Make app check token result sendable

Author: daymxn

FirebaseAI/Sources/GenerativeAIService.swift

@@ -213,7 +213,7 @@ struct GenerativeAIService {
   private func fetchAppCheckToken(appCheck: AppCheckInterop) async throws
     -> FIRAppCheckTokenResultInterop {
     if useLimitedUseAppCheckTokens {
-      if let token = await appCheck.getLimitedUseToken?() {
+      if let token = await getLimitedUseAppCheckToken(appCheck: appCheck) {
         return token
       }
 
@@ -234,6 +234,25 @@ struct GenerativeAIService {
     return await appCheck.getToken(forcingRefresh: false)
   }
 
+  private func getLimitedUseAppCheckToken(appCheck: AppCheckInterop) async -> FIRAppCheckTokenResultInterop? {
+    // At the moment, `await` doesn’t get along with Objective-C’s optional protocol methods.
+    await withCheckedContinuation { (continuation: CheckedContinuation<FIRAppCheckTokenResultInterop?, Never>) in
+      guard
+        useLimitedUseAppCheckTokens,
+        // `getLimitedUseToken(completion:)` is an optional protocol method. Optional binding
+        // is performed to make sure `continuation` is called even if the method’s not implemented.
+        let limitedUseTokenClosure = appCheck.getLimitedUseToken
+      else {
+        return continuation.resume(returning: nil)
+      }
+
+      limitedUseTokenClosure { tokenResult in
+        // The placeholder token should be used in the case of App Check error.
+        continuation.resume(returning: tokenResult)
+      }
+    }
+  }
+
   private func httpResponse(urlResponse: URLResponse) throws -> HTTPURLResponse {
     // The following condition should always be true: "Whenever you make HTTP URL load requests, any
     // response objects you get back from the URLSession, NSURLConnection, or NSURLDownload class

FirebaseAI/Tests/Unit/Fakes/AppCheckInteropFake.swift

@@ -52,9 +52,9 @@ class AppCheckInteropFake: NSObject, AppCheckInterop {
     fatalError("\(#function) not implemented.")
   }
 
-  private class AppCheckTokenResultInteropFake: NSObject, FIRAppCheckTokenResultInterop {
-    var token: String
-    var error: Error?
+  private class AppCheckTokenResultInteropFake: NSObject, FIRAppCheckTokenResultInterop, @unchecked Sendable {
+    let token: String
+    let error: Error?
 
     init(token: String, error: Error?) {
       self.token = token

FirebaseAppCheck/Interop/Public/FirebaseAppCheckInterop/FIRAppCheckTokenResultInterop.h

@@ -18,6 +18,7 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+NS_SWIFT_SENDABLE
 @protocol FIRAppCheckTokenResultInterop <NSObject>
 
 /// App Check token in the case of success or a dummy token in the case of a failure.

FirebaseAppCheck/Sources/Core/FIRAppCheckTokenResult.h

@@ -20,6 +20,7 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+NS_SWIFT_SENDABLE
 @interface FIRAppCheckTokenResult : NSObject <FIRAppCheckTokenResultInterop>
 
 - (instancetype)initWithToken:(NSString *)token error:(nullable NSError *)error;