Shrekt Shrekt - 1 month ago 7
C# Question

Convert C# To NodeJS

Hi so am trying to convert this C# function to NodeJS but it does not work I don't really know what is wrong lemme show some code and outputs

C#:

private static byte[] ConvertMsg(byte[] message, byte type = 255, byte cmd = 255)
{
int msgLength = message.Length;
byte[] bArray = new byte[msgLength + 3];
bArray[0] = type;
bArray[1] = cmd;
Buffer.BlockCopy(message, 0, bArray, 2, msgLength);
bArray[msgLength + 2] = 0;
return bArray;
}

static void Main()
{

byte[] encrypted = ConvertMsg(Encoding.Default.GetBytes("hi"),3,3);
Console.WriteLine($"Encrypted: {Convert.ToBase64String(encrypted)}");

Console.ReadKey();
}


Output:

AwNoaQA=


NodeJS:

function ConvertMsg(message, type=255, cmd=255){
let length = message.length;
let bArray = Buffer.alloc(length+3);
bArray[0] = type;
bArray[1] = cmd;

bArray.copy(message,0,length);

bArray[length + 2] = 0;
return bArray;
}

let encrypted = ConvertMsg(Buffer.from("hi"),3,3);
console.log(encrypted.toString("base64"));


Output:

AwMAAAA=


As you can see the output is not the same any help is much appreciated, please explain when you answer I would like to learn more thank you.

Answer

According to Buffer documentation, .copy(target[, targetStart[, sourceStart[, sourceEnd]]])

Copies data from a region of buf to a region in target even if the target memory region overlaps with buf.

Here

// means copy 'bArray' starting from length to 'message' starting from 0
bArray.copy(message, 0, length); 

You do not copy contents of message to bArray. You do the opposite thing - you copy bArray contents, which is [3, 3, 0, 0, 0] by now to message, and actually overwrite your message.

Then, you output this bArray, which results in AwMAAAA= which is Base64 representation of [3, 3, 0, 0, 0].

You may want to change your function in this way:

function ConvertMsg(message, type=255, cmd=255){
    let length = message.length;
    let bArray = Buffer.alloc(length + 3);

    bArray[0] = type;
    bArray[1] = cmd;

    // means copy 'message' starting from 0 to 'bArray' starting from 2
    message.copy(bArray, 2);

    bArray[length + 2] = 0;
    return bArray;
}
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