Calldata

The Walnut Simulation Form contains multiple form fields, see screenshot below. This document contains information on how to construct the raw calldata for Walnut Simulations.

For step-by-step guide to fill this form, proceed to Example: Simulate new Transaction or Example: Re-simulate existing Transaction.

The generic format of the calldata field on Walnut (all values in hexadecimal format) is:

  <number of contract calls, in hexadecimal format>
  <contract address, in hexadecimal format>
  <function selector, in hexadecimal format>
  <number of function arguments, in hexadecimal format>
  [argument 0 in hexadecimal format]
  [argument 1 in hexadecimal format]
  [argument n in hexadecimal format]

Where:

Number of Contract Calls: The total number of contract calls being made during the simulation.
Contract Address: Address of the invoked contract.
Function Selector: A unique hexadecimal identifier for the contract’s entry point. This can be generated using:
starkli selector <function_name>
Number of Arguments: The number of arguments expected by the Function Selector.
Calldata (Contract Function Arguments): The Function Selector arguments, encoded in hexadecimal format.

Example

Open this example on Walnut (click re-simulate) to open the simulation form with the raw calldata.

  0x1
  0x4718f5a0fc34cc1af16a1cdee98ffb20c31f5cd61d6ab07201858f4287c938d
  0x83afd3f4caedc6eebf44246fe54e38c95e3179a5ec9ea81740eca5b482d12e
  0x3
  0x5b8a53ea75b7bf0a881fe99de9f52eab6c0b995578ae8dbd3c533458b347dc6
  0x4563918244f40000
  0x0

Example explanation:

Line 1: 0x1 represents that transaction is invoking one contract.
Line 2: 0x4718f5a0fc34cc1af16a1cdee98ffb20c31f5cd61d6ab07201858f4287c938d represents the address of the Starknet Token (STRK) contract being invoked.
Line 3: 0x83afd3f4caedc6eebf44246fe54e38c95e3179a5ec9ea81740eca5b482d12e represents the function selector for the transfer function of the Starknet Token (STRK) contract.
Line 4: 0x3 represents that this function accept 3 raw arguments.
Line 5: 0x5b8a53ea75b7bf0a881fe99de9f52eab6c0b995578ae8dbd3c533458b347dc6 represents the recipient address, the first argument of the transfer function.
Line 6 and 7: 0x4563918244f40000 and 0x0 represent the amount to transfer, serialized as low 128 bits and high 128 bits of a u256. Since the value fits within 128 bits, the high part is 0. For more details on how Cairo serialize types, see Serialization of Cairo Types.