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This specification is for John Hoffman's proposed extension to the
BitTorrent metadata format. This extension is not official as of this
* "announce-list"
In addition to the standard "announce" key, in the main area of the
metadata file and not part of the "info" section, will be a new key,
"announce-list". This key will refer to a list of lists of URLs, and
will contain a list of tiers of announces. If the client is compatible
with the multitracker specification, and if the "announce-list" key is
present, the client will ignore the "announce" key and only use the
URLs in "announce-list".
* order of processing
The tiers of announces will be processed sequentially; all URLs in each
tier must be checked before the client goes on to the next tier. URLs
within each tier will be processed in a randomly chosen order; in other
words, the list will be shuffled when first read, and then parsed in
order. In addition, if a connection with a tracker is successful, it
will be moved to the front of the tier.
* examples.
d['announce-list'] = [ [tracker1], [backup1], [backup2] ]
On each announce, first try tracker1, then if that cannot be reached,
try backup1 and backup2 respectively. On the next announce, repeat
in the same order. This is meant for when the trackers are standard
and can not share information.
d['announce-list'] = [[ tracker1, tracker2, tracker3 ]]
First, shuffle the list. (For argument's sake, we'll say the list
has already been shuffled.) Then, if tracker1 cannot be reached, try
tracker2. If tracker2 can be reached, the list is now:
tracker2,tracker1,tracker3. From then on, this will be the order the
client tries. If later neither tracker2 nor tracker1 can be reached,
but tracker3 responds, then the list will be changed to:
tracker3,tracker2,tracker1, and will be tried in that order in the
future. This form is meant for trackers which can trade peer
information and will cause the clients to help balance the load
between the trackers.
d['announce-list'] = [ [ tracker1, tracker2 ], [backup1] ]
The first tier, consisting of tracker1 and tracker2, is shuffled.
Both trackers 1 and 2 will be tried on each announce (though perhaps
in varying order) before the client tries to reach backup1.
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