fn execute(self: L1Handler) -> SyscallResult<()>

Executes a #[l1_handler] function to mock a message arriving from Ethereum.

📝 Note

Execution of the #[l1_handler] function may panic like any other function. It works like a regular SafeDispatcher would with a function call. For more info about asserting panic data check out handling panic errors

struct L1Handler {
    contract_address: ContractAddress,
    function_selector: felt252,
    from_address: felt252,
    payload: Span::<felt252>,


  • contract_address - The target contract address
  • function_selector - Selector of the #[l1_handler] function
  • from_address - Ethereum address of the contract that sends the message
  • payload - The message payload that may contain any Cairo data structure that can be serialized with Serde

It is important to note that when executing the l1_handler, the from_address may be checked as any L1 contract can call any L2 contract.

For a contract implementation:

// ...
struct Storage {
    l1_allowed: felt252,


fn process_l1_message(ref self: ContractState, from_address: felt252, data: Span<felt252>) {
    assert(from_address == self.l1_allowed.read(), 'Unauthorized l1 contract');
// ...

We can use execute method to test the execution of the #[l1_handler] function that is not available through contracts dispatcher:

use snforge_std::L1Handler;

fn test_l1_handler_execute() {
    // ...
    let data: Array<felt252> = array![1, 2];

    let mut payload_buffer: Array<felt252> = ArrayTrait::new();
    // Note the serialization here.
    data.serialize(ref payload_buffer);

    let mut l1_handler = L1HandlerTrait::new(

    l1_handler.from_address = 0x123;
    l1_handler.payload = payload.span();