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iOS SDK
The Yorkie iOS SDK enables you to efficiently build collaborative applications. On the client side, you can create documents that automatically sync with remote peers with minimal effort.
If you want to install the SDK, refer to the Getting Started with iOS SDK.
Client
Client is a normal client that communicates with the server. It holds documents and sends local changes to the server to synchronize with other replicas.
For more information about Client, please refer to the Client.
Creating a Client
Create a Client using Client(). After activation, the Client connects to the server and is ready to use.
let client = Client("https://api.yorkie.dev", ClientOptions(apiKey: "xxxxxxxxxxxxxxxxxxxx"))try await client.activate()
The API key is used to identify the project in Yorkie. You can get the API key of the project you created in the Dashboard.
For CLI users, you can create Clients without an API key. In this case, the Client is created with a local rpcAddr.
let client = Client("http://localhost:{{port}}")try await client.activate()
For more information about CLI, please refer to the CLI.
Creating a Client with Auth Token
Configure authentication for the client by setting up an authTokenInjector to provide tokens for Auth Webhook verification.
If a codes.Unauthenticated error occurs, the authTokenInjector is called again with the webhook's response reason, enabling automatic token refresh.
For more information about Auth Webhook, please refer to the Auth Webhook.
struct MyAuthTokenInjector: AuthTokenInjector {func getToken(reason: String?) async throws -> String {if reason == "token expired" {return await refreshAccessToken()}return accessToken}}let client = Client("https://api.yorkie.dev", ClientOptions(apiKey: "xxxxxxxxxxxxxxxxxxxx", authTokenInjector: MyAuthTokenInjector()))
Syncing Documents Manually
In SyncMode.manual, the client does not automatically synchronize documents with the server. You must manually call the sync(document:) method to synchronize the document when necessary.
try await client.sync(doc)
Deactivate the Client
When the client is no longer needed, you can deactivate it to release resources and disconnect from the server.
try await client.deactivate()
This will detach all documents attached to the client for efficient garbage collection.
Document
Document is the primary data type in Yorkie, providing a JSON-like updating experience that makes it easy to represent your application's model.
A Document can be updated without being attached to the client, and its changes automatically propagate to other clients when the Document is attached to the Client or when the network is restored.
For more information about Document, please refer to the Document.
Creating a Document
Create a Document using Document(key:).
let doc = Document(key: "doc-1")
The document key identifies the Document in Yorkie. It is a string that you can freely define, but it can only contain a-z, A-Z, 0-9, -, ., _, ~ and must be between 4 and 120 characters.
The initializer also accepts a DocumentOptions value for document-scope settings:
let doc = Document(key: "doc-1", opts: DocumentOptions(disableGC: false, disablePresence: true))
disableGC: Disables local garbage collection for this document. This argument is required (it has no default). See Disabling GC.enableDevtools(Optional): Enables the Devtools recorder for this document. Defaults tofalse.disablePresence(Optional): Declares that this document does not use presence. Defaults tofalse. See Disabling Presence.
The disablePresence value seeds the attach-time option of the same name: when the disablePresence attach option is omitted, the document's value is used. DocumentOptions.disableGC gates local garbage collection and is set independently of the attach-time disableGC option, which controls the server wire contract.
Attaching the Document
When you attach, the client notifies the server that it is subscribing to this document. If the document does not exist on the server, it is created, and any local changes are sent to the server. If the server already has a document associated with the provided key, it sends the existing changes to the client, which applies them to synchronize the document.
Once attached, the document synchronizes with other clients, ensuring that any modifications made by one client instantly propagate to all other clients collaborating on the same document.
The attach method accepts several options:
initialPresence: Sets the client's initial presence when attaching to the document. The presence is shared with other users participating in the document. It must be serializable to JSON.syncMode(Optional): Specifies the synchronization mode. The default value isSyncMode.realtime, which automatically pushes and pulls changes. If you set it toSyncMode.manual, you must handle synchronization manually. See Changing Synchronization Mode for the full list, includingSyncMode.pollingfor stream-less periodic sync.documentPollInterval(Optional): Poll interval as aTimeIntervalin seconds. Used only whensyncModeisSyncMode.polling. Defaults to3.0. (Note: unlike the JS SDK's millisecond value, iOS uses seconds.)disableGC(Optional): Opts the attachment out of server-sideVersionVectortracking, reducing per-PushPullpayload for high-fan-out workloads. Defaults tofalse. See Disabling GC before enabling.disablePresence(Optional): Opts the attachment out of presence map propagation for documents that don't need presence (e.g.JSONCounter-only, form, or read-mostly documents). Defaults to the document's seeded value (falseunless set viaDocumentOptions). See Disabling Presence before enabling.
