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0.16.0 | Feb 14, 2020 |
#2199 in Network programming
52,526 downloads per month
Used in 95 crates
(4 directly)
1.5MB
27K
SLoC
Implementation of the Gossipsub protocol.
Gossipsub is a P2P pubsub (publish/subscription) routing layer designed to extend upon floodsub and meshsub routing protocols.
Overview
Note: The gossipsub protocol specifications (https://github.com/libp2p/specs/tree/master/pubsub/gossipsub) provide an outline for the routing protocol. They should be consulted for further detail.
Gossipsub is a blend of meshsub for data and randomsub for mesh metadata. It provides bounded degree and amplification factor with the meshsub construction and augments it using gossip propagation of metadata with the randomsub technique.
The router maintains an overlay mesh network of peers on which to efficiently send messages and metadata. Peers use control messages to broadcast and request known messages and subscribe/unsubscribe from topics in the mesh network.
Important Discrepancies
This section outlines the current implementation's potential discrepancies from that of other implementations, due to undefined elements in the current specification.
-
Topics - In gossipsub, topics configurable by the
hash_topics
configuration parameter. Topics are of typeTopicHash
. The current go implementation uses raw utf-8 strings, and this is default configuration in rust-libp2p. Topics can be hashed (SHA256 hashed then base64 encoded) by setting thehash_topics
configuration parameter to true. -
Sequence Numbers - A message on the gossipsub network is identified by the source
PeerId
and a nonce (sequence number) of the message. The sequence numbers in this implementation are sent as raw bytes across the wire. They are 64-bit big-endian unsigned integers. When messages are signed, they are monotonically increasing integers starting from a random value and wrapping around u64::MAX. When messages are unsigned, they are chosen at random. NOTE: These numbers are sequential in the current go implementation.
Peer Discovery
Gossipsub does not provide peer discovery by itself. Peer discovery is the process by which peers in a p2p network exchange information about each other among other reasons to become resistant against the failure or replacement of the boot nodes of the network.
Peer discovery can e.g. be implemented with the help of the Kademlia protocol in combination with the Identify protocol. See the Kademlia implementation documentation for more information.
Using Gossipsub
Gossipsub Config
The Config
struct specifies various network performance/tuning configuration
parameters. Specifically it specifies:
This struct implements the Default
trait and can be initialised via
[Config::default()
].
Behaviour
The Behaviour
struct implements the libp2p_swarm::NetworkBehaviour
trait allowing it to
act as the routing behaviour in a libp2p_swarm::Swarm
. This struct requires an instance of
PeerId
and Config
.
Example
For an example on how to use gossipsub, see the chat-example.
Dependencies
~10–18MB
~245K SLoC