Resources
- See
NetDriver.h - See also NetConnection
- See also Channel
About
More details in
NetDriver.h
UNetDrivers are responsible for managing sets of UNetConnections, and data that can be shared between them.
Under normal circumstances, there will exist only a single NetDriver (created on Client and Server) for “standard” game traffic and connections.
The Server NetDriver will maintain a list of NetConnections, each representing a player that is in the game. It is responsible for replicating Actor Data. Client NetDrivers will have a single NetConnection representing the connection to the Server.
Startup
More details in
NetDriver.h
Whenever a server Loads a map (via UEngine::LoadMap), we will make a call into UWorld::Listen.
That code is responsible for creating the main Game Net Driver, parsing out settings, and calling UNetDriver::InitListen.
And ultimately, that code will be responsible for figuring out what how exactly we listen for client connections. Once the server is listening, it’s ready to start accepting client connections.
Whenever a client wants to Join a server, they will first establish a new UPendingNetGame in UEngine::Browse with the server’s IP. UPendingNetGame::Initialize and UPendingNetGame::InitNetDriver are responsible for initializing settings and setting up the NetDriver respectively.
Clients will immediately setup a UNetConnection for the server as a part of this initialization, and will start sending data to the server on that connection, initiating the handshaking process.
On both Clients and Server, UNetDriver::TickDispatch is typically responsible for receiving network data.
After the UNetDriver and UNetConnection have completed their handshaking process on Client and Server, UPendingNetGame::SendInitialJoin will be called on the Client to kick off game level handshaking (this is where AGameModeBase::PreLogin, AGameModeBase::GameWelcomePlayer, … will be called).
For more details about handling connections, disconnections and more see NetDriver.h.
Data Transmission
More details in
NetDriver.h
UNetDriver and UNetConnection work with Packets and Bunches.
Packets are blobs of data that are sent between pairs of NetConnections on Host and Client.
Packets consist of meta data about the packet (such as header information and acknowledgments), and Bunches.
Bunches are blobs of data that are sent between pairs of Channels on Host and Client.
When a Connection receives a Packet, that packet will be disassembled into individual bunches.
Those bunches are then passed along to individual Channels to be processed further.
A Packet may contain no bunches, a single bunch, or multiple bunches.
Because size limits for bunches may be larger than the size limits of a single packet, UE supports the notion of partial bunches.
See also Replication Flow.
For more information about handling data loss and how reliable RPCs are handled, see NetDriver.h.