Fix rare crash in WebSocketClient when updating the engine (#3888)

Author: laevandus

Sources/StreamChat/WebSocketClient/WebSocketClient.swift

@@ -121,7 +121,9 @@ class WebSocketClient {
         }
 
         do {
-            engine = try createEngineIfNeeded(for: endpoint)
+            try engineQueue.sync {
+                self.engine = try createEngineIfNeeded(for: endpoint)
+            }
         } catch {
             return
         }

TestTools/StreamChatTestTools/SpyPattern/Spy/RequestEncoder_Spy.swift

@@ -13,10 +13,10 @@ final class RequestEncoder_Spy: RequestEncoder, Spy {
 
     weak var connectionDetailsProviderDelegate: ConnectionDetailsProviderDelegate?
 
-    var encodeRequest: Result<URLRequest, Error>? = .success(URLRequest(url: .unique()))
-    var onEncodeRequestCall: (() -> Void)?
-    var encodeRequest_endpoints: [AnyEndpoint] = []
-    var encodeRequest_completion: ((Result<URLRequest, Error>) -> Void)?
+    @Atomic var encodeRequest: Result<URLRequest, Error>? = .success(URLRequest(url: .unique()))
+    @Atomic var onEncodeRequestCall: (() -> Void)?
+    @Atomic var encodeRequest_endpoints: [AnyEndpoint] = []
+    @Atomic var encodeRequest_completion: ((Result<URLRequest, Error>) -> Void)?
 
     func encodeRequest<ResponsePayload>(
         for endpoint: Endpoint<ResponsePayload>,

Tests/StreamChatTests/WebSocketClient/WebSocketClient_Tests.swift

@@ -378,6 +378,15 @@ final class WebSocketClient_Tests: XCTestCase {
             self.webSocketClient.connectEndpoint = .webSocketConnect(userInfo: UserInfo(id: "user_\(index)"))
         })
     }
+    
+    func test_recreatingEngineConcurrently() {
+        DispatchQueue.concurrentPerform(iterations: 100, execute: { _ in
+            self.webSocketClient.initialize()
+            // Change mocked request so that connect recreates the engine
+            requestEncoder.encodeRequest = .success(.init(url: .unique()))
+            self.webSocketClient.connect()
+        })
+    }
 
     // MARK: - Event handling tests