Dynamically Determine the Length of value Based on the flags Bitmask

[jiawei14755]

Description

When parsing/serializing a buffer, I need to dynamically determine the length of the value field in a structure based on certain bits in the flags bitmask. For example:

• If a specific bit (e.g., 0x08) is set in flags, parse value as uint8
• Otherwise, parse value as uint16

Current Code Example

Currently, I’m using the restructure library with the following code:

const r = require('restructure');

const uint8 = new r.Struct({
    flags: r.uint8,
    value: r.uint8
});

const uint16 = new r.Struct({
    flags: r.uint8,
    value: r.uint16,
});

const buffer = Buffer.from([0x08, 0x34, 0x12]);
let flags = buffer.readUInt8();

if (flags & 0x8) {
    console.log(uint8.fromBuffer(buffer));
} else {
    console.log(uint16.fromBuffer(buffer));
}

Problem

This approach is limited since it requires manually determining the structure type based on flags. I would prefer a more dynamic way to define this directly within the restructure structure, allowing flags to control the size of value without extra conditionals.