[Ethereum] How to convert string to bytes32 in web3js

nodejssolidityweb3js

I have a contract with a public variable that's bytes32. If I enter the value 20160528 then it auto converts to bytes32. Is there anyway to convert it back from the nodejs terminal? I've been trying

web3.toAscii(testInstance.Date.call())

but it just gives me nonsense. Here is the the test code:

contract test {
  bytes32 public Date;

  function test(bytes32 _date){
      Date=_date; 
  }
}

Best Answer

For web3 0.x:

You need to use web3.fromAscii(val) to write correct bytes32 input to contract.

And you are right, anyone can read it with web3.toAscii(val).

Full web3.js code in terms of your designations:

//sets bytes32
testInstance.test.sendTransaction(web3.fromAscii("20160528"), options);

//gets bytes32
testInstance.Date.call(function(err, val) {
    if  (err) console.log(err);
    console.log(web3.toAscii(val));
    // will print "20160528"
 });

For web3 1.0:

Note: fromAscii has been deprecated

You need to use web3.utils.asciiToHex(val) to write correct bytes32 input to contract.

And you are right, anyone can read it with web3.utils.hexToAscii(val).

Full web3.js code in terms of your designations:

//sets bytes32
testInstance.methods.test(web3.utils.asciiToHex("20160528")).send(options);

//gets bytes32
testInstance.methods.Date().call(function(err, val) {
    if  (err) console.log(err);
    console.log(web3.utils.hexToAscii(val));
    // will print "20160528"
 });

Related Solutions

[Ethereum] Solidity return string not hex

Use web3.js like contractInstance.getItem.call(key).

Or mark getItem as constant: function getItem(address key) constant returns (string) and then you can use:

contractInstance.getItem(key)

web3.js will automatically decode the bytes for you. Contracts only have binary data, hex is a more compact way of viewing that data, and that's why you see hex. The binary data is also encoded according to an ABI, so that values can be distinguished, for example between what's just a number and a string.

[Ethereum] Why can I store over 32 characters in bytes32

bytes-x(1~32) can store a string, if the length of string is greater than x, then the part out of length will be dropped. It's a simple test contract

pragma solidity ^0.4.13;

contract Bytes32Test {

    bytes32 msg;

    function add(bytes32 _msg){
        msg = _msg;
    }

    function show() constant returns (bytes32){
        return msg;
    }

}

and i invoke add function by a param 'some string over 32 characters in length that can seem to be up to 128 characters in length to be stored in bytes32', and now we call show function, the result is

0x736f6d6520737472696e67206f76657220333220636861726163746572732069

the result is "some string over 32 characters i" if we convert it from hex to ascii.

> web3.toAscii("0x736f6d6520737472696e67206f76657220333220636861726163746572732069")
"some string over 32 characters i"

Hope it helps~