Web3.js – Is Transaction Data the Same as Transaction Input in Web3.js?

transactionsweb3js

The Ethereum RPC API documentation accepts a data field when requesting to sendTransaction.

I notice that when I retrieve a historical transaction from the blockchain, I get back an input field and no data field, such as when using the web3 getTransaction function.

Are the data and input fields equivalent, or are there any differences?

Best Answer

It's the same thing.

When you're going to send a transaction, the data is the combination of: method, parameters which are defined in the ABI, and they're encoded.

data: tokenContract.methods.setPoints(user, point).encodeABI()

When you decode the input data then you'll see something like:

{
  "method": "addLiquidity",
  "types": [
    "address",
    "address",
    "uint256",
    "uint256",
    "uint256",
    "uint256",
    "address",
    "uint256"
  ],
  "inputs": [
    "f45b409a2b978ec02Bb6084e6Acc42867a78Ee9c",
    "326C977E6efc84E512bB9C30f76E30c160eD06FB",
    {
      "type": "BigNumber",
      "hex": "0x043c33c1937564800000"
    },
    {
      "type": "BigNumber",
      "hex": "0x038d7ea4c68000"
    },
    {
      "type": "BigNumber",
      "hex": "0x01"
    },
    {
      "type": "BigNumber",
      "hex": "0x01"
    },
    "f39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
    {
      "type": "BigNumber",
      "hex": "0x61fcafda"
    }
  ],
  "names": [
    "tokenA",
    "tokenB",
    "amountADesired",
    "amountBDesired",
    "amountAMin",
    "amountBMin",
    "to",
    "deadline"
  ]
}

This is created by the encodeABI() function. There's an online lab to check for the input. You can use it to check the input data. Given we can decode it manually, but it faster to use tool.

Related Solutions

Private Blockchain – Extracting Data from an Account

The data you're sending is part of the transaction, but it is not "added" to the account. There is storage associated with accounts (accessed via eth.getStorageAt(address,location)) but it will be empty unless a contract stores data there.

Since the data is associated only with the transaction, not with the account, the best way to access it is to use filters

var filter = eth.filter({fromBlock:0,toBlock:"latest", address:eth.accounts[1]});
var data = [];
filter.get(function(error,result){
    data.append(eth.getTransaction(result.transactionHash).data);
});

console.log(data)

Alternatively, you could create a contract that simply records all data sent to it:

contract Store {

    bytes[] public data;

    function(){
        data.push(msg.data);
    }
}

Then just fetch the data with store.data(index);

[Ethereum] Ethereum transaction binary data field

Stepping into the web3 javascript functions when sending a transaction yielded some insight. Turns out the data field is made up of the following:

The signature of the method. This is obtained by doing a sha3 (256 bit by the looks of it) on the hex-encoded method prototype and truncating it to 8 characters.
The arguments to the method. These are just converted to hex format.

Both of the above are serialised into a single buffer.

From that, you could build your own transaction data using the method prototype (e.g. myMethod(uint8,uint16)).

Best Answer

Related Solutions

Private Blockchain – Extracting Data from an Account

[Ethereum] Ethereum transaction binary data field

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