Requeing requests

[pavlokomarov]

Hi!

How can I implement such as RetryMiddleware, that should retry requests after some errors?

I see, that Guzzle Promise have not assign onRejected callback now, and exceptions that thrown in Client are not handled.

[pavlokomarov]

I were sketched some changes to implement this functionality in https://github.com/roach-php/core/pull/15