Parsing contract method output as an array of fields

Question

I have a constant method in a Smart Contract that returns this array:

(uint256 _field1, uint256 _field2, uint256 _field3, address _field4, string _field5)

When invoking it I got this hex result:

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

How can I parse it? How can I know the exact padding for every field? Thx!

Answer 1

If you want to do it in NodeJs, you can create a file named decodeParams.js and which contains:

#!/usr/bin/nodejs

const Web3 = require("web3");
const web3 = new Web3();
const Coder = require("./node_modules/web3/lib/solidity/coder.js");

var result = Coder.decodeParams(
    [ "uint256", "uint256", "uint256", "address", "string" ],
    "0000000000000000000000000000000000000000000000000000000000000001" + // Split for personal readability
    "0000000000000000000000000000000000000000000000000000000000000000" +
    "0000000000000000000000000000000000000000000000000000000058581b50" + 
    "000000000000000000000000f28dafbfeb41bf32869c9d498da0d651d0206ed4" +
    "00000000000000000000000000000000000000000000000000000000000000a000000000000000000000000000000000000000000000000000000000000000414869204a75616e2c2074686973206973206d61726b65747061792073656e64696e6720666972737420626c6f636b636861696e2065766572206d6573736167652100000000000000000000000000000000000000000000000000000000000000");

console.log("0x" + result[0].toString(16));
console.log("0x" + result[1].toString(16));
console.log("0x" + result[2].toString(16));
console.log("0x" + result[3]);
console.log(web3.toUtf8(result[4]));

Then to make this work:

$ npm install web3
$ chmod u+x decodeParams.js
$ ./decodeParams.js 
0x1
0x0
0x58581b50
0x0xf28dafbfeb41bf32869c9d498da0d651d0206ed4
...

Answer 2

Well, I found the answer myself... just a juxtaposition of fields like this, in PHP code:

list($_field1, $_field2, $_field3, $_zeros, $_field4, $_field5) = sscanf($output, "0x%64s%64s%64s%24s%40s%s");
$_field1 = hexdec($_field1);
$_field2 = hexdec($_field2);
$_field3 = hexdec($_field3);
$_field4 = '0x' . $_field4;
$_field5 = hexstr($_field5);
echo "\n<hr>list = ($_field1, $_field2, $_field3, $_field4, $_field5)";