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114 lines
5.8 KiB
Markdown
114 lines
5.8 KiB
Markdown
DHT protocol
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============
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Follows pretty much the principle of the torrent DHT: http://www.bittorrent.org/beps/bep_0005.html (READ IT)
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But:
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Vastly simplified packet format and encryption.
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Boostrapping:
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The first time you install the client we bootstrap it with a node. (bandwidth should not be a problem as the client only needs to be sent one reply.)
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Basics
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------
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(All the numbers here are just guesses and are probably not optimal values)
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client list: A list of node ids closest (mathematically see bittorrent doc) to ours matched with ip addresses + port number corresponding to that id and a timestamp containing the time or time since the client was successfully pinged.
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"friends" list: A list containing the node_ids of all our "friends" or clients we want to connect to.
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Also contains the ip addresses + port + node_ids + timestamp(of last ping like in the client list) of the 8 clients closest (mathematically see bittorrent doc) to each "friend"
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One pinged lists:
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-One for storing a list of ips along with their ping_ids and a timestamp for the ping requests
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Entries in the pinged lists expire after 5 seconds.
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If one of the lists becomes full, the expire rate reduces itself one second or the new ping takes the place of the oldest one.
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Entries in client list and "friends" list expire after 300 seconds without ping response.
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Each client stores a maximum of 32 entries in its client list.
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Each client in the client list and "friends" list is pinged every 60 seconds.
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Each client in the client list and "friends" list has a timestamp which denote the last time it was successfully pinged.
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If the corresponding clients timestamp is more than 130 seconds old it is considered bad.
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Send a get nodes request every 20 seconds to a random good node for each "friend" in our "friends" list.
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Send a get nodes request every 20 seconds to a random good node in the client list.
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When a client receives any request from another
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-----------------------------------------------
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-Respond to the request
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-Ping request is replied to with with a ping response containing the same encrypted data
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-Get nodes request is replied with a send nodes reply containing the same encrypted data and the good nodes from the client list and/or the "friends" list that are closest to the requested_node_id
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-If the requesting client is not in the client list:
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-If there are no bad clients in the list and the list is full:
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-If the id of the other client is closer (mathematically see bittorrent doc) than at least one of the clients in the list or our "friends" list:
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-Send a ping request to the client.
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-if not forget about the client.
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-If there are bad clients and/or the list isn't full:
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-Send a ping request to the client
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When a client receives a response
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---------------------------------
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-Ping response
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-If the node was previously pinged with a matching ping_id (check in the corresponding pinged list.)
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-If the node is in the client list the matching client's timestamp is set to current time.
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-If the node is in the "friends" list the matching client's timestamp is set to current time for every occurrence.
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-If the node is not in the client list:
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-If the list isn't full, add it to the list.
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-If the list is full, the furthest away (mathematically see bittorrent doc) bad client is replaced by the new one.
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-If the list is filled with good nodes replace the furthest client with it only if it is closer than the replaced node.
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-for each friend in the "friends" list:
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-If that friend's client list isn't full, add that client to it
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-If that friend's client list contains bad clients, replace the furthest one with that client.
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-If that friend's client list contains only good clients
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-If the client is closer to the friend than one of the other clients, it replaces the farthest one
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-If not, nothing happens.
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-Send nodes
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-If the ping_id matches what we sent previously (check in the corresponding pinged list.):
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-Each node in the response is pinged.
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Protocol
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--------
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Node format:
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```
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[char array (node_id), length=32 bytes][ip (in network byte order), length=4 bytes][port (in network byte order), length=2 bytes][Padding , length=2 bytes]
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```
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see also: DHT.h (Node4_format struct)
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IPv6 Node format:
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see: DHT.h (Node_format struct)
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Valid queries and Responses:
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Ping(Request and response):
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```
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[byte with value: 00 for request, 01 for response][char array (client node_id), length=32 bytes][random 24 byte nonce][Encrypted with the nonce and private key of the sender: [random 8 byte (ping_id)]]
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```
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ping_id = a random integer, the response must contain the exact same number as the request
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Get nodes (Request):
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Packet contents:
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```
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[byte with value: 02][char array (client node_id), length=32 bytes][random 24 byte nonce][Encrypted with the nonce and private key of the sender:[char array: requested_node_id (node_id of which we want the ip), length=32 bytes][Encrypted data (must be sent back unmodified by in the response), length=NODES_ENCRYPTED_MESSAGE_LENGTH bytes]]
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```
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Valid replies: a send_nodes packet
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Send_nodes (response (for ipv4 addresses)):
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```
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[byte with value: 03][char array (client node_id), length=32 bytes][random 24 byte nonce][Encrypted with the nonce and private key of the sender:[Nodes in node format, length=40 * (number of nodes (maximum of 8 nodes)) bytes][Encrypted data, length=NODES_ENCRYPTED_MESSAGE_LENGTH bytes]]
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```
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Send_nodes_IPv6 (response (for ipv6 addresses)):
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```
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[byte with value: 04][char array (client node_id), length=32 bytes][random 24 byte nonce][Encrypted with the nonce and private key of the sender:[Nodes in ipv6_node format, length=56 * (number of nodes (maximum of 8 nodes)) bytes][Encrypted data, length=NODES_ENCRYPTED_MESSAGE_LENGTH bytes]]
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```
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