Ethers.js: JsonRpcProvider giving UnhandledPromiseRejectionWarning when detectNetwork rejects

[zemse]

Sorry if I'm interrupting too much. Running into issues :(

I am in a situation where ganache takes a while to start while my node js script loads up quickly. I am passing url into JsonRpcProvider constructor. But this throws up UnhandledPromiseRejectionWarning that I am not able to silence. It's breaking my pre-commit hook.

I digged in to the ethers.js code base and found that the networkOrReady promise is getting rejected in my case and there is no way to silence the warning.

https://github.com/ethers-io/ethers.js/blob/d817416bae2fbc7adb8391fd038613241b7ab8ba/packages/providers/src.ts/json-rpc-provider.ts#L233-L241

You can reproduce this with:

const ethers = require('ethers');

(async () => {
  try {
    const provider = new ethers.providers.JsonRpcProvider(
      'http://localhost:7545'
    );
  } catch (error) {
    console.log('Error is silenced');
  }
})();

Analyzing if this is a bug or not, if we take a web app example where user inputs a URL of node which can be valid or might not be. The developer should be able to catch the error without having it leak into the browser console.

Also, I started getting this when I updated from beta.189 to 5.0.1 (@ethersproject/providers moved from 5.0.0-beta.169 to 5.0.1).

[ricmoo]

It should allow a deferred detectNetwork on error, but maybe I broke that when I added the "any" network support.

Looking into this now.

(keep bugging me; I expect some rough patches with the new release, so I'd like to take care of them as soon as possible ;))

[ricmoo]

Oh, also keep in mind the constructor won't throw if the network cannot be detected, since that can only be discovered asynchronously.

I think it makes sense to make the provider.ready promise stall (with exponential backoff) until the network has been successfully detected though.

So, after this change you'll be able to do:

(() => {
  const provider = new JsonRpcProvider();
  await provider.ready;

  // Now the provider is ready to go and you can call it normally
})();

[ricmoo]

Can you try out 5.0.2 and let me know if that solves your issue?

[ricmoo]

(keeping in mind you will need to await provider.ready)

[zemse]

Thank you! This solves the problem.

[stoplion]

Is this still the way to go about fixing this error? I'm looking in the newest docs, not seeing any provider.ready in the new version.

[ricmoo]

If you are starting up a JsonRpcProvider before the node is running, this will still work exactly as you want. I’ll be sure to add it to the docs. I’m working on them this week. :)