Contract event listener not firing sometimes

[atropos0902]

I am using JsonRpcProvider and listen to contract event by following.

const provider = new ethers.providers.JsonRpcProvider(RPC_URL)
const signer = new ethers.Wallet(process.env.WALLET_PRIVATE_KEY, provider)
const managedSigner = new NonceManager(signer)

export const contract = new ethers.Contract(
  { CONTRACT_ADDRESS },
  { CONTRACT_ABI },
  managedSigner
)

contract.on('some event', () => {
 // handle event
})

The problem is that sometimes the contract event is not firing.
Did I miss something?

[atropos0902]

@ricmoo Seems like it's missing almost 20% of the events.
Can you please let me know how to resolve the issue?
Thank you!

[ricmoo]

What backend are you using?

[atropos0902]

What backend are you using?

node.js

[ricmoo]

I mean, infura vs alchemy vs running your own geth instance, etc. :)

[atropos0902]

Not quite sure since I am still a newbie in crypto.
Btw, I am working on bsc mainnet.

[atropos0902]

I mean, infura vs alchemy vs running your own geth instance, etc. :)

const provider = new ethers.providers.JsonRpcProvider(RPC_URL)
const signer = new ethers.Wallet(process.env.WALLET_PRIVATE_KEY, provider)
const managedSigner = new NonceManager(signer)

export const contract = new ethers.Contract(
  { CONTRACT_ADDRESS },
  { CONTRACT_ABI },
  managedSigner
)

contract.on('some event', () => {
 // handle event
})

[ricmoo]

What is the RPC_URL? Are you running your own infrastructure?

I’ve heard reports of BSC not being reliable for events, but I don’t personally use it, so perhaps someone else can provide more insight.

Moving to discussions.

[atropos0902]

I wonder if the block event is triggered before the logs are indexed, so the getBlockNumber returns a value so the getLogs for that value doesn’t get the event because the node hasn’t indexed them yet and by the time they are ready, it’s already moved into the next block.

I’m going to try putting a filter ID json-rpc provider, which may help this, in v5.6.

@ricmoo I think you are right.

[atropos0902]

I wonder if the block event is triggered before the logs are indexed, so the getBlockNumber returns a value so the getLogs for that value doesn’t get the event because the node hasn’t indexed them yet and by the time they are ready, it’s already moved into the next block.
I’m going to try putting a filter ID json-rpc provider, which may help this, in v5.6.

@ricmoo I think you are right.

@ricmoo Sorry...
I saw an event which is triggered (with contract.on) but still indexing on bsc scan.

[ricmoo]

Yes, I am fairly certain this is why it is only happening on BSC and Polygon, they must have modified their Geth to accommodate the decreased block time, to prevent event indexing from holding it up.

I have some ideas I’m putting into v6 that will help with this, but am considering putting them into v5.6 as well. I need to experiment though.

Is there a faucet for either of these networks anyone can share?

[atropos0902]

Can we have it on v5.6?
That's the only hope.

[claasahl]

@ricmoo

Is there a faucet for either of these networks anyone can share?

https://testnet.binance.org/faucet-smart

Hope this helps.

[shaanfye]

Have a related question - do we know why filtering for events with provider versus contract returns different values? When I use by contract, I get more information underneath like:

removeListener: [Function (anonymous)], getBlock: [Function (anonymous)], getTransaction: [Function (anonymous)], getTransactionReceipt: [Function (anonymous)], event: 'Transfer', eventSignature: 'Transfer(address,address,uint256)', decode: [Function (anonymous)], args: [ '0x68b3465833fb72A70ecDF485E0e4C7bD8665Fc45', '0xC70bB2736e218861DCa818d1e9f7A1930Fe61E5b', BigNumber { _hex: '0x1549dcdf5d730000', _isBigNumber: true }, src: '0x68b3465833fb72A70ecDF485E0e4C7bD8665Fc45', dst: '0xC70bB2736e218861DCa818d1e9f7A1930Fe61E5b', wad: BigNumber { _hex: '0x1549dcdf5d730000', _isBigNumber: true } ] }

[atropos0902]

I think you should parse the log for events from the provider.

[atropos0902]

#422
#487

[shaanfye]

I am trying to as such:
const get_transfer = async (contract) => { filter = { address: contract, topics: [ ethers.utils.id("Transfer(address,address,uint256)"), ], } provider.on(filter, (log, event) => { // Emitted whenever a DAI token transfer occurs console.log(log); console.log(event); }) }

The event portion shows up as "undefined."

[atropos0902]

@shaanfye You still didn't find the solution?

[ricmoo]

The contract has the ABI, so it knows how to interpret the events. That’s by design. :)

[ricmoo]

I believe this should have been address in v5.6 as part #2274.

Please try it out and let me know.#2478

Thanks! :)

[shivapendem]

If you are using or planning to get the active events then this is not a better option, but to have a update with the previous events even after some time here is the sample that is working for me from long time,

var web3 = new Web3(new Web3.providers.HttpProvider("<#infuralink>"));
const ABI=[....];
const Contract = new web3.eth.Contract(ABI,"contractaddress");

result would be the latest block number,
Contract.getPastEvents("EventName",{fromBlock: result - 1000 ,toBlock: result},(error, events) => {
// events
console.log(events);
});

[Haianh9999]

@ricmoo I am using JsonRpcProvider to listen for events from the blockchain with contract.on. However, sometimes I miss events. Could you help me to resolve it? 🙇

[Haianh9999]

I'm using ether with nodejs to listen event.

[formysister]

Depending on performance of RPC Url and it's nodes, contract event can't be missed generally. Missing contract event is never strange on EVM networks.

Catching smart contract events is not recommended for product projects. Instead of using contract events, you need to research about mempool monitoring.

Thank you