Onchain.ABI (onchain v0.5.0)

ABI encoding/decoding for Ethereum contract calls.

Wraps the abi library (a dep of signet) with 0x-prefixed hex string handling and consistent error tuples. Consumers work with hex strings from RPC; this module bridges the gap.

Type Signatures

decode_response/2 expects tuple type syntax for return values, e.g. "(uint256)" or "(uint256,bool)". This is the standard pattern for decoding eth_call responses — NOT function signatures with names.

Error Format

Encode errors: {:error, {:encode_error, reason}}
Decode errors: {:error, {:decode_error, reason}}

Where reason is either:

A string from the upstream exception message
A tuple like {:invalid_hex, hex_data} preserving the original hex error

Functions

Function	Purpose
`encode_call/2`	Function signature + params → hex calldata
`encode_call!/2`	Same, raises on error
`decode_response/2`	Type signature + hex data → decoded values
`decode_response!/2`	Same, raises on error

API Functions

Function	Arity	Description	Param Kinds
`decode_response!`	2	Decode hex-encoded ABI response data to Elixir values. Raises on error.	`type_signature: value`, `hex_data: value`
`decode_response`	2	Decode hex-encoded ABI response data to Elixir values.	`type_signature: value`, `hex_data: value`
`encode_call!`	2	Encode a function call to 0x-prefixed hex calldata. Raises on error.	`signature: value`, `params: value`
`encode_call`	2	Encode a function call to 0x-prefixed hex calldata.	`signature: value`, `params: value`

Summary

Functions

decode_response(type_signature, hex_data)

Decode hex-encoded ABI response data to Elixir values.

decode_response!(type_signature, hex_data)

Decode hex-encoded ABI response data to Elixir values. Raises on error.

encode_call(signature, params)

Encode a function call to 0x-prefixed hex calldata.

encode_call!(signature, params)

Encode a function call to 0x-prefixed hex calldata. Raises on error.

Functions

decode_response(type_signature, hex_data)

@spec decode_response(String.t(), String.t()) ::
  {:ok, list()} | {:error, {:decode_error, term()}}

Decode hex-encoded ABI response data to Elixir values.

Parameters

type_signature - Tuple type signature, e.g. "(uint256)" or "(uint256,bool)" (value)
hex_data - 0x-prefixed hex string of ABI-encoded data (value)

Returns

List of decoded values ({:ok, list} | {:error, {:decode_error, reason}})

# descripex:contract
%{
  params: %{
    type_signature: %{
      description: "Tuple type signature, e.g. \"(uint256)\" or \"(uint256,bool)\"",
      kind: :value
    },
    hex_data: %{
      description: "0x-prefixed hex string of ABI-encoded data",
      kind: :value
    }
  },
  returns: %{
    type: "{:ok, list} | {:error, {:decode_error, reason}}",
    description: "List of decoded values"
  }
}

decode_response!(type_signature, hex_data)

@spec decode_response!(String.t(), String.t()) :: list()

Decode hex-encoded ABI response data to Elixir values. Raises on error.

Parameters

type_signature - Tuple type signature, e.g. "(uint256)" or "(uint256,bool)" (value)
hex_data - 0x-prefixed hex string of ABI-encoded data (value)

Returns

List of decoded values (list)

# descripex:contract
%{
  params: %{
    type_signature: %{
      description: "Tuple type signature, e.g. \"(uint256)\" or \"(uint256,bool)\"",
      kind: :value
    },
    hex_data: %{
      description: "0x-prefixed hex string of ABI-encoded data",
      kind: :value
    }
  },
  returns: %{type: :list, description: "List of decoded values"}
}

encode_call(signature, params)

@spec encode_call(String.t(), list()) ::
  {:ok, String.t()} | {:error, {:encode_error, term()}}

Encode a function call to 0x-prefixed hex calldata.

Parameters

signature - Function signature, e.g. "balanceOf(address)" (value)
params - List of parameter values matching the signature (value)

Returns

0x-prefixed hex-encoded calldata ({:ok, hex_string} | {:error, {:encode_error, reason}})

# descripex:contract
%{
  params: %{
    signature: %{
      description: "Function signature, e.g. \"balanceOf(address)\"",
      kind: :value
    },
    params: %{
      description: "List of parameter values matching the signature",
      kind: :value
    }
  },
  returns: %{
    type: "{:ok, hex_string} | {:error, {:encode_error, reason}}",
    description: "0x-prefixed hex-encoded calldata",
    example: "0x70a08231..."
  }
}

encode_call!(signature, params)

@spec encode_call!(String.t(), list()) :: String.t()

Encode a function call to 0x-prefixed hex calldata. Raises on error.

Parameters

signature - Function signature, e.g. "balanceOf(address)" (value)
params - List of parameter values matching the signature (value)

Returns

0x-prefixed hex-encoded calldata (string)

# descripex:contract
%{
  params: %{
    signature: %{
      description: "Function signature, e.g. \"balanceOf(address)\"",
      kind: :value
    },
    params: %{
      description: "List of parameter values matching the signature",
      kind: :value
    }
  },
  returns: %{type: :string, description: "0x-prefixed hex-encoded calldata"}
}