Ensure thread safety

Source/Bridge.swift

@@ -5,6 +5,7 @@ public enum BridgeError: Error {
     case missingWebView
 }
 
+@MainActor
 protocol Bridgable: AnyObject {
     var delegate: BridgeDelegate? { get set }
     var webView: WKWebView? { get }
@@ -17,25 +18,30 @@ protocol Bridgable: AnyObject {
 
 /// `Bridge` is the object for configuring a web view and
 /// the channel for sending/receiving messages
+@MainActor
 public final class Bridge: Bridgable {
+    public typealias InitializationCompletionHandler = () -> Void
     weak var delegate: BridgeDelegate?
     weak var webView: WKWebView?
 
-    public static func initialize(_ webView: WKWebView) {
+    nonisolated public static func initialize(_ webView: WKWebView, completion: InitializationCompletionHandler?) {
+        Task { @MainActor in
+            await initialize(webView)
+            completion?()
+        }
+    }
+
+    public static func initialize(_ webView: WKWebView) async {
         if getBridgeFor(webView) == nil {
             initialize(Bridge(webView: webView))
         }
     }
-
+    
     init(webView: WKWebView) {
         self.webView = webView
         loadIntoWebView()
     }
 
-    deinit {
-        webView?.configuration.userContentController.removeScriptMessageHandler(forName: scriptHandlerName)
-    }
-
     // MARK: - Internal API
 
     /// Register a single component
@@ -72,15 +78,14 @@ public final class Bridge: Bridgable {
 //        let replyMessage = message.replacing(data: data)
 //        callBridgeFunction("send", arguments: [replyMessage.toJSON()])
 //    }
-    @MainActor
     @discardableResult
-    func evaluate(javaScript: String) async throws -> Any {
+    func evaluate(javaScript: String) async throws -> Any? {
         guard let webView else {
             throw BridgeError.missingWebView
         }
 
         do {
-            return try await webView.evaluateJavaScript(javaScript)
+            return try await webView.evaluateJavaScriptAsync(javaScript)
         } catch {
             logger.error("Error evaluating JavaScript: \(error)")
             throw error
@@ -90,7 +95,7 @@ public final class Bridge: Bridgable {
     /// Evaluates a JavaScript function with optional arguments by encoding the arguments
     /// Function should not include the parens
     /// Usage: evaluate(function: "console.log", arguments: ["test"])
-    func evaluate(function: String, arguments: [Any] = []) async throws -> Any {
+    func evaluate(function: String, arguments: [Any] = []) async throws -> Any? {
         try await evaluate(javaScript: JavaScript(functionName: function, arguments: arguments).toString())
     }
 
@@ -151,7 +156,7 @@ public final class Bridge: Bridgable {
     // MARK: - JavaScript Evaluation
 
     @discardableResult
-    private func evaluate(javaScript: JavaScript) async throws -> Any {
+    private func evaluate(javaScript: JavaScript) async throws -> Any? {
         do {
             return try await evaluate(javaScript: javaScript.toString())
         } catch {
@@ -168,7 +173,6 @@ public final class Bridge: Bridgable {
 }
 
 extension Bridge: ScriptMessageHandlerDelegate {
-    @MainActor
     func scriptMessageHandlerDidReceiveMessage(_ scriptMessage: WKScriptMessage) async throws {
         if let event = scriptMessage.body as? String, event == "ready" {
             try await delegate?.bridgeDidInitialize()
@@ -183,3 +187,23 @@ extension Bridge: ScriptMessageHandlerDelegate {
         logger.warning("Unhandled message received: \(String(describing: scriptMessage.body))")
     }
 }
+
+private extension WKWebView {
+    /// NOTE: The async version crashes the app with `Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value`
+    /// in case the function doesn't return anything.
+    /// This is a workaround. See https://forums.developer.apple.com/forums/thread/701553 for more details.
+    @discardableResult
+    func evaluateJavaScriptAsync(_ str: String) async throws -> Any? {
+        return try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Any?, Error>) in
+            DispatchQueue.main.async {
+                self.evaluateJavaScript(str) { data, error in
+                    if let error = error {
+                        continuation.resume(throwing: error)
+                    } else {
+                        continuation.resume(returning: data)
+                    }
+                }
+            }
+        }
+    }
+}

