Describing how to use Swift protocols to refactor obj-c networking layer to Swift while improving project architecture and test coverage. CocoaHeads-Berlin Sep 16

1. Protocol-Oriented Networking
@mostafa_amer

2. Starting Point
#import <AFNetworking/AFNetworking.h>
@interface GHAPIClient : AFHTTPSessionManager
+ (instancetype)sharedClient;
-(void)fetchGitHubUserWithName:(NSString *)name
completionHandler:(void(^)(id result, NSError *error))handler;
@end

3. Starting Point
#import <AFNetworking/AFNetworking.h>
@interface GHAPIClient : AFHTTPSessionManager
+ (instancetype)sharedClient;
-(void)fetchGitHubUserWithName:(NSString *)name
completionHandler:(void(^)(id result, NSError *error))handler;
@end
• Client has too many responsibilities

4. Starting Point
#import <AFNetworking/AFNetworking.h>
@interface GHAPIClient : AFHTTPSessionManager
+ (instancetype)sharedClient;
-(void)fetchGitHubUserWithName:(NSString *)name
completionHandler:(void(^)(id result, NSError *error))handler;
@end
• Client has too many responsibilities
• Client is tightly coupled to the network library

5. Starting Point
#import <AFNetworking/AFNetworking.h>
@interface GHAPIClient : AFHTTPSessionManager
+ (instancetype)sharedClient;
-(void)fetchGitHubUserWithName:(NSString *)name
completionHandler:(void(^)(id result, NSError *error))handler;
@end
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test

6. Starting Point
#import <AFNetworking/AFNetworking.h>
@interface GHAPIClient : AFHTTPSessionManager
+ (instancetype)sharedClient;
-(void)fetchGitHubUserWithName:(NSString *)name
completionHandler:(void(^)(id result, NSError *error))handler;
@end
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test
• Implementation details is not hidden

7. Decoupling
protocol NetworkServiceType {
func requestEndpoint(path: String,
method: HTTPMethod,
parameters: [String: Any]?,
handler: (Data?, Error?) -> ())
}

8. Decoupling
class NetworkService: AFHTTPSessionManager, NetworkServiceType {
func requestEndpoint(path: String, method: HTTPMethod, parameters: [String : Any]?,
handler: (Data?, Error?) -> ()) {
}
}

9. Decoupling
class NetworkService: AFHTTPSessionManager, NetworkServiceType {
func requestEndpoint(path: String, method: HTTPMethod, parameters: [String : Any]?,
handler: (Data?, Error?) -> ()) {
switch method {
case .GET:
get(path,
parameters: parameters,
success: {_, result in
handler(result, nil)
},
failure: {_, error in
handler(nil, error)
}
)
}
}
}

10. Hide Implementation
@interface GHAPIClient : AFHTTPSessionManager
+ (instancetype)sharedClient;
- (void)fetchListWithCompletionHandler:(void(^)(id result, NSError *error))handler;
@end
#import <AFNetworking/AFNetworking.h>

11. Hide Implementation
@interface GHAPIClient : NSObject
+ (instancetype)sharedClient;
- (void)fetchListWithCompletionHandler:(void(^)(id result, NSError *error))handler;
@end

12. @interface GHAPIClient()
@end
@implementation GHAPIClient
- (instancetype)initWithBaseURL:(NSURL *)baseURL {
self = [super init];
if(self) {
}
return self;
}
+ (instancetype)sharedClient {
static GHAPIClient *_instance = nil;
if(! _instance) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [[GHAPIClient alloc] init];
});
}
return _instance;
}
Refactoring Client

13. Refactoring Client
@interface GHAPIClient()
@property (nonatomic, strong) id<NetworkServiceType> network;
@end
@implementation GHAPIClient
- (instancetype)initWithBaseURL:(NSURL *)baseURL {
self = [super init];
if(self) {
}
return self;
}
+ (instancetype)sharedClient {
static GHAPIClient *_instance = nil;
if(! _instance) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [[GHAPIClient alloc] init];
});
}
return _instance;
}

14. Refactoring Client
@interface GHAPIClient()
@property (nonatomic, strong) id<NetworkServiceType> network;
@end
@implementation GHAPIClient
- (instancetype)initWithNetworkService:(id<NetworkServiceType>)service {
self = [super init];
if(self) {
_network = service;
}
return self;
}
+ (instancetype)sharedClient {
static GHAPIClient *_instance = nil;
if(! _instance) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [[GHAPIClient alloc] init];
});
}
return _instance;
}

