Unpacker for FSG: A Complete Guide to Extracting Game Files

Unpacker for FSG: A Complete Guide to Extracting Game Files

What “FSG” likely means

FSG commonly refers to a proprietary archive/container format used by some game developers to bundle assets (models, textures, audio, scripts). This guide assumes FSG is an archive format holding multiple file types and metadata, not a filesystem driver.

Goals of an unpacker

• Extract individual files and directory structure from an FSG archive.
• Identify file types by signatures and extensions.
• Handle compression and simple encryption if present.
• Preserve metadata (timestamps, order) where possible.

Tools you’ll need

• Hex editor (HxD, 010 Editor)
• Command-line utilities (xxd, hexdump)
• Scripting language (Python with struct, binwalk, pathlib)
• binwalk (to detect embedded files)
• zlib/lzma libraries (if archive uses common compression)
• Optional: Game-specific community tools/forums for signatures

Step-by-step unpacking workflow

1. Create backups

   • Copy the original .fsg file; never work on the original.

2. Inspect file header

   • Open in a hex editor. Look at the first 16–64 bytes for magic bytes, version, or header size.
   • Record offsets for later.

3. Search for known signatures

   • Run binwalk and hexdump to find embedded file signatures (PNG, OGG, ZIP, DDS).
   • Note offsets for each match.

4. Map archive structure

   • Look for patterns: repeated entry headers, offset tables, length fields.
   • Common layout: [global header][directory table][data blocks]. Directory table entries often contain filename offset, data offset, size, flags.

5. Detect compression/encryption

   • If data blocks start with zlib (0x78 0x9C) or LZMA signatures, mark as compressed.
   • If values look random (high entropy) and no known signatures, mild encryption may be present—look for XOR with single-byte key or simple rotation by checking frequency of bytes in repeated known file headers.

6. Prototype extraction script (Python)

   • Read header, parse directory entries, seek to data offsets, read lengths, detect compression signature, decompress if needed, write outputs using detected file extension or guessed type via python-magic.

   Example (outline):

   Code
   Copy CodeCopied
   with open(‘archive.fsg’,‘rb’) as f: header = f.read(header_size)
   
    
   # parse entries: for each entry -> name_offset, data_offset, size, flags f.seek(name_offset); name = read_cstring(f) f.seek(data_offset); data = f.read(size) if is_zlib(data): data = zlib.decompress(data) with open(name,'wb') as out: out.write(data) 
   
   
   

7. Handle unknown compression

   • Try common decompressors (zlib, LZ4, LZMA, Brotli).
   • If single-byte XOR suspected, brute-force XOR keys by checking for known file signatures after XOR.

8. Recover filenames

   • Filenames may be stored in the archive or as a separate table. If missing, infer names from file signatures (e.g., image_0001.png).

9. Automate and batch process

   • Add logging, error handling, multiprocessing for large archives.

10. Validate extracted files

    • Open images/audio, run file-type checks, compare sizes, and ensure decompression completed without errors.

Legal and ethical notes

Do not unpack archives from games you do not own or distribute extracted assets without permission. Respect license and copyright.

Troubleshooting tips

• If directory table looks encrypted, search for XOR patterns by comparing two similar archives.
• If offsets seem relative, try adding base offset found in header.
• Use community resources (modding forums, GitHub) for existing unpackers or format docs.

Quick checklist

• Backup original
• Identify header and table layout
• Detect compression/encryption
• Write extraction script with decompression and filename recovery
• Validate outputs and iterate

If you want, I can produce a concrete Python extractor template tailored to a sample FSG file (provide one or its hex header).