L2 integration #1649

yrong · 2025-12-09T17:01:04Z

Resolves: https://linear.app/snowfork/issue/SNO-1660

Context

This PR includes a POC demonstrating L2 integration using the Across protocol. The implementation is based primarily on the following documentation:

https://docs.across.to/reference/selected-contract-functions#deposit

https://docs.across.to/instant-bridging/embedded-crosschain-actions/crosschain-actions-integration-guide/using-the-generic-multicaller-handler-contract

https://docs.across.to/reference/api-reference#bridge-with-suggested-fees-api

For the GatewayV2 integration, we deployed an adaptor contract on Ethereum L1 as well as on each supported L2 (for example, Base in this POC). The adaptor contracts have already been deployed.

L1 Adaptor: https://sepolia.etherscan.io/address/0xf50FE3BA4306829a96A2d1E9d9518929E47753a6

L2 Adaptor: https://sepolia.basescan.org/address/0x5a7C107757ce0EDB72d65E4aa02e9cc40f5FcEC3

Wrap an API/SDK
Transfer USDC from L1 to L2

contracts git:(ron/l2-integration-across) ✗ make test-snowbridge-l1-adaptor

Transfer USDC from L2 to AssetHub

operations git:(ron/l2-integration-across) ✗ pnpm transferUSDCFromL2ToAH

L2: https://sepolia.basescan.org/tx/0x1313889af68675450f8382ae59a7791087a0d8fbc73332bdf912c13eefbf13da

L1: https://sepolia.etherscan.io/tx/0xbf180c9a99905d11b6a6ec994d48f9412c623f9ee16072f3efdb6f6e651d049b

BH: https://bridgehub-westend.subscan.io/extrinsic/9805450-2

AH: https://assethub-westend.subscan.io/event/13382672-25

Transfer USDC from AssetHub back to L2

➜  operations git:(ron/l2-integration-across) ✗ pnpm transferUSDCFromAHToL2

AH: https://assethub-westend.subscan.io/xcm_message/westend-7fa829ede3433924bcea7e37f5d21eef6584a5be

L1: https://sepolia.etherscan.io/tx/0x077c2b4e3fcbba2db421c867860c63961bcf5b56352caf105d19787b02c5f427

L2: https://sepolia.basescan.org/tx/0xa5a6fb920737e29771b3aea8e7028514f11dc6d056b6a836f228f2ede7faba9b

I prefer to start with limited support initially — transfer native Ether/WETH and stablecoins such as USDC and USDT. The adapter can be extended later to support arbitrary token swaps via a composable swap call on the source or the destination, if needed.

codecov · 2025-12-11T00:48:32Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.02%. Comparing base (1cf39a2) to head (cd9172e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1649   +/-   ##
=======================================
  Coverage   91.02%   91.02%           
=======================================
  Files          19       19           
  Lines         903      903           
  Branches      164      164           
=======================================
  Hits          822      822           
  Misses         64       64           
  Partials       17       17

Flag	Coverage Δ
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Copilot

Pull request overview

This PR implements L2 integration using the Across protocol to enable bridging between Ethereum L1, L2 chains (specifically Base Sepolia), and Polkadot AssetHub. It's a proof-of-concept (POC) demonstrating cross-chain token transfers including USDC and ETH/WETH.

Key Changes

Added Solidity adaptor contracts (SnowbridgeL1Adaptor and SnowbridgeL2Adaptor) to handle L1↔L2 token swaps via Across protocol
Implemented TypeScript API/SDK wrappers for L2 transfers in both directions (Polkadot→L2 and L2→Polkadot)
Extended asset registry and environment configuration to support L2 chains with token swap routes

Reviewed changes

Copilot reviewed 47 out of 51 changed files in this pull request and generated 25 comments.

