Adding back-off during retries for REST handler

[LJNeon]

Which application or package is this feature request for?

rest

Feature

I want to implement exponential back-off when a request is retried due to a 5xx or timeout error. However currently retries are always immediate, so I would need to set RESTOptions#retries to 0 and then create a function like this:

await handleRetry(() => client.users.send(/* .. */));
// instead of
await client.users.send(/* .. */);

This is far from ideal, and it seems reasonable to implement this in the library instead.

Ideal solution or implementation

Adding to the RESTOptions seems like the obvious choice.

Alternative solutions or implementations

No response

Other context

This was sparked by a question in the discord server.

[imnaiyar]

Relevant reasoning

[aroman]

strongly agree. we've discovered that sometimes, discord's API calls take 10s+, despite not being ratelimited (i.e. they do not return 429, just take a long time).

our workaround is lowering the timeout from 15s (default) to 3s. however, it'd be much nicer to be able to do some sort of exponential backoff.

As for an API, I'd propose that timeout could take a number or a function, like:

timeout: (retryCount: number) => number
so you could let API users implement whatever timeout logic they want