2016-04-03 12:56:41 +00:00
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=========================
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BEP9 Information Recovery
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=========================
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.. meta::
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:author: sponge
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:created: 2011-02-23
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:thread: http://zzz.i2p/topics/860
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:lastupdated: 2011-02-23
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2016-04-25 06:09:22 +00:00
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:status: Dead
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2016-04-03 12:56:41 +00:00
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.. contents::
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2016-04-25 06:09:22 +00:00
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Overview
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========
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This proposal is about adding full information recovery to I2P's implementation
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of BEP9.
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Motivation
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==========
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2016-04-03 12:56:41 +00:00
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BEP9 does not send the entire torrent file, thus losing several important
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dictionary items, and changes the torrent files total SHA1. This is bad for
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maggot links, and bad because important information is lost. Tracker lists,
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comments, and any additional data is gone. A way to recover this information is
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important, and it needs to add as little as possible to the torrent file. It
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also must not be circular dependent. Recovery information should not affect
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current clients in any way. torrents that are trackerless (tracker URL is
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literally 'trackerless') do not contain the extra field, as they are specific to
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using the maggot protocol of discovery and download, which does not ever lose
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the information in the first place.
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Solution
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========
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All that needs to be done is to compress the information that would be lost, and
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store it in the info dictionary.
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Implementation
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--------------
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1. Generate the normal info dictionary.
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2. Generate the main dictionary, and leave out the info entry.
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3. Bencode, and compress he main dictionary with gzip.
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4. Add the compressed main dictionary to the info dictionary.
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5. Add info to the main dictionary.
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6. Write the torrent file
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Recovery
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--------
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1. Decompress the recovery entry in the info dict.
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2. Bendecode the recovery entry.
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3. Add info to the recovered dictionary.
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4. For maggot-aware clients, you can now verify that the SHA1 is correct.
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5. Write out the recovered torrent file.
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Discussion
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==========
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Using the above outlined method, the size of the torrent increase is very small,
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200 to 500 bytes is typical. Robert will be shipping with the new info
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dictionary entry creation, and it will not be able to be turned off. Here is the
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structure::
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main dict {
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Tracker strings, comments, etc...
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info : {
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gzipped main bencoded dict minus the info dictionary and all other
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usual info
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}
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}
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