Show a summary per file

File	Description
contracts/scripts/l2-integration/across/SnowbridgeL1Adaptor.sol	L1 adaptor contract for depositing tokens to L2 via Across
contracts/scripts/l2-integration/across/SnowbridgeL2Adaptor.sol	L2 adaptor contract for sending tokens to Polkadot via L1 gateway
web/packages/api/src/toEthereumSnowbridgeV2.ts	Added `buildL2Call` function for L2 transfer fee estimation and calldata generation
web/packages/api/src/toPolkadotSnowbridgeV2.ts	Added `createL2TransferImplementation` for L2→Polkadot transfers
web/packages/api/src/transfers/polkadotToL2/erc20ToL2.ts	Implementation for transferring ERC20 tokens from Polkadot to L2
web/packages/api/src/transfers/l2ToPolkadot/erc20ToAH.ts	Implementation for transferring ERC20 tokens from L2 to Polkadot AssetHub
web/packages/api/src/across/api.ts	Wrapper for Across API fee estimation
web/packages/api/src/index.ts	Extended Context class with L2 adapter and configuration accessors
web/packages/api/src/environment.ts	Added L2 bridge configuration type and Across endpoints
web/packages/api/src/assets_v2.ts	Added `findL2TokenAddress` helper and registry build support for L2 chains
web/packages/operations/src/*.ts	Operation scripts for testing L2 transfers
web/packages/registry/src/westend_sepolia.registry.json	Registry updates with Base Sepolia chain and token mappings
contracts/scripts/l2-integration/across/test/*.s.sol	Test scripts for adaptor contracts

Files not reviewed (1)

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Copilot · 2026-01-06T06:21:09Z

web/packages/api/src/xcmbuilders/toEthereum/erc20FromAH.ts

                        assets: {
                            wild: {
-                                allCounted: 2,
+                                allCounted: 3,


The allCounted value is hardcoded to 3, but this change may need to be context-dependent. When transferring to L2, there might be different numbers of assets to deposit. This should be calculated dynamically based on the actual number of assets rather than hardcoded.

Copilot · 2026-01-06T06:21:10Z

web/packages/api/src/across/api.ts

+        amount: amount.toString(),
+    }
+    apiEndpoint += "/suggested-fees?" + new URLSearchParams(params)
+    let response = await fetch(apiEndpoint)


The HTTP response status should be checked before attempting to parse the JSON. If the API returns a non-200 status code, parsing the response as JSON might fail or return an error object instead of the expected fee data.

Suggested change

let response = await fetch(apiEndpoint)

let response = await fetch(apiEndpoint)

if (!response.ok) {

throw new Error(`Failed to fetch suggested fees: ${response.status} ${response.statusText}`)

}

Copilot · 2026-01-06T06:21:10Z

contracts/scripts/l2-integration/across/SnowbridgeL1Adaptor.sol

+        require(params.inputToken == address(0));
+        require(params.inputAmount > params.outputAmount, "Input and output amount mismatch");


The error messages in the require statements are not descriptive. Consider using more specific error messages that include information about what went wrong. For example, "Input token must be zero address" instead of just checking equality.

Suggested change

require(params.inputToken == address(0));

require(params.inputAmount > params.outputAmount, "Input and output amount mismatch");

require(params.inputToken == address(0), "Input token must be zero address for native ETH deposits");

require(params.inputAmount > params.outputAmount, "Input amount must be greater than output amount");

Copilot · 2026-01-06T06:21:11Z

web/packages/operations/src/transfer_to_ethereum_l2.ts

+    const ETHEREUM_ACCOUNT = new Wallet(
+        process.env.ETHEREUM_KEY ??
+            "0x5e002a1af63fd31f1c25258f3082dc889762664cb8f218d86da85dff8b07b342",


The same hardcoded private key appears in multiple operation files across the codebase. This is a security concern even for test code. These hardcoded keys should be removed or the files should be clearly marked as test-only code with appropriate warnings.

