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