Limit and add optional "offset" & "count" parameters for "delegators" RPC

[shryder]

Summary

Limit the amount of delegators returned by the "delegators" RPC and add the optional parameters "offset" and "count".

What problem would be solved by this feature?

If I send multiple "delegators" RPC commands to my node for the rep NF#1 for example (it has ~16 million delegators)

1. If the server is not strong enough, it would crash after few requests. 100% disk and cpu load. (Is this a small attack vector maybe? create millions of dust accounts and delegate to nf#1 and call delegators rpc on public nodes)
2. If the server is strong enough, it would take a really long time to fetch all delegators.

The second problem is for services having to cache this data instead of getting up-to-date information through the RPC when desired.

Are there any previous requests for this feature?

I don't know

Do you have a suggested solution?

So my suggestion is

1. Set a limit to the amount of delegators returned by this RPC command
2. Add the optional fields "offset" and "count" to facilitate viewing this data.
3. Exclude dust amounts from the response (make the dust amount configurable maybe)

The first suggestion is so the weak nodes don't crash
The second and third is so the user/service doesn't have to wait a long time to get the current delegators list.

Explorers currently make the request every once in a while and cache the delegators instead of showing live data.

If this feature is approved, would you be willing to submit a pull request with the solution?

I would

Possible solution

No response

Supporting files

No response

[shryder]

The account_history RPC action has the count parameter required. Should it be the same for this RPC?