Copilot · 2026-01-06T06:21:11Z

web/packages/operations/src/transfer_from_l2_to_polkadot.ts

+    const ETHEREUM_ACCOUNT = new Wallet(
+        process.env.ETHEREUM_KEY ??
+            "0x5e002a1af63fd31f1c25258f3082dc889762664cb8f218d86da85dff8b07b342",


The same hardcoded private key appears in multiple operation files across the codebase. This is a security concern even for test code. These hardcoded keys should be removed or the files should be clearly marked as test-only code with appropriate warnings.

Copilot · 2026-01-06T06:21:16Z

web/packages/api/src/transfers/l2ToPolkadot/erc20ToAH.ts

+            )
+        }
+
+        let l2BridgeFeeInEther = 0n


The initial value of l2BridgeFeeInEther is unused, since it is always overwritten.

Copilot · 2026-01-06T06:21:16Z

web/packages/api/src/transfers/l2ToPolkadot/erc20ToAH.ts

+            beneficiaryMultiAddress(beneficiaryAccount)
+
+        let assets: any = [],
+            value = 0n,


The initial value of value is unused, since it is always overwritten.

Copilot · 2026-01-06T06:21:16Z

web/packages/api/src/transfers/l2ToPolkadot/erc20ToAH.ts

+
+        let assets: any = [],
+            value = 0n,
+            outputAmount = 0n


The initial value of outputAmount is unused, since it is always overwritten.

Copilot · 2026-01-06T06:21:16Z

web/packages/api/src/transfers/l2ToPolkadot/erc20ToAH.ts

+        } else {
+            value = fee.totalFeeInWei
+            outputAmount = amount - fee.l2BridgeFeeInL2Token!
+            assets = [encodeNativeAsset(tokenAddress, outputAmount)]


The value assigned to assets here is unused.

Copilot · 2026-01-06T06:21:17Z

web/packages/api/src/toEthereumSnowbridgeV2.ts

+    const l2TokenAddress = findL2TokenAddress(registry, l2ChainId, tokenAddress)!
+    const l1Adapter = context.l1Adapter()
+    let l1AdapterAddress = await l1Adapter.getAddress()
+    let l2BridgeFeeInL1Token = 0n


The initial value of l2BridgeFeeInL1Token is unused, since it is always overwritten.

claravanstaden

Looks great @yrong! Have you thought about upgradeability for the adapter contracts? Or is it not a concern? I am thinking specifically about inflight transactions while upgrading.

claravanstaden · 2026-01-06T08:32:23Z

contracts/scripts/l2-integration/across/SnowbridgeL1Adaptor.sol

Do we need to audit these contracts?

claravanstaden · 2026-01-06T08:32:47Z

contracts/scripts/l2-integration/across/Types.sol

+struct SwapParams {
+    address inputToken;
+    address outputToken;
+    uint256 inputAmount;
+    uint256 outputAmount;
+    uint256 destinationChainId;
+}
+
+struct SendParams {


Needs docs.

claravanstaden · 2026-01-06T08:34:49Z

contracts/scripts/l2-integration/across/interfaces/ISpokePool.sol

Perhaps we should move all the L2 contracts that need to be deployed to /src?

claravanstaden · 2026-01-06T08:36:02Z

contracts/scripts/l2-integration/across/data/tokens.json

Are these files used for tests? Or just for reference?

claravanstaden · 2026-01-06T08:37:20Z

contracts/scripts/l2-integration/across/SnowbridgeL2Adaptor.sol

+    IGatewayV2 public immutable GATEWAY;
+    WETH9 public immutable L1_WETH9;
+    WETH9 public immutable L2_WETH9;
+    uint32 public TIME_BUFFER;


Would this value ever need to be changed?

claravanstaden · 2026-01-06T08:39:13Z

contracts/scripts/l2-integration/across/SnowbridgeL1Adaptor.sol

+            bytes32(uint256(uint160(params.inputToken))),
+            bytes32(uint256(uint160(params.outputToken))),


