Decoding contract output of web3 eth call

Question

I have written data to a contract using sendRawTransaction, and am trying to fetch it using web3.eth.call for the function :
function checkRecord(uint id, bytes email) constant returns (uint id2, bytes email2, bytes hash) {..}

I create call data as
var callData = contract.checkRecord.getData(id, email)
to get
'0xf1e8a43c0000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000156d617467656f2e3230303840676d61696c2e636f6d0000000000000000000000'

and fetch result as
result = web3.eth.call({'to': address, 'from': account, 'data': callData})

where result is
'0x0000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000006000000000000000000000000000000000000000000000000000000000000000a000000000000000000000000000000000000000000000000000000000000000156d617467656f2e3230303840676d61696c2e636f6d00000000000000000000000000000000000000000000000000000000000000000000000000000000000000'

How do i decode the result back to (uint, bytes, bytes) ?

Answer 1

you can use web3 built-in functionality:

web3.eth.abi.decodeParameters(typesArray, hexString);

see link

Answer 2

The easiest way is 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:

Answer 3

As the web3 documentation points out web3.eth.call returns a String, which is the returned data of the call, e.g. a codes functions return value. In your case the result string contains a uint (which is an alias for uint256) and two dynamically-sized byte arrays.

Split the result into 32-byte chunks and then apply a toAscii(hexString) function on the chunks.

With this method you'll get that the uint is the number 2 padded with zeroes, it looks like this: 0x0000000000000000000000000000000000000000000000000000000000000002. The first byte array is {96,160,21,[email protected]}. The second byte array contains only zeros.