Merge pull request #15180 from tiborvass/fix-v1-mirror-fallback

registry: allow fallback on unknown errors

registry/registry.go

@@ -17,6 +17,7 @@ import (
 	"github.com/Sirupsen/logrus"
 	"github.com/docker/distribution/registry/api/errcode"
 	"github.com/docker/distribution/registry/api/v2"
+	"github.com/docker/distribution/registry/client"
 	"github.com/docker/distribution/registry/client/transport"
 	"github.com/docker/docker/autogen/dockerversion"
 	"github.com/docker/docker/pkg/parsers/kernel"
@@ -211,8 +212,14 @@ func ContinueOnError(err error) bool {
 		return ContinueOnError(v.Err)
 	case errcode.Error:
 		return shouldV2Fallback(v)
+	case *client.UnexpectedHTTPResponseError:
+		return true
 	}
-	return false
+	// let's be nice and fallback if the error is a completely
+	// unexpected one.
+	// If new errors have to be handled in some way, please
+	// add them to the switch above.
+	return true
 }
 
 // NewTransport returns a new HTTP transport. If tlsConfig is nil, it uses the