Merge pull request #29 from hotwired/async-javascript-take-2

Async javascript take 2

.gitignore

@@ -1,7 +1,7 @@
 build
 node_modules
 *.log
-
 *.xcuserstate
-
 *.xcbkptlist
+.swiftpm
+xcuserdata

Source/Bridge.swift

@@ -8,21 +8,20 @@ public enum BridgeError: Error {
 protocol Bridgable: AnyObject {
     var delegate: BridgeDelegate? { get set }
     var webView: WKWebView? { get }
-    
-    func register(component: String)
-    func register(components: [String])
-    func unregister(component: String)
-    func reply(with message: Message)
+
+    func register(component: String) async throws
+    func register(components: [String]) async throws
+    func unregister(component: String) async throws
+    func reply(with message: Message) async throws
 }
 
 /// `Bridge` is the object for configuring a web view and
 /// the channel for sending/receiving messages
 public final class Bridge: Bridgable {
-    typealias CompletionHandler = (_ result: Any?, _ error: Error?) -> Void
-
+    public typealias InitializationCompletionHandler = () -> Void
     weak var delegate: BridgeDelegate?
     weak var webView: WKWebView?
-    
+
     public static func initialize(_ webView: WKWebView) {
         if getBridgeFor(webView) == nil {
             initialize(Bridge(webView: webView))
@@ -33,39 +32,39 @@ public final class Bridge: Bridgable {
         self.webView = webView
         loadIntoWebView()
     }
-
-    deinit {
-        webView?.configuration.userContentController.removeScriptMessageHandler(forName: scriptHandlerName)
-    }
-
+
     // MARK: - Internal API
-    
+
     /// Register a single component
     /// - Parameter component: Name of a component to register support for
-    func register(component: String) {
-        callBridgeFunction(.register, arguments: [component])
+    @MainActor 
+    func register(component: String) async throws {
+        try await callBridgeFunction(.register, arguments: [component])
     }
-    
+
     /// Register multiple components
     /// - Parameter components: Array of component names to register
-    func register(components: [String]) {
-        callBridgeFunction(.register, arguments: [components])
+    @MainActor 
+    func register(components: [String]) async throws {
+        try await callBridgeFunction(.register, arguments: [components])
     }
-    
+
     /// Unregister support for a single component
     /// - Parameter component: Component name
-    func unregister(component: String) {
-        callBridgeFunction(.unregister, arguments: [component])
+    @MainActor 
+    func unregister(component: String) async throws {
+        try await callBridgeFunction(.unregister, arguments: [component])
     }
-    
+
     /// Send a message through the bridge to the web application
     /// - Parameter message: Message to send
-    func reply(with message: Message) {
+    @MainActor
+    func reply(with message: Message) async throws {
         logger.debug("bridgeWillReplyWithMessage: \(String(describing: message))")
         let internalMessage = InternalMessage(from: message)
-        callBridgeFunction(.replyWith, arguments: [internalMessage.toJSON()])
+        try await callBridgeFunction(.replyWith, arguments: [internalMessage.toJSON()])
     }
-    
+
 //    /// Convenience method to reply to a previously received message. Data will be replaced,
 //    /// while id, component, and event will remain the same
 //    /// - Parameter message: Message to reply to
@@ -74,28 +73,27 @@ public final class Bridge: Bridgable {
 //        let replyMessage = message.replacing(data: data)
 //        callBridgeFunction("send", arguments: [replyMessage.toJSON()])
 //    }
-
-    /// Evaluates javaScript string directly as passed in sending through the web view
-    func evaluate(javaScript: String, completion: CompletionHandler? = nil) {
-        guard let webView = webView else {
-            completion?(nil, BridgeError.missingWebView)
-            return
+    @discardableResult
+    @MainActor
+    func evaluate(javaScript: String) async throws -> Any? {
+        guard let webView else {
+            throw BridgeError.missingWebView
         }
-
-        webView.evaluateJavaScript(javaScript) { result, error in
-            if let error = error {
-                logger.error("Error evaluating JavaScript: \(error)")
-            }
-
-            completion?(result, error)
+
+        do {
+            return try await webView.evaluateJavaScriptAsync(javaScript)
+        } catch {
+            logger.error("Error evaluating JavaScript: \(error)")
+            throw error
         }
     }
-    
+
     /// 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] = [], completion: CompletionHandler? = nil) {
-        evaluate(javaScript: JavaScript(functionName: function, arguments: arguments), completion: completion)
+    @MainActor
+    func evaluate(function: String, arguments: [Any] = []) async throws -> Any? {
+        try await evaluate(javaScript: JavaScript(functionName: function, arguments: arguments).toString())
     }
 
