copy: prevent potential deadlock if close before fully written

We also need an additional check to avoid setting both the error and
response which can create a race where they can arrive in the receiving
thread in either order.

If we hit an error, we don't need to send the response.

> There is a condition where the registry (unexpectedly, not to spec)
> returns 201 or 204 on the put before the body is fully written. I would
> expect that the http library would issue close and could fall into a
> deadlock here. We could just read respC and call setResponse. In that
> case ErrClosedPipe would get returned and Commit shouldn't be called
> anyway.

Signed-off-by: Justin Chadwell <me@jedevc.com>

remotes/docker/pusher.go

@@ -301,6 +301,7 @@ func (p dockerPusher) push(ctx context.Context, desc ocispec.Descriptor, ref str
 			err := remoteserrors.NewUnexpectedStatusErr(resp)
 			log.G(ctx).WithField("resp", resp).WithField("body", string(err.(remoteserrors.ErrUnexpectedStatus).Body)).Debug("unexpected response")
 			pushw.setError(err)
+			return
 		}
 		pushw.setResponse(resp)
 	}()
@@ -436,6 +437,8 @@ func (pw *pushWriter) Write(p []byte) (n int, err error) {
 			pw.Close()
 		case p := <-pw.pipeC:
 			return 0, pw.replacePipe(p)
+		case resp := <-pw.respC:
+			pw.setResponse(resp)
 		}
 	}
 	status.Offset += int64(n)