uncaughtException when instantiating JsonRpcProvider and adding subscription in bad network conditions

[deodad]

Ethers Version

6.2.0

Search Terms

No response

Describe the Problem

When instantiating a JsonRpcProvider and setting up a listener, an thrown exception is thrown if the rpc url returns a bad status code and there doesn't seem to be any way to catch it.

https://replit.com/@deodad/Ethers-Uncaught-Exception?v=1

Code Snippet

import { JsonRpcProvider } from "ethers";
import nock from 'nock';

process.on('uncaughtException', (err) => {
  console.error("but instead it is caught here, uncaught exception:", err)
  process.exit(1);
})

nock.back.setMode('lockdown');
nock('https://eth-goerli.g.alchemy.com').post('/v2/apikey').reply(500);

/** 
 * How do we instantiate a JsonRpcProvider and attach event listeners 
 * in a way that we avoid any uncaughtExceptions?
*/
(async () => {
  try {
    const provider = new JsonRpcProvider('https://eth-goerli.g.alchemy.com/v2/apikey');
    await provider.on('block', console.log)
  } catch (e) {
    console.log("we want to deal with the error here")
  }
})()

Contract ABI

No response

Errors

No response

Environment

node.js (v12 or newer)

Environment (Other)

No response

[ricmoo]

I found the problem, which was in the poll loop of the PollingBlockSubscriber; when it crashed it threw and failed to re-schedule the next poll.

You still won't be able to get the error in the try block, since the provider.on is actually successful at installing a listener. It's during the next listener poll that things go awry.

In the next minor bump, I'll add an "error" event and a Type that includes the necessary details, that can be listened to in order to trap event errors.

But I think for your purposes, just "not crashing" is your main concern. :)

You won't get any block events until the network conditions have improved; but once the link is back up, you will get all previous blocks backfilled.

Make sense?

[ricmoo]

(also, huge thanks for providing a concise example to reproduce against ;))

[ricmoo]

This should be fixed in v6.2.1. Let me know if you have any feedback. And I'll add the "error" event in v6.3.

Thanks!

[deodad]

@ricmoo incredible thank you for turning this around so quickly!

the error emitter sounds great and yes for now not crashing is our main concern :)