Provide an arbitrary data persistence mechanism on storage instances (#5637)

* Provide a library data mechanism on storage instances

This could allow most singletons to no longer need NSCoding, they just store the individual fields they need with an appropriately unique key

* Additional  tests

And no more implicit removal

* Implement read error capture

* Make test file data keys more unique

Also, there _should_ be an error reading from a non-existent file.

Author: mikehaney24

GoogleDataTransport/GDTCORLibrary/GDTCORFlatFileStorage.m

@@ -51,6 +51,27 @@ + (NSString *)archivePath {
   return archivePath;
 }
 
++ (NSString *)libraryDataPath {
+  static NSString *libraryDataPath;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    libraryDataPath =
+        [GDTCORRootDirectory() URLByAppendingPathComponent:NSStringFromClass([self class])
+                                               isDirectory:YES]
+            .path;
+    libraryDataPath = [libraryDataPath stringByAppendingPathComponent:@"gdt_library_data"];
+    if (![[NSFileManager defaultManager] fileExistsAtPath:libraryDataPath isDirectory:NULL]) {
+      NSError *error;
+      [[NSFileManager defaultManager] createDirectoryAtPath:libraryDataPath
+                                withIntermediateDirectories:YES
+                                                 attributes:0
+                                                      error:&error];
+      GDTCORAssert(error == nil, @"Creating the library data path failed: %@", error);
+    }
+  });
+  return libraryDataPath;
+}
+
 + (instancetype)sharedInstance {
   static GDTCORFlatFileStorage *sharedStorage;
   static dispatch_once_t onceToken;
@@ -187,6 +208,54 @@ - (void)removeEvents:(NSSet<NSNumber *> *)eventIDs {
   });
 }
 
+#pragma mark - GDTCORStorageProtocol
+
+- (void)libraryDataForKey:(nonnull NSString *)key
+               onComplete:
+                   (nonnull void (^)(NSData *_Nullable, NSError *_Nullable error))onComplete {
+  dispatch_async(_storageQueue, ^{
+    NSString *dataPath = [[[self class] libraryDataPath] stringByAppendingPathComponent:key];
+    NSError *error;
+    NSData *data = [NSData dataWithContentsOfFile:dataPath options:0 error:&error];
+    if (onComplete) {
+      onComplete(data, error);
+    }
+  });
+}
+
+- (void)storeLibraryData:(NSData *)data
+                  forKey:(nonnull NSString *)key
+              onComplete:(nonnull void (^)(NSError *_Nullable error))onComplete {
+  if (!data || data.length <= 0) {
+    if (onComplete) {
+      onComplete([NSError errorWithDomain:NSInternalInconsistencyException code:-1 userInfo:nil]);
+    }
+    return;
+  }
+  dispatch_async(_storageQueue, ^{
+    NSError *error;
+    NSString *dataPath = [[[self class] libraryDataPath] stringByAppendingPathComponent:key];
+    [data writeToFile:dataPath options:NSDataWritingAtomic error:&error];
+    if (onComplete) {
+      onComplete(error);
+    }
+  });
+}
+
+- (void)removeLibraryDataForKey:(nonnull NSString *)key
+                     onComplete:(nonnull void (^)(NSError *_Nullable error))onComplete {
+  dispatch_async(_storageQueue, ^{
+    NSError *error;
+    NSString *dataPath = [[[self class] libraryDataPath] stringByAppendingPathComponent:key];
+    if ([[NSFileManager defaultManager] fileExistsAtPath:dataPath]) {
+      [[NSFileManager defaultManager] removeItemAtPath:dataPath error:&error];
+      if (onComplete) {
+        onComplete(error);
+      }
+    }
+  });
+}
+
 #pragma mark - Private helper methods
 
 /** Saves the event's dataObject to a file using NSData mechanisms.

GoogleDataTransport/GDTCORLibrary/Public/GDTCORStorageProtocol.h

@@ -25,6 +25,8 @@ NS_ASSUME_NONNULL_BEGIN
 /** Defines the interface a storage subsystem is expected to implement. */
 @protocol GDTCORStorageProtocol <NSObject, GDTCORLifecycleProtocol>
 
+@required
+
 /** Stores an event and calls onComplete with a non-nil error if anything went wrong.
  *
  * @param event The event to store
@@ -36,6 +38,32 @@ NS_ASSUME_NONNULL_BEGIN
 /** Removes the events from storage. */
 - (void)removeEvents:(NSSet<NSNumber *> *)eventIDs;
 
+/** Persists the given data with the given key.
+ *
+ * @param data The data to store.
+ * @param key The unique key to store it to.
+ * @param onComplete An block to be run when storage of the data is complete.
+ */
+- (void)storeLibraryData:(NSData *)data
+                  forKey:(NSString *)key
+              onComplete:(void (^)(NSError *_Nullable error))onComplete;
+
+/** Retrieves the stored data for the given key.
+ *
+ * @param key The key corresponding to the desired data.
+ * @param onComplete The callback to invoke with the data once it's retrieved.
+ */
+- (void)libraryDataForKey:(NSString *)key
+               onComplete:(void (^)(NSData *_Nullable data, NSError *_Nullable error))onComplete;
+
+/** Removes data from storage and calls the callback when complete.
+ *
+ * @param key The key of the data to remove.
+ * @param onComplete The callback that will be invoked when removing the data is complete.
+ */
+- (void)removeLibraryDataForKey:(NSString *)key
+                     onComplete:(void (^)(NSError *_Nullable error))onComplete;
+
 @end
 
