Errorf("error occurred: %v", err)
 	}
 }
+
+// Issue 36820
+// Test that we use the older backward compatible cancellation protocol
+// when a RoundTripper is registered via RegisterProtocol.
+func TestAltProtoCancellation(t *testing.T) {
+	defer afterTest(t)
+	tr := &Transport{}
+	c := &Client{
+		Transport: tr,
+		Timeout:   time.Millisecond,
+	}
+	tr.RegisterProtocol("timeout", timeoutProto{})
+	_, err := c.Get("timeout://bar.com/path")
+	if err == nil {
+		t.Error("request unexpectedly succeeded")
+	} else if !strings.Contains(err.Error(), timeoutProtoErr.Error()) {
+		t.Errorf("got error %q, does not contain expected string %q", err, timeoutProtoErr)
+	}
+}
+
+var timeoutProtoErr = errors.New("canceled as expected")
+
+type timeoutProto struct{}
+
+func (timeoutProto) RoundTrip(req *Request) (*Response, error) {
+	select {
+	case <-req.Cancel:
+		return nil, timeoutProtoErr
+	case <-time.After(5 * time.Second):
+		return nil, errors.New("request was not canceled")
+	}
+}