https://github.com/openwrt/openwrt/issues/9619#issuecomment-1722333145

extract_gzip_trailing_data.py

# See: https://github.com/openwrt/openwrt/issues/9619#issuecomment-1722333145
from tkinter import *
from tkinter import filedialog
from tkinter import messagebox
import gzip
import os
import os.path

def find_gzip_size(gz_filepath):
    st = os.stat(gz_filepath)
    size = st.st_size
    min = 0
    max = size
    with open(gz_filepath, mode='rb') as f:
        gz_data = f.read()
    while True:
        try:
            gzip.decompress(gz_data[0:size])
            return size
        except EOFError:
            min = size
        except gzip.BadGzipFile:
            max = size
        size = (max-min) // 2 + min
        

def find_trailing_data(gz_filepath):
    with open(gz_filepath, mode='rb') as f:
        gz_data = f.read()
    gz_size = find_gzip_size(gz_filepath)
    messagebox.showinfo('detected size', f'{gz_size} bytes')
    
    gz_dirname = os.path.dirname(gz_filepath)
    new_gz_name = 'purified.' + os.path.basename(gz_filepath)
    new_gz_filepath = os.path.join(gz_dirname, new_gz_name)
    
    with open(new_gz_filepath, 'wb') as f:
        f.write(gz_data[0:gz_size])
        
    trailing_filepath = gz_filepath + '.trailing.raw'
    with open(trailing_filepath, 'wb') as f:
        f.write(gz_data[gz_size:])

    messagebox.showinfo('complete', message=f"""purified: {new_gz_filepath}
trailing: {trailing_filepath}""")

def ui():
    root = Tk()
    root.withdraw()
    
    gz_filepath = filedialog.askopenfilename()
    if gz_filepath == '':
        return
    find_trailing_data(gz_filepath)

ui()