try await clientA.attach(doc, ["color": "blue", "cursor": ["x": 0, "y": 0]], .manual)
Initializing root
The root manages the application's data, such as primitives, arrays, Counters, and Text within the Document. You can set initial values when calling Document.attach() using the initialRoot option.
try await client.attach(doc, initialRoot: ["list": [Int32(1), Int32(2), Int32(3)]])
The initial values are partially applied. For each element in initialRoot:
- If the key doesn't exist, the element is applied.
- If the key already exists in the Document, that element is discarded. You don't need to worry about overwriting existing values.
// Another client tries to attach with initialRoot option:try await client2.attach(doc, initialRoot: ["list": [], // this update will be discarded"counter": JSONCounter(value: Int32(0)) // this update will be applied])// final state// root = {// list: [1, 2, 3],// counter: 0// }
We support element types for Primitives, and Custom CRDT types.
Elements added by initialRoot are not sent to the server during the attach process. They are applied locally to the Document after push-pull during attach.
Disabling GC
For documents whose workload never produces tombstones — typically JSONCounter-only or primitive-value replacement documents — you can attach with disableGC: true. The server then skips minVersionVector tracking for this attachment and omits the response VersionVector, which removes a per-PushPull cost that scales with the number of active clients.
try await client.attach(doc, disableGC: true)
disableGC only controls the wire contract with the server. Misuse on documents that use JSONText, JSONTree, or JSONArray deletions leads to undefined garbage-collection behavior on this client — tombstones may accumulate without being purged. Only enable it for workloads you are certain never produce tombstones.
Disabling Presence
For documents that don't need presence — typically JSONCounter-only, form, or read-mostly documents — you can attach with disablePresence: true. The server then strips the presence map from snapshots and changes, and no presence updates are propagated for the attachment. Any presence.set calls inside doc.update are silently dropped.
try await client.attach(doc, disablePresence: true)
disablePresence is fixated on the first attach and is immutable afterwards. If a later attach specifies a different value, the server returns the persisted value rather than the requested one. To change it, create a new document key, or have an administrator update the value directly in storage.
Updating presence
The Document.update() method allows you to make changes to the current user's presence.
Specified properties are changed while the existing presence object is updated by merging the new changes. Properties not specified in the update function remain unchanged.
try await doc.update { root, presence inpresence.set(["cursor": ["x": 1, "y": 1]])}// final state// presence = { color: 'blue', cursor: { x: 1, y: 1 } }// we can see that the changes made were merged and the final state of the current user's presence is as we desire
Important: Properties in presence are replaced entirely, not merged.
To preserve nested properties, include all fields in your update:
// ❌ This loses the 'color' propertypresence.set(["cursor": ["x": 1, "y": 1]])// ✅ This preserves all propertiespresence.set(["cursor": ["x": 1, "y": 1, "color": "red"]])
Getting presence
Retrieve presence information for clients participating in the document.
Getting specific client presence:
await doc.getPresence(client.id!)
Getting your own presence:
await doc.getMyPresence()
Getting all presences:
let users = await doc.getPresences()
Document.subscribePresence(.presence)
This method subscribes to presence-related changes. You are notified whenever clients watch, unwatch, or modify their presence.
The initialized event occurs when the client list needs to be initialized, such as when you first connect a watch stream to a document, when the connection is lost, or when it is reconnected.
Subscribe before attaching the document to ensure you receive the initial initialized event.
await doc.subscribePresence { event inif event.type == .initialized {// Array of other users currently participating in the document// event.value;}if event.type == .watched {// A user has joined the document editing in online// event.value;}if event.type == .unwatched {// A user has left the document editing// event.value;}if event.type == .presenceChanged {// A user has updated their presence// event.value;}}
Use .myPresence and .others topics to distinguish between your own events and those of others.
Document.subscribePresence(.myPresence)
This method subscribes to changes in the presence of the current client that has attached to the document.
