Rename obfuscated files using a .par2 file for SABnzbd, by parsing the .par2 file and matching the source files.

deobfuscate_par2.py

#!/usr/bin/env python

import os
import sys
import struct
import fnmatch
import hashlib
from os import path

# see: http://parchive.sourceforge.net/docs/specifications/parity-volume-spec/article-spec.html
STRUCT_PACKET_HEADER = struct.Struct("<"
    "8s"  # Magic sequence
    "Q"   # Length of the entire packet (including header), must be multiple of 4
    "16s" # MD5 Hash of packet
    "16s" # Recovery Set ID
    "16s" # Packet type
)

PACKET_TYPE_FILE_DESC = 'PAR 2.0\x00FileDesc'
STRUCT_FILE_DESC_PACKET = struct.Struct("<"
    "16s" # File ID
    "16s" # MD5 hash of the entire file
    "16s" # MD5 hash of the first 16KiB of the file
    "Q"   # Length of the file
)

def decodePar(dir, parfile):
    with open(path.join(dir, parfile), 'rb') as file:
        while (True):
            header = file.read(STRUCT_PACKET_HEADER.size)
            if not header: break # file rully read

            (_, packetLength, _, _, packetType) = STRUCT_PACKET_HEADER.unpack(header)
            bodyLength = packetLength - STRUCT_PACKET_HEADER.size

            # only process File Description packets
            if (packetType != PACKET_TYPE_FILE_DESC):
                # skip this packet
                file.seek(bodyLength, os.SEEK_CUR)
                continue

            chunck = file.read(STRUCT_FILE_DESC_PACKET.size)
            (_, _, hash16k, filelength) = STRUCT_FILE_DESC_PACKET.unpack(chunck)

            # filename makes up for the rest of the packet, padded with null characters
            targetName = file.read(bodyLength - STRUCT_FILE_DESC_PACKET.size).rstrip('\0')
            targetPath = path.join(dir, targetName)

            # file already exists, skip it
            if (path.exists(targetPath)):
                print "File already exists: " + targetName
                continue

            # find and rename file
            srcPath = findFile(dir, filelength, hash16k)
            if (srcPath is not None):
                os.rename(srcPath, targetPath)
                print "Renamed file from " + path.basename(srcPath) + " to " + targetName
            else:
                print "No match found for: " + targetName

def findFile(dir, filelength, hash16k):
    for filename in os.listdir(dir):
        filepath = path.join(dir, filename)

        # check if the size matches as an indication
        if (path.getsize(filepath) != filelength): continue

        with open(filepath, 'rb') as file:
            data = file.read(16 * 1024)
            m = hashlib.md5()
            m.update(data)

            # compare hash to confirm the match
            if (m.digest() == hash16k):
                return filepath
    return None

# find par2 files
outputDir = os.environ['SAB_COMPLETE_DIR']
for root, dirnames, filenames in os.walk(outputDir):
    for filename in fnmatch.filter(filenames, '*.par2'):
        decodePar(root, filename)

sys.exit(0)