FIRInstanceIDCheckinService: make sure tasks are not submitted to an invalidated NSURLSession (#2548)

FIRInstanceIDCheckinService: make sure tasks are not submitted to an invalidated NSURLSession (#2548)

Author: maksymmalyhin

Example/InstanceID/Tests/FIRInstanceIDCheckinServiceTest.m

@@ -134,6 +134,29 @@ - (void)testCheckinServiceAddsFirebaseUserAgentToHTTPHeader {
                                }];
 }
 
+- (void)testCheckinServiceFailsWithErrorAfterStopFetching {
+  [self.checkinService stopFetching];
+
+  XCTestExpectation *checkinCompletionExpectation =
+      [self expectationWithDescription:@"Checkin Completion"];
+
+  [self.checkinService
+      checkinWithExistingCheckin:nil
+                      completion:^(FIRInstanceIDCheckinPreferences *preferences, NSError *error) {
+                        [checkinCompletionExpectation fulfill];
+                        XCTAssertNil(preferences);
+                        XCTAssertNotNil(error);
+                        XCTAssertEqual(error.code, kFIRInstanceIDErrorCodeRegistrarFailedToCheckIn);
+                      }];
+
+  [self waitForExpectationsWithTimeout:5
+                               handler:^(NSError *error) {
+                                 if (error) {
+                                   XCTFail(@"Checkin Timeout Error: %@", error);
+                                 }
+                               }];
+}
+
 #pragma mark - Stub
 
 - (FIRInstanceIDCheckinPreferences *)stubCheckinCacheWithValidData {

Firebase/InstanceID/FIRIMessageCode.h

@@ -65,6 +65,7 @@ typedef NS_ENUM(NSInteger, FIRInstanceIDMessageCode) {
   kFIRInstanceIDMessageCodeService004 = 7004,
   kFIRInstanceIDMessageCodeService005 = 7005,
   kFIRInstanceIDMessageCodeService006 = 7006,
+  kFIRIntsanceIDInvalidNetworkSession = 7007,
   // FIRInstanceIDCheckinStore.m
   // DO NOT USE 8002, 8004 - 8008
   kFIRInstanceIDMessageCodeCheckinStore000 = 8000,

Firebase/InstanceID/FIRInstanceIDCheckinService.m

@@ -74,6 +74,15 @@ - (void)checkinWithExistingCheckin:(FIRInstanceIDCheckinPreferences *)existingCh
                         completion:(FIRInstanceIDDeviceCheckinCompletion)completion {
   _FIRInstanceIDDevAssert(completion != nil, @"completion required");
 
+  if (self.session == nil) {
+    FIRInstanceIDLoggerError(kFIRIntsanceIDInvalidNetworkSession,
+                             @"Inconsistent state: NSURLSession has been invalidated");
+    NSError *error =
+        [NSError errorWithFIRInstanceIDErrorCode:kFIRInstanceIDErrorCodeRegistrarFailedToCheckIn];
+    completion(nil, error);
+    return;
+  }
+
   NSURL *url = [NSURL URLWithString:kDeviceCheckinURL];
   NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
 
@@ -179,6 +188,8 @@ - (void)checkinWithExistingCheckin:(FIRInstanceIDCheckinPreferences *)existingCh
 
 - (void)stopFetching {
   [self.session invalidateAndCancel];
+  // The session cannot be reused after invalidation. Dispose it to prevent accident reusing.
+  self.session = nil;
 }
 
 #pragma mark - Private