gossip

Solana's Gossip Specification

This post will describe how Solana's gossip protocol works in-depth, as well as implementation details of Sig's gossip.

For an introduction to Solana's gossip protocol, check out the technical sections of our Sig announcement blog post.

Checkout the full associated blog post here: https://blog.syndica.io/sig-engineering-1-gossip-protocol/.

Repository File Outline

• service.zig: main logic for reading, processing, and sending gossip messages
• table.zig: where gossip data is stored
• data.zig: various gossip data structure definitions
• pull_request.zig: logic for sending pull requests
• pull_response.zig: logic for sending pull responses (/handling incoming pull requests)
• gossip_shards.zig: datastructure which stores gossip data hashes for quick lookup - used in gossip_table and constructing pull responses
• active_set.zig: logic for deriving a list of peers to send push messages to
• ping_pong.zig: logic for sending ping/pong messages as a heartbeat check

A gossip spy is, in essence, software written to do two things: store data and send/receive requests.

Benchmarks

benchmarks are located at the bottom of service.zig.

to run the benchmarks:

• build sig in ReleaseSafe (ie, zig build -Doptimize=ReleaseSafe)
• run ./zig-out/bin/benchmark gossip

this includes processing times for pings, push messages, pull responses, and pull requests.

Fuzzing

the fuzzing client is located in fuzz.zig.

to run the client

• start a sig gossip in a terminal (ie, listening on 8001)
• build the fuzz client in ReleaseSafe (ie, zig build -Doptimize=ReleaseSafe)
• run the fuzz client pointing to sig with some seed and some number of random messages to send: ./zig-out/bin/fuzz <entrypoint> <seed> <num_messages> (eg, ./zig-out/bin/fuzz 127.0.0.1:8001 19 100000)

Architecture

Gossip Service

The gossip service runs three main threads:

• verify packet
• process messages
• build messages

and two auxillary threads for reading and writing to the gossip socket.

Verify Messages

The verify messages thread verifies all incoming packets and forwards valid gossip messages to the process messages thread.

Process Messages

The process messages thread handles all verified incoming gossip messages.

Handle Ping Messages

Handle Pong Messages

Handle Pull Requests

Handle Pull Responses

Handle Push Messages

Handle Prune Messages

Build Messages

The build messages thread uses the internal gossip service state to achieve two primary objectives:

• build pull requests to obtain missing data from peers
• build push messages to inform peers of our current state

Build Pull Requests

Build Push Messages