Source/BridgeComponent.swift

@@ -1,5 +1,6 @@
 import Foundation
 
+@MainActor
 protocol BridgingComponent: AnyObject {
     static var name: String { get }
     var delegate: BridgingDelegate { get }
@@ -22,6 +23,7 @@ protocol BridgingComponent: AnyObject {
     func viewDidDisappear()
 }
 
+@MainActor
 open class BridgeComponent: BridgingComponent {
     public typealias ReplyCompletionHandler = (Result<Bool, Error>) -> Void
 
@@ -30,7 +32,7 @@ open class BridgeComponent: BridgingComponent {
     /// Subclasses must provide their own implementation of this property.
     ///
     /// - Note: This property is used for identifying the component.
-    open class var name: String {
+    nonisolated open class var name: String {
         fatalError("BridgeComponent subclass must provide a unique 'name'")
     }
 
@@ -149,7 +151,7 @@ open class BridgeComponent: BridgingComponent {
 
     @discardableResult
     /// Replies to the web with the last received message for a given `event`, replacing its `jsonData`
-    /// with the provided `Encodable` object. 
+    /// with the provided `Encodable` object.
     ///
     /// NOTE: If a message has not been received for the given `event`, the reply will be ignored.
     ///
@@ -275,3 +277,4 @@ open class BridgeComponent: BridgingComponent {
 
     private var receivedMessages = [String: Message]()
 }
+

Source/BridgeDelegate.swift

@@ -3,6 +3,7 @@ import WebKit
 
 public protocol BridgeDestination: AnyObject {}
 
+@MainActor
 public protocol BridgingDelegate: AnyObject {
     var location: String { get }
     var destination: BridgeDestination { get }
@@ -24,6 +25,7 @@ public protocol BridgingDelegate: AnyObject {
     func bridgeDidReceiveMessage(_ message: Message) -> Bool
 }
 
+@MainActor
 public final class BridgeDelegate: BridgingDelegate {
     public let location: String
     public unowned let destination: BridgeDestination
@@ -153,4 +155,3 @@ public final class BridgeDelegate: BridgingDelegate {
         return component
     }
 }
-

Tests/BridgeComponentTests.swift

@@ -3,6 +3,7 @@ import XCTest
 import WebKit
 import Strada
 
+@MainActor
 class BridgeComponentTest: XCTestCase {
     private var delegate: BridgeDelegateSpy!
     private var destination: AppBridgeDestination!
@@ -223,6 +224,6 @@ class BridgeComponentTest: XCTestCase {
     }
 }
 
-private extension TimeInterval {
+extension TimeInterval {
     static let expectationTimeout: TimeInterval = 5
 }

Tests/BridgeDelegateTests.swift

@@ -3,6 +3,7 @@ import XCTest
 import WebKit
 @testable import Strada
 
+@MainActor
 class BridgeDelegateTests: XCTestCase {
     private var delegate: BridgeDelegate!
     private var destination: AppBridgeDestination!

Tests/BridgeTests.swift

@@ -2,32 +2,67 @@ import XCTest
 import WebKit
 @testable import Strada
 
+@MainActor
 class BridgeTests: XCTestCase {
-    func testInitWithANewWebViewAutomaticallyLoadsIntoWebView() {
+    func testInitWithANewWebViewAutomaticallyLoadsIntoWebView() async {
         let webView = WKWebView()
         let userContentController = webView.configuration.userContentController
         XCTAssertTrue(userContentController.userScripts.isEmpty)
 
-        Bridge.initialize(webView)
+        await Bridge.initialize(webView)
         XCTAssertEqual(userContentController.userScripts.count, 1)
     }
 
-    func testInitWithTheSameWebViewDoesNotLoadTwice() {
+    func testInitWithTheSameWebViewDoesNotLoadTwice() async {
         let webView = WKWebView()
         let userContentController = webView.configuration.userContentController
         XCTAssertTrue(userContentController.userScripts.isEmpty)
 
-        Bridge.initialize(webView)
+        await Bridge.initialize(webView)
         XCTAssertEqual(userContentController.userScripts.count, 1)
 
