How to batch list into a single bytes object?

Question

Let's say I have a string list of parameters

["Example String", "vitalikbuterin", "1000"]

How can I encode this list into a bytes object, and then decode the bytes to get the exact same list?

Answer 1

You could convert string arrays to bytes where each byte is a character and you can use byte 0x00 as a separator.

Here's a contract with the 2 methods you need to pack or unpack a string[] memory to/from a bytes memory

// SPDX-License-Identifier: GPL-3.0

pragma solidity 0.8.18;

contract StringsAndBytes {
    function packString(string[] memory list) external pure returns (bytes memory){
        bytes memory packedArray;
        if (list.length == 0) {
            return packedArray;
        }
        packedArray = abi.encodePacked(list[0]);
        for (uint i = 1; i < list.length; i++) {
            packedArray = abi.encodePacked(packedArray, hex"00", list[i]);
        }
        return packedArray;
    }

    function unpackString(bytes memory pack) external pure returns (string[] memory) {
        if (pack.length == 0) {
            string[] memory emptyArray;
            return emptyArray;
        }
        uint256 elementCount = 1;
        for (uint i = 0; i < pack.length; i++) {
            if (pack[i] == 0x00) {
                elementCount++;
            }
        }
        string[] memory list = new string[](elementCount);
        uint256 arrayIndex = 0;
        string memory element = "";
        for (uint i = 0; i < pack.length; i++) {
            if (pack[i] == 0x00) {
                list[arrayIndex] = element;
                element = "";
                arrayIndex++;
                continue;
            }
            element = string(abi.encodePacked(element, pack[i]));
        }
        list[arrayIndex] = element;
        return list;
    }
}

Now if I call

packString(["Example String", "vitalikbuterin", "1000"])

I get: 0x4578616d706c6520537472696e6700766974616c696b6275746572696e0031303030

Then i can call

unpackString("0x4578616d706c6520537472696e6700766974616c696b6275746572696e0031303030")

I get ["Example String", "vitalikbuterin", "1000"]

Edit: Simpler but non-packed

I had never used abi.decode before in my life. I made this answer, then I thought I'd ask an AI that shall not be named, it gave me a much simpler almost working code (that I fixed) but the resulting bytes end up with a lot of zeroes:

// SPDX-License-Identifier: GPL-3.0

pragma solidity ^0.8.0;

contract StringsAndBytesByAI {
    function encodeStringList(string[] memory stringList) public pure returns (bytes memory) {
        return abi.encode(stringList);
    }

    function decodeStringList(bytes memory encodedList) public pure returns (string[] memory) {
        string[] memory decodedList = abi.decode(encodedList, (string[]));
        
        return decodedList;
    }
}

calling

encodeStringList(["Example String", "vitalikbuterin", "1000"])

gives the following result:

0x00000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000003000000000000000000000000000000000000000000000000000000000000006000000000000000000000000000000000000000000000000000000000000000a000000000000000000000000000000000000000000000000000000000000000e0000000000000000000000000000000000000000000000000000000000000000e4578616d706c6520537472696e67000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000e766974616c696b6275746572696e00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000043130303000000000000000000000000000000000000000000000000000000000

And it can be reversed:

decodeStringList("0x00000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000003000000000000000000000000000000000000000000000000000000000000006000000000000000000000000000000000000000000000000000000000000000a000000000000000000000000000000000000000000000000000000000000000e0000000000000000000000000000000000000000000000000000000000000000e4578616d706c6520537472696e67000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000e766974616c696b6275746572696e00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000043130303000000000000000000000000000000000000000000000000000000000")

Result: ["Example String", "vitalikbuterin", "1000"]

If you need to optimize for storage, use the first one, if you need to optimize for computation, use the second one.

Answer 2

Hello you can use this website to encode https://www.rapidtables.com/convert/number/hex-to-decimal.html

Answer 3

Batching a list into a single bytes object can be done by using the encode_abi() function from Solidity. This function takes a list of elements and returns a bytes object with the data stored in the proper format.

Answer 4

To batch list into a single bytes object, you can use the "bytearray" function in Python. This function takes a list of values and returns a bytes object.

For example, if you have a list of numbers such as [1,2,3,4], you can create a bytes object using this code:

bytearray([1,2,3,4])

This will return a bytes object containing the values 1,2,3,4.