The Application Binary Interface (ABI) of Solidity describes how to transform binary data to types which the Solidity programming language understands. For instance, if we want to call a function bark(uint32,bool) on a Solidity-created contract contract Dog, what data parameter do we pass into our Ethereum transaction? This project allows us to encode such function calls.
The latest version (>= 0.5.0) of ex_abi requires Rust because it uses a Rust NIF for KECCAK-256 hash. You can also try using 0.4.0, it doesn't have a Rust requirement because it uses a C NIF. But 0.4.0 does not support OTP 23.
If available in Hex, the package can be installed
by adding ex_abi to your list of dependencies in mix.exs:
def deps do
[
{:ex_abi, "~> 0.5"}
]
endDocumentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/ex_abi.
To encode a function call, pass the ABI spec and the data to pass in to ABI.encode/1.
iex> ABI.encode("baz(uint,address)", [50, <<1::160>> |> :binary.decode_unsigned])
<<162, 145, 173, 214, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 50, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, ...>>That transaction can then be sent via JSON-RPC Client ethereumex.
Decode is generally the opposite of encoding, though we generally leave off the function signature from the start of the data. E.g. from above:
iex> ABI.decode("baz(uint,address)", "00000000000000000000000000000000000000000000000000000000000000320000000000000000000000000000000000000000000000000000000000000001" |> Base.decode16!(case: :lower))
[50, <<0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1>>]Both ABI.encode/2 and ABI.decode/2 can accept a function selector as the first parameter. For example:
selector = %ABI.FunctionSelector{
function: "startInFlightExit",
input_names: [
"inFlightTx",
"inputTxs",
"inputUtxosPos",
"inputTxsInclusionProofs",
"inFlightTxWitnesses"
],
inputs_indexed: nil,
method_id: <<90, 82, 133, 20>>,
returns: [],
type: :function,
types: [
tuple: [
:bytes,
{:array, :bytes},
{:array, {:uint, 256}},
{:array, :bytes},
{:array, :bytes}
]
]
}
ABI.encode(selector, params)To parse function selector from the abi json, use ABI.parse_specification/2:
iex> [%{
...> "inputs" => [
...> %{"name" => "_numProposals", "type" => "uint8"}
...> ],
...> "payable" => false,
...> "stateMutability" => "nonpayable",
...> "type" => "constructor"
...> }]
...> |> ABI.parse_specification
[%ABI.FunctionSelector{function: nil, input_names: ["_numProposals"], inputs_indexed: nil, method_id: <<99, 53, 230, 34>>, returns: [], type: :constructor, types: [uint: 8]}]By default, decode and encode functions try to decode/encode input (params that passed to the function). To decode/encode output pass :output as the third parameter:
selector = %FunctionSelector{
function: "getVersion",
input_names: [],
inputs_indexed: nil,
method_id: <<13, 142, 110, 44>>,
returns: [:string],
type: :function,
types: []
}
data =
"0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000d312e302e342b6136396337363300000000000000000000000000000000000000"
|> Base.decode16!(case: :lower)
expected_result = ["1.0.4+a69c763"]
assert expected_result == ABI.decode(selector, data, :output)
assert data == ABI.encode(selector, expected_result, :output)Currently supports:
-
uint<M> -
int<M> -
address -
uint -
int -
bool -
fixed<M>x<N> -
ufixed<M>x<N> -
fixed -
bytes<M> -
<type>[M] -
bytes -
string -
<type>[] -
(T1,T2,...,Tn)
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