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Swap on L1 Uniswap from L2

This smart contract example allows someone with funds on L2 to be able to swap using L1 Uniswap and then get the swapped assets back to L2. In this example, L1 will refer to Ethereum and L2 will refer to Aztec.

The flow will be:

  1. The user withdraws their “input” assets to L1 (i.e. burn them on L2 and create a L2 to L1 message to withdraw)
  2. We create an L2 → L1 message to swap on L1
  3. On L1, the user gets their input tokens, consumes the swap message, and executes the swap
  4. The user deposits the “output” tokens to the output token portal so it can be deposited into L2
  5. We will assume that token portals and token bridges for the input and output tokens must exist. These are what we built in the token bridge tutorial.

The execution of swap on L1 should be designed such that any 3rd party can execute the swap on behalf of the user. This helps maintain user privacy by not requiring links between L1 and L2 activity.

This reference will cover:

  1. Uniswap Portal - a contract on L1 that talks to the input token portal to withdraw the assets, executes the swap, and deposits the swapped tokens back to L2
  2. Uniswap L2 contract - a contract on L2 that creates the needed messages to perform the swap on L1

This diagram describes the private flow.

This code works alongside a token portal that you can learn to build in this tutorial.