Cancelling order

Advanced orders / Eth-Flow

Part 2/ Eth-Flow/Cancelling order

In the previous tutorials we have created an Eth-flow order and showed how to view it. Let's say for some reason we want to cancel the order (like instead of buying 1 xDAI worth of COW, you now want to buy 200 xDAI worth of COW)! In this tutorial we will show how to cancel an order.

In order to cancel an Eth-flow order, we need to pass to invalidateOrder the original parameter that was passed to createOrder. There are a couple of ways to do this:

• Lookup the calldata of the transaction that created the order, and replace the function selector with the invalidateOrder function selector
• Lookup the logs of the transaction that created the order and reconstruct the EthFlowOrder.Data struct from the OrderPlacement event log

We will use the second method in this tutorial.

Reconstructing the EthFlowOrder.Data struct

From the EthFlowOrder.Data struct technical reference, we can see that the struct's fields are a subset of the GPv2Order.Data struct and an additional int64 field called quoteId.

Fortunately, in the OrderPlacement event log, we can see that the order field is the GPv2Order.Data struct, and the data field is a solidity-packed tuple containing the quoteId field and the validTo field. This means that we can reconstruct the EthFlowOrder.Data struct from the OrderPlacement event log!

Extract quoteId from data field

First let's write a helper function to extract the quoteId from the solidity packed data log field:

import type { Web3Provider } from '@ethersproject/providers'
import { BigNumber, Contract, utils } from "ethers";
import { SupportedChainId, UnsignedOrder } from '@cowprotocol/cow-sdk'
import { onchainOrderToHash } from '/src/lib/gpv2Order';
import abi from './ethFlow.abi.json'

// ...

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

	const decodePackedData = (data: string) => {
		// Ensure data is of correct length (8 bytes for int64 + 4 bytes for uint32)
		if (data.length !== 2 * (8 + 4) + 2) { // +2 for '0x'
			throw new Error('Invalid data length');
		}

		// Extract quoteId (int64) and validTo (uint32) from the data
		const quoteIdBytes = data.slice(2, 2 + 16); // 8 bytes for int64
		const validToBytes = data.slice(2 + 16); // 4 bytes for uint32

		// Convert hex strings to BigNumber
		const quoteId = BigNumber.from('0x' + quoteIdBytes).toNumber();
		const validTo = BigNumber.from('0x' + validToBytes).toNumber();

		return { quoteId, validTo };
	}

	// ...

As the data field is a solidity-packed tuple, the field lengths are fixed. Therefore we can extract the quoteId and validTo fields by slicing the data field into the correct lengths, and converting the hex strings to BigNumbers.

Reconstruct EthFlowOrder.Data struct

Now that we have a way to extract the quoteId from the data field, we can define a function to reconstruct the EthFlowOrder.Data struct from the OrderPlacement event log:

import type { Web3Provider } from '@ethersproject/providers'
import { BigNumber, Contract, utils } from "ethers";
import { SupportedChainId, UnsignedOrder } from '@cowprotocol/cow-sdk'
import { onchainOrderToOrder, onchainOrderToHash } from '/src/lib/gpv2Order';
import abi from './ethFlow.abi.json'

// ...

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

	const onchainEthFlowOrder = (onchainOrder: any, data: any): EthFlowOrder => {
		const order = onchainOrderToOrder(onchainOrder);
		const { quoteId } = decodePackedData(data);

		return {
			buyToken: order.buyToken,
			sellAmount: order.sellAmount.toString(),
			buyAmount: order.buyAmount.toString(),
			receiver: order.receiver, 
			appData: order.appData.toString(),
			feeAmount: order.feeAmount.toString(),
			partiallyFillable: order.partiallyFillable,
			validTo: order.validTo.valueOf(),
			quoteId,
		}
	}

	// ...
}

Get transaction receipt

Let's use a known transaction hash to extract the OrderPlacement event log:

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

	const txHash = '0x04d05fc2c953cc63608c19a79869301d62b1f077e0f795f716619b21f693f00c';
	const receipt = await provider.getTransactionReceipt(txHash);

	// ...
}

The transaction hash above is from the gnosis chain network. Attempting to cancel this order will result in a revert, as the order has already been cancelled. If you want to try this tutorial, create an Eth-flow order first.

Process event logs

Now that we have the transaction receipt, we can extract the OrderPlacement event logs from it, reconstructing the EthFlowOrder.Data struct and cancelling the orders:

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

	let cancelledOrders = [];

	for (const log of receipt.logs) {
		if (log.address !== ethFlowAddress) {
			continue;
		}

		const parsedLog = iface.parseLog(log);
		if (parsedLog.name === 'OrderPlacement') {
			const [, onchainOrder, , data] = parsedLog.args;
			const ethFlowOrder = onchainEthFlowOrder(onchainOrder, data);

			try {
				const tx = await ethFlowContract.invalidateOrder(ethFlowOrder);
				const receipt = await tx.wait();
				cancelledOrders.push({
					ethFlowOrderUid: ethFlowOrderUid(onchainOrder),
					receipt,
				});
			} catch (err) {
				throw new Error(err);
			}
		}
	}

	return {
		cancelledOrders,
	}
}

Above we:

• Filter out all logs that are not from the ethFlowAddress (i.e. this way we force that we don't accidentally look at logs from the other environment's CoWSwapEthFlow contract)
• Parse the log using the ABI
• Extract the GPv2Order.Data struct and data field from the OrderPlacement event
• Reconstruct the EthFlowOrder.Data struct from the OrderPlacement event log
• Cancel the order using the ethFlowContract.invalidateOrder function
• Wait for the transaction to be confirmed
• Push the cancelled order to the cancelledOrders array

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. Confirm transactions in Rabby
4. Observe all orders being cancelled in the output panel

Errors

You may receive some errors associated with reverts with eth_estimateGas calls. This is likely because the order has already been cancelled (such as the orders in the example above).