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Metamask: Understanding ERC-20 Transfers and Approvals
As we continue to build applications that interact with the Ethereum blockchain, it is essential to understand how Metamask facilitates secure transactions between the browser and contract addresses. In this article, we will delve into the world of ERC-20 transfers and explore the concept of approvals.
ERC-20: A Smart Contract Standard for Token Transactions
Ethereum introduced the ERC-20 standard in 2015 as a set of rules and protocols that govern the creation, trading, and transfer of tokens on the blockchain. These tokens are digital assets that can be stored, transferred, and used across different platforms.
ERC-20 tokens have gained widespread popularity due to their versatility and ease of use. They can represent various types of digital assets, such as cryptocurrencies like Bitcoin or Ethereum, as well as financial instruments like stablecoins and utility tokens.
Transferring ERC-20 tokens from the browser to the contract
When a user wants to transfer an ERC-20 token from the browser to a contract address, they interact with the MetaMask wallet. Here’s what happens under the hood:
- The user initiates the transaction by sending a “transfer” message to the Ethereum network.
- Metamask verifies the identity of the sender and ensures that the transaction is authorized using their private key.
- Once verified, the transaction is broadcast to the blockchain, where it is validated by nodes such as L1 gas nodes or Layer 2 networks (e.g. Optimism or Polygon).
- If the transaction is valid, the contract address with the receiving ERC-20 token is identified and the transfer is made.
Approvals: The Key to Secure Transactions
To facilitate secure transactions, Metamask introduces a concept called approvals. Approvals allow users to specify the conditions under which they will approve or reject a transaction. This adds an extra layer of security to transactions, ensuring that only authorized parties can initiate transfers.
There are two types of approvals:
- Approval Types
: Users can choose from predefined approval types, such as:
true: Approve the transfer.
false: Reject the transfer.
- Conditional Approval: Users can also specify the conditions under which transactions are allowed or rejected. For example, a user could approve transfers only when they have a minimum balance of ERC-20 tokens.
How to Request an Approval in User-Side Code
To enable an ERC-20 transfer using Metamask and user-side approvals, you can follow these steps:
- Initialize the MetaMask wallet with your private key.
- Submit a transaction to initiate the transfer (e.g., method “transfer”).
- Define a conditional approval using the “approvalType” field (e.g., “true”) or specify conditions for approval (e.g., minimum balance requirement).
Here is an example code snippet in Solidity:
solidity pragma ^0.8.0;
import "
contract MyContract {
using SafeERC20 for (address, uint256);
struct token {
address tokenAddress;
balance uint256;
}
function transfer(address recipient, amount uint256) public {
// Define approval type
bool approved = false;
// Specify conditions for approval
if (balance > 10) { // minimum balance requirement
// Approve transfer with conditional approval
require(approved, "Transfer not allowed");
return;
}
// Initiate transaction using MetaMask API
//...
}
}
In this example, users can approve or reject transactions based on their conditions.
