Rate-Limiting is not handled gracefully

[hmmwhatsthisdo]

Slack's API has a rate-limit of one message per second. PowerShell/PSSlack overruns even the (unspecified) burst-limit rather quickly, and doesn't make any attempt at waiting/re-trying the request.

Even more concerning is that Slack appears to threaten revoking API tokens if an application continues to send messages while being rate-limited.

It would likely be best to augment Send-SlackApi to be mindful of the burst/average rate-limit, and gracefully recover from HTTP 429 API responses.

[RamblingCookieMonster]

Hiyo!

Good catch! Completely agreed!

There might be some complexity though - A few initial thoughts:

• Rate limit might need to take place at a higher level, although presumably we can write a function to do this for us. For example, unless we store persistent data on what is happening in the module, logic like this would bypass any limits in Send-SlackApi. Doing it at the Send-SlackMessage or other higher level functions would work... but again, could be bypassed by a user level function using Send-SlackMessage quickly (I certainly do this, oops!)
• A generic pipeline rate-limiter that we could instruct users to use in cases of high volume might be worth considering. Maybe.

Anyhow! Totally open to ideas and PRs : D this would definitely be handy

Cheers!

[hmmwhatsthisdo]

So, a little bit of empirical testing appears to suggest that Slack's rate-limiting is using an algorithm similar to the leaky bucket algorithm, with a bucket size of 25 requests and a leak rate of 1 request per second. (I can reliably get around 30 requests in over a course of 5 seconds.)

My thoughts on how to handle rate-limiting on the client side are as follows:

• Implement a leaky bucket of a similar dimensions inside the module. This would likely entail a dictionary of strings (API tokens/URLs) to integers (current bucket volume) and DateTime objects (last drip). If the bucket is too full, have Send-SlackApi block until 1 second after the last "drip" time.
• Wrap Invoke-RestMethod in a try/catch to handle HTTP 429 responses from the Slack API. If we receive a 429, block for some amount of time (500ms/1s/etc.) and try again.
• Some combination of 1 and 2.