-        Bridge.initialize(webView)
+        await Bridge.initialize(webView)
         XCTAssertEqual(userContentController.userScripts.count, 1)
     }
+
+    func testInitWithANewWebViewAutomaticallyLoadsIntoWebView() {
+        let webView = WKWebView()
+        let userContentController = webView.configuration.userContentController
+        XCTAssertTrue(userContentController.userScripts.isEmpty)
+
+        let expectation = expectation(description: "Wait for completion.")
+        Bridge.initialize(webView) {
+            XCTAssertEqual(userContentController.userScripts.count, 1)
+            expectation.fulfill()
+        }
+
+        wait(for: [expectation], timeout: .expectationTimeout)
+    }
+
+    func testInitWithTheSameWebViewDoesNotLoadTwice() {
+        let webView = WKWebView()
+        let userContentController = webView.configuration.userContentController
+        XCTAssertTrue(userContentController.userScripts.isEmpty)
+
+        let expectation1 = expectation(description: "Wait for completion.")
+        Bridge.initialize(webView) {
+            XCTAssertEqual(userContentController.userScripts.count, 1)
+            expectation1.fulfill()
+        }
+
+        let expectation2 = expectation(description: "Wait for completion.")
+
+        Bridge.initialize(webView) {
+            XCTAssertEqual(userContentController.userScripts.count, 1)
+            expectation2.fulfill()
+        }
+
+        wait(for: [expectation1, expectation2], timeout: .expectationTimeout)
+    }
 
     /// NOTE: Each call to `webView.evaluateJavaScript(String)` will throw an error.
     /// We intentionally disregard any thrown errors (`try? await bridge...`)
     /// because we validate the evaluated JavaScript string ourselves.
-    @MainActor
     func testRegisterComponentCallsJavaScriptFunction() async throws {
         let webView = TestWebView()
         let bridge = Bridge(webView: webView)
@@ -37,7 +72,6 @@ class BridgeTests: XCTestCase {
         XCTAssertEqual(webView.lastEvaluatedJavaScript, "window.nativeBridge.register(\"test\")")
     }
 
-    @MainActor
     func testRegisterComponentsCallsJavaScriptFunction() async throws {
         let webView = TestWebView()
         let bridge = Bridge(webView: webView)
@@ -47,7 +81,6 @@ class BridgeTests: XCTestCase {
         XCTAssertEqual(webView.lastEvaluatedJavaScript, "window.nativeBridge.register([\"one\",\"two\"])")
     }
 
-    @MainActor
     func testUnregisterComponentCallsJavaScriptFunction() async throws {
         let webView = TestWebView()
         let bridge = Bridge(webView: webView)
@@ -57,7 +90,6 @@ class BridgeTests: XCTestCase {
         XCTAssertEqual(webView.lastEvaluatedJavaScript, "window.nativeBridge.unregister(\"test\")")
     }
 
-    @MainActor
     func testSendCallsJavaScriptFunction() async throws {
         let webView = TestWebView()
         let bridge = Bridge(webView: webView)
@@ -78,7 +110,6 @@ class BridgeTests: XCTestCase {
         XCTAssertEqual(webView.lastEvaluatedJavaScript, "window.nativeBridge.replyWith({\"component\":\"page\",\"event\":\"connect\",\"data\":{\"title\":\"Page-title\"},\"id\":\"1\"})")
     }
 
-    @MainActor
     func testEvaluateJavaScript() async throws {
         let webView = TestWebView()
         let bridge = Bridge(webView: webView)
@@ -88,7 +119,6 @@ class BridgeTests: XCTestCase {
         XCTAssertEqual(webView.lastEvaluatedJavaScript, "test(1,2,3)")
     }
 
-    @MainActor
     func testEvaluateJavaScriptReturnsErrorForNoWebView() async throws {
         let bridge = Bridge(webView: WKWebView())
         bridge.webView = nil
@@ -101,7 +131,6 @@ class BridgeTests: XCTestCase {
         XCTAssertEqual(bridgeError, BridgeError.missingWebView)
     }
 
-    @MainActor
     func testEvaluateFunction() async throws {
         let webView = TestWebView()
         let bridge = Bridge(webView: webView)

Tests/ComponentTestExample/ComposerComponentTests.swift

@@ -2,6 +2,7 @@ import XCTest
 import WebKit
 import Strada
 
+@MainActor
 final class ComposerComponentTests: XCTestCase {
     private var delegate: BridgeDelegateSpy!
     private var destination: AppBridgeDestination!