Approving sell token

Simple orders / Basic orders

Part 1/ Basic orders/Approving sell token

For an order to be tradeable on CoW Protocol, the owner needs to approve the GPv2VaultRelayer to spend the token they want to trade.

A list of the core deployed contracts can be found here.

Contract (token) interaction

For interacting with contracts, the tutorials use ethers.js.

To interact with a contract, we need to know:

• the contract address
• the ABI

Additionally, if we want to make a transaction, we must have a signer (e.g. a wallet).

Contract address

The contract to be interacted with is the token we want to trade. In this tutorial, we use the wxDAI token, and assign it's address 0xe91d153e0b41518a2ce8dd3d7944fa863463a97d to a const.

At the same time, we assign the address of the GPv2VaultRelayer to a const:

import type { Web3Provider } from '@ethersproject/providers';

export async function run(provider: Web3Provider): Promise<unknown> {
  const relayerAddress = '0xC92E8bdf79f0507f65a392b0ab4667716BFE0110';
  const tokenAddress = '0xe91d153e0b41518a2ce8dd3d7944fa863463a97d';

  // ...
}

approve ABI

You may either set a limited approval (at least the amount of tokens you want to trade) or an unlimited approval. To do this, we use the approve function of the ERC-20 token standard.

We can set this function's ABI as a const:

import type { Web3Provider } from '@ethersproject/providers';

export async function run(provider: Web3Provider): Promise<unknown> {
  // ...

  const approveAbi = [
	{
	  inputs: [
		{ name: '_spender', type: 'address' },
		{ name: '_value', type: 'uint256' },
	  ],
	  name: 'approve',
	  outputs: [{ type: 'bool' }],
	  stateMutability: 'nonpayable',
	  type: 'function',
	},
  ];

  // ...
}

Signer

To make a transaction, we need a signer. In this tutorial, we use an injected Web3Provider, such as Rabby. We can get the signer from the provider:

import type { Web3Provider } from '@ethersproject/providers';

export async function run(provider: Web3Provider): Promise<unknown> {
  // ...

  const signer = provider.getSigner();

  // ...
}

Connect to the contract

To interact with the contract, we need to connect to it. We can do this by using the Contract class from ethers.js:

import type { Web3Provider } from '@ethersproject/providers';
import { Contract } from '@ethersproject/contracts';

export async function run(provider: Web3Provider): Promise<unknown> {
  // ...

  const wxDai = new Contract(tokenAddress, approveAbi, signer);

  // ...
}

Execute the approve

Now we have everything we need to execute the approve function. We will now give the relayerAddress unlimited approval to spend the tokenAddress token.

import type { Web3Provider } from '@ethersproject/providers';
import { Contract } from '@ethersproject/contracts';
import { ethers } from 'ethers';

export async function run(provider: Web3Provider): Promise<unknown> {
  // ...

  const wxDai = new Contract(tokenAddress, approveAbi, signer);

  const tx = await wxDai.approve(relayerAddress, ethers.constants.MaxUint256);
  console.log('tx', tx);
  const receipt = await tx.wait();

  return receipt;
}

Run the code

To run the snippet, we simply press the "Run" button in the bottom right panel (the web container).

When running the script, we will be asked to connect a wallet. We can use Rabby for this.

1. Accept the connection request in Rabby
2. Click "Run"
3. Observe the tx object in the browser's console
4. On successful confirmation of the transaction, the receipt object will be returned to the output panel