Use JsonRpcProvider as listener instead of WebsocketProvider

[therealjmj]

Describe the Feature

In ethers v5, we could listen for query events through a Json RPC, which I believe used a polling mechanism.

In ethers v6, the usage of eth_getFilterChanges restricts to websocket endpoints.

Is there a way to get the ethers v5 functionality for JSON event queries? Maybe with some kind of enum setting to decide whether to poll or filter? A few RPC providers (ie Pokt, and many public utility RPCs) don't even offer websocket RPCs, so the current functionality is a bit restrictive.

For context - our purpose uses a private RPC (proxied endpoint), which doesn't quite work for websockets. While suboptimal, additional polled queries are OK.

Code Example

No response

[therealjmj]

Ah! It looks like I can pass in option "polling" to JsonRpcProvider to get this behavior -

ethers.js/src.ts/providers/provider-jsonrpc.ts

Lines 632 to 637 in c785c1e

	if (sub.type === "event") {
	if (this._getOption("polling")) {
	return new PollingEventSubscriber(this, sub.filter);
	}
	return new FilterIdEventSubscriber(this, sub.filter);
	}

[therealjmj]

For anyone else experiencing this... try this wrapper class:

import { JsonRpcProvider } from 'ethers';

/**
 * Uses a setting in JsonRpcProvider to poll for events,
 * rather than using sparsely-implemented eth_filter events.
 */
export class PollingJsonRpcProvider extends JsonRpcProvider {
  constructor(url: string) {
    super(url, undefined, { polling: true });
  }
}

[ricmoo]

Yes, it is built-into the JsonRpcApiProvider super-class for anyone to enable the feature as necessary.

In v5, it never used eth_getFilterChanges and instead managed the sliding window manually (widening it and performing in-memory deduplication).

This allows you to force polling instead of filter IDs. Also note that if it tries using a filter ID and the result is null or the subscribe method throws, it will automatically downgrade to use polling. :)

I'm going to move this to a QA discussion and mark your above solution in case anyone looks for it in the future. :)