Should add a sanity check that inputToken > outputToken, same as depositNativeEther

require(params.inputAmount > params.outputAmount, "Input and output amount mismatch");

claravanstaden · 2026-01-06T08:46:29Z

web/packages/api/src/toEthereumSnowbridgeV2.ts

+    registry: AssetRegistry,
+    tokenAddress: string,
+): TransferInterfaceToL2 {
+    // Todo: Support PNA transfers to L2


Should perhaps throw an error if a PNA tokenAddress is provided?

claravanstaden · 2026-01-06T08:50:28Z

web/packages/api/src/toEthereum_v2.ts

        sourceDryRunError: any
        assetHubDryRunError: any
        bridgeHubDryRunError?: any
+        l2BridgeDryRunError?: string


Is this used anywhere?

yrong added 3 commits December 9, 2025 16:10

L2 integration with Across

1955a2a

Move canocal integration out

2cab025

Rename command

3d9ce80

github-actions bot added the Component: Ethereum label Dec 9, 2025

yrong mentioned this pull request Dec 9, 2025

L2 integration #1643

Closed

yrong changed the title ~~L2 integration Using Across~~ L2 integration Dec 9, 2025

yrong added 3 commits December 10, 2025 17:06

Transact from L2 to L1

9ad6d63

Fix build

40a3ed1

Update dependencies

4d5ae73

yrong added 12 commits December 12, 2025 16:31

Seperate interfaces

1dc9808

Add to common types

bd149b9

Add a Snowbridge L2 Frontend

d1c3ea2

Reorder deposit logic

3c2bb98

Fix deployer

9b76a34

E2E transact from L2 to AH

e5b6254

Add IXcm precompile

820e519

Add adaptor contracts

b164330

Cleanup

e2c68fb

Transact from AH to L2

0d2d38f

Polish

8f6a31b

Merge branch 'main' into ron/l2-integration-across

7fdde4e

github-actions bot added Component: Smoke Tests Component: Web labels Dec 16, 2025

yrong added 6 commits December 16, 2025 07:31

Merge branch 'main' into ron/l2-integration-across

778c7ea

Polish

0dab570

Update westend registry

2f7a631

Approve the Gateway contract to spend the output ERC20 token

d93c694

Improve building across transact

8f779da

Fix recipient

c538adc

yrong added 19 commits December 17, 2025 04:03

Add API scripts

a1c11d7

Update contract address

6a7d95e

L2 sdk interfaces

9a919ec

Build L2 Asset registry

f950129

Update asset registry

a50e503

Add topic Id for tracing

758dae9

SDK from l2 to AH

3b0f501

Across estimation API

d1c2218

Add uniswap adaptor

c85226e

Transfer from AH to L2

feb1e89

Test transfer from AH to L2

5ca6077

Test Uniswap

621b8ac

Refactoring

3447186

Rename

eb1dbc6

Send Ether from L1 to L2

9323ed2

Polish

088a8f9

Cleanup

8900e08

Support native Ether

0efb650

Merge branch 'main' into ron/l2-integration-across

619efb9

yrong marked this pull request as ready for review January 6, 2026 03:31

yrong requested review from alistair-singh, claravanstaden and Copilot January 6, 2026 06:12

Copilot started reviewing on behalf of yrong January 6, 2026 06:13 View session

Copilot AI reviewed Jan 6, 2026

View reviewed changes

Fix sendParams

ee8becd

claravanstaden reviewed Jan 6, 2026

View reviewed changes

Fix Ether transfer

cd9172e

		require(params.inputToken == address(0));
		require(params.inputAmount > params.outputAmount, "Input and output amount mismatch");

		bytes32(uint256(uint160(params.inputToken))),
		bytes32(uint256(uint160(params.outputToken))),

L2 integration #1649

Are you sure you want to change the base?

L2 integration #1649

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yrong commented Dec 9, 2025 •

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