L2 Reads from Appchain

Pylon enables your appchain contracts to read data from the settlement L2 chain using the l2Read function. This allows you to access L2 state without leaving your appchain, enabling seamless cross-chain data access.

How It Works

The l2Read function is available through the SettlementPort contract deployed on your appchain. It takes a target address on the L2 and encoded function call data, then returns the result from the L2 contract.

Basic Usage

Here's how to use l2Read in your appchain contract:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.29;

interface IL2Reader {
    function l2Read(address _to, bytes calldata _data) external view returns (bytes memory);
}

contract MyAppContract {
    address public immutable settlementPort;
    
    constructor(address _settlementPort) {
        settlementPort = _settlementPort;
    }
    
    function getL2TokenBalance(address tokenContract, address account) external view returns (uint256) {
        // Encode the balanceOf function call
        bytes memory data = abi.encodeWithSignature("balanceOf(address)", account);
        
        // Perform the L2 read
        bytes memory result = IL2Reader(settlementPort).l2Read(tokenContract, data);
        
        // Decode the result
        return abi.decode(result, (uint256));
    }
    
    function getL2ContractData(address targetContract, bytes calldata callData) external view returns (bytes memory) {
        // Direct L2 read with custom call data
        return IL2Reader(settlementPort).l2Read(targetContract, callData);
    }
}

Key Points

• View Function: l2Read is a view function, so it doesn't modify state

• Synchronous: The read appears synchronous to your contract, but the data is pre-fetched by the sequencer

• Error Handling: The function will revert if the L2 call fails

Common Use Cases

• Reading token balances on L2

• Checking L2 contract state

• Accessing L2 price feeds

• Reading L2 governance data

• Cross-chain data validation

Integration Example

function processL2Data(address l2Contract) external view returns (bool) {
    try IL2Reader(settlementPort).l2Read(l2Contract, abi.encodeWithSignature("getStatus()")) returns (bytes memory result) {
        bool status = abi.decode(result, (bool));
        return status;
    } catch {
        // Handle L2 read failure
        return false;
    }
}

This pattern enables your appchain contracts to seamlessly integrate with L2 data while maintaining the performance benefits of your appchain.