Astral Chain PKZ repacker made in Python. Requires the Zstandard Python library (obviously). For more modding stuff, visit https://cabalex.github.io/astral-extractor/

zstd_repacker.py

import zstandard
import os
import sys
import math
from struct import unpack, pack


print(
    "--- ASTRAL EXTRACTOR PKZ REPACKER ---",
    "\nMade by Cabalex - Companion program to the Astral Extractor",
    "\nhttps://cabalex.github.io/astral-extractor",
    "\nUsing the Python ZStandard library because the JS one only works up to 16 MB.\n",
)


if not os.path.isdir("replacement/"):
    os.mkdir('replacement')

replacementFiles = [x for x in os.listdir('replacement/') if len(x.split(".")) > 1]

if len(replacementFiles) == 0:
    print("No use repacking a file without any files to repack with! Insert any files you wanna replace in the replacement/ folder.")
    print("Curious about what files are in the PKZ you're repacking? Visit the Astral Extractor.")
    exit()

if len(sys.argv) == 1:
    print(
        "--- HELP ---"
        "Insert your files that are to be replaced in the .PKZ in the replacement/ folder, e.g. .DAT/.DTT, .BIN, etc.",
        "\nThen, run the program with 'zstd-repacker.py <filename>.pkz' to repack 'em.",
        "\nNOTE: In a lot of cases, you don't need to repack PKZ files- You can just place them in the folder and everything works.",
        "\nHowever, if you are using Ryujinx (Yuzu is fine), or repacking files in core/, event/, or Text/, then you'll need this. :)"
    )
    exit()

filename = sys.argv[1]
f = open(filename, 'rb')
print("[!] Reading PKZ...")
tmpFiles = []
magic, unk, size, numFiles, offset_file_descriptors, fileNameTableLength = unpack('2IQ2IQ', f.read(32))

for i in range(numFiles):
    unpacked = unpack('4Q', f.read(32))
    tmpFiles.append({
        'nameOffset': unpacked[0],
        'size': unpacked[1],
        'offset': unpacked[2],
        'compressedSize': unpacked[3],
        'kind': 'extracted'
    })
filestrings = f.read(fileNameTableLength)
fileNames = [x for x in filestrings.decode('utf-8').split("\x00") if x][1:] # Remove all empty space + 'ZStandard'

files = {}
offset = tmpFiles[0]['offset']
compressor = zstandard.ZstdCompressor()
for i, fname in enumerate(fileNames):
    files[fname] = tmpFiles[i]
    files[fname]['newOffset'] = offset
    if fname in replacementFiles:
        print(f"[+] Found {fname} - Repacking with ZSTD...")
        files[fname]['kind'] = "custom"
        files[fname]['size'] = os.stat(f"replacement/{fname}").st_size
        # Probably not the most optimized but eh
        with open(f"replacement/{fname}", 'rb') as rawf:
            files[fname]['fp'] = compressor.compress(rawf.read())
        files[fname]['compressedSize'] = len(files[fname]['fp'])
    offset += math.ceil(files[fname]['compressedSize']/64)*64 # Padded to 64 byte increments


print("[!] Repacking everything...")
# Repack nameTable
nameTableOffsets = []
nameTableStr = b"ZStandard\x00\x00\x00\x00\x00\x00\x00"
for fname in fileNames:
    nameTableOffsets.append(len(nameTableStr))
    nameTableStr += fname.encode('utf-8')
    nameTableStr += b''.join([b'\x00'] * (8 - (len(nameTableStr) % 8)))

# Repack
newf = open(filename.replace(".pkz", "new.pkz"), 'wb')
newf.write(pack('2IQ2IQ', magic, unk, 32 + len(nameTableStr) + sum([math.ceil(x['compressedSize']/64)*64 for x in files.values()]), numFiles, 32, len(nameTableStr)))

for i, fname in enumerate(fileNames):
    newf.write(pack('4Q', nameTableOffsets[i], files[fname]['size'], files[fname]['newOffset'], files[fname]['compressedSize']))
newf.write(nameTableStr)

if newf.tell() < math.ceil(newf.tell()/64)*64:
        newf.write(b''.join([b'\x00'] * (math.ceil(newf.tell()/64)*64 - newf.tell())))

# Write files and padding
for fname in fileNames:
    if files[fname]['kind'] == 'custom':
        newf.write(files[fname]['fp'])
    else:
        f.seek(files[fname]['offset'])
        newf.write(f.read(files[fname]['compressedSize']))
    if newf.tell() < math.ceil(newf.tell()/64)*64:
        newf.write(b''.join([b'\x00'] * (math.ceil(newf.tell()/64)*64 - newf.tell())))


f.close()
newf.close()
print(f"--- Finished, {len([x for x in files.values() if x['kind'] == 'custom'])} files replaced ({len(fileNames)} files in PKZ) ---")