Sendgrid-csharp: Add Rate Limiting Support

[thinkingserious]

We would like to add support for v3 Web API rate limits, as described here.

_How would you like this to be implemented?_ Or please give a thumbs up to express your interest in us implementing to move this task up our queue.

PRs are always welcome as well :)

[xt0rted]

I've updated from v6 to v8 but I'm not using the library directly. Instead I'm using it via WebJobs.Extensions.SendGrid. Since this is a task that listens to a queue and sends the email as they come in, and there can be multiple instances if I scale out, having support for rate limit checking would be very useful.

[Jericho]

I'm curious how you will implement this feature.

In the StrongGrid library, I have added a IRetryStrategy parameter to the Client constructor which allows any custom strategy to be provided (this is particularly useful during unit testing where I can provide a mocked retry strategy) and also I have provided a default implementation of this interface which uses the "rate limit reset" header to calculate how much time to wait before retrying the same HTTP request.

[thinkingserious]

Hi @Jericho,

We have not considered implementation just yet, but it sounds like you have an elegant solution. I'll be sure to check out your implementation when the time comes.

[thinkingserious]

Please see here.

[Jericho]

@thinkingserious the PR you reference retries requests when a response with HTTP status code in the 500-504 range is received which does not address "rate limiting" because the HTTP status code is 429.

[thinkingserious]

Since there has been no activity on this issue since March 1, 2020, we are closing this issue. Please feel free to reopen or create a new issue if you still require assistance. Thank you!