registry: debugTransport should print with testing.T.Log

It should not print to STDOUT so that it only prints the debugTransport
output if there was an error in one of the registry tests.

Signed-off-by: Tibor Vass <tibor@docker.com>

docs/registry.go

@@ -200,23 +200,26 @@ func DockerHeaders(metaHeaders http.Header) []transport.RequestModifier {
 	return modifiers
 }
 
-type debugTransport struct{ http.RoundTripper }
+type debugTransport struct {
+	http.RoundTripper
+	log func(...interface{})
+}
 
 func (tr debugTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 	dump, err := httputil.DumpRequestOut(req, false)
 	if err != nil {
-		fmt.Println("could not dump request")
+		tr.log("could not dump request")
 	}
-	fmt.Println(string(dump))
+	tr.log(string(dump))
 	resp, err := tr.RoundTripper.RoundTrip(req)
 	if err != nil {
 		return nil, err
 	}
 	dump, err = httputil.DumpResponse(resp, false)
 	if err != nil {
-		fmt.Println("could not dump response")
+		tr.log("could not dump response")
 	}
-	fmt.Println(string(dump))
+	tr.log(string(dump))
 	return resp, err
 }
 

docs/registry_test.go

@@ -26,7 +26,7 @@ func spawnTestRegistrySession(t *testing.T) *Session {
 	if err != nil {
 		t.Fatal(err)
 	}
-	var tr http.RoundTripper = debugTransport{NewTransport(ReceiveTimeout, endpoint.IsSecure)}
+	var tr http.RoundTripper = debugTransport{NewTransport(ReceiveTimeout, endpoint.IsSecure), t.Log}
 	tr = transport.NewTransport(AuthTransport(tr, authConfig, false), DockerHeaders(nil)...)
 	client := HTTPClient(tr)
 	r, err := NewSession(client, authConfig, endpoint)