Module implementing the Ethereum ABI in Javascript. Can be used with RPC libraries for communication or with ethereumjs-vm to implement a fully fledged simulator.

Usage

Manual encoding and decoding

There are three methods of interest:

• methodID to create a function signature
• rawEncode to encode fields and
• rawDecode to decode fields

Example code:

var abi = require('ethereumjs-abi')

// returns the encoded binary (as a Buffer) data to be sent
var encoded = abi.rawEncode([ "address" ], [ "0x0000000000000000000000000000000000000000" ])

// returns the decoded array of arguments
var decoded = abi.rawDecode([ "address" ], data)

Encoding and decoding aided by the JSON ABI definition

Supporting the JSON ABI definition:

var  abi = [{"constant":false,"inputs":[{"name":"val","type":"int256"}],"name":"setVal","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[],"name":"getVal","outputs":[{"name":"","type":"int256"}],"payable":false,"stateMutability":"nonpayable","type":"function"}]

var encoded = ABI.encode(abi,"setVal",[1234]);

console.log(encoded.toString("hex"));

Output :
5362f8a200000000000000000000000000000000000000000000000000000000000004d2


var decoded = abi.decode(abi, 'setVal', '5362f8a200000000000000000000000000000000000000000000000000000000000004d2')

Output:
decoded[0].type ====> 'int256'
decoded[0].value ====> 1234

Simple encoding and decoding

var abi = require('ethereumjs-abi')

// returns the encoded binary (as a Buffer) data to be sent
var encoded = abi.simpleEncode("balanceOf(address):(uint256)", "0x0000000000000000000000000000000000000000")

// returns the decoded array of arguments
var decoded = abi.simpleDecode("balanceOf(address):(uint256)", data)

Solidity tightly packed formats

This library also supports creating Solidity's tightly packed data constructs, which are used together with sha3, sha256 and ripemd160 to create hashes.

Solidity code:

contract HashTest {
  function testSha3() returns (bytes32) {
   address addr1 = 0x43989fb883ba8111221e89123897538475893837;
   address addr2 = 0;
   uint val = 10000;
   uint timestamp = 1448075779;

   return sha3(addr1, addr2, val, timestamp); // will return 0xc3ab5ca31a013757f26a88561f0ff5057a97dfcc33f43d6b479abc3ac2d1d595
 }
}

Creating the same hash using this library:

var abi = require('ethereumjs-abi')
var BN = require('bn.js')

abi.soliditySHA3(
    [ "address", "address", "uint", "uint" ],
    [ new BN("43989fb883ba8111221e89123897538475893837", 16), 0, 10000, 1448075779 ]
).toString('hex')

For the same data structure:

• sha3 will return 0xc3ab5ca31a013757f26a88561f0ff5057a97dfcc33f43d6b479abc3ac2d1d595
• sha256 will return 0x344d8cb0711672efbdfe991f35943847c1058e1ecf515ff63ad936b91fd16231
• ripemd160 will return 0x000000000000000000000000a398cc72490f72048efa52c4e92067e8499672e7 (NOTE: it is 160bits, left padded to 256bits)

Note that ripemd160() in Solidity returns bytes20 and if you cast it to bytes32, it will be right padded with zeroes.

Using Serpent types

Serpent uses a different notation for the types, even though it will serialize to the same ABI.

We provide two helpers to convert between these notations:

• fromSerpent: convert a Serpent notation to the ABI notation
• toSerpent: the other way around

Example usage:

abi.fromSerpent('s')    // [ 'bytes' ]
abi.fromSerpent('i')    // [ 'int256' ]
abi.fromSerpent('a')    // [ 'int256[]' ]
abi.fromSerpent('b8')   // [ 'bytes8' ]
abi.fromSerpent('b8i')  // [ 'bytes8', 'int256' ]

abi.toSerpent([ 'bytes' ])             // 's'
abi.toSerpent([ 'int256' ])            // 'i'
abi.toSerpent([ 'int256[]' ])          // 'a'
abi.toSerpent([ 'bytes8' ])            // 'b8'
abi.toSerpent([ 'bytes8', 'int256' ])  // 'b8i'

It is to be used in conjunction with rawEncode and rawDecode:

var encoded = abi.rawEncode(abi.fromSerpent("i"), [ "0x0000000000000000000000000000000000000000" ])

var decoded = abi.rawDecode([...abi.fromSerpent("i"), ...abi.fromSerpent("i")], data)

Note: Serpent uses arbitary binary fields. If you want to store strings it is preferable to ensure it is stored as UTF8. new Buffer(<string>, 'utf8') can be used to ensure it is properly encoded.