The possible event.type are: initialized, presenceChanged.
await doc.subscribePresence(.myPresence) { event in// Do something}
Document.subscribePresence(.others)
This method subscribes to changes in the presence of other clients participating in the document.
The possible event.type are: watched, unwatched, presenceChanged.
await doc.subscribePresence(.others) { event inif event.type == .watched {addUser(event.value)}if event.type == .unwatched {removeUser(event.value)}if event.type == .presenceChanged {updateUser(event.value)}}
Editing the Document
Document.update(:,message:) modifies a Document. The optional message parameter allows you to add a description to the change. If the Document is attached to the Client, all changes automatically synchronize with other Clients.
let message = "update document for test";try await doc.update({ root, _ inroot.todos = Array<String>()(root.todos as? JSONArray)?.append("todo-1")root.obj = ["name": "yorkie", "age": Int64(14)]root.counter = JSONCounter(Int64(0))(root.counter as? JSONCounter<Int64>)?.increase(1)}, message: message);
Under the hood, root in the update function creates a change, a set of operations. Every element has a unique ID created by the logical clock. Yorkie uses this ID to track each object.
You can get the contents of the Document using doc.getRoot().
let root = doc.getRoot()print(root.todos!) // Optional(["todo-1"])print(root.obj!) // {"name":"yorkie","age":14}print((root.obj as! JSONObject).name!) // yorkieprint(root.counter!) // 1
Subscribing to Document
Subscribe to various Document events, such as changes, connection status, and synchronization status using the document.subscribe() method.
By subscribing to these events, you can update the UI in real-time and handle exceptions that may occur during synchronization.
Document.subscribe()
A Document can be modified by changes generated remotely or locally. Whenever the Document is modified, change events are triggered. You can subscribe to these events using the document.subscribe(callback) method to receive updates in real-time, which is useful for updating the UI when the Document changes.
The callback is called with an event object, and the event.type property indicates the source of the change, which can be one of the following values: statusChanged, connectionChanged, syncStatusChanged, snapshot, localChange, remoteChange, initialized, watched, unwatched, presenceChanged, broadcast, localBroadcast or authError.
For more information about document events, please refer to the DocEvent.
await self.document.subscribe { event, _ inif event.type == .snapshot {// `snapshot` delivered when the entire document is updated from the server.} else if event.type == .localChange {// `local-change` delivered when calling document.update from the current client.} else if let event = event as? RemoteChangeEvent {// `remote-change` delivered when the document is updated from other clients.let changeInfo = event.value// You can access the operations that have been applied to the document.changeInfo.operations.forEach { op in// e.g.) { type: 'increase', value: 1, path: '$.counter' }switch (op.type) {case .increase:// ...breakdefault:break}}} else {// others case...}}
When the event.type is localChange or remoteChange, the event.value is a changeInfo, which has operations and message properties.
For more information about changeInfo for document events, please refer to the ChangeInfo.
The snapshot event is triggered when a snapshot is received from the server. This occurs when the number of changes that a document needs to fetch from the server exceeds a certain SnapshotThreshold. Instead of sending numerous changes, the server sends a snapshot of the document. In such cases, update your application with data from the Yorkie Document.
The available Event Types are:
| Event Types | Description |
|---|---|
Snapshot | Document snapshot received from server |
LocalChange | Document changed by current client |
RemoteChange | Document changed by another client |
PresenceChanged | Presence data changed (see Presence section) |
SyncStatusChanged | Sync status changed (Synced, SyncFailed) |
StreamConnectionChanged | Connection status changed (Connected, Disconnected) |
DocumentStatusChanged | Document status changed |
Broadcast | Broadcast message received |
AuthError | Authentication error occurred |
If a client has not synchronized for a prolonged period and then makes a sync request, it might receive a snapshot event.
Ensure your application processes these snapshot events correctly to maintain document synchronization.
Document.subscribe("$.path")
You can also subscribe to changes for a specific path in the Document using doc.subscribe(targetPath, callback) with a path argument, such as $.todos, where the $ sign indicates the document root.
The callback function is called when the target path and its nested values change.
This feature lets you subscribe to changes for a specific part of the document and perform different actions based on the updated values.
await doc.subscribe("$.todos") { event in// The callback will be called when the root.todos or its nested values change.Task {let target = try? await target.getValueByPath(path: "$.todos") // You can get the value by path.}// Do something...}
Document.subscribeConnection()
After attaching the document to the client, the document continuously synchronizes with the server in real-time. This is achieved by maintaining a watch stream connection between the client and the server, which allows the client to receive events and updates from other users.
