decode.py

#! /usr/bin/env python3

import argparse
import cv2
import base64
import hashlib
import json
import os
from pyzbar.pyzbar import decode, ZBarSymbol

def find_free_name(location, name):
    while os.path.exists(os.path.join(location, name)):
        name = f'copy-{name}'
    return name

def main():

    parser = argparse.ArgumentParser(
            description="Decode a QR-code sequence into a file")

    parser.add_argument("input_dir", help="Directory with pics to decode")
    parser.add_argument("--output_dir", "-o", default=".",
            help="Directory for output file, default is the current one")

    args = parser.parse_args()

    split_content = list()
    first = True
    output_name = 'UNKNOWN_FILENAME'
    checksum = None
    for fname in os.listdir(args.input_dir):
        img = cv2.imread(os.path.join(args.input_dir, fname))
        scanned = decode(img, symbols=[ZBarSymbol.QRCODE])
        if len(scanned) != 1:
            print(f"ERROR: couldn't detect a QR-code in {fname}")
            exit(1)

        descriptor = json.loads(scanned[0].data)

        if first:
            first = False
            output_name = descriptor['filename']
            checksum = descriptor['checksum']
            continue

        split_content.append(base64.b64decode(descriptor['data'].encode('utf-8')))

    content = b''.join(split_content)
    os.makedirs(args.output_dir, exist_ok=True)
    output_name = find_free_name(args.output_dir, output_name)
    with open(os.path.join(args.output_dir, output_name), 'wb') as f:
        f.write(content)
    print(f"Stored to {os.path.join(args.output_dir, output_name)}")

    if checksum != hashlib.sha256(content).hexdigest():
        print("ERROR: invalid checksum!")
        exit(1)

if __name__ == "__main__":
    main()