Metamask: ReferenceError: Buffer is not defined

Understanding Login Authentication in MetaMask

As a digital asset enthusiast, you are probably familiar with Metamask, the popular wallet app that allows for seamless interaction between your Ethereum accounts and decentralized applications (dApps). One of the interesting features of Metamask is its ability to handle signedTypedData authentication using Web3.js. However, I would like to take this opportunity to delve into a common issue that can arise when implementing MetaMask’s signed-data login token: the undefined ‘Buffer’ error.

Problem

When you try to validate signedTypedData with Metamask, it expects a Buffer object as input. This is because the eth.util.signTypedData() function returns an Ethereum transaction hash in hexadecimal string format (e.g., “0x…”).

However, when working with typed data or other types that do not conform to the buffer interface, such as signedTypedData, Metamask throws an error. Specifically, it throws a “ReferenceError” because the buffer is not defined.

The Solution

To resolve this issue, you will need to make sure that the data you are inputting is compatible with the buffer interface. Here are some approaches:

• Define your data type. typed: If possible, define your exact type. signedTypedData in the Buffer object. You can use TypeScript or JavaScript built-in types to specify this.

import * as Web3 from 'web3';
const typedData = {
// your data typed here,
type: Buffer.from('your-type-here'),
value: "your-value-here",
};
const transactionHash = web3.eth.util.signTypedData(typedData);

• Use a polyfill: If you are working with older browsers or versions of Node.js without support for TypedArrays, consider using a polyfill such as typedarray-buffer or typedarray-polyfill. These libraries provide an alternative implementation of the buffer interface.

const { buffer } = require('buffer');
const typedData = {
type: "Buffer",
value: Buffer.from('your-type-here'),
};
const transactionHash = web3.eth.util.signTypedData(typedData);

Conclusion

The implementation of the MetaMask typed login token requires some care when working with typed data. By following the tips mentioned above, you should be able to resolve the undefined Buffer error and successfully validate signedTypedData with your application.

Remember to always check the official documentation for any library or API you use, as their behavior may change over time. Happy coding!

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