To monitor the connection status of the stream, use a callback function that triggers whenever the connection status changes. The possible values for event.value are StreamConnectionStatus.connected and StreamConnectionStatus.disconnected.
When the watch stream is disconnected, the user is offline and will not receive real-time updates from other users.
await self.document.subscribeConnection { event, _ inlet event = event as! ConnectionChangedEventif event.value == .connected {// The watch stream is connected.} else if event.value == .disconnected {// The watch stream is disconnected.}}
For more information about StreamConnectionStatus, please refer to the StreamConnectionStatus.
Document.subscribeSync()
If the document is attached to the client in SyncMode.realtime, the document automatically synchronizes with the server in real-time.
In this mode, the document synchronizes in the background, and you can track the synchronization status using the sync event. The possible event.value values are DocumentSyncStatus.synced and DocumentSyncStatus.syncFailed.
await self.document.subscribeSync { event, _ inlet event = event as! SyncStatusChangedEventif event.value == .synced {// The document is synchronized with the server.} else if event.value == .syncFailed {// The document failed to synchronize with the server.}}
For more information about DocumentSyncStatus, please refer to the DocumentSyncStatus.
Document.subscribeAuthError()
Subscribe to authentication error events using doc.subscribeAuthError().
This event triggers when an unauthenticated error occurs during PushPull or WatchDocuments operations, specifically when the system automatically refreshes the token and retries the operation.
await doc.subscribeAuthError { event, _ inguard let authErrorEvent = event as? AuthErrorEvent else { return }// authErrorEvent.value contains:// - reason: string// - method: 'PushPull' | 'WatchDocuments'}
This subscription allows you to monitor when token refreshes occur due to authentication errors. For more information about Auth Webhook, see the Auth Webhook documentation.
Broadcasting a Message
Broadcasting allows clients to share custom events with other clients connected to the same document. Unlike document updates or presence changes, broadcasts are ephemeral messages that are not persisted in the document state.
// Step 1: Define your message structurelet payload = Payload(["message": "Hello!"])// Step 2: Broadcast to topictry await doc.broadcast(topic: "chat", payload: payload)// Step 3: Subscribe and handletry await doc.subscribeBroadcast { event, _ inguard let event = event as? BroadcastEvent else { return }print("Received: \(event.value.payload["message"] ?? "")")}
The broadcast event contains:
topic: A string identifying the type of broadcast messagepayload: The data being broadcast (must be JSON serializable)clientID: The ID of the client that sent the broadcast
This feature is useful for sending temporary messages or signals between clients, such as:
- Chat messages
- Cursor movement notifications
- Application-specific events
- User action notifications
Broadcast messages are not persisted and are only delivered to clients currently connected to the document. Clients that connect later will not receive previous broadcast messages.
Changing Synchronization Mode
To change the synchronization mode for a document, use client.changeSyncMode(doc, syncMode).
Yorkie offers five SyncModes:
-
SyncMode.realtime: Local changes are automatically pushed to the server, and remote changes are pulled from the server. -
SyncMode.realtimePushOnly: Only local changes are pushed, and remote changes are not pulled. -
SyncMode.realtimeSyncOff: Changes are not synchronized, but the watch stream remains active. -
SyncMode.manual: Synchronization no longer occurs in real-time, and the watch stream is disconnected. Manual handling is required for synchronization. -
SyncMode.polling: The sync loop runs without opening a watch stream.PushPullChangesruns at the polling interval, so remote changes arrive on the next tick (latency ≈ the interval). Recommended for large, low-interactivity documents where broadcast events are not needed; not suitable for collaborative editing — useSyncMode.realtimefor that. Set the interval with thedocumentPollIntervalattach option (TimeIntervalin seconds, default3.0).
// Enable automatic synchronization of both local and remote changes.try await client.changeSyncMode(doc, realtime)// Only push local changes automatically.try await client.changeSyncMode(doc, .realtimePushOnly)// Synchronization turned off, but the watch stream remains active.try await client.changeSyncMode(doc, .realtimeSyncOff)// Stream-less periodic sync at the document's poll interval.try await client.changeSyncMode(doc, .polling)// Synchronization turned off, and the watch stream is disconnected.try await client.changeSyncMode(doc, manual)try await client.sync(doc) // Trigger synchronization manually using the sync function.
