Handling of byte types by either truffle or web3 seems to be incorrect

Issue

Handling of byte types by either truffle or web3 seems to be incorrect.

Steps to Reproduce

On-Chain:

contract MyContract {
    function func(bytes4 x) public pure returns (bytes4) {
        return x;
    }
}

Off-Chain:

contract("Test", function() {
    it("test", async function() {
        let myContract = await artifacts.require("MyContract.sol").new();
        let retVal = await myContract.func(0x00012345);
        console.log(retVal);
    });
});

Expected Behavior

Print 0x00012345

Actual Results

Print 0x12345000

It seems that every leading zero digit in hexadecimal format (i.e., every leading chunk of 4 zero bits) is forced to become trailing somehow.

This happens on client side for sure (you may confirm it by adding require(x == 0x12345000) inside the on-chain function above.

It seems to be the case for other byte types as well (e.g. bytes1, bytes2, etc).

Environment

• Operating System: Windows 10
• Ethereum client: ganache-cli: 6.1.0
• truffle version: 4.1.3
• node version: 8.9.3
• npm version: 5.5.1

[barakman]

@cgewecke: Yes, thank you for clarifying it!

[cgewecke]

@barakman If you quote the bytes when you pass them into the function

await myContract.func("0x00012345");

does that resolve it? Think JS is interpreting the input as a number rather than bytes and Solidity formats these differently. It looks like uint is left-aligned in the word, bytes right-aligned, based on encodings docs at over at solidity here.