Merge pull request #691 from Iterable/evan/MOB-7021-retry-for-failed-requests

[MOB-7021] Implement retry mechanism to the iOS SDK for failed network requests

Author: evantk91

swift-sdk/Internal/NetworkHelper.swift

@@ -28,6 +28,9 @@ extension NetworkError: LocalizedError {
 }
 
 struct NetworkHelper {
+    static let maxRetryCount = 5
+    static let retryDelaySeconds = 2
+    
     static func getData(fromUrl url: URL, usingSession networkSession: NetworkSessionProtocol) -> Pending<Data, Error> {
         let fulfill = Fulfill<Data, Error>()
 
@@ -52,8 +55,9 @@ struct NetworkHelper {
     static func sendRequest<T>(_ request: URLRequest,
                                converter: @escaping (Data) throws -> T?,
                                usingSession networkSession: NetworkSessionProtocol) -> Pending<T, NetworkError> {
-        #if NETWORK_DEBUG
+        
         let requestId = IterableUtil.generateUUID()
+        #if NETWORK_DEBUG
         print()
         print("====================================================>")
         print("sending request: \(request)")
@@ -73,29 +77,65 @@ struct NetworkHelper {
         #endif
 
         let fulfill = Fulfill<T, NetworkError>()
-        
-        networkSession.makeRequest(request) { data, response, error in
-            let result = createResultFromNetworkResponse(data: data,
-                                                         converter: converter,
-                                                         response: response,
-                                                         error: error)
 
-            switch result {
-            case let .success(value):
-                #if NETWORK_DEBUG
-                print("request with id: \(requestId) successfully sent, response:")
-                print(value)
-                #endif
-                fulfill.resolve(with: value)
-            case let .failure(error):
+        func sendRequestWithRetries(request: URLRequest, requestId: String, retriesLeft: Int) {
+            networkSession.makeRequest(request) { data, response, error in
+                let result = createResultFromNetworkResponse(data: data,
+                                                             converter: converter,
+                                                             response: response,
+                                                             error: error)
+                switch result {
+                    case let .success(value):
+                        handleSuccess(requestId: requestId, value: value)
+                    case let .failure(error):
+                        handleFailure(requestId: requestId, request: request, error: error, retriesLeft: retriesLeft)
+                }
+            }
+        }
+        
+        func handleSuccess(requestId: String, value: T) {
+            #if NETWORK_DEBUG
+            print("request with id: \(requestId) successfully sent, response:")
+            print(value)
+            #endif
+            fulfill.resolve(with: value)
+        }
+        
+        func handleFailure(requestId: String, request: URLRequest, error: NetworkError, retriesLeft: Int) {
+            if shouldRetry(error: error, retriesLeft: retriesLeft) {
+                retryRequest(requestId: requestId, request: request, error: error, retriesLeft: retriesLeft)
+            } else {
                 #if NETWORK_DEBUG
                 print("request with id: \(requestId) errored")
                 print(error)
                 #endif
                 fulfill.reject(with: error)
             }
+            
         }
 
+        func shouldRetry(error: NetworkError, retriesLeft: Int) -> Bool {
+            return error.httpStatusCode ?? 0 >= 500 && retriesLeft > 0
+        }
+        
+        func retryRequest(requestId: String, request: URLRequest, error: NetworkError, retriesLeft: Int) {
+            #if NETWORK_DEBUG
+            print("retry attempt: \(maxRetryCount-retriesLeft+1) for url: \(request.url?.absoluteString ?? "")")
+            print(error)
+            #endif
+            
+            var delay: DispatchTimeInterval = .seconds(0)
+            if retriesLeft <= 3 {
+                delay = .seconds(retryDelaySeconds)
+            }
+            
+            DispatchQueue.global().asyncAfter(deadline: .now() + delay) {
+                sendRequestWithRetries(request: request, requestId: requestId, retriesLeft: retriesLeft - 1)
+            }
+        }
+        
+        sendRequestWithRetries(request: request, requestId: requestId, retriesLeft: maxRetryCount)
+        
         return fulfill
     }
 

tests/unit-tests/IterableAPIResponseTests.swift

@@ -152,6 +152,30 @@ class IterableAPIResponseTests: XCTestCase {
         wait(for: [xpectation], timeout: testExpectationTimeout)
     }
 
+    func testSendRequestWithRetry() {
+        let xpectation = expectation(description: "retry on status code >= 500")
+        
+        let networkSession = MockNetworkSession { _ in
+            MockNetworkSession.MockResponse(statusCode: 503,
+                                            data: Data(),
+                                            delay: 0)
+        }
+        
+        let iterableRequest = IterableRequest.post(PostRequest(path: "", args: nil, body: [:]))
+        
+        let apiClient = createApiClient(networkSession: networkSession)
+        var urlRequest = apiClient.convertToURLRequest(iterableRequest: iterableRequest)!
+        urlRequest.timeoutInterval = 1
+                
+        RequestSender.sendRequest(urlRequest, usingSession: networkSession).onError { sendError in
+            xpectation.fulfill()
+            XCTAssert(sendError.reason!.lowercased().contains("internal server error"))
+        }
+        
+        wait(for: [xpectation], timeout: testExpectationTimeout)
+    }
+
+    
     func testNetworkTimeoutResponse() {
         let xpectation = expectation(description: "timeout network response")