To start a document in polling mode from the beginning, pass it at attach time along with an optional interval:
try await client.attach(doc, [:], .polling, documentPollInterval: 5.0)
Detaching the Document
If the document is no longer needed, detach it to improve the efficiency of garbage collection removing CRDT tombstones. For more information about GC, see Garbage Collection.
try await client.detach(doc)
Custom CRDT types
Custom CRDT types are specialized data types for applications such as text editors and counters, unlike general JSON data types such as JSONObject and JSONArray. Create custom CRDT types in the callback function of document.update.
JSONText
JSONText provides support for collaborative text editing. Contents in JSONText can have attributes; for example, characters can be bold, italic, or underlined.
try await doc.update{ root inroot.text = JSONText() // {"text":[]}(root.text as? JSONText)?.edit(0, 0, "hello") // {"text":[{"val":"hello"}]}(root.text as? JSONText)?.edit(0, 1, "H") // {"text":[{"val":"H"},{"val":"ello"}]}(root.text as? JSONText)?.setStyle(fromIdx: 0, toIdx: 1, attributes: ["bold": true]) // {"text":[{"attrs":{"bold":"true"},"val":"H"},{"val":"ello"}]}}
Selection using presence
Temporary client information, such as text selection, does not need to be stored in the document permanently. Instead, share it using presence.
When transmitting text selection information, convert the index, which can vary based on the text state, into the position used by Yorkie.JSONText. The converted position selection can then be sent and applied through presence.
Here is an example where presence is used to share text selection between users in UITextView.
- When the text selection is changed:
let range: NSRange // eg. selected range converted from selectedTextRange of UITextViewlet fromIdx = range.locationlet toIdx = range.location + range.lengthtry await doc.update { root, presence inif let range = try? (root.content as? JSONText)?.indexRangeToPosRange((fromIdx, toIdx)) {presence.set(["from": range.0, "to": range.1])}}
- When applying other user's selection changes:
await doc.subscribePresence(.others) { event inif let event = event as? PresenceChangedEvent {if let fromPos: TextPosStruct = decodePresence(event.value["from"]),let toPos: TextPosStruct = decodePresence(event.value["to"]) {if let (fromIdx, toIdx) = try? await(document.getRoot().content as? JSONText)?.posRangeToIndexRange((fromPos, toPos)) {// Handle the updated selection in the editor}}}}private func decodePresence<T: Decodable>(_ dictionary: Any?) -> T? {guard let dictionary = dictionary as? [String: Any],let data = try? JSONSerialization.data(withJSONObject: dictionary, options: [])else {return nil}return try? JSONDecoder().decode(T.self, from: data)}
Text selection can be efficiently shared using presence. Refer to the following example for complete code:
An example of Text Editor: Text Editor example
JSONCounter
JSONCounter supports integer types with addition and subtraction operations. If integer data needs to be modified simultaneously by multiple clients, use JSONCounter instead of primitives.
try await doc.update{ root inroot.counter = JSONCounter(value: Int64(1)) // {"counter":1}(root.counter as? JSONCounter<Int64>)?.increase(value: 2) // {"counter":3}(root.counter as? JSONCounter<Int64>)?.increase(value: 3) // {"counter":6}(root.counter as? JSONCounter<Int64>)?.increase(value: -4) // {"counter":2}}
Channel
Channel is a communication channel that enables real-time pub/sub messaging and presence tracking between clients. Unlike Documents, which persist and synchronize data, Channels are designed for ephemeral, real-time communication such as chat messages, notifications, and presence indicators.
For more information about Channel, please refer to the Channel.
Creating a Channel
Create a Channel with a unique key and attach it to the Client. The Channel initializer is throwing, because it validates the key:
let channel = try Channel(key: "room-123")try await client.attachChannel(channel)
The channel key identifies the Channel in Yorkie. Clients with the same channel key can communicate with each other through pub/sub messaging.
