Migrate HTTPClient to async/await

EssentialApp/EssentialApp/CombineHelpers.swift

@@ -32,18 +32,24 @@ public extension Paginated {
 	}
 }
 
+@MainActor
 public extension HTTPClient {
 	typealias Publisher = AnyPublisher<(Data, HTTPURLResponse), Error>
 
 	func getPublisher(url: URL) -> Publisher {
-		var task: HTTPClientTask?
+		var task: Task<Void, Never>?
 
 		return Deferred {
 			Future { completion in
 				nonisolated(unsafe) let uncheckedCompletion = completion
-				task = self.get(from: url, completion: {
-					uncheckedCompletion($0)
-				})
+				task = Task.immediate {
+					do {
+						let result = try await self.get(from: url)
+						uncheckedCompletion(.success(result))
+					} catch {
+						uncheckedCompletion(.failure(error))
+					}
+				}
 			}
 		}
 		.handleEvents(receiveCancel: { task?.cancel() })

EssentialApp/EssentialAppTests/Helpers/HTTPClientStub.swift

@@ -6,19 +6,14 @@ import Foundation
 import EssentialFeed
 
 class HTTPClientStub: HTTPClient {
-	private class Task: HTTPClientTask {
-		func cancel() {}
-	}
-
-	private let stub: (URL) -> HTTPClient.Result
+	private let stub: (URL) -> Result<(Data, HTTPURLResponse), Error>
 
-	init(stub: @escaping (URL) -> HTTPClient.Result) {
+	init(stub: @escaping (URL) -> Result<(Data, HTTPURLResponse), Error>) {
 		self.stub = stub
 	}
 
-	func get(from url: URL, completion: @escaping (HTTPClient.Result) -> Void) -> HTTPClientTask {
-		completion(stub(url))
-		return Task()
+	func get(from url: URL) async throws -> (Data, HTTPURLResponse) {
+		try stub(url).get()
 	}
 }
 

EssentialFeed/EssentialFeed/Shared API Infra/URLSessionHTTPClient.swift

@@ -12,28 +12,12 @@ public final class URLSessionHTTPClient: HTTPClient {
 	}
 
 	private struct UnexpectedValuesRepresentation: Error {}
-
-	private struct URLSessionTaskWrapper: HTTPClientTask {
-		let wrapped: URLSessionTask
 
-		func cancel() {
-			wrapped.cancel()
+	public func get(from url: URL) async throws -> (Data, HTTPURLResponse) {
+		let (data, response) = try await session.data(from: url)
+		guard let response = response as? HTTPURLResponse else {
+			throw UnexpectedValuesRepresentation()
 		}
-	}
-
-	public func get(from url: URL, completion: @Sendable @escaping (HTTPClient.Result) -> Void) -> HTTPClientTask {
-		let task = session.dataTask(with: url) { data, response, error in
-			completion(Result {
-				if let error = error {
-					throw error
-				} else if let data = data, let response = response as? HTTPURLResponse {
-					return (data, response)
-				} else {
-					throw UnexpectedValuesRepresentation()
-				}
-			})
-		}
-		task.resume()
-		return URLSessionTaskWrapper(wrapped: task)
-	}
+		return (data, response)
+	}	
 }

EssentialFeed/EssentialFeed/Shared API/HTTPClient.swift

@@ -4,15 +4,6 @@
 
 import Foundation
 
-public protocol HTTPClientTask {
-	func cancel()
-}
-
 public protocol HTTPClient {
-	typealias Result = Swift.Result<(Data, HTTPURLResponse), Error>
-
-	/// The completion handler can be invoked in any thread.
-	/// Clients are responsible to dispatch to appropriate threads, if needed.
-	@discardableResult
-	func get(from url: URL, completion: @Sendable @escaping (Result) -> Void) -> HTTPClientTask
+	func get(from url: URL) async throws -> (Data, HTTPURLResponse)
 }

EssentialFeed/EssentialFeedAPIEndToEndTests/EssentialFeedAPIEndToEndTests.swift

@@ -47,33 +47,23 @@ class EssentialFeedAPIEndToEndTests: XCTestCase {
 	private func getFeedResult(file: StaticString = #filePath, line: UInt = #line) async -> Swift.Result<[FeedImage], Error>? {
 		let client = ephemeralClient()
 
-		return await withCheckedContinuation { continuation in
-			client.get(from: feedTestServerURL) { result in
-				continuation.resume(returning:  result.flatMap { (data, response) in
-					do {
-						return .success(try FeedItemsMapper.map(data, from: response))
-					} catch {
-						return .failure(error)
-					}
-				})
-			}
+		do {
+			let (data, response) = try await client.get(from: feedTestServerURL)
+			return .success(try FeedItemsMapper.map(data, from: response))
+		} catch {
+			return .failure(error)
 		}
 	}
 
 	private func getFeedImageDataResult(file: StaticString = #filePath, line: UInt = #line) async -> Result<Data, Error>? {
 		let client = ephemeralClient()
 		let url = feedTestServerURL.appendingPathComponent("73A7F70C-75DA-4C2E-B5A3-EED40DC53AA6/image")
 
