Downloading a Torrent with libtorrent-python

Question

I have the following python code:

import libtorrent as lt
import time

ses = lt.session()
ses.listen_on(6881, 6891)
params = {
    'save_path': '/home/downloads/',
    'storage_mode': lt.storage_mode_t(2),
    'paused': False,
    'auto_managed': True,
    'duplicate_is_error': True}
link = "magnet:?xt=urn:btih:4MR6HU7SIHXAXQQFXFJTNLTYSREDR5EI&tr=http://tracker.vodo.net:6970/announce"
handle = lt.add_magnet_uri(ses, link, params)
ses.start_dht()

print 'downloading metadata...'
while (not handle.has_metadata()):
    time.sleep(1)
print 'got metadata, starting torrent download...'
while (handle.status().state != lt.torrent_status.seeding):
    s = handle.status()
    state_str = ['queued', 'checking', 'downloading metadata', \
                'downloading', 'finished', 'seeding', 'allocating']
    print '%.2f%% complete (down: %.1f kb/s up: %.1f kB/s peers: %d) %s %.3' % \
                (s.progress * 100, s.download_rate / 1000, s.upload_rate / 1000, \
                s.num_peers, state_str[s.state], s.total_download/1000000)
    time.sleep(5)

Which seems to work fine, but then slows down to less than a byte/s:

$ python test.py 
downloading metadata...
got metadata, starting torrent download...
0.00% complete (down: 195.0 kb/s up: 8.0 kB/s peers: 28) checking 3.069
0.00% complete (down: 133.0 kb/s up: 5.0 kB/s peers: 28) checking 3.342
0.00% complete (down: 29.0 kb/s up: 1.0 kB/s peers: 28) checking 3.359
0.00% complete (down: 5.0 kb/s up: 0.0 kB/s peers: 28) checking 3.398
0.00% complete (down: 4.0 kb/s up: 0.0 kB/s peers: 28) checking 3.401
0.00% complete (down: 0.0 kb/s up: 0.0 kB/s peers: 28) checking 3.405
0.00% complete (down: 0.0 kb/s up: 0.0 kB/s peers: 28) checking 3.408
0.00% complete (down: 0.0 kb/s up: 0.0 kB/s peers: 28) checking 3.412

It slows down and never completes. Any idea why this happens?

Answer 1

The problem turned out to be trivial. The save_path did not exist, thus the libtorrent library downloaded as long as it did not have to flush the cache, but once it attempted to write the file, it failed and could not continue downloading, therefore the slowdown and eventual halt. Once an existing path was added it worked fine.