By default a channel syncs in realtime, opening a watch stream so broadcast events are delivered as they happen. For large channels where you only need an approximate session count and don't need broadcast events, create the channel with isRealtime: false — no watch stream is opened, and you refresh the count on your own cadence with syncChannel:
// Realtime (default): opens a watch stream for broadcast events.let roomChannel = try Channel(key: "room-123")try await client.attachChannel(roomChannel)// Non-realtime: stream-less, for large viewer counts where broadcast is not needed.let viewerChannel = try Channel(key: "viewer-room", isRealtime: false)try await client.attachChannel(viewerChannel)
Unlike the JS SDK, iOS sets a channel's sync behavior at construction time via the isRealtime flag rather than an attach option. There is no per-attach channelHeartbeatInterval; the client uses a fixed 5-second heartbeat interval internally.
Hierarchical Channel Keys
Channels support a hierarchical structure using periods (.) as separators, allowing you to organize channels into logical groups and subgroups. This structure is particularly useful for managing complex applications with multiple rooms, sections, or nested contexts.
let roomChannel = try Channel(key: "room-1")let sectionChannel = try Channel(key: "room-1.section-a")let userChannel = try Channel(key: "room-1.section-a.user-123")try await client.attachChannel(roomChannel)try await client.attachChannel(sectionChannel)try await client.attachChannel(userChannel)
Each level in the hierarchy maintains its own presence count and can be used independently:
room-1might track all users in a game roomroom-1.section-amight track users in a specific section of that roomroom-1.section-a.user-123might track presence for a specific user's context
Channel Key Restrictions:
The key is validated when the Channel is created (a YorkieError is thrown otherwise):
| Rule | Invalid Examples | Valid Examples |
|---|---|---|
| Cannot be empty or contain whitespace | ❌ ""❌ room 1 | ✅ room-1 |
| Cannot start with a period | ❌ .room-1❌ .room-1.section-1 | ✅ room-1✅ room-1.section-1 |
| Cannot end with a period | ❌ room-1.❌ room-1.section-1. | ✅ room-1✅ room-1.section-1 |
| Cannot contain consecutive periods | ❌ room-1..section-1❌ room..section..subsection | ✅ room-1.section-1✅ room.section.subsection |
Important: Distribute First-Level Channel Keys
Yorkie servers determine which server handles a channel based on a combination of your project and the first-level key of the channel. Using the same first-level key for all channels means that a single server manages all your channels, which can lead to performance bottlenecks and uneven load distribution.
Design your channel key structure to naturally distribute traffic across different first-level prefixes for optimal performance.
// ✅ Good: Distributed first-level keystry Channel(key: "game-1.room-a")try Channel(key: "chat-1.thread-1")try Channel(key: "chat-2.thread-1")try Channel(key: "notification-1.user-123")// ❌ Bad: Same first-level key// All channels share 'app' as first level - avoid this!try Channel(key: "app.game-1")try Channel(key: "app.game-2")try Channel(key: "app.chat-1")try Channel(key: "app.notification-1")
Broadcast
Channels support a pub/sub pattern for broadcasting ephemeral messages to all connected clients. Subscribe to a topic with subscribeTopic, and send messages with broadcast.
// Subscribe to messages on a specific topicchannel.subscribeTopic("chat") { event inprint("[\(event.topic)] \(event.payload["message"] ?? "")")print("From: \(event.clientID)")}// Broadcast a message to all clients in the same channeltry channel.broadcast(topic: "chat", payload: Payload(["message": "Hello, world!"]))
The ChannelBroadcastEvent object contains:
topic: The topic name you subscribed topayload: The message data as aPayload(must be JSON serializable)clientID: The ID of the client that sent the broadcast
You can subscribe to multiple topics on the same channel, and subscribeBroadcast receives every remote broadcast regardless of topic:
channel.subscribeTopic("chat") { event inprint("Chat message: \(event.payload)")}channel.subscribeTopic("notification") { event inprint("Notification: \(event.payload)")}// Or handle all broadcast topics in one placechannel.subscribeBroadcast { event inprint("[\(event.topic)] \(event.payload)")}try channel.broadcast(topic: "chat", payload: Payload(["message": "Hello!"]))try channel.broadcast(topic: "notification", payload: Payload(["type": "user-joined", "user": "Alice"]))
You can also broadcast without a Channel reference by using the channel key directly on the client:
try await client.broadcast("room-123", topic: "chat", payload: Payload(["message": "Hello!"]), options: nil)
Broadcast messages are ephemeral and only delivered to clients currently connected to the channel. Messages are not persisted or stored, so clients that join later will not receive previous messages.
