I am implementing a binary protocol and sending a buffer to a server. One of the fields, Password, is defined as follows in the documentation:

Data Type: Fixed String
Length: 32 bytes
Offset: 58

Description:
Fixed size of 32 bytes.
Encoded as a character array.
Must be completely filled with valid characters (space padding if required).
Valid characters: 0-9, A-Z, a-z, !, #, $, %, &, *, +, -, ., /, =, @, _.

I have attched below images to get Idea of padding len and offset.

Image of Datatype table

Image of field details table

Here’s my code for constructing the buffer:

const createGatewayRequest = () => {
    const buffer = Buffer.alloc(96); // Total message size: 96 bytes
    let offset = 0;

    // 1. BodyLen: 4 bytes (unsigned int, little-endian)
    buffer.writeUInt32LE(96, offset); 
    offset += 4;

    // 2. TemplateID: 2 bytes (unsigned int, little-endian)
    buffer.writeUInt16LE(10020, offset); 
    offset += 2;

    // 3. NetworkMsgID: 8 bytes (Fixed String, zero-padded)
    buffer.fill(0x00, offset, offset + 8); 
    offset += 8;

    // 4. Pad2: 2 bytes (not used, zero-padded)
    buffer.fill(0x00, offset, offset + 2);
    offset += 2;

    // 5. MsgSeqNum: 4 bytes (unsigned int, little-endian, must be set to 1)
    buffer.writeUInt32LE(1, offset); 
    offset += 4;

    // 6. SenderSubID: 4 bytes (not used, set to 0xFFFFFFFF)
    buffer.writeUInt32LE(0xFFFFFFFF, offset);
    offset += 4;

    // 7. PartyIDSessionID: 4 bytes (unsigned int, little-endian)
    const partyIDSessionID = 123123123;
    buffer.writeUInt32LE(partyIDSessionID, offset); 
    offset += 4;
    
    // 8. DefaultCstmApplVerID: 30 bytes (ASCII, padded with spaces)
    const defaultCstmApplVerID = '2.4';
    buffer.write(defaultCstmApplVerID.padEnd(30, ' '), offset, 30, 'ascii');
    offset += 30;

    // 9. Password: 32 bytes (ASCII, padded with spaces)
    const Password = "pwd12345";
    buffer.write(Password.padStart(32, ' '), offset, 32, 'ascii');
    offset += 32;

    buffer.fill(0x00, offset, offset + 6);
    offset += 6;

    console.log('Gateway Request (hex):', buffer.toString('hex'));

    return buffer; 
};