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LiveKit allows participants to send arbitrary data to other participants in the room using data channels. This is useful for sending text messages, custom signaling, or any application-specific data.

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Publishing Data

Send data to other participants using the publish(data:options:) method: 
let message = "Hello, world!"
let data = message.data(using: .utf8)!

try await room.localParticipant.publish(data: data)

​
Data Publish Options

Control delivery behavior using DataPublishOptions: 
let options = DataPublishOptions(
    reliable: true,                    // Use reliable data channel
    destinationIdentities: [],         // Send to specific participants (empty = all)
    topic: "chat"                      // Optional topic/channel identifier
)

try await room.localParticipant.publish(data: data, options: options)
Options:
  • reliable: When true, uses TCP-like reliable delivery. When false, uses UDP-like lossy delivery for lower latency
  • destinationIdentities: Array of participant identities to receive the data. Empty array sends to all participants
  • topic: Optional string to categorize messages (useful for filtering on the receiving end)

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Reliable vs. Lossy Delivery

Best for: Chat messages, file transfers, critical data
let options = DataPublishOptions(reliable: true)
try await room.localParticipant.publish(data: data, options: options)
  • Guarantees delivery and order
  • Higher latency under poor network conditions
  • Uses TCP-like transmission

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Receiving Data

Implement the RoomDelegate protocol to receive data messages: 
class MyRoomDelegate: RoomDelegate {
    func room(
        _ room: Room,
        participant: RemoteParticipant?,
        didReceiveData data: Data,
        topic: String?
    ) {
        // Handle received data
        if let message = String(data: data, encoding: .utf8) {
            print("Received message: \(message)")
            print("From participant: \(participant?.identity ?? "unknown")")
            print("Topic: \(topic ?? "none")")
        }
    }
}

// Add delegate to room
room.add(delegate: MyRoomDelegate())

​
Filtering by Topic

Use topics to organize different types of data messages: 
func room(
    _ room: Room,
    participant: RemoteParticipant?,
    didReceiveData data: Data,
    topic: String?
) {
    switch topic {
    case "chat":
        handleChatMessage(data, from: participant)
    case "game-state":
        handleGameState(data)
    case "reaction":
        handleReaction(data, from: participant)
    default:
        print("Unknown topic: \(topic ?? "none")")
    }
}

​
Sending to Specific Participants

Send data to one or more specific participants: 
// Send to a single participant
let targetIdentity = Participant.Identity("user123")
let options = DataPublishOptions(
    reliable: true,
    destinationIdentities: [targetIdentity]
)

try await room.localParticipant.publish(data: data, options: options)

// Send to multiple participants
let identities = [
    Participant.Identity("user123"),
    Participant.Identity("user456")
]

let options = DataPublishOptions(
    reliable: true,
    destinationIdentities: identities
)

try await room.localParticipant.publish(data: data, options: options)

​
Size Limits

Each data payload must not exceed 15KB. For larger data: 
func sendLargeData(_ data: Data) async throws {
    let chunkSize = 15_000  // 15KB
    let chunks = stride(from: 0, to: data.count, by: chunkSize).map {
        data[$0..<min($0 + chunkSize, data.count)]
    }
    
    for (index, chunk) in chunks.enumerated() {
        let metadata = "chunk-\(index)-of-\(chunks.count)"
        try await room.localParticipant.publish(
            data: chunk,
            options: DataPublishOptions(
                reliable: true,
                topic: metadata
            )
        )
    }
}

​
Setting Default Options

Set default data publish options when creating a room: 
let roomOptions = RoomOptions(
    defaultDataPublishOptions: DataPublishOptions(
        reliable: true,
        topic: "default"
    )
)

let room = Room(roomOptions: roomOptions)

// This will use the default options
try await room.localParticipant.publish(data: data)

​
Use Cases

​
Chat Messages

struct ChatMessage: Codable {
    let text: String
    let timestamp: Date
}

func sendChatMessage(_ text: String) async throws {
    let message = ChatMessage(text: text, timestamp: Date())
    let data = try JSONEncoder().encode(message)
    
    try await room.localParticipant.publish(
        data: data,
        options: DataPublishOptions(
            reliable: true,
            topic: "chat"
        )
    )
}

​
Real-time Cursor Position

struct CursorPosition: Codable {
    let x: Double
    let y: Double
}

func sendCursorPosition(_ position: CursorPosition) async throws {
    let data = try JSONEncoder().encode(position)
    
    try await room.localParticipant.publish(
        data: data,
        options: DataPublishOptions(
            reliable: false,  // Low latency, lossy OK
            topic: "cursor"
        )
    )
}

​
Reactions

func sendReaction(_ emoji: String) async throws {
    let data = emoji.data(using: .utf8)!
    
    try await room.localParticipant.publish(
        data: data,
        options: DataPublishOptions(
            reliable: true,
            topic: "reaction"
        )
    )
}

​
Error Handling

Handle errors when publishing data: 
do {
    try await room.localParticipant.publish(data: data)
} catch {
    print("Failed to publish data: \(error)")
    
    if let lkError = error as? LiveKitError {
        switch lkError.type {
        case .invalidState:
            print("Data channel is not open")
        default:
            print("Other error: \(lkError)")
        }
    }
}

​
See Also

  • LocalParticipant.swift:117 (publish(data:options:))
  • Core/DataChannelPair.swift

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