     static func initialize(_ bridge: Bridge) {
@@ -106,23 +104,24 @@ public final class Bridge: Bridgable {
     static func getBridgeFor(_ webView: WKWebView) -> Bridge? {
         return instances.first { $0.webView == webView }
     }
-    
+
     // MARK: Private
 
     private static var instances: [Bridge] = []
     /// This needs to match whatever the JavaScript file uses
     private let bridgeGlobal = "window.nativeBridge"
-    
+
     /// The webkit.messageHandlers name
     private let scriptHandlerName = "strada"
-
-    private func callBridgeFunction(_ function: JavaScriptBridgeFunction, arguments: [Any]) {
+
+    @MainActor
+    private func callBridgeFunction(_ function: JavaScriptBridgeFunction, arguments: [Any]) async throws {
         let js = JavaScript(object: bridgeGlobal, functionName: function.rawValue, arguments: arguments)
-        evaluate(javaScript: js)
+        try await evaluate(javaScript: js)
     }
 
     // MARK: - Configuration
-    
+
     /// Configure the bridge in the provided web view
     private func loadIntoWebView() {
         guard let configuration = webView?.configuration else { return }
@@ -131,17 +130,18 @@ public final class Bridge: Bridgable {
         if let userScript = makeUserScript() {
             configuration.userContentController.addUserScript(userScript)
         }
-        
+
         let scriptMessageHandler = ScriptMessageHandler(delegate: self)
         configuration.userContentController.add(scriptMessageHandler, name: scriptHandlerName)
     }
 
     private func makeUserScript() -> WKUserScript? {
         guard
-            let path = PathLoader().pathFor(name: "strada", fileType: "js") else {
-                return nil
+            let path = PathLoader().pathFor(name: "strada", fileType: "js")
+        else {
+            return nil
         }
-        
+
         do {
             let source = try String(contentsOfFile: path)
             return WKUserScript(source: source, injectionTime: .atDocumentStart, forMainFrameOnly: true)
@@ -150,18 +150,20 @@ public final class Bridge: Bridgable {
             return nil
         }
     }
-    
+
     // MARK: - JavaScript Evaluation
-
-    private func evaluate(javaScript: JavaScript, completion: CompletionHandler? = nil) {
+
+    @discardableResult
+    @MainActor
+    private func evaluate(javaScript: JavaScript) async throws -> Any? {
         do {
-            evaluate(javaScript: try javaScript.toString(), completion: completion)
+            return try await evaluate(javaScript: javaScript.toString())
         } catch {
             logger.error("Error evaluating JavaScript: \(String(describing: javaScript)), error: \(error)")
-            completion?(nil, error)
+            throw error
         }
     }
-    
+
     private enum JavaScriptBridgeFunction: String {
         case register
         case unregister
@@ -170,18 +172,37 @@ public final class Bridge: Bridgable {
 }
 
 extension Bridge: ScriptMessageHandlerDelegate {
+    @MainActor
     func scriptMessageHandlerDidReceiveMessage(_ scriptMessage: WKScriptMessage) {
-        if let event = scriptMessage.body as? String,
-            event == "ready" {
+        if let event = scriptMessage.body as? String, event == "ready" {
             delegate?.bridgeDidInitialize()
             return
         }
-        
+
         if let message = InternalMessage(scriptMessage: scriptMessage) {
             delegate?.bridgeDidReceiveMessage(message.toMessage())
             return
         }
-        
+
         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
+    @MainActor
+    func evaluateJavaScriptAsync(_ javaScriptString: String) async throws -> Any? {
+        return try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Any?, Error>) in
+            evaluateJavaScript(javaScriptString) { data, error in
+                if let error {
+                    continuation.resume(throwing: error)
+                } else {
+                    continuation.resume(returning: data)
+                }
+            }
+        }
+    }
+}