[Ethereum] Subscribing to events using ethers / hardhat network

ethers.jsexpresshardhatnodejswebsocket

I have a basic node express application. It connects to my locally running hardhat network via ethers & websocket. The connection seems to work, since I can query the blockchain succesfully (for instance await ethers.getBlockNumber() returns the correct block number).

However, my event listeners do not seem to work. The callbacks are never triggered.

Code example:
I'm using a loader function when I initialize the express app. When it is executed, I connect to the websocket provider. Then I successfully print the current block number to the console. Then I register an event listener on the "block" event (taken from the documentation). However, the listener never fires.

I'm connecting to the hardhat network, which is configured to produce a new block every five seconds (I can see that this is the case in the hardhat console). I would expect the listener to be fired every five seconds, always when a new block is mined.

What am I missing?

import { ethers } from "ethers";

export default async ({ expressApp }) => {
  const provider = new ethers.providers.WebSocketProvider(
    "ws://localhost:8545"
  );

  console.log(await provider.getBlockNumber());

  provider.on("block", () => console.log("new block"));

  expressLoader({ app: expressApp });
};

EDIT:
If I use the JsonRpcProviderinstead of WebSocketProviderand the following url http://localhost:8545 the callbacks are fired. What do I need to do to achieve the same behavior with websocket?

Best Answer

I do have the same issue.

nomiclabs has related open issue

provider.on("block", () => console.log("new block"));

Above code works via http -- because it has interval polling strategy underneath. So it is not notified via ws subscription, but requesting is there a new block.

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