tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
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snapshot-hack.py (3610B)

      1 #!/usr/bin/python3
      2 # This Source Code Form is subject to the terms of the Mozilla Public
      3 # License, v. 2.0. If a copy of the MPL was not distributed with this
      4 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
      5 
      6 import subprocess
      7 import sys
      8 import threading
      9 import urllib.request
     10 from urllib.parse import urlparse, urlunparse
     11 
     12 # This script interposes between APT and its HTTP method. APT sends queries on
     13 # stdin, and expect responses on stdout. We intercept those and change the
     14 # snapshot.debian.org URLs it requests on the fly, if the equivalent URLs
     15 # exist on deb.debian.org.
     16 
     17 URI_HEADER = "URI: "
     18 
     19 
     20 def url_exists(url):
     21    try:
     22        req = urllib.request.Request(url, method="HEAD")
     23        response = urllib.request.urlopen(req)
     24        return response.getcode() == 200
     25    except Exception:
     26        return False
     27 
     28 
     29 def write_and_flush(fh, data):
     30    fh.write(data)
     31    fh.flush()
     32 
     33 
     34 def output_handler(proc, url_mapping, lock):
     35    for line in proc.stdout:
     36        if line.startswith(URI_HEADER):
     37            url = line[len(URI_HEADER) :].rstrip()
     38            # APT expects back the original url it requested.
     39            with lock:
     40                original_url = url_mapping.get(url, None)
     41            if original_url:
     42                write_and_flush(sys.stdout, line.replace(url, original_url))
     43                continue
     44        write_and_flush(sys.stdout, line)
     45 
     46 
     47 def main():
     48    proc = subprocess.Popen(
     49        ["/usr/lib/apt/methods/http"],
     50        stdin=subprocess.PIPE,
     51        stdout=subprocess.PIPE,
     52        text=True,
     53    )
     54    url_mapping = {}
     55    lock = threading.Lock()
     56    output_thread = threading.Thread(
     57        target=output_handler, args=(proc, url_mapping, lock), daemon=True
     58    )
     59    output_thread.start()
     60 
     61    while True:
     62        try:
     63            line = sys.stdin.readline()
     64        except KeyboardInterrupt:
     65            # When apt cuts the connection, we receive a KeyboardInterrupt.
     66            break
     67        if not line:
     68            break
     69 
     70        if line.startswith(URI_HEADER):
     71            url = line[len(URI_HEADER) :].rstrip()
     72            url_parts = urlparse(url)
     73            # For .deb packages, if we can find the file on deb.debian.org, take it
     74            # from there instead of snapshot.debian.org, because deb.debian.org will
     75            # be much faster. Hopefully, most files will be available on deb.debian.org.
     76            if url_parts.hostname == "snapshot.debian.org" and url_parts.path.endswith(
     77                ".deb"
     78            ):
     79                # The url is assumed to be of the form
     80                # http://snapshot.debian.org/archive/section/yymmddThhmmssZ/...
     81                path_parts = url_parts.path.split("/")
     82                # urlparse().path always starts with a / so path_parts is
     83                # expected to look like ["", "archive", "section", "yymmddThhmmssZ", ...]
     84                # we want to remove "archive" and "yymmddThhmmssZ" to create an url
     85                # on deb.debian.org.
     86                path_parts.pop(3)
     87                path_parts.pop(1)
     88                modified_url = urlunparse(
     89                    url_parts._replace(
     90                        netloc="deb.debian.org", path="/".join(path_parts)
     91                    )
     92                )
     93                if url_exists(modified_url):
     94                    with lock:
     95                        url_mapping[modified_url] = url
     96                    write_and_flush(proc.stdin, line.replace(url, modified_url))
     97                    continue
     98        write_and_flush(proc.stdin, line)
     99 
    100    proc.stdin.close()
    101    output_thread.join()
    102 
    103 
    104 if __name__ == "__main__":
    105    main()