Subscription

When we had initially set up Apollo, we used just the network transport. But subscriptions is an advanced use case which needs more configuration. So we have to add ApolloWebSocket. Add apollowebsocket.framework and starscream.framework from your Carthage/Build/IOS to libraries.

Now we need to update our ApolloClient instance to point to the subscription server.

Open Todo/NetworkManager.swift and update the following:

Todo/NetworkManager.swift

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import Foundation
import Apollo

class NetworkManager {
    static let shared = NetworkManager()
    let graphEndpoint = "https://hasura.io/learn/graphql"
+    let graphWSEndpoint = "wss://hasura.io/learn/graphql"
    var apolloClient : ApolloClient?
    
    private init (){
    }
    
    func setApolloClient(accessToken: String){
        self.apolloClient = {
            let authPayloads = ["Authorization": "Bearer \(accessToken)"]
            let configuration = URLSessionConfiguration.default
            configuration.httpAdditionalHeaders = authPayloads
            
+            let map: GraphQLMap = authPayloads
+            let wsEndpointURL = URL(string: graphWSEndpoint)!
            let endpointURL = URL(string: graphEndpoint)!
+            var request = URLRequest(url: wsEndpointURL)
+            request.setValue("Bearer \(accessToken)", forHTTPHeaderField: "Authorization")
+            let websocket = WebSocketTransport(request: request, sendOperationIdentifiers: false, reconnectionInterval: 30000, connectingPayload: map)
+            let splitNetworkTransport = SplitNetworkTransport(
+                httpNetworkTransport: HTTPNetworkTransport(
+                    url: endpointURL,
+                    session: URLSession(configuration: configuration)
+                ),
+                webSocketNetworkTransport: websocket
+            )
-            return ApolloClient(networkTransport: HTTPNetworkTransport(url: endpointURL, configuration: configuration))
+            return ApolloClient(networkTransport: splitNetworkTransport)
            }()
    }

}

Note that we are replacing HTTPNetworkTransport with SplitNetworkTransport and hence all GraphQL queries go through a single websocket connection.