Backroll is a pure Rust implementation of GGPO rollback networking library.

This is still in an early beta stage. At time of writing, the public facing API is stable, and has undergone limited testing. There may still be notable bugs that have not been found yet.

• (Almost) 100% pure safe Rust. No unsafe pointer manipulation.
• Type safety. backroll-rs heavily utilizes generics and associated types to avoid serialization overhead and potentially unsafe type conversions when saving and loading game state.
• Abstracted transport layer protocols - integrate and use any transport layer library you need. Comes with a raw UDP socket based implementation.
• Configurable at runtime - Many of the hard-coded constants in GGPO are exposed as configuration parameters during session initialization.
• Reduced memory usage - Backroll's use of generics potentially shrinks down the sizes of many data types.
• Vectorized input compression scheme - Backroll utilizes the same XOR + RLE encoding, but it's written to maximize CPU utilization.
• Multithreaded I/O - All network communications run within an async task pool. I/O polling is no longer manual, nor blocks your game's execution.

This repo contains the following crates:

• backroll - the main Backroll interface, intended to be used as the original GGPO.
• backroll_transport - An isolated set of transport layer abstractions.
• backroll_transport_udp - A transport layer implementation using raw UDP sockets.
• backroll_transport_steam - A transport layer implementation using the Steam provided networking utilities. Enables access to the Steam Datagram Relay service.
• bevy_backroll - a integration plugin for bevy. (Complete, untested).
• lib - third-party linking dependencies (i.e. Steam) for easier local development

Due to linking requirements for backroll_transport_steam, local builds that include the crate currently only build when the Steamworks SDK is available.

According to steamworks-rs, at build time the STEAM_SDK_LOCATION env var must be set to a copy of the Steamworks SDK to properly link against.

The Backroll repo has an embedded copy of the Steamworks SDK saved within it. If you are using Rust nightly v1.52+, cargo will automatically set this variable and use the embedded copy of the Steamworks SDK. This is unfortunately unavailable to stable Rust until configurable-env stablizes.

If you are not using Steamworks, you can ignore this entirely. However, blanket workspace builds (i.e. cargo build in the repo root) will include the crate by default. Using cargo dependencies via path should still work so long as Steam support is not needed.