ABI & Contracts

The Rust simulation environment (currently) expects transactions to provide ABI encoded arguments from Python. VERBS provides utilities to create Python types representing contract ABI’s, with functionality to encode/decode data and also directly interact with the EVM.

ABI Type

For example given a parsed ABI JSON Python object

abi_json = [
    {
        "name": "foo",
        "inputs": [
            {"internalType": "int256", "name": "a", "type": "int256"}
        ],
        "outputs": [],
        "stateMutability": "view",
        "type": "function",
    },
    {
        "name": "bar",
        "anonymous": False,
        "inputs": [
            {
                "indexed": False,
                "internalType": "int256",
                "name": "b",
                "type": "int256"
            }
         ],
         "type": "event"
    }
 ]

using

Abi = get_abi("Foo", abi_json)

will create a Python type with attributes foo and bar which can then be used to encode and decode arguments

encoded_args = Abi.foo.encode([1, 2, 3])
...
result = Abi.foo.decode(encoded_results)
...
event_data = Abi.bar.decode(encoded_event_data)

The ABI type also has convenience functions to create transactions and to directly interact with the EVM (encoding and decoding data)

# Transaction submitted by agent inside a simulation step
transaction = Abi.foo.transaction(sender, address, [1, 2, 3])
# Directly call the EVM (without committing) and decode result
result = Abi.foo.call(env, sender, address, [1, 2, 3])
# Directly call the EVM (and commit results) and decode result
result = Abi.foo.execute(env, sender, address, [1, 2, 3])

The ABI type also defines a constructor attribute that aids deploying contracts

deploy_address = abi.constructor.deploy(
    env, bytecode_hex, constructor_args
)

Initialisation

ABI types can be created from multiple formats

• Python JSON data structure (i.e. a list of dicts)

• A JSON string

• A JSON/ABI file

See verbs.abi for more details.