15. Refactoring Client
@interface GHAPIClient()
@property (nonatomic, strong) id<NetworkServiceType> network;
@end
@implementation GHAPIClient
- (instancetype)initWithNetworkService:(id<NetworkServiceType>)service {
self = [super init];
if(self) {
_network = service;
}
return self;
}
+ (instancetype)sharedClient {
static GHAPIClient *_instance = nil;
if(! _instance) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSURL *baseURL = [NSURL URLWithString:@"https://api.github.com"];
NetworkService *service = [[NetworkService alloc] initWithBaseURL:baseURL];
_instance = [[GHAPIClient alloc] initWithNetworkService:service];
});
}
return _instance;
}

16. Testing Client
class NetworkMock: NetworkServiceType {
var response: Data?
var error: Error?
func requestEndpoint(path: String,
method: HTTPMethod,
parameters: [String : Any]?,
handler: (Data?, Error?) -> ()) {
handler(response, error)
}
}

17. class APIClientSpecs: QuickSpec {
override func spec() {
var mock: NetworkMock!
var sut: GHAPIClient!
beforeEach {
mock = NetworkMock()
sut = GHAPIClient(networkService: mock)
}
}
}
Testing Client
class NetworkMock: NetworkServiceType {
var response: Data?
var error: Error?
func requestEndpoint(path: String,
method: HTTPMethod,
parameters: [String : Any]?,
handler: (Data?, Error?) -> ()) {
handler(response, error)
}
}

18. Testing Client
class NetworkMock: NetworkServiceType {
var response: Data?
var error: Error?
func requestEndpoint(path: String,
method: HTTPMethod,
parameters: [String : Any]?,
handler: (Data?, Error?) -> ()) {
handler(response, error)
}
}
class APIClientSpecs: QuickSpec {
override func spec() {
var mock: NetworkMock!
var sut: GHAPIClient!
beforeEach {
mock = NetworkMock()
sut = GHAPIClient(networkService: mock)
}
it("handle error") {
mock.data = // Data from JSON file
sut.fetchGitHubUser(loginName: "mosamer") { (_, error) in
expect(error).notTo(beNil())
}
}
}
}

19. Client Again
- (void)fetchGitHubUser:(NSString *)name
completionHandler:(void (^)(id, NSError *))handler {
[self.network requestEndpointWithPath:[NSString stringWithFormat:@“users/%@”,name]
method:HTTPMethodGET
parameters:nil
handler:^(id result, NSError *error) {
handler(result, error);
}];
}

20. Client Again
- (void)fetchGitHubUser:(NSString *)name
completionHandler:(void (^)(id, NSError *))handler {
[self.network requestEndpointWithPath:[NSString stringWithFormat:@“users/%@”,name]
method:HTTPMethodGET
parameters:nil
handler:^(id result, NSError *error) {
handler(result, error);
}];
}
• Client still has too many responsibilities

21. Client Again
- (void)fetchGitHubUser:(NSString *)name
completionHandler:(void (^)(id, NSError *))handler {
[self.network requestEndpointWithPath:[NSString stringWithFormat:@“users/%@”,name]
method:HTTPMethodGET
parameters:nil
handler:^(id result, NSError *error) {
handler(result, error);
}];
}
• Client still has too many responsibilities
• Client lacks general handlers

22. More Protocols

23. More Protocols
protocol Resource {
var path: String { get }
var method: HTTPMethod { get }
var parameters: [String: Any]? { get }
}

24. More Protocols
protocol Response {}
protocol Resource {
var path: String { get }
var method: HTTPMethod { get }
var parameters: [String: Any]? { get }
associatedtype ResponseType: Response
}

25. More Protocols
protocol Response {}
protocol Resource {
var path: String { get }
var method: HTTPMethod { get }
var parameters: [String: Any]? { get }
associatedtype ResponseType: Response
func parse(response: Data) -> (ResponseType?, Error?)
}

26. Define Endpoints
struct GitHubUserEndpoint: Resource {
private let name: String
init(loginName: String) {
name = loginName
}
var path: String { return "users/(name)" }
var method: HTTPMethod { return .GET }
var parameters: [String : Any]? { return nil }
func parse(response: Data) -> ( GitHubUser?, Error?) {
// Parse JSON -> data model object
}
}
struct GitHubUser: Response {
// Define data model
}

27. Testing Endpoints
class GitHubUserEndpointSpecs: QuickSpec {
override func spec() {
var sut: GitHubUserEndpoint!
beforeEach {
sut = GitHubUserEndpoint(loginName: "mosamer")
}
}
}

