P2P Messages
Steam Networking Messages sends data directly between players, without an Unreal Engine network connection. Use it for things outside regular replication, for example chat, invites or small game data between players in a lobby. Steam handles NAT traversal and relays the traffic when a direct connection isn't possible.
The nodes are called on Get Steam Networking Messages and are in the SteamCore|NetworkingMessages category.
This is Valve's replacement for the old SteamCore|Networking P2P functions (Send P2P Packet and Read P2P Packet). Use Networking Messages for new code.
Prerequisites
- Steam is running and the game is launched as a Standalone Game or a packaged build.
- Both players are logged in to Steam. To test, you need two Steam accounts on two computers.
Sending a Message
Call Send Message To User with:
| Input | Description |
|---|---|
| Steam ID Remote | The player to send to. |
| Data | The message as a byte array. |
| Send Type | Reliable messages arrive in order and are resent if lost. Unreliable messages can be lost but have less overhead. The No Nagle and No Delay variants send immediately instead of waiting to batch messages. |
| Channel | A number the receiver reads from. Use different channels to keep different kinds of messages apart. |
| Auto Restart Broken Session | Starts a new session automatically if the previous one failed. |
It returns OK when the message was queued. The first message to a player opens a session, which can take a moment.
Accepting Sessions
When another player sends you their first message, the Session Request delegate is broadcast with their Steam ID. Call Accept Session With User to accept. Messages from that player are not delivered until you accept or send a message to them yourself.
Only accept sessions from players you expect, for example members of your lobby.
Receiving Messages
Messages are not pushed to you. Call Receive Messages On Channel regularly, for example from Event Tick or a timer, with the channel and the maximum number of messages to read. Messages contains, for each message:
| Field | Description |
|---|---|
| Sender | The Steam ID of the player who sent it. |
| Payload | The message data. |
| Channel | The channel it was sent on. |
| Message Number | An increasing number per session. |
Closing Sessions
Sessions time out after a few minutes without traffic. To end one right away, call Close Session With User, or Close Channel With User to close a single channel. The session closes when all its channels are closed.
Session Status
Get Session Connection Info returns the state of the session with a player: Connecting, Finding Route, Connected, Closed By Peer or Problem Detected Locally. Info contains the ping, connection quality, whether the traffic is relayed, and the reason the session ended.
If a session can't be established or breaks, the Session Failed delegate is broadcast with the same information.
Dedicated Servers
On a dedicated server, the nodes use the game server's own Steam identity automatically.