321 lines
17 KiB
ReStructuredText
321 lines
17 KiB
ReStructuredText
Bittorrent udp-tracker protocol extension
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=========================================
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:Author: Arvid Norberg, arvid@rasterbar.com
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.. contents:: Table of contents
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:depth: 2
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:backlinks: none
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introduction
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------------
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A tracker with the protocol "udp://" in its URI
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is supposed to be contacted using this protocol.
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This protocol is supported by
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xbt-tracker_.
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.. _xbt-tracker: http://xbtt.sourceforge.net
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For additional information and descritptions of
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the terminology used in this document, see
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the `protocol specification`__
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__ http://wiki.theory.org/index.php/BitTorrentSpecification
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All values are sent in network byte order (big endian). The sizes
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are specified with ANSI-C standard types.
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If no response to a request is received within 15 seconds, resend
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the request. If no reply has been received after 60 seconds, stop
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retrying.
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connecting
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----------
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Client sends packet:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int64_t | connection_id | Must be initialized to 0x41727101980 |
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| | | in network byte order. This will |
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| | | identify the protocol. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | action | 0 for a connection request |
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+-------------+---------------------+----------------------------------------+
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| int32_t | transaction_id | Randomized by client. |
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+-------------+---------------------+----------------------------------------+
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Server replies with packet:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int32_t | action | Describes the type of packet, in this |
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| | | case it should be 0, for connect. |
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| | | If 3 (for error) see errors_. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | transaction_id | Must match the transaction_id sent |
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| | | from the client. |
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+-------------+---------------------+----------------------------------------+
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| int64_t | connection_id | A connection id, this is used when |
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| | | further information is exchanged with |
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| | | the tracker, to identify you. |
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| | | This connection id can be reused for |
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| | | multiple requests, but if it's cached |
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| | | for too long, it will not be valid |
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| | | anymore. |
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+-------------+---------------------+----------------------------------------+
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announcing
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----------
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Client sends packet:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int64_t | connection_id | The connection id acquired from |
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| | | establishing the connection. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | action | Action. in this case, 1 for announce. |
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| | | See actions_. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | transaction_id | Randomized by client. |
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+-------------+---------------------+----------------------------------------+
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| int8_t[20] | info_hash | The info-hash of the torrent you want |
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| | | announce yourself in. |
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+-------------+---------------------+----------------------------------------+
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| int8_t[20] | peer_id | Your peer id. |
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+-------------+---------------------+----------------------------------------+
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| int64_t | downloaded | The number of byte you've downloaded |
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| | | in this session. |
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+-------------+---------------------+----------------------------------------+
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| int64_t | left | The number of bytes you have left to |
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| | | download until you're finished. |
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+-------------+---------------------+----------------------------------------+
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| int64_t | uploaded | The number of bytes you have uploaded |
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| | | in this session. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | event | The event, one of |
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| | | |
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| | | * none = 0 |
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| | | * completed = 1 |
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| | | * started = 2 |
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| | | * stopped = 3 |
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+-------------+---------------------+----------------------------------------+
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| uint32_t | ip | Your ip address. Set to 0 if you want |
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| | | the tracker to use the ``sender`` of |
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| | | this udp packet. |
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+-------------+---------------------+----------------------------------------+
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| uint32_t | key | A unique key that is randomized by the |
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| | | client. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | num_want | The maximum number of peers you want |
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| | | in the reply. Use -1 for default. |
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+-------------+---------------------+----------------------------------------+
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| uint16_t | port | The port you're listening on. |
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+-------------+---------------------+----------------------------------------+
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| uint16_t | extensions | See extensions_ |
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+-------------+---------------------+----------------------------------------+
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Server replies with packet:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int32_t | action | The action this is a reply to. Should |
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| | | in this case be 1 for announce. |
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| | | If 3 (for error) see errors_. |
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| | | See actions_. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | transaction_id | Must match the transaction_id sent |
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| | | in the announce request. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | interval | the number of seconds you should wait |
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| | | until reannouncing yourself. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | leechers | The number of peers in the swarm that |
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| | | has not finished downloading. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | seeders | The number of peers in the swarm that |
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| | | has finished downloading and are |
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| | | seeding. |
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+-------------+---------------------+----------------------------------------+
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The rest of the server reply is a variable number of the following structure:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int32_t | ip | The ip of a peer in the swarm. |
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+-------------+---------------------+----------------------------------------+
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| uint16_t | port | The peer's listen port. |
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+-------------+---------------------+----------------------------------------+
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scraping
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--------
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Client sends packet:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int64_t | connection_id | The connection id retreived from the |
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| | | establishing of the connection. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | action | The action, in this case, 2 for |
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| | | scrape. See actions_. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | transaction_id | Randomized by client. |
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+-------------+---------------------+----------------------------------------+
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The following structure is repeated for each info-hash to scrape, but limited by
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the MTU.
