Making minor changes for retry handler-

 - Added 504 status code
 - Removed unused global variable of retryPower
 - Changed check for internal server error to service unavailable status code
 - Added unit tests for the same

Author: Vikas Dadheech

MSGraphCoreSDK/MSGraphCoreSDK/Common/MSConstants.h

@@ -26,6 +26,7 @@ typedef NS_ENUM(NSInteger, MSClientErrorCode)
     MSClientErrorCodeInternalServerError         = 500,
     MSClientErrorCodeNotImplemented              = 501,
     MSClientErrorCodeServiceUnavailable          = 503,
+    MSClientErrorCodeGatewayTimeout              = 504,
     MSClientErrorCodeInsufficientStorage         = 507,
     MSClientErrorCodeUnknownError                = 999,
 };

MSGraphCoreSDK/MSGraphCoreSDK/Middleware/Implementations/RetryHandler/MSRetryHandler.m

@@ -12,7 +12,6 @@
 
 #define DELAY_SECONDS 10;
 #define DEFAULT_MAX_RETRIES 10;
-#define DEFAULT_RETRY_POWER 1;
 
 @interface MSURLSessionTask()
 
@@ -29,7 +28,6 @@ @interface MSRetryHandler()
 @implementation MSRetryHandler
 {
     NSInteger maxRetries;
-    double retryPower;
 }
 
 - (instancetype)init
@@ -38,7 +36,6 @@ - (instancetype)init
     if(self)
     {
         maxRetries = DEFAULT_MAX_RETRIES;
-        retryPower = DEFAULT_RETRY_POWER;
     }
     return self;
 }
@@ -111,7 +108,8 @@ - (void)execute:(MSURLSessionTask *)task retriesAttempted:(NSInteger)retriesAtte
 - (BOOL)isRetry:(NSInteger)statusCode
 {
     if (statusCode == MSClientErrorCodeTooManyRequests ||
-        statusCode == MSClientErrorCodeInternalServerError)
+        statusCode == MSClientErrorCodeServiceUnavailable ||
+        statusCode == MSClientErrorCodeGatewayTimeout)
     {
         return true;
     }
@@ -144,8 +142,7 @@ - (double)retryDelay:(NSHTTPURLResponse *)response andRetryCount:(NSInteger)retr
     }
     else
     {
-        retryPower = pow(2, retryCount);
-        delay = retryPower*DELAY_SECONDS;
+        delay = pow(2, retryCount)*DELAY_SECONDS;
     }
     return delay;
 }

MSGraphCoreSDK/MSGraphCoreSDKTests/Middleware/Implementations/MSRetryHandlerTests.m

@@ -111,6 +111,54 @@ - (void)testExecuteWithRedirectResopnseAndMaxRetries {
     [self checkCompletionBlockCodeInvoked];
 }
 
+- (void)testExecuteWithRetryResopnse503AndSuccessfullRetry {
+    XCTestExpectation *retryWaitExpectation = [[XCTestExpectation alloc] initWithDescription:@"Waiting for retry attempt execution"];
+
+    HTTPRequestCompletionHandler requestCompletion = ^(id data, NSURLResponse * _Nullable response, NSError * _Nullable error){
+        [self completionBlockCodeInvoked];
+        XCTAssertNil(error);
+        XCTAssertNotNil(response);
+        XCTAssertEqual(((NSHTTPURLResponse *)response).statusCode, MSExpectedResponseCodesOK);
+        XCTAssertNotNil(data);
+        [retryWaitExpectation fulfill];
+    };
+
+   __block NSHTTPURLResponse *retryResponseWith503 = [[NSHTTPURLResponse alloc] initWithURL:[NSURL URLWithString:MSGraphBaseURL] statusCode:MSClientErrorCodeServiceUnavailable HTTPVersion:@"foo" headerFields:nil];
+    OCMStub([self.mockHttpProvider execute:[OCMArg any] withCompletionHandler:[OCMArg any]]).andDo(^(NSInvocation *invocation){
+        HTTPRequestCompletionHandler completionHandler;
+        [invocation getArgument:&completionHandler atIndex:3];
+        completionHandler([NSData new], retryResponseWith503, nil);
+        retryResponseWith503 = self->_OKResponse;
+    });
+    [self.retryHandler execute:_mockDataTask withCompletionHandler:requestCompletion];
+    [self waitForExpectations:@[retryWaitExpectation] timeout:12.0];
+    [self checkCompletionBlockCodeInvoked];
+}
+
+- (void)testExecuteWithRetryResopnse504AndSuccessfullRetry {
+    XCTestExpectation *retryWaitExpectation = [[XCTestExpectation alloc] initWithDescription:@"Waiting for retry attempt execution"];
+
+    HTTPRequestCompletionHandler requestCompletion = ^(id data, NSURLResponse * _Nullable response, NSError * _Nullable error){
+        [self completionBlockCodeInvoked];
+        XCTAssertNil(error);
+        XCTAssertNotNil(response);
+        XCTAssertEqual(((NSHTTPURLResponse *)response).statusCode, MSExpectedResponseCodesOK);
+        XCTAssertNotNil(data);
+        [retryWaitExpectation fulfill];
+    };
+
+    __block NSHTTPURLResponse *retryResponseWith504 = [[NSHTTPURLResponse alloc] initWithURL:[NSURL URLWithString:MSGraphBaseURL] statusCode:MSClientErrorCodeGatewayTimeout HTTPVersion:@"foo" headerFields:nil];
+    OCMStub([self.mockHttpProvider execute:[OCMArg any] withCompletionHandler:[OCMArg any]]).andDo(^(NSInvocation *invocation){
+        HTTPRequestCompletionHandler completionHandler;
+        [invocation getArgument:&completionHandler atIndex:3];
+        completionHandler([NSData new], retryResponseWith504, nil);
+        retryResponseWith504 = self->_OKResponse;
+    });
+    [self.retryHandler execute:_mockDataTask withCompletionHandler:requestCompletion];
+    [self waitForExpectations:@[retryWaitExpectation] timeout:12.0];
+    [self checkCompletionBlockCodeInvoked];
+}
+
 - (void)testExecuteWithNormalResponse {
     HTTPRequestCompletionHandler requestCompletion = ^(id data, NSURLResponse * _Nullable response, NSError * _Nullable error){
         [self completionBlockCodeInvoked];