Cancelling on-chain

Simple orders / Basic orders

Part 1/ Basic orders/Cancelling on-chain

The preferred way to cancel an order is off-chain, notably because it is free. However, this places trust in the API to cancel the order. If you want to enforce the cancellation of an order, you can do so on-chain. This will cost gas, but will ensure that the order is cancelled.

To cancel, we will send an invalidateOrder transaction to the GPv2Settlement contract.

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

Contract (GPv2Settlement) 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 and orderUid

The contract to be interacted with is the GPv2Settlement contract. We assign it's address 0x9008D19f58AAbD9eD0D60971565AA8510560ab41 to a const.

At the same time, we assign the orderUid of the order we want to cancel to a const.

import type { Web3Provider } from '@ethersproject/providers';
import { SupportedChainId } from '@cowprotocol/cow-sdk';

export async function run(provider: Web3Provider): Promise<unknown> {
  // ...
  const settlementAddress = '0x9008D19f58AAbD9eD0D60971565AA8510560ab41';
  const orderUid = '0x8464affce2df48b60f6976e51414dbc079e9c30ef64f4c1f78c7abe2c7f96a0c29104bb91ada737a89393c78335e48ff4708727e659523a1';
  // ...
}

invalidateOrder ABI

The contract's invalidateOrder function is used to cancel an order. We can retrieve the ABI for this function from the contract's verified code on Gnosisscan. We can set this function's ABI as a const:

import type { Web3Provider } from '@ethersproject/providers';
import { SupportedChainId } from '@cowprotocol/cow-sdk';

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

	const invalidateOrderAbi = [
		{
			"inputs": [
				{ "internalType": "bytes", "name": "orderUid", "type": "bytes" }
			],
			"name": "invalidateOrder",
			"outputs": [],
			"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';
import { SupportedChainId } from '@cowprotocol/cow-sdk';

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 { SupportedChainId } from '@cowprotocol/cow-sdk';
import { Contract } from '@ethersproject/contracts';

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

  const settlement = new Contract(settlementAddress, invalidateOrderAbi, signer);

  // ...
}

Execute the invalidateOrder

Now we have everything we need to execute the invalidateOrder function. In order to do this, we pass the orderUid to the function:

import type { Web3Provider } from '@ethersproject/providers';
import { SupportedChainId } from '@cowprotocol/cow-sdk';
import { Contract } from '@ethersproject/contracts';

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

	const tx = await settlement.invalidateOrder(orderUid);
	console.log('tx', tx);
	const receipt = await tx.wait();

	return receipt;
}

Run the code

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

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

1. Accept the connection request in Rabby
2. Press the "Run" button again
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