Tracking Online Sessions
Channels automatically track the number of connected clients, making it easy to display session counters. Subscribe to presence changes with subscribePresenceChange, and read the current value with getSessionCount().
// Subscribe to presence (session count) changeschannel.subscribePresenceChange { event inprint("Sessions: \(event.count)")}// Get the current session countlet count = channel.getSessionCount()print("Currently \(count) sessions")
For a non-realtime channel (isRealtime: false), no watch stream delivers updates automatically. Call syncChannel to refresh the count on demand; it returns the latest session count:
let count = try await client.syncChannel(viewerChannel)
The session count is automatically updated when clients connect or disconnect from a realtime channel.
Sessions are connection-based and managed for scalability. In abnormal cases (such as app crashes or network partitions), a client might not detach cleanly, so the server may keep the session counted until it is considered stale and cleaned up. This means the displayed count can be approximate and may lag briefly. Avoid using session counts as a source of truth for critical business logic such as billing, authorization, or settlements.
Handling Channel Errors
Subscribe to authentication and sync errors to surface an error state in your UI. A subsequent successful event on the channel implies recovery — there is no separate "recovered" event.
channel.subscribeAuthError { event in// event.reason, event.method}channel.subscribeSyncError { event in// event.error, event.method}
You can also observe every channel event in one place with subscribeAll { event in ... }, switching on event.type (ChannelEventType).
Detaching a Channel
When you're done with a channel, detach it to clean up resources and stop receiving messages:
try await client.detachChannel(channel)
This is a local cleanup — the server reclaims the session automatically once heartbeats stop.
Use Cases
Channels are ideal for:
- Chat applications: Real-time messaging without persistence
- Live notifications: Temporary alerts and updates
- Presence indicators: Showing who's online or in a room
- Cursor sharing: Broadcasting cursor positions in collaborative tools
- Event broadcasting: Sending signals or triggers between clients
For persistent data that needs to be synchronized and stored, use Document instead.
Logger Options
The Logger outputs SDK events to the console for debugging purposes. To modify these options, use the Logger.logLevel variable.
Logger.logLevel = .error
The available log levels for setLogLevel are:
| LogLevel | Description |
|---|---|
LogLevel.Trivial | Most verbose level, displays all logs |
LogLevel.Debug | Detailed information for debugging |
LogLevel.Info | General information |
LogLevel.Warn | Warnings and potential issues |
LogLevel.Error | Errors and unexpected behavior |
LogLevel.Fatal | Critical errors, may lead to termination |
Adjust the log level for flexible control over log verbosity in your application.
Performance Best Practices
- Use
SyncMode.realtimePushOnlyfor write-heavy operations - Batch updates within single
doc.update()call - Detach documents when switching contexts
- Use
Logger.logLevel = .errorin production
Common Use Cases
Real-time Collaborative Text Editing
// Initialize texttry await doc.update { root, _ inroot.content = JSONText()}// Handle text changestry await doc.update { root, presence in(root.content as? JSONText)?.edit(0, 0, "Hello")// Share cursor positionif let range = try? (root.content as? JSONText)?.indexRangeToPosRange((0, 5)) {presence.set(["selection": ["from": range.0, "to": range.1]])}}
Shared Counter
try await doc.update { root, _ inroot.likes = JSONCounter(value: Int64(0))}// Increment likestry await doc.update { root, _ in(root.likes as? JSONCounter<Int64>)?.increase(value: 1)}
Live Cursor Tracking
// Update cursor positiontry await doc.update { root, presence inpresence.set(["cursor": ["x": 100, "y": 200]])}// Subscribe to others' cursorsawait doc.subscribePresence(.others) { event inif event.type == .presenceChanged {// Update UI with new cursor positions}}
Troubleshooting
Document Not Syncing
- Verify
SyncModeis set to.realtime - Check network connection using
subscribeConnection() - Ensure client is properly activated
Presence Not Updating
- Subscribe to presence events before attaching document
- Verify presence data is JSON serializable
- Check that document is attached to client
Memory Issues
- Detach unused documents
- Set appropriate
Logger.logLevel - Monitor document size and consider splitting large documents
Reference
For details on how to use the iOS SDK, please refer to iOS SDK Reference.