 NS_ASSUME_NONNULL_END

GoogleDataTransport/GDTCORTests/Common/Fakes/GDTCORStorageFake.m

@@ -28,4 +28,27 @@ - (void)storeEvent:(GDTCOREvent *)event
 - (void)removeEvents:(NSSet<NSNumber *> *)eventIDs {
 }
 
+- (void)libraryDataForKey:(nonnull NSString *)key
+               onComplete:
+                   (nonnull void (^)(NSData *_Nullable, NSError *_Nullable error))onComplete {
+  if (onComplete) {
+    onComplete(nil, nil);
+  }
+}
+
+- (void)storeLibraryData:(NSData *)data
+                  forKey:(nonnull NSString *)key
+              onComplete:(nonnull void (^)(NSError *_Nullable error))onComplete {
+  if (onComplete) {
+    onComplete(nil);
+  }
+}
+
+- (void)removeLibraryDataForKey:(nonnull NSString *)key
+                     onComplete:(nonnull void (^)(NSError *_Nullable))onComplete {
+  if (onComplete) {
+    onComplete(nil);
+  }
+}
+
 @end

GoogleDataTransport/GDTCORTests/Unit/GDTCORFlatFileStorageTest.m

@@ -445,6 +445,86 @@ - (void)testStoringEventsDuringTerminate {
   }
 }
 
+- (void)testSaveAndLoadLibraryData {
+  __weak NSData *weakData;
+  NSString *dataKey = NSStringFromSelector(_cmd);
+  @autoreleasepool {
+    NSData *data = [@"test data" dataUsingEncoding:NSUTF8StringEncoding];
+    weakData = data;
+    XCTestExpectation *expectation = [self expectationWithDescription:@"storage completion called"];
+    [[GDTCORFlatFileStorage sharedInstance] storeLibraryData:data
+                                                      forKey:dataKey
+                                                  onComplete:^(NSError *_Nullable error) {
+                                                    XCTAssertNil(error);
+                                                    [expectation fulfill];
+                                                  }];
+    [self waitForExpectations:@[ expectation ] timeout:10.0];
+  }
+  XCTAssertNil(weakData);
+  XCTestExpectation *expectation = [self expectationWithDescription:@"retrieval completion called"];
+  [[GDTCORFlatFileStorage sharedInstance]
+      libraryDataForKey:dataKey
+             onComplete:^(NSData *_Nullable data, NSError *_Nullable error) {
+               [expectation fulfill];
+               XCTAssertNil(error);
+               XCTAssertEqualObjects(@"test data",
+                                     [[NSString alloc] initWithData:data
+                                                           encoding:NSUTF8StringEncoding]);
+             }];
+  [self waitForExpectations:@[ expectation ] timeout:10.0];
+}
+
+- (void)testSavingNilLibraryData {
+  XCTestExpectation *expectation = [self expectationWithDescription:@"storage completion called"];
+  [[GDTCORFlatFileStorage sharedInstance] storeLibraryData:[NSData data]
+                                                    forKey:@"test data key"
+                                                onComplete:^(NSError *_Nullable error) {
+                                                  XCTAssertNotNil(error);
+                                                  [expectation fulfill];
+                                                }];
+  [self waitForExpectations:@[ expectation ] timeout:10.0];
+}
+
+- (void)testSaveAndRemoveLibraryData {
+  NSString *dataKey = NSStringFromSelector(_cmd);
+  NSData *data = [@"test data" dataUsingEncoding:NSUTF8StringEncoding];
+  XCTestExpectation *expectation = [self expectationWithDescription:@"storage completion called"];
+  [[GDTCORFlatFileStorage sharedInstance] storeLibraryData:data
+                                                    forKey:dataKey
+                                                onComplete:^(NSError *_Nullable error) {
+                                                  XCTAssertNil(error);
+                                                  [expectation fulfill];
+                                                }];
+  [self waitForExpectations:@[ expectation ] timeout:10.0];
+  expectation = [self expectationWithDescription:@"retrieval completion called"];
+  [[GDTCORFlatFileStorage sharedInstance]
+      libraryDataForKey:dataKey
+             onComplete:^(NSData *_Nullable data, NSError *_Nullable error) {
+               [expectation fulfill];
+               XCTAssertNil(error);
+               XCTAssertEqualObjects(@"test data",
+                                     [[NSString alloc] initWithData:data
+                                                           encoding:NSUTF8StringEncoding]);
+             }];
+  [self waitForExpectations:@[ expectation ] timeout:10.0];
+  expectation = [self expectationWithDescription:@"removal completion called"];
+  [[GDTCORFlatFileStorage sharedInstance] removeLibraryDataForKey:dataKey
+                                                       onComplete:^(NSError *error) {
+                                                         [expectation fulfill];
+                                                         XCTAssertNil(error);
+                                                       }];
+  [self waitForExpectations:@[ expectation ] timeout:10.0];
+  expectation = [self expectationWithDescription:@"retrieval completion called"];
+  [[GDTCORFlatFileStorage sharedInstance]
+      libraryDataForKey:dataKey
+             onComplete:^(NSData *_Nullable data, NSError *_Nullable error) {
+               [expectation fulfill];
+               XCTAssertNotNil(error);
+               XCTAssertNil(data);
+             }];
+  [self waitForExpectations:@[ expectation ] timeout:10.0];
+}
+
 /** Tests migration from v1 of the storage format to v2. */
 - (void)testMigrationFromOldVersion {
   static NSString *base64EncodedArchive =