abiparser

Application Binary Inteface (ABI) Parser For Ethereum & Co.

abiparser - application binary interface (abi) parser machinery / helper for Ethereum & Co. (blockchain) contracts

• home :: github.com/rubycocos/blockchain
• bugs :: github.com/rubycocos/blockchain/issues
• gem :: rubygems.org/gems/abiparser
• rdoc :: rubydoc.info/gems/abiparser

Usage

Functions Signature Hashes / Selectors & Interface (Type) Ids

You can calculate the function selectors (or "sighash", that is, signature hash) by hashing the function signature e.g. supportsInterface(bytes4) with the Keccak 256-Bit algorithm and than use the first 4 bytes, that is, 0x01ffc9a7 (out of 32 bytes), that is, 0x01ffc9a7a5cef8baa21ed3c5c0d7e23accb804b619e9333b597f47a0d84076e2. Example:

require 'abiparser'

sig = 'supportsInterface(bytes4)'
pp keccak256( sig )[0,4].hexdigest
#=> "0x01ffc9a7"

Note: The String#hexdigest (also known as String#bin_to_hex) helper converts a binary string (with BINARY/ASCII-8BIT encoding) into a hex(adecimal) string.

You can calcuate interface (type) ids by xor-ing (^) together the sighashes. If the interface only has one function than the interface (type) id equals the function sighash (by definition).

interface ERC165 {
    /// @notice Query if a contract implements an interface
    /// @param interfaceID The interface identifier, as specified in ERC-165
    /// @dev Interface identification is specified in ERC-165.
    /// @return `true` if the contract implements `interfaceID` and
    ///  `interfaceID` is not 0xffffffff, `false` otherwise
  function supportsInterface(bytes4 interfaceID) external view returns (bool);
}
// The interface identifier for this interface is 0x01ffc9a7.

If you check the sighash for supportsInterface(bytes4), that is, 0x01ffc9a7 (see above) than - bingo! - the interface id for ERC165 matches up.

Let's try to calculate the ERC20 standard (fungible) token interface where the official id is 0x36372b07 by xor-ing (^) together all function sighashes:

pp (keccak256('totalSupply()')[0,4] ^
    keccak256('balanceOf(address)')[0,4] ^
    keccak256('allowance(address,address)')[0,4] ^
    keccak256('transfer(address,uint256)')[0,4] ^
    keccak256('approve(address,uint256)')[0,4] ^
    keccak256('transferFrom(address,address,uint256)')[0,4]).hexdigest
#=> "0x36372b07"

# or where   def sig(bin) = keccak256(bin)[0,4])

pp (sig('totalSupply()') ^
    sig('balanceOf(address)') ^
    sig('allowance(address,address)') ^
    sig('transfer(address,uint256)') ^
    sig('approve(address,uint256)') ^
    sig('transferFrom(address,address,uint256)')).hexdigest
#=> "0x36372b07"

Voila! Or re(use) the builtin pre-defined interfaces. Example:

pp IERC165.inteface_id             #=> "0x01ffc9a7"
pp IERC20.interface_id             #=> "0x36372b07"
pp IERC721.interface_id            #=> "0x80ac58cd"
pp IERC721_METADATA.interface_id   #=> "0x5b5e139f"
pp IERC721_ENUMERABLE.interface_id #=> "0x780e9d63"

Yes, you can. Define your own interface. Let's have a looksie at the built-ins. Example:

IERC165 = ABI::Interface.new(
  'supportsInterface(bytes4)'
)

IERC20  = ABI::Interface.new(
   'totalSupply()',
   'balanceOf(address)',
   'allowance(address,address)',
   'transfer(address,uint256)',
   'approve(address,uint256)',
   'transferFrom(address,address,uint256)'
)

IERC721 = ABI::Interface.new(
  'balanceOf(address)',
  'ownerOf(uint256)',
  'approve(address,uint256)',
  'getApproved(uint256)',
  'setApprovalForAll(address,bool)',
  'isApprovedForAll(address,address)',
  'transferFrom(address,address,uint256)',
  'safeTransferFrom(address,address,uint256)',
  'safeTransferFrom(address,address,uint256,bytes)' )

IERC721_METADATA = ABI::Interface.new(
  'name()',
  'symbol()',
  'tokenURI(uint256)' )

IERC721_ENUMERABLE = ABI::Interface.new(
  'tokenOfOwnerByIndex(address,uint256)',
  'totalSupply()',
  'tokenByIndex(uint256)' )

...

To be continued...

License

The scripts are dedicated to the public domain. Use it as you please with no restrictions whatsoever.

Questions? Comments?

Post them on the D.I.Y. Punk (Pixel) Art reddit. Thanks.