Interactions

Creating and managing settlement interactions with the CoW Protocol SDK

Interactions

Settlement interactions enable CoW Protocol settlements to execute arbitrary smart contract calls at specific execution stages.

Interaction Interface

interface Interaction {
  target: string;       // Smart contract address
  value: BigNumberish;  // ETH value to send
  callData: string;     // Encoded function call data
}

InteractionLike

A flexible partial type with optional fields:

interface InteractionLike {
  target: string;
  value?: BigNumberish;  // Defaults to 0
  callData?: string;     // Defaults to "0x"
}

Execution Stages

enum InteractionStage {
  PRE = 0,   // Before token transfers
  INTRA = 1, // During trading (after sells, before buys)
  POST = 2,  // After all trading
}

PRE Stage

Executes before token transfers. Useful for:

• EIP-2612 permit calls
• Token wrapping (e.g., ETH to WETH)
• Setting up approvals

encoder.encodeInteraction({
  target: tokenAddress,
  callData: token.interface.encodeFunctionData("permit", [
    owner, spender, value, deadline, v, r, s
  ]),
}, InteractionStage.PRE);

INTRA Stage

Executes during trading, after sell tokens arrive but before buy tokens are distributed. Default stage if none specified.

// Uniswap swap for liquidity sourcing
encoder.encodeInteraction({
  target: uniswapRouter,
  callData: router.interface.encodeFunctionData("exactInputSingle", [params]),
}, InteractionStage.INTRA);

POST Stage

Executes after all trading concludes. Used for cleanup:

// WETH unwrapping
encoder.encodeInteraction({
  target: wethAddress,
  callData: weth.interface.encodeFunctionData("withdraw", [amount]),
}, InteractionStage.POST);

Helper Functions

normalizeInteraction

Converts an InteractionLike into a complete Interaction with default values:

import { normalizeInteraction } from "@cowprotocol/contracts";

const interaction = normalizeInteraction({
  target: contractAddress,
  // value defaults to 0
  // callData defaults to "0x"
});

normalizeInteractions

Handles arrays of interactions:

import { normalizeInteractions } from "@cowprotocol/contracts";

const interactions = normalizeInteractions([
  { target: addr1, callData: data1 },
  { target: addr2, callData: data2 },
]);

Integration with SettlementEncoder

The encodeInteraction() method adds interactions to settlements. If no stage is specified, InteractionStage.INTRA is the default.

const encoder = new SettlementEncoder(domain);

// Pre-settlement permit
encoder.encodeInteraction(permitInteraction, InteractionStage.PRE);

// Intra-settlement swap (default stage)
encoder.encodeInteraction(swapInteraction);

// Post-settlement cleanup
encoder.encodeInteraction(unwrapInteraction, InteractionStage.POST);

Common Use Cases

• EIP-2612 permit calls for gasless approvals
• Uniswap/Curve swaps for liquidity sourcing
• WETH wrapping/unwrapping
• Post-settlement fee distributions

Best Practices

• Select appropriate stages based on token balance availability
• Minimize interactions for gas efficiency
• Ensure all calls will succeed (failures cause the entire settlement to revert)
• Be cautious with reentrancy risks