README.md

polling-account-fetcher

Fetch Solana Accounts on an interval while keeping the amount of requests under the rate limit of the RPC

Building from source

yarn install
yarn build

Overview

The polling account fetcher was created in response to the GenesysGo rate limit on their previously free unlimited RPC
By sending 10 x 100 publickeys in one getMultipleAccounts rpc call we can theoretically reach 10k accounts per second (assuming there is a 10tps rate limit).

How it works

Depending on if you are using a anchor program or a custom decoding function you can add a public key to the accounts map via the provided addProgram or addConstructAccount methods.
For example PythNetwork's javascript client doesn't use an Anchor Program/IDL, but does provide a function to decode the PythPriceData.
The PollingAccountFetcher constructor takes two parameters: frequency ( in milliseconds ) and requestsPerSecond
The PollingAccountFetcher.fetch() is called by setInterval(() => {}, frequency)
Once all the data is returned, the pollingAccountFetcher will parse each returned account data and send the data back through the AccountToPoll's onFetch(data: any) => void callback
If there is an issue during the rpc call it will retry 5 times before aborting

Install

yarn add polling-account-fetcher

Usage

import { PollingAccountsFetcher } from 'polling-account-fetcher';

// new PollingAccountsFetcher(rpcUrl: string, frequencyInMS: number, requestsPerSecond: number)
const pollingAccountsFetcher = new PollingAccountsFetcher('https://api.mainnet-beta.solana.com', 1000, 5);

// this example of adding a program account uses the 'accountKey' to decode the data received from the getMultipleAccounts rpc call
pollingAccountsFetcher.addProgram(accountKey, accountPublicKey, Program<Idl>, (data : any) => {
    console.log(data);
}, error => {
    console.error(error);
}, initialAccountData?);

//this example of adding an account but uses a custom decode function (not an anchor program)
pollingAccountsFetcher.addConstructAccount(accountPublicKey, (data: Buffer) => {
    // function used to parse the account buffer
    return parseAccountBuffer(data);
}, (decodedAccountData: any) => {
    // do something with the decodedAccountData
}, (error) => {
    console.error(error);
}, initialAccountData?);

// start the account polling
pollingAccountsFetcher.start();

// stop the account polling
pollingAccountsFetcher.stop();

// the latest data on any account can be accesed through the accounts map: Map<string, AccountToPoll<T>>
const account = pollingAccountsFetcher.accounts.get(publicKey.toBase58())

export type AccountToPoll<T> = {
    data: T // the latest data (account)
    raw: string // the latest raw data retrieved
    accountKey: string // account on the anchor program (used for decoding the buffer data returned by the rpc call)
    accountPublicKey: string // the publickey of the account
    program: Program<Idl> // the anchor program associated with the account
    slot: number // the latest slot from the retrieved data (to prevent updating to old data)
    constructAccount: (buffer: Buffer) => any // used by .addConstructAccount
    onFetch: (data: T) => void // called when new data is retrieved 
    onError: (error: any) => void // called when there was an error
}

// this is called by the polling account fetcher, it is here to help in understanding of how the polling account fetcher works
// this is how the polling account fetcher decodes the data retrieved from the RPC call
// if the accountToPoll has an associated anchor program, use the anchor program to decode the account
// otherwise if there is a custom decode function on the accountToPoll use that
constructAccount(accountToPoll: AccountToPoll<any>, buffer: Buffer) : any {
    if (accountToPoll.program !== undefined) {
        return accountToPoll.program.account[
            accountToPoll.accountKey
        ].coder.accounts.decode(
            this.capitalize(accountToPoll.accountKey),
            buffer
        );
    } else if (accountToPoll.constructAccount !== undefined) {
        return accountToPoll.constructAccount(buffer);
    }
}