Module bones_framework::networking

Networked multi-player plugin.

Jumpy uses a Peer-to-Peer, rollback networking model built on GGRS.

Messages are serialized/deserialized to a binary representation using serde and the postcard crate.

The major facets of our networking are:

• Matchmaking: How we connect clients to each-other and start an network match.
• Synchronization: How we synchronize a network game between multiple players.

Matchmaking

There are currently two different matchmaking strategies: online and lan. Both of those modules contain their own matchmaker with docs on how it works. Eventually we will probably have additional matchmakers for Steam and the browser.

Regardless of the matchmaker, the goal is to find a match and establish a connection to the other players. Once a match is established, the matchmaker must provide an implementation of NetworkSocket that may be used to send GGRS, reliable, and unreliable messages.

Each matchmaker is free to implement this socket with whatever networking transport they wish, allowing the Steam matchmaker, for example, to use the steam networking library, and the browser matchmaker to use WebTransport or WebRTC.

Synchronization

Match synchronization, as mentioned above, is accomplished with GGRS, wich is a re-imagining of the GGPO network SDK.

The NetworkSocket trait, which matchmakers are required to implement for their sockets, is required to return an implementation of GGRS’s NonBlockingSocket trait, so that it can send it’s unreliable messages. The exact method for sending these messages depends on the matchmaker.

The key requirement for rollback networking is:

• The synchronized game loop must be deterministic.
• We must have the ability to snapshot and restore the game state.
• We must be able to run up to 8 game simulation frames in 16ms ( to achieve a 60 FPS frame rate, even in the case where we have to rollback and re-simulate ).

The integration with GGRS is implemented by the GgrsSessionRunner.

Input

GgrsSessionRunner is generic over a couple of input traits, some of which have associated types with other trait bounds. This provides an API for game to define their input collection, control mapping, etc to be used by bones in networking.

Development & Debugging

Here are some tips for debugging networking features while developing.

Local Sync Test

It can be cumbersome to start a new networked match every time you need to troubleshoot some part of the game that may not be rolling back or restoring properly. To help with this, you can run the game with the --sync-test-check-distance 7 to make the game test rolling back and forward 8 times every frame as a test when starting a local game.

This allows you to test the rollback without having to connect to a server. If things start popping around the map or having other weird behaviors that they don’t have without the sync-test mode, then you know you have a rollback issue.

ℹ️ Note: Just because you don’t have an issue in sync test mode, doesn’t mean that there is no determinism issues. You still have to test network games with multiple game instances. There are some non-determinism issues that only exhibit themselves when restarting the game.

Modules

• certs
  QUIC certificate utilities.
• debug
  network_debug_session_plugin may be installed to open network diagnostics egui window:
• input
  Input traits required by networking. These traits are networking specific, either only used in networking, or extending other traits from crate::input for networking.
• lan
  LAN matchmaking and socket implementation.
• online
  Contains the online matchmaker and the NetworkSocket implementation.
• prelude
  Module prelude.
• proto
  Serializable data types for network messages used by the game.

Structs

• BoxedNonBlockingSocket
  A type-erased ggrs::NonBlockingSocket implementation.
• GameMessage
  Wraps ggrs::Message with included match_id, used to determine if message received from current match.
• GgrsConfig
  The ggrs::Config implementation used by Jumpy.
• GgrsSessionRunner
  SessionRunner implementation that uses ggrs for network play.
• GgrsSessionRunnerInfo
  The info required to create a GgrsSessionRunner.
• NetworkInfo
  Resource updated each frame exposing current frame and last confirmed of online session.
• NetworkMatchSocket
  Resource containing the NetworkSocket implementation while there is a connection to a network game.

Enums

• NetworkError
  Possible errors returned by network loop.
• NetworkInputStatus
  Indicates if input from networking is confirmed, predicted, or if player is disconnected.
• SocketTarget
  The destination for a reliable network message.

Constants

• MAX_PLAYERS
  Max players in networked game
• NETWORK_FRAME_RATE_FACTOR
  Muliplier for framerate that will be used when playing an online match.
• NETWORK_LOCAL_INPUT_DELAY_DEFAULT
  Amount of frames GGRS will delay local input.
• NETWORK_MAX_PREDICTION_WINDOW_DEFAULT
  Number of frames client may predict beyond confirmed frame before freezing and waiting for inputs from other players. Default value if not specified in GgrsSessionRunnerInfo.

Statics

• NETWORK_ENDPOINT
  The network endpoint used for all QUIC network communications.

Traits

• GgrsSocket
  Automatically implemented for NetworkSocket + ggrs::NonBlockingSocket<usize>.
• NetworkSocket
  Trait that must be implemented by socket connections establish by matchmakers.