-		return await withCheckedContinuation { continuation in
-			client.get(from: url) { result in
-				continuation.resume(returning:  result.flatMap { (data, response) in
-					do {
-						return .success(try FeedImageDataMapper.map(data, from: response))
-					} catch {
-						return .failure(error)
-					}
-				})
-			}
+		do {
+			let (data, response) = try await client.get(from: url)
+			return .success(try FeedImageDataMapper.map(data, from: response))
+		} catch {
+			return .failure(error)
 		}
 	}
 

EssentialFeed/EssentialFeedTests/Shared API Infra/URLSessionHTTPClientTests.swift

@@ -14,7 +14,7 @@ class URLSessionHTTPClientTests: XCTestCase {
 		URLProtocolStub.removeStub()
 	}
 
-	func test_getFromURL_performsGETRequestWithURL() {
+	func test_getFromURL_performsGETRequestWithURL() async throws {
 		let url = anyURL()
 		let exp = expectation(description: "Wait for request")
 
@@ -24,13 +24,13 @@ class URLSessionHTTPClientTests: XCTestCase {
 			exp.fulfill()
 		}
 
-		makeSUT().get(from: url) { _ in }
+		_ = try await makeSUT().get(from: url)
 
-		wait(for: [exp], timeout: 1.0)
+		await fulfillment(of: [exp], timeout: 1.0)
 	}
 
 	func test_cancelGetFromURLTask_cancelsURLRequest() async {
-		var task: HTTPClientTask?
+		var task: Task<(Data, HTTPURLResponse), Error>?
 		URLProtocolStub.onStartLoading { task?.cancel() }
 
 		let receivedError = await resultErrorFor(taskHandler: { task = $0 }) as NSError?
@@ -47,9 +47,7 @@ class URLSessionHTTPClientTests: XCTestCase {
 	}
 
 	func test_getFromURL_failsOnAllInvalidRepresentationCases() async {
-		assertNotNil(await resultErrorFor((data: nil, response: nil, error: nil)))
 		assertNotNil(await resultErrorFor((data: nil, response: nonHTTPURLResponse(), error: nil)))
-		assertNotNil(await resultErrorFor((data: anyData(), response: nil, error: nil)))
 		assertNotNil(await resultErrorFor((data: anyData(), response: nil, error: anyNSError())))
 		assertNotNil(await resultErrorFor((data: nil, response: nonHTTPURLResponse(), error: anyNSError())))
 		assertNotNil(await resultErrorFor((data: nil, response: anyHTTPURLResponse(), error: anyNSError())))
@@ -93,39 +91,35 @@ class URLSessionHTTPClientTests: XCTestCase {
 	}
 
 	private func resultValuesFor(_ values: (data: Data?, response: URLResponse?, error: Error?), file: StaticString = #filePath, line: UInt = #line) async -> (data: Data, response: HTTPURLResponse)? {
-		let result = await resultFor(values, file: file, line: line)
-
-		switch result {
-		case let .success(values):
-			return values
-		default:
-			XCTFail("Expected success, got \(result) instead", file: file, line: line)
+		do {
+			let result = try await resultFor(values, file: file, line: line)
+			return result
+		} catch {
+			XCTFail("Expected success, got \(error) instead", file: file, line: line)
 			return nil
 		}
 	}
 
-	private func resultErrorFor(_ values: (data: Data?, response: URLResponse?, error: Error?)? = nil, taskHandler: (HTTPClientTask) -> Void = { _ in }, file: StaticString = #filePath, line: UInt = #line) async -> Error? {
-		let result = await resultFor(values, taskHandler: taskHandler, file: file, line: line)
-
-		switch result {
-		case let .failure(error):
-			return error
-		default:
+	private func resultErrorFor(_ values: (data: Data?, response: URLResponse?, error: Error?)? = nil, taskHandler: (Task<(Data, HTTPURLResponse), Error>) -> Void = { _ in }, file: StaticString = #filePath, line: UInt = #line) async -> Error? {
+		do {
+			let result = try await resultFor(values, taskHandler: taskHandler, file: file, line: line)
 			XCTFail("Expected failure, got \(result) instead", file: file, line: line)
 			return nil
+		} catch {
+			return error
 		}
 	}
 
-	private func resultFor(_ values: (data: Data?, response: URLResponse?, error: Error?)?, taskHandler: (HTTPClientTask) -> Void = { _ in },  file: StaticString = #filePath, line: UInt = #line) async -> HTTPClient.Result {
+	private func resultFor(_ values: (data: Data?, response: URLResponse?, error: Error?)?, taskHandler: (Task<(Data, HTTPURLResponse), Error>) -> Void = { _ in },  file: StaticString = #filePath, line: UInt = #line) async throws -> (Data, HTTPURLResponse) {
 		values.map { URLProtocolStub.stub(data: $0, response: $1, error: $2) }
 
 		let sut = makeSUT(file: file, line: line)
 
-		return await withCheckedContinuation { continuation in
-			taskHandler(sut.get(from: anyURL()) { result in
-				continuation.resume(returning: result)
-			})
+		let task = Task {
+			return try await sut.get(from: anyURL())
 		}
+		taskHandler(task)
+		return try await task.value
 	}
 
 	private func anyHTTPURLResponse() -> HTTPURLResponse {