add threading assertions/checks

Author: garyodonoghue

AdyenNetworking/APIClient/APIClient.swift

@@ -109,7 +109,7 @@ public final class APIClient: APIClientProtocol {
         self.urlSession = URLSession(
             configuration: configuration ?? Self.buildDefaultConfiguration(),
             delegate: urlSessionDelegate,
-            delegateQueue: .main
+            delegateQueue: nil
         )
         self.responseValidator = responseValidator
         self.coder = coder
@@ -136,10 +136,14 @@ public final class APIClient: APIClientProtocol {
                         }
                     }
 
-                completionHandler(result)
+                DispatchQueue.main.sync {
+                    completionHandler(result)
+                }
             }.resume()
         } catch {
-            completionHandler(.failure(error))
+            DispatchQueue.main.sync {
+                completionHandler(.failure(error))
+            }
         }
     }
 
@@ -148,15 +152,22 @@ public final class APIClient: APIClientProtocol {
         completionHandler: @escaping CompletionHandler<R.ResponseType>
     ) where R: Request, R.ResponseType == DownloadResponse {
         do {
-            urlSession.downloadTask(with: try buildUrlRequest(from: request)) { [weak self] result in
+            urlSession.downloadTask(with: try buildUrlRequest(from: request)) { [weak self]
+                result in
+                assert(!Thread.isMainThread, "Should not be running on main thread!!")
                 guard let self = self else { return }
                 let result = result
                     .flatMap { response in .init(catching: { try self.handle(response, request) }) }
                     .map(\.responseBody)
-                completionHandler(result)
+                
+                DispatchQueue.main.sync {
+                    completionHandler(result)
+                }
             }.resume()
         } catch {
-            completionHandler(.failure(error))
+            DispatchQueue.main.sync {
+                completionHandler(.failure(error))
+            }
         }
     }
 
@@ -224,11 +235,13 @@ public final class APIClient: APIClientProtocol {
 
 
         try DispatchQueue.global(qos: .default).sync {
+            assert(!Thread.isMainThread, "Should not be running on main thread!!")
             if let data = try? Data(contentsOf: result.url) {
                 try responseValidator?.validate(data, for: request, with: result.headers)
             }
         }
 
+        assert(!Thread.isMainThread, "Should not be running on main thread!!")
         return HTTPResponse(
             headers: result.headers,
             statusCode: result.statusCode,

Networking Demo AppTests/APIClientTests.swift

@@ -284,13 +284,15 @@ class APIClientTests: XCTestCase {
         let downloadProgressExpectation = expectation(description: "Expect download progress to reach 100%.")
 
         let request = TestAsyncDownloadRequest { progress in
+            XCTAssertFalse(Thread.isMainThread, "Shouldn't be on main thread")
             if progress == 1.0 {
                 downloadProgressExpectation.fulfill()
             }
             print("Download progress: \(progress)")
         }
         let mockValidator = MockResponseValidator()
         mockValidator.onValidated = {
+            XCTAssertFalse(Thread.isMainThread, "Shouldn't be on main thread")
             responseValidationException.fulfill()
             throw ValidationError.invalidResponse
         }
@@ -304,6 +306,31 @@ class APIClientTests: XCTestCase {
         }
         await waitForExpectations(timeout: 10, handler: nil)
     }
+    
+    // todo remove 
+    func testDownloadThreading() throws {
+        let apiClientExpectation = expectation(description: "Expect api client to download image file.")
+        let request = TestDownloadRequest()
+        let api = APIClient(apiContext: SimpleAPIContext())
+        let fileManager = FileManager.default
+        
+        api.perform(request) { result in
+            switch result {
+                case .success(let downloadResponse):
+                    do {
+                        let image = UIImage(data: try Data(contentsOf: downloadResponse.url))
+                        XCTAssertNotNil(image)
+                        try fileManager.removeItem(at: downloadResponse.url)
+                        apiClientExpectation.fulfill()
+                    } catch {
+                        XCTFail(error.localizedDescription)
+                    }
+                case let .failure(error):
+                    XCTFail(error.localizedDescription)
+            }
+        }
+        waitForExpectations(timeout: 10, handler: nil)
+    }
 }
 
 enum ValidationError: Error {