How to encode and decode ABI data?
Can someone show me an example with web3js library?
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Are you talking about decoding the input and output of a call to a contract? Oe the contract itself? If the former, why? web3 will provide you with stub methods that let you call contract methods without having to do this yourself. – Nick Johnson Apr 26 '16 at 14:05
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If the question is about abi params, you can take a look at these two web3.js files:
https://github.com/ethereum/web3.js/blob/master/test/coder.encodeParam.js https://github.com/ethereum/web3.js/blob/master/test/coder.decodeParam.js
Although these functions are not a part of public web3.js interface. Mostly because they need a proper refactor.
There is also a command line tool created especially for encoding function calls and retrieving output data.
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There is alternative JS tool, which should be ready in couple of days: github.com/jacogr/ethabi-js – debris May 19 '16 at 8:27
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In case you need an online tool to encode parameters to abi format you can use https://abi.hashex.org/. It has functionality to auto parse contract's abi to get function names and parameter types and provides convenient way to enter their values.
Here is an example of using this service
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I modified web3 npm library by including the following line
Web3.SolidityCoder = require('./lib/solidity/coder');
after the Web3 object gets created.
In the client side, you can use it with following code.
web3 = require('web3'); // This will import the web3 library.
web3.SolidityCoder.encodeParams([types array], [values array])
web3.SolidityCoder.decodeParams([types array], encodedData)
This of course is a hack and is suitable for quick testing, if this would be a recommended approach, I could push changes to official web3 library. I'll check with them.
Update: There is a getData() method available in web3.js which you can use for this purpose. Here is the link to documentation: https://github.com/ethereum/wiki/wiki/JavaScript-API#contract-methods
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web3 1.0:
web3.eth.abi.decodeParameter('address', '0000000000000000000000001829d79cce6aa43d13e67216b355e81a7fffb220')
you should receive:
0x1829D79cCE6aA43D13E67216b355E81A7FfFB220
you can also try:
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The easiest way to to use "abi-decoder". I forked the repository and created index.html for easy usage.
You can download and use it from: https://github.com/Muhammad-Altabba/abi-decoder (you can later check it at https://github.com/ConsenSys/abi-decoder once they will accept my Pull-Request)
To download and run using NPM:
npm install abi-decoder
bower install abi-decoder
Then download https://github.com/Muhammad-Altabba/abi-decoder/index.html to the same directory. Then open the file "index.html" in browser.
You will get:
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If you mean the data for sending a message, a simple way is to encode it like this:
contract = web3.eth.contract(abi).at(cAddr);
payload = contract['transfer'].getData(to, amont);
The payload is just what you want.
