How to implement graphql subscription using apollo ios client

Question

I am trying to implement graphql subscription using apollo ios client. But not able to figure it out as lack of documentation examples. Example given on apollo documentation is:

let apollo: ApolloClient = {
  let configuration = URLSessionConfiguration.default
  // Add additional headers as needed
  configuration.httpAdditionalHeaders = ["Authorization": "Bearer <token>"] // Replace `<token>`

  let url = URL(string: "http://localhost:8080/graphql")!

  return ApolloClient(networkTransport: HTTPNetworkTransport(url: url, configuration: configuration))
}()

APOLLO IOS GUIDE: Creating a client

Answer 1

Implement the subscription in apollo ios graphql client by following below steps.

1. Using cocoapods:

   1. pod 'Apollo'
   2. pod 'Apollo/WebSocket'
   3. pod install

2. To create client to support subscription and authentication. Add below code in AppDelegate.swift:

   1. Websocket - we have to use WebSocketTransport and URLRequest
   2. Authentication - we have to pass auth parameters in connection params connectingPayload to server. And for http we are passing it in headers as mentioned in question snippet.
   3. SplitNetworkTransport- To combine both http and websocket to create client. we have to use httpNetworkTransport and webSocketNetworkTransport

lazy var apollo: ApolloClient = {
    let authPayloads = [
        "Authorization": "Bearer "
    ]
    let configuration = URLSessionConfiguration.default
    configuration.httpAdditionalHeaders = authPayloads


let map: GraphQLMap = authPayloads 
let wsEndpointURL = URL(string: "ws://localhost:8080/subscriptions")!
let endpointURL = URL(string: "http://localhost:8080/api")!
let websocket = WebSocketTransport(request: URLRequest(url: wsEndpointURL), connectingPayload: map)
let splitNetworkTransport = SplitNetworkTransport(
    httpNetworkTransport: HTTPNetworkTransport(
        url: endpointURL,
        configuration: configuration
    ), 
    webSocketNetworkTransport: websocket
)
return ApolloClient(networkTransport: splitNetworkTransport)


}()