Use an Oracle to get a token value on Polygon? (Using web3.js)

oraclespolygonsolidityweb3js

I'm currently developing a simple project. After a payment is done, I call a smart contract to mint some coins and send them to a wallet.

All good over there, but I need to know the value in USD of the payment done to know how much coins will I mint.

I'm currently working on the Mumbai Testnet, so my coins would be MATIC and This Coin

I read about "aggregator interface v3" on this link:

https://stackoverflow.com/questions/69233678/using-web3js-get-coin-price-on-uniswap-and-sushiswap-exchange-without-using-thei

However, I don't know exactly how to use it on my case. The example gets the price for ETH/USD pair on Kovan network, how do I get the address I would need to instanciate the aggregator? Would it work on Mumbai Testnet and/or Polygon Mainnet?

Of course, all this will be up on Polygon Mainnet so if the uses are different somehow, let me know!

Thanks for your time!

Best Answer

Uniswap oracles can be very useful, but they can also be quite risky. Bad actors can manipulate the price in the uniswap pool if the liquidity is low enough, then exploit your protocol using the manipulated price. The tellor oracle, alternatively, includes a token-incentivized dispute mechanism to prevent oracle manipulation for profit. Tellor relies on a network of anon reporters to submit good data, monitor it for faults, and dispute bad data if necessary.

You mentioned that you want to read the ETH/USD feed on chain. Reporters on tellor are currently maintaining that feed actively, so you could simply read the tellor oracle on chain using a getter function, without the need to maintain the feed in any way yourself.

Related Solutions

[Ethereum] how are we sending funds on polygon through contract

The issue is that your contract is not deployed on Mainnet.

It is deployed on Testnet, but on Mainnet there is no contract code associated with the address.

You should try to deploy it again on Mainnet. As you know, if you use the same address and same nonce as on testnet, you should have the same address for your Mainnet contract.

If you want to receive the MATIC that you sent to the address back, you should add a withdraw function to your contract that transfers all the contract balance to msg.sender. Otherwise, this MATIC will be lost forever.

EDIT: I think that this is your contract on Mainnet. The address is not the same as on Testnet, althought they both start by 0x39! You called the wrong address on Mainnet.

[Ethereum] Listen to events in the Polygon network using Web3.py

For future readers, apparently Polygon does not support eth_newFilter so a way to get events thru Web3 is subscribing to logs (currently available thru Web3.js) or using get_logs (if u wanna do it in python), I found an example in a reddit post, goes like this:

from web3 import Web3
from web3._utils.events import get_event_data

w3 = Web3(Web3.HTTPProvider("<Infura host>"))
contract = w3.eth.contract(address="0x33..", abi=abi['abi'])
event_template = contract.events.<EVENT_NAME>
events = w3.eth.get_logs({'fromBlock':from_block, 'toBlock': from_block+10000, 'address':"0x33.."})


def handle_event(event, event_template):
    try:
        result = get_event_data(event_template.web3.codec, event_template._get_event_abi(), event)
        return True, result
    except:
        return False, None

for event in events: 
    suc, res = self.handle_event(event=event, event_template=event_template)   
    if suc:
        print("Event found", res)

Best Answer

Related Solutions

[Ethereum] how are we sending funds on polygon through contract

[Ethereum] Listen to events in the Polygon network using Web3.py

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