Fake It ’Til You Make It Staying Productive when Working with Web Services Josh Johnson | @jnjosh | jnjosh.com 

Most Apps Require Web Services 

“My API is perfect and has no bugs!” — A really lucky person 

“Welcome to the Real World” — Morpheus 

You still need to make progress! What can you do? 

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Dummy Data 

Build it as if you have the API 

Agree on an API spec 

Wait? There is no API. How can we build it? 

Build your own lightweight API 

Sinatra Using tools like Sinatra you can quickly define API endpoints to match tha API spec get '/episodes/:episode' do last_modified episodes.first[:published] content_type :json episodes.select { |e| e[:number] == params[:episode].to_i }.to_json end 㱺 GET http://api.testing.com/episodes/8 

The Do it Yourself API 

Dummy Data + The Do it Yourself API 

NSURLProtocol and the URL Loading System 

How does NSURLProtocol help us? 

Let's download an image! NSString *kittenImageString = @"http://cutekittenimages.com/kittens_cute_kitten.jpg"; NSURL *url = [NSURL URLWithString:kittenImageString]; NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; [request addValue:@"image/jpeg" forHTTPHeaderField:@"Content-Type"]; [NSURLConnection sendAsynchronousRequest:request queue:self.imageQueue completionHandler: ^(NSURLResponse *response, NSData *data, NSError *connectionError) { UIImage *kittenImage = [UIImage imageWithData:data scale:0.0]; [[NSOperationQueue mainQueue] addOperation:[NSBlockOperation blockOperationWithBlock:^{ self.imageView.image = kittenImage; }]]; }]; 

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Introducing TWTHasslehoffImageProtocol @import Foundation; @interface TWTHasselhoffImageProtocol : NSURLProtocol @end 

Register the Hasselhoff Protocol - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { [NSURLProtocol registerClass:[TWTHasselhoffImageProtocol class]]; return YES; } 

Implement the Hasselhoff Image Protocol + (BOOL)canInitWithRequest:(NSURLRequest *)request { NSSet *validContentTypes = [NSSet setWithArray:@[ @"image/png", @"image/jpg", @"image/jpeg" ]]; return [validContentTypes containsObject:request.allHTTPHeaderFields[@"Content-Type"]]; } + (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request { return request; } 

Implement the Hasselhoff Image Protocol - (void)startLoading { id client = self.client; NSURLRequest *request = self.request; NSDictionary *headers = @{ @"Content-Type": @"image/jpeg" }; NSData *imageData = UIImageJPEGRepresentation([UIImage imageNamed:@"David_Hasselhoff.jpeg"], 1.0); NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] initWithURL:request.URL statusCode:200 HTTPVersion:@"HTTP/1.1" headerFields:headers]; [client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed]; [client URLProtocol:self didLoadData:imageData]; [client URLProtocolDidFinishLoading:self]; } - (void)stopLoading { // Must be implemented } 

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This is great and all, but it is a canned example. 

HolyMockURL, it's URLMock https://github.com/twotoasters/URLMock 

Let's check the weather! - (NSOperation *)fetchTemperatureForLatitude:(NSNumber *)latitude longitude:(NSNumber *)longitude success:(void (^)(NSNumber *))successBlock failure:(void (^)(NSError *))failureBlock { NSParameterAssert(latitude && ABS(latitude.doubleValue) <= 90.0); NSParameterAssert(longitude && ABS(longitude.doubleValue) <= 180.0); return [self.operationManager GET:@"weather" parameters:@{ @"lat" : latitude, @"lon" : longitude } success:^(AFHTTPRequestOperation *operation, id response) { if (successBlock) { successBlock([response valueForKeyPath:@"main.temp"]); } } failure:^(AFHTTPRequestOperation *operation, NSError *error) { if (failureBlock) { failureBlock(error); } }]; } 

A pretty bad unit test - (void)testFetchTemperatureForLatitudeLongitude { __block NSNumber *temperature = nil; [self.APIClient fetchTemperatureForLatitude:@(35.99) longitude:@(-78.9) success:^(NSNumber *kelvins) { temperature = kelvins; } failure:nil]; // Assert that temperature != nil before 2.0s elapse UMKAssertTrueBeforeTimeout(2.0, temperature != nil, @"temperature isn't set in time"); } 

Let's use URLMock + (void)setUp { [super setUp]; [UMKMockURLProtocol enable]; [UMKMockURLProtocol setVerificationEnabled:YES]; } + (void)tearDown { [UMKMockURLProtocol setVerificationEnabled:NO]; [UMKMockURLProtocol disable]; [super tearDown]; } - (void)setUp { [super setUp]; [UMKMockURLProtocol reset]; … } 

A better unit test, with URLMock - (void)testFetchTemperatureForLatitudeLongitudeCorrectData { // setting up latitude, longitude and tempearture to expect NSURL *temperatureURL = [self temperatureURLWithLatitude:latitude longitude:longitude]; [UMKMockURLProtocol expectMockHTTPGetRequestWithURL:temperatureURL responseStatusCode:200 responseJSON:@{ @"main" : @{ @"temp" : temperature } }]; __block BOOL succeeded = NO; __block BOOL failed = NO; __block NSNumber *kelvins = nil; [self.APIClient fetchTemperatureForLatitude:latitude longitude:longitude success:^(NSNumber *temperatureInKelvins) { succeeded = YES; kelvins = temperatureInKelvins; } failure:^(NSError *error) { failed = YES; }]; UMKAssertTrueBeforeTimeout(1.0, succeeded, @"success block is not called"); UMKAssertTrueBeforeTimeout(1.0, !failed, @"failure block is called"); UMKAssertTrueBeforeTimeout(1.0, [kelvins isEqualToNumber:temperature], @"incorrect temperature"); NSError *verificationError = nil; XCTAssertTrue([UMKMockURLProtocol verifyWithError:&verificationError], @"verification failed"); } 

Test for errors, with URLMock - (void)testFetchTemperatureForLatitudeLongitudeError { … NSURL *temperatureURL = [self temperatureURLWithLatitude:latitude longitude:longitude]; [UMKMockURLProtocol expectMockHTTPGetRequestWithURL:temperatureURL responseError:[self randomError]]; __block BOOL succeeded = NO; __block BOOL failed = NO; [self.APIClient fetchTemperatureForLatitude:latitude longitude:longitude success:^(NSNumber *temperature) { succeeded = YES; } failure:^(NSError *error) { failed = YES; }]; UMKAssertTrueBeforeTimeout(1.0, !succeeded, @"success block is called"); UMKAssertTrueBeforeTimeout(1.0, failed, @"failure block is not called"); NSError *verificationError = nil; XCTAssertTrue([UMKMockURLProtocol verifyWithError:&verificationError], @"verification failed"); } 

URLMock https://github.com/twotoasters/URLMock 

Working with a Web Service is a pain. 

Thank you! Questions? Josh Johnson | @jnjosh | jnjosh.com https://github.com/twotoasters/URLMock https://objectivetoast.com