UTF-16 Big Endian Encoding for Custom Packer

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But don’t worry, this tutorial will have you packing like a pro in no time!

First off, what UTF-16 big endian encoding is and how it works. Essentially, each character in your text is represented by 2 bytes (or 16 bits), with the most significant byte coming first. This means that if you have a string like “Hello, world!”, it would be stored as:

0x48 0x65 0x6C 0x6C 0x6F 0x2C 0x20 0x77 0x6F 0x72 0x6C 0x64 0x21

But if you’re using a little endian machine (like most modern computers), this can cause some issues. That’s because the bytes are stored in reverse order, which means that when you read them back out, they need to be swapped around. This is where UTF-16 big endian encoding comes in it allows us to store our text in a way that doesn’t require any byte swapping on little endian machines!

So how do we pack this data into a custom format? Well, first off, let’s create a simple Python script to handle the packing and unpacking. Here’s what it might look like:

# Import the struct module to handle binary data
import struct

# Define a function to pack text into UTF-16 big endian bytes
def pack_utf16be(text):
    # Add a BOM (Byte Order Mark) to indicate the encoding
    bom = b'\x00\xfe'
    # Use the struct module to pack the text into big endian bytes
    # The '>H' format string specifies that each character will be packed as an unsigned short (2 bytes)
    # The '*' operator unpacks the characters from the text string
    # The map() function applies the ord() function to each character, converting it to its corresponding Unicode code point
    # The result is a tuple of packed bytes, which is then joined with the BOM and returned
    return bom + struct.pack('>H'*len(text), *map(ord, text))

# Define a function to unpack data as UTF-16 big endian bytes and convert it to a string
def unpack_utf16be(data):
    # Use the struct module to unpack the data as big endian bytes
    # The '>H' format string specifies that each character is an unsigned short (2 bytes)
    # The '*' operator unpacks the bytes into a tuple
    # The list comprehension iterates through the tuple and converts each character to its corresponding Unicode code point
    # The chr() function converts the code point to its corresponding character
    # The result is a list of characters, which is then joined into a string and returned
    return ''.join([chr(x) for x in struct.unpack('>H'*(len(data)/2), data[2:]) if x != 0xFFFE])

Let’s break this down a bit. The `pack_utf16be()` function takes our text and converts it to UTF-16 big endian bytes using the Python struct module. We first add a byte order mark (BOM) of 0xFFFE, which is used to indicate that we’re using UTF-16 big endian encoding. Then we use `struct.pack()` with the ‘>H’ format string to pack each character as a 2-byte unsigned integer in big endian order.

The `unpack_utf16be()` function takes our packed data and unpacks it using the same struct module, but this time we use ‘H’. This is because we want to read the bytes as little endian integers (since that’s what our machine uses), but then convert them back to characters in big endian order.

So let’s test out our script! Here’s an example usage:

# Import the struct module to work with binary data
import struct

# Define a function to pack a string into UTF-16 big endian format
def pack_utf16be(text):
    # Initialize an empty list to store the packed data
    packed_data = []
    # Loop through each character in the string
    for char in text:
        # Use the struct module to pack the character as a big endian unsigned short
        # '<H' indicates little endian format, which is what our machine uses
        # '>H' indicates big endian format, which is what we want for UTF-16
        # '!' can also be used to indicate big endian format
        # Append the packed data to the list
        packed_data.append(struct.pack('>H', ord(char)))
    # Return the packed data as a bytes object
    return b''.join(packed_data)

# Define a function to unpack UTF-16 big endian data into a string
def unpack_utf16be(data):
    # Initialize an empty string to store the unpacked text
    unpacked_text = ''
    # Loop through the data in steps of 2, since each character is represented by 2 bytes
    for i in range(0, len(data), 2):
        # Use the struct module to unpack the data as a big endian unsigned short
        # '<H' indicates little endian format, which is what our machine uses
        # '>H' indicates big endian format, which is what we want for UTF-16
        # '!' can also be used to indicate big endian format
        # Convert the unpacked data back to a character and append it to the string
        unpacked_text += chr(struct.unpack('>H', data[i:i+2])[0])
    # Return the unpacked text
    return unpacked_text

# Define a test string
text = "Hello, world!"
# Pack the string into UTF-16 big endian format
packed_data = pack_utf16be(text)
# Print the packed data
print("Packed data:", packed_data)
# Unpack the data into a string
unpacked_text = unpack_utf16be(packed_data)
# Print the unpacked text
print("Unpacked text:", unpacked_text)

This should output:

# The following code is used to unpack data and convert it into readable text.

# First, we define a variable "packed_data" and assign it a string of bytes using the "b" prefix.
packed_data = b'\x00\xfeHello, world!\x00'

# Next, we use the "decode()" method to convert the bytes into a string, using the "utf-8" encoding.
unpacked_text = packed_data.decode("utf-8")

# Finally, we print the unpacked text, which should now be readable.
print("Unpacked text:", unpacked_text)

# Output: Unpacked text: Hello, world!

# The "b" prefix is used to indicate that the data is in bytes format.
# The "decode()" method is used to convert the bytes into a string.

And there you have it UTF-16 big endian encoding for custom packers! Of course, this is just a simple example and there are many other ways to handle packing and unpacking data. But hopefully this tutorial has given you a good starting point for your own projects!

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