Decoder and encoder for the Ethereum ABI
JavaScript
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holgerd77 Merge pull request #62 from ritave/patch-2
Fix serpent examples of rawEncode / rawDecode
Latest commit 00ba846 Jul 1, 2018

README.md

ethereumjs-abi

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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

Planned for the future is supporting the JSON ABI definition:

var abi = require('ethereumjs-abi')

// need to have the ABI definition in JSON as per specification
var tokenAbi = [{"constant":true,"inputs":[{"name":"","type":"address"}],"name":"balanceOf","outputs":[{"name":"","type":"uint256"}],"type":"function"},{"constant":false,"inputs":[{"name":"_to","type":"address"},{"name":"_value","type":"uint256"}],"name":"transfer","outputs":[{"name":"success","type":"bool"}],"type":"function"},{"inputs":[],"type":"constructor"}]

var encoded = abi.encode(tokenAbi, "balanceOf(uint256 address)", [ "0x0000000000000000000000000000000000000000" ])

var decoded = abi.decode(tokenAbi, "balanceOf(uint256 address)", data)

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.

Contributing

I am more than happy to receive improvements. Please send me a pull request or reach out on email or twitter.

There is a lot missing, grep for FIXME in the source code to find inspiration.

License

Copyright (C) 2015 Alex Beregszaszi

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.