P2P

The P2P interface sends packets directly between players, with NAT traversal and Epic relay servers when a direct connection is not possible. Players are addressed by their Product User Id, no IP addresses or open ports are needed.

• EOS P2P documentation

tip

For normal Unreal replication you don't need these nodes. The EOSCore NetDriver uses P2P for you, see Configuring Online Subsystem. Use the P2P nodes for your own messages, for example chat or a lobby handshake.

Common Nodes

Node	Use
EOS_P2P_SendPacket	Sends data to a remote user on a socket name and channel. The first packet opens the connection
EOS_P2P_AddNotifyPeerConnectionRequest	Called when a remote user wants to connect
EOS_P2P_AcceptConnection	Accepts the connection (call it for incoming requests, or before you send to open both ways)
EOS_P2P_GetNextReceivedPacketSize + EOS_P2P_ReceivePacket	Reads received packets, call it every tick
EOS_P2P_CloseConnection / EOS_P2P_CloseConnections	Closes one or all connections on a socket
EOS_P2P_AddNotifyPeerConnectionEstablished / Interrupted / Closed	Connection state changes

Settings

Node	Use
EOS_P2P_QueryNATType + EOS_P2P_GetNATType	Finds the local NAT type
EOS_P2P_SetRelayControl / EOS_P2P_GetRelayControl	Allows, forces or forbids relay servers. Forcing relays hides player IP addresses from each other
EOS_P2P_SetPortRange / EOS_P2P_GetPortRange	Limits the local UDP ports
EOS_P2P_SetPacketQueueSize + EOS_P2P_AddNotifyIncomingPacketQueueFull	Limits the packet queues
EOS_P2P_ClearPacketQueue	Drops the queued outgoing packets to one user on a socket

Example

The example sends text messages between two players on a socket named CHAT. Both players run the same Blueprint.

1. Accepting connections

Call StartP2P once after login. EOS_P2P_AddNotifyPeerConnectionRequest calls OnP2PConnectionRequest when another player sends the first packet on the CHAT socket. The event accepts the connection with EOS_P2P_AcceptConnection, using the user ids and socket from the request.

2. Sending a message

SendChatMessage takes the Remote User Id of the other player and the text to send. Core String To Byte turns the text into bytes and EOS_P2P_SendPacket sends them on channel 1 with Reliability EOS_PR_ReliableOrdered, so messages arrive and arrive in order. Channels go from 0 to 255, the default is 0. They let you keep different kinds of messages apart on the same socket.

The remote user id is the Product User Id of the other player, for example from a lobby member or a session.

3. Receiving messages

Packets are queued until you read them, so call ReceivePackets every tick or from a looping timer:

1. EOS_P2P_GetNextReceivedPacketSize returns EOS_Success and the size when a packet is waiting, and EOS_NotFound when the queue is empty. Requested Channel -1 reads from any channel, set it to a channel number to read only that channel.
2. EOS_P2P_ReceivePacket reads the packet. Max Data Size Bytes is the size from step 1.
3. Core Bytes To String turns the data back into text. Out Peer Id says who sent it.

To read every waiting packet in one tick, repeat the two calls until GetNextReceivedPacketSize no longer returns EOS_Success.