Yorkie

iOS SDK

Through Yorkie iOS SDK, you can efficiently build collaborative applications. On the client-side implementation, you can create Documents that are automatically synced 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 can communicate with the server. It has Documents and sends changes of the Document from local to the server to synchronize with other replicas in remote.

Creating a Client

We can create a Client using Client(rpcAddress: RPCAddress(host:,port:), options:). After the Client has been activated, it is connected to the server and ready to use.

let client = Client(rpcAddress: RPCAddress(host: "api.yorkie.dev", port: 443), options: ClientOptions(
    apiKey: "xxxxxxxxxxxxxxxxxxxx"
))
try await client.activate()

Subscribing to Client events

We can use client.eventStream to subscribe to client-based events, such as status-changed, stream-connection-status-changed and peer-changed.

target.eventStream.sink { event in
    switch event.type {
    case .statusChanged:
        ()
    case .streamConnectionStatusChanged:
        ()
    default:
        break
    }
}

By using the value of the stream-connection-status-changed event, it is possible to determine whether the Client is connected to the network.

If you want to know about other ClientEvents, please refer to the ClientEventType.

Presence

Presence is a feature that allows you to display information about users who are currently using a collaborative application. Presence is often used in collaborative applications such as document editors, chat apps, and other real-time applications.

var optionA = ClientOptions()
optionA.presence = ["username": "alice", "color": "blue"]

let clientA = Client(rpcAddress: rpcAddress, options: optionA)
try await clientA.activate()

let docA = Document(key: "doc-1")
try await clientA.attach(docA)

Then, another Client is created and attaches a Document with the same name as before.

var optionB = ClientOptions()
optionB.presence = ["username": "alice", "color": "blue"]

let clientB = Client(rpcAddress: rpcAddress, options: optionA)
try await clientB.activate()

let docB = Document(key: "doc-1")
try await clientB.attach(docB)

When a new peer registers or leaves, the peers-changed event is fired, and the other peer's clientID and presence can be obtained from the event.

clientA.eventStream.sink { event in
    if let event = event as? PeerChangedEvent {
        let peers = event.value.peers["doc-1"]
        switch event.value.type {
        case .initialized:
            displayPeers(peers)
        case .watched:
            peers.forEach { addPeer($0) }
            // peer as follows:
            // {
            //   clientID: 'xxxxxxxxxxxxxxxxxxxx',
            //   presence: ["username": "bob", "color": "red"]
            // }
        case .unwatched:
            peers.forEach { removePeer($0) }
        case .presenceChanged:
            peers.forEach { updatePeer($0) }
        }
    }
}

In the code above, clientA receives a watched event from clientB because clientB attached the Document with the key doc-1.

Presence can include their names, colors, and other identifying details.

Document

Document is a primary data type in Yorkie, which provides 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 are automatically propagated to other peers when the Document is attached to the Client or when the network is restored.

Creating a Document

We can create a Document using Document(key: "doc-key"). Let's create a Document with a key and attach it to the Client.

let doc = Document(key: docKey)
try await client.attach(doc);

After attaching the Document to the Client, all changes to the Document are automatically synchronized with remote peers.

Changing Syncronization Mode

If you want to change syncronization mode, you can use client.pause(doc) and client.resume(doc).

// Pause real-time sync.
await client.pause(doc);

// Resume real-time sync.
await client.resume(doc);

Editing the Document

Document.update(:,message:) enables you to modify a Document. The optional message allows you to add a description to the change. If the Document is attached to the Client, all changes are automatically synchronized with other Clients.

let message = "update document for test";
try await doc.update({ root in
  root.obj = [:]                      // {"obj":{}}
  let obj = root.obj as! JSONObject
  obj.num = Int64(1)                  // {"obj":{"num":1}}
  obj.obj = ["str": "a"]              // {"obj":{"num":1,"obj":{"str":"a"}}}
  obj.arr = [Int64(1), Int64(2)]      // {"obj":{"num":1,"obj":{"str":"a"},"arr":[1,2]}}
}, message: message);

Under the hood, root in the update function creates a change, a set of operations, using a JavaScript proxy. Every element has its unique ID, created by the logical clock. This ID is used by Yorkie to track which object is which.

You can get the contents of the Document using doc.getRoot().

let root = doc.getRoot()
print(root.obj!) // {"num":1,"obj":{"str":"a"},"arr":[1,2]}
let obj = root.obj as! JSONObject
print(obj.num!)  // 1
print(obj.obj!)  // {"str":"a"}
print(obj.arr!)  // [1,2]

Subscribing to Document events

A Document is modified by changes generated remotely or locally in Yorkie. When the Document is modified, change events occur, to which we can subscribe using document.subscribe. Here, we can do post-processing such as repaint in the application using the path of the change events.

await target.eventStream.sink { event in
    switch event {
    case let event as LocalChangeEvent:
        print(event)
    case let event as RemoteChangeEvent:
        for changeInfo in event.value {
            print(changeInfo.change.message)
            for path in changeInfo.paths {
                if path.starts(with: "$.obj.num") {
                    // root.obj.num is changed
                } else if path.starts(with: "$.obj") {
                    // root.obj is changed
                }
            }
        }
    }
}

Detaching the Document

If the document is no longer used, it should be detached to increase the efficiency of GC removing CRDT tombstones. For more information about GC, please refer to Garbage Collection.

try await client.detach(doc)

Custom CRDT types

Custom CRDT types are data types that can be used for special applications such as text editors and counters, unlike general JSON data types such as JSONObject and JSONArray. Custom CRDT types can be created in the callback function of document.update.

JSONText

JSONText provides supports for collaborative text editing. JSONText has selection information for sharing the cursor position. In addition, contents in Text can have attributes; for example, characters can be bold, italic, or underlined.

try await doc.update{ root in
    root.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)?.select(0, 1)
    (root.text as? JSONText)?.setStyle(fromIdx: 0, toIdx: 1, attributes: ["bold": true])    // {"text":[{"attrs":{"bold":"true"},"val":"H"},{"val":"ello"}]}
}

An example of Text Editor: Text Editor example

JSONCounter

JSONCounter supports integer types changing with addition and subtraction. If an integer data needs to be modified simultaneously, JSONCounter should be used instead of primitives.

try await doc.update{ root in
    root.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}
}

Reference

For details on how to use the iOS SDK, please refer to iOS SDK Reference.