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int8_t[20] | info_hash | The info hash that is to be scraped. |
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+-------------+---------------------+----------------------------------------+
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Server replies with packet:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int32_t | action | The action, should in this case be |
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| | | 2 for scrape. |
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| | | If 3 (for error) see errors_. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | transaction_id | Must match the sent transaction id. |
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+-------------+---------------------+----------------------------------------+
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The rest of the packet contains the following structures once for each info-hash
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you asked in the scrape request.
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int32_t | complete | The current number of connected seeds. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | downloaded | The number of times this torrent has |
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| | | been downloaded. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | incomplete | The current number of connected |
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| | | leechers. |
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+-------------+---------------------+----------------------------------------+
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errors
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------
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In case of a tracker error,
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server replies packet:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int32_t | action | The action, in this case 3, for error. |
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| | | See actions_. |
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+-------------+---------------------+----------------------------------------+
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| int32_t | transaction_id | Must match the transaction_id sent |
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| | | from the client. |
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+-------------+---------------------+----------------------------------------+
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| int8_t[] | error_string | The rest of the packet is a string |
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| | | describing the error. |
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+-------------+---------------------+----------------------------------------+
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actions
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-------
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The action fields has the following encoding:
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* connect = 0
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* announce = 1
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* scrape = 2
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* error = 3 (only in server replies)
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extensions
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----------
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The extensions field is a bitmask. The following
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bits are assigned:
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* 1 = authentication_.
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* 2 = `request string`_.
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If multiple bits are present in the extension field, the extension
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bodies are appended to the packet in the order of least significant
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bit first. For instance, if both bit 1 and 2 are set, the extension
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represented by bit 1 comes first, followed by the extension represented
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by bit 2.
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authentication
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~~~~~~~~~~~~~~
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The packet will have an authentication part
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appended to it. It has the following format:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int8_t | username_length | The number of characters in the |
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| | | username. |
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+-------------+---------------------+----------------------------------------+
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| int8_t[] | username | The username, the number of characters |
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| | | as specified in the previous field. |
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+-------------+---------------------+----------------------------------------+
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| uint8_t[8] | passwd_hash | sha1(packet + sha1(password)) |
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| | | The packet in this case means the |
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| | | entire packet except these 8 bytes |
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| | | that are the password hash. These are |
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| | | the 8 first bytes (most significant) |
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| | | from the 20 bytes hash calculated. |
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+-------------+---------------------+----------------------------------------+
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request string
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--------------
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The request string extension is meant to allow torrent creators pass along
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cookies back to the tracker. This can be useful for authenticating that a
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torrent is allowed to be tracked by a tracker for instance. It could also
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be used to authenticate users by generating torrents with unique tokens
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in the tracker URL for each user. The extension body has the following format:
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+-------------+---------------------+----------------------------------------+
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| size | name | description |
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+=============+=====================+========================================+
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| int16_t | request length | The number of bytes in the request |
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| | | string. |
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+-------------+---------------------+----------------------------------------+
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| int8_t[] | request string | The string that comes after the host- |
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| | | name and port in the udp tracker URL. |
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| | | Typically this starts with "/announce" |
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| | | The bittorrent client is not expected |
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| | | to append query string arguments for |
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| | | stats reporting, like "uploaded" and |
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| | | "downloaded" since this is already |
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| | | reported in the udp tracker protocol. |
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| | | However, the client is free to add |
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| | | arguments as extensions. |
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+-------------+---------------------+----------------------------------------+
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credits
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-------
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Protocol designed by Olaf van der Spek and extended by Arvid Norberg
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