28. Testing Endpoints
class GitHubUserEndpointSpecs: QuickSpec {
override func spec() {
var sut: GitHubUserEndpoint!
beforeEach {
sut = GitHubUserEndpoint(loginName: "mosamer")
}
it("build path") {
expect(sut.path) == "users/mosamer"
}
}
}

29. Testing Endpoints
class GitHubUserEndpointSpecs: QuickSpec {
override func spec() {
var sut: GitHubUserEndpoint!
beforeEach {
sut = GitHubUserEndpoint(loginName: "mosamer")
}
it("build path") {
expect(sut.path) == "users/mosamer"
}
it("GET method") {
expect(sut.method) == HTTPMethod.GET
}
}
}

30. Testing Endpoints
class GitHubUserEndpointSpecs: QuickSpec {
override func spec() {
var sut: GitHubUserEndpoint!
beforeEach {
sut = GitHubUserEndpoint(loginName: "mosamer")
}
it("build path") {
expect(sut.path) == "users/mosamer"
}
it("GET method") {
expect(sut.method) == HTTPMethod.GET
}
it("without parameters") {
expect(sut.parameters).to(beNil())
}
}
}

31. Testing Endpoints
class GitHubUserEndpointSpecs: QuickSpec {
override func spec() {
var sut: GitHubUserEndpoint!
beforeEach {
sut = GitHubUserEndpoint(loginName: "mosamer")
}
it("build path") {
expect(sut.path) == "users/mosamer"
}
it("GET method") {
expect(sut.method) == HTTPMethod.GET
}
it("without parameters") {
expect(sut.parameters).to(beNil())
}
it("parse response") {
let userJSON = Data() /* Data from JSON file */
let (user, _) = sut.parse(response: userJSON)
/*
Check user properties are fetched correctly
*/
}
}
}

32. Client One MoreTime
- (void)fetchGitHubUser:(NSString *)name
completionHandler:(void (^)(id, NSError *))handler {
[self.network requestEndpointWithPath:[NSString stringWithFormat:@“users/%@”,name]
method:HTTPMethodGET
parameters:nil
handler:^(id result, NSError *error) {
handler(result, error);
}];
}

33. Client One MoreTime
- (void)fetchGitHubUser:(NSString *)name
completionHandler:(void (^)(id, NSError *))handler {
[self.network requestEndpointWithPath:[NSString stringWithFormat:@“users/%@”,name]
method:HTTPMethodGET
parameters:nil
handler:^(id result, NSError *error) {
handler(result, error);
}];
}
func user(loginName: String, completionhandler: (GitHubUser?, Error?) -> ()) {
let endpoint = GitHubUserEndpoint(loginName: loginName)
request(endpoint, handler: completionhandler)
}

34. Client - General Handlers
private func request<R: Resource>(_ endpoint: R,
handler:(R.ResponseType?, Error?) -> ()) {
}
}
}
extension GHAPIClient {
func user(loginName: String, completionhandler: (GitHubUser?, Error?) -> ()) {
let endpoint = GitHubUserEndpoint(loginName: loginName)
request(endpoint, handler: completionhandler)
}

35. Client - General Handlers
private func request<R: Resource>(_ endpoint: R,
handler:(R.ResponseType?, Error?) -> ()) {
network.requestEndpoint(path: endpoint.path,
method: endpoint.method,
parameters: endpoint.parameters) { (data, error) in
if let _ = error {
handler(nil, error)
return
}
guard let data = data else {
handler(nil, nil)
return
}
let (result, error) = endpoint.parse(response: data)
handler(result, error)
}
}
}
extension GHAPIClient {
func user(loginName: String, completionhandler: (GitHubUser?, Error?) -> ()) {
let endpoint = GitHubUserEndpoint(loginName: loginName)
request(endpoint, handler: completionhandler)
}

36. Summary

37. Summary
• Client has too many responsibilities

38. Summary
• Client has too many responsibilities

39. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library

40. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library

41. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test

42. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test

43. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test
• Implementation details is not hidden

44. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test
• Implementation details is not hidden

45. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test
• Implementation details is not hidden
• Client still has too many responsibilities

46. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test
• Implementation details is not hidden
• Client still has too many responsibilities

47. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test
• Implementation details is not hidden
• Client still has too many responsibilities
• Client lacks general handlers

48. Summary
• Client has too many responsibilities
• Client is tightly coupled to the network library
• Client is hard to test
• Implementation details is not hidden
• Client still has too many responsibilities
• Client lacks general handlers

49. @mostafa_amer
Questions?

50. ThankYou
@mostafa_amer
Questions?