实现一个bittorent客户端，我从跟踪器得到403

Question

I was trying my hand at implementing a bittorrent client in python (I know there are libs out there that can do this for me easily, but I'm just trying to learn new things).

I downloaded and managed to succesfully decode the torrent file, however when I try to do the GET request at the tracker I get back a 403 response and I have no idea why. This is what I tried (this is code copied from the python shell):

>>> f = open("torrents/test.torrent")
>>> torrentData = bencoder.decode(f.read())
>>> torrentData["announce"]
'http://reactor.flro.org:8080/announce.php?passkey=d59fc5b5b9e2664895ad1c68a3621caf'
>>> params["info_hash"] = sha1(bencoder.encode(torrentData["info"])).digest()
>>> params["peer_id"] = '-AZ-1234-12345678901'
>>> params["left"] = sum(f["length"] for f in torrentData["info"]["files"])
>>> params["port"] = 6890
>>> params["uploaded"] = 0
>>> params["downloaded"] = 0
>>> params["compact"] = 1
>>> params["event"] = "started"
>>> params
{'uploaded': 0, 'compact': 1, 'info_hash': '\xab}\x19\x0e\xac"\x9d\xcf\xe5g\xd4R\xae\xee\x1e\xd7\
>>> final_url = torrentData["announce"] + "&" + urllib.urlencode(params)
>>> final_url
'http://reactor.flro.org:8080/announce.php?passkey=d59fc5b5b9e2664895ad1c68a3621caf&uploaded=0&co
>>> urllib2.urlopen(final_url)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/
    return opener.open(url, data, timeout)
  File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/
    response = meth(req, response)
  File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/
    'http', request, response, code, msg, hdrs)
  File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/
    return self._call_chain(*args)
  File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/
    result = func(*args)
  File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
urllib2.HTTPError: HTTP Error 403: Forbidden

Am I missing something from the params folder? I also tried this torrent in my uTorrent client and it worked so the tracker is working fine. I even tried the naked announce url (without the params) and same thing. From what I read from the bittorrent specification there is no mention of a 403 response from the tracker.

I'd be very happy if you guys could help me out with this.

Answer 1

To reduce the amount of variables it is better to test against a tracker you're running locally, eg opentracker is a good choice since it imposes few requirements.

Errors you only get on specific trackers but not on others are likely due to additional requirements imposed by the tracker administrators and not by the bittorrent protocol itself.

The major exceptions are that many public trackers may not allow non-compact announces or require UDP announces instead of HTTP ones.

Answer 2

Ok I managed to figure out the issue. It's kinda silly but it's actually because the request to the tracker didn't have any headers, and that tracker actually needed an user-agent otherwise it would reject the request. All I had to do was add a user-agent to the request.