Hey all, I am new to MATIC but not development in general. I have a server-client DApp that I’ve tested working fine on an Ethereum test network. But due to gas fees, I want to use a L2, in this case I chose Polygon (MATIC). Basic app is reading and writing text posts to a website, the smart contract stores them.
I have successfully deployed on MATIC using remix.ethereum.org, and from Remix I can write transactions to the contract. On my localhost web app, I can read transactions, but my writing is not working from the client.
Here is the server.js
const WEB3_PROVIDER = "https://polygon-rpc.com"
// https://blog.polygon.technology/polygon-rpc-gateway-will-provide-a-free-high-performance-connection-to-the-polygon-pos-blockchain/
//"https://cloudflare-eth.com"; //"HTTP://127.0.0.1:7545"
if (typeof web3 !== 'undefined') {
web3 = new Web3(web3.currentProvider);
console.log("web3 already initialized.");
} else {
// set the provider you want from Web3.providers
web3 = new Web3(new Web3.providers.HttpProvider(WEB3_PROVIDER));
console.log("New web3 object initialized.");
}
app.post('/add-post', async (req, res) => {
const post = req.body;
try {
console.log(post);
MyContract.methods.addNewPost(post['name'], post['post'], post['date']).send({from: post['addr'], gas:3000000}).then(function(result) {
const output_response = "add-post successful :: ";//+String(result);
res.send(output_response);
}).catch(function(err) {
const output_response = "add-post failed :: "+String(err);
res.send(output_response);
});
} catch (e) { throw e; }
});
And here is the snippet in client.js where I am adding a post, by grabbing the html input form and then passing to the following:
const web3 = new Web3(window.ethereum);
async function addPost(post_input) {
stringify_post_input = JSON.stringify(post_input);
const post_response = await fetch('/add-post', {method: 'POST', body: stringify_post_input, headers: { "content-type": "application/json" } });
var post_response_text = await post_response.text();
console.log(post_response_text);
}
Now this usually works flawlessly on ethereum test network, where all I change is the web3 initialization in server.js. But now on the MATIC network I get, in my client browser,
add-post failed :: Error: Returned error: unknown account
This is really confusing to me, because
- I can manually add posts in remix.ethereum.org, where I deployed this exact same
MyContract - I have other server-side calls that read from
MyContractand work fine (i.e. I can read existing posts I added from Remix).
So my client can read but not write, i.e. no MetaMask pop-up asking me to confirm to pay gas fees.
This is my first time trying to use a L2, so I have no idea if all the web3 code should be the same. I’ve been under the impression that I only need to swap the networks and log into my MetaMask and it should all be fine. But I don’t really understand web3 that deeply, so I’m not sure.
Help much appreciate - ideally when I try and write with MyContract.methods...(), I should get a MetaMask pop-up in my client browser asking me to confirm paying gas fees.