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RNCryptor

CCCryptor (AES encryption) wrappers for iOS and Mac. -- For Swift, see swift branch and release 4.0.

https://groups.google.com/forum/#!forum/rncryptor

Memory issues when encrypting/decrypting a large file with RNCryptor on iOS

I'm trying to use RNCryptor to encrypt and decrypt large files (600+MB) on iOS. On the github I found example code on how to use the library asynchronously on streams. This code is similar to the answer of Rob Napier on a question about this same subject.

However, although I think I implemented the code correctly, the app uses up to 1.5 GB of memory (in the iPad 6.1 simulator). I thought the code was supposed to prevent the app from keeping more than one block of data in-memory? So what is going wrong?

In my controller, I create a 'CryptController' which I message with encrypt/decrypt requests.

  // Controller.m
  NSString *password = @"pw123";
  self.cryptor = [[CryptController alloc] initWithPassword:password];

  //start encrypting file
  [self.cryptor streamEncryptRequest:self.fileName andExtension:@"pdf" withURL:[self samplesURL]];

  //wait for encryption to finish
  NSDate *timeout = [NSDate dateWithTimeIntervalSinceNow:1];
  do {
    [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
                             beforeDate:timeout];
  } while (![self.cryptor isFinished]);

In CryptController I have:

- (void)streamEncryptionDidFinish {
  if (self.cryptor.error) {
    NSLog(@"An error occurred. You cannot trust decryptedData at this point");
  }
  else {
    NSLog(@"%@ is complete. Use it as you like", [self.tempURL lastPathComponent]);
  }
  self.cryptor = nil;
  self.isFinished = YES;
}

- (void) streamEncryptRequest:(NSString *)fileName andExtension:(NSString *)ext withURL:(NSURL *)directory {

  //Make sure that this number is larger than the header + 1 block.
  int blockSize = 32 * 1024;

  NSString *encryptedFileName = [NSString stringWithFormat:@"streamEnc_%@", fileName];
  self.tempURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
  self.tempURL = [self.tempURL URLByAppendingPathComponent:encryptedFileName isDirectory:NO];
  self.tempURL = [self.tempURL URLByAppendingPathExtension:@"crypt"];

  NSInputStream *decryptedStream = [NSInputStream inputStreamWithURL:[[directory URLByAppendingPathComponent:fileName isDirectory:NO] URLByAppendingPathExtension:ext]];
  NSOutputStream *cryptedStream = [NSOutputStream outputStreamWithURL:self.tempURL append:NO];

  [cryptedStream open];
  [decryptedStream open];

  __block NSMutableData *data = [NSMutableData dataWithLength:blockSize];
  __block RNEncryptor *encryptor = nil;

  dispatch_block_t readStreamBlock = ^{
    [data setLength:blockSize];
    NSInteger bytesRead = [decryptedStream read:[data mutableBytes] maxLength:blockSize];
    if (bytesRead < 0) {
      //Throw an error
    }
    else if (bytesRead == 0) {
      [encryptor finish];
    }
    else {
      [data setLength:bytesRead];
      [encryptor addData:data];
      //NSLog(@"Sent %ld bytes to encryptor", (unsigned long)bytesRead);
    }
  };

  encryptor = [[RNEncryptor alloc] initWithSettings:kRNCryptorAES256Settings
                                           password:self.password
                                            handler:^(RNCryptor *cryptor, NSData *data) {
                                              //NSLog(@"Encryptor received %ld bytes", (unsigned long)data.length);
                                              [cryptedStream write:data.bytes maxLength:data.length];
                                              if (cryptor.isFinished) {
                                                [decryptedStream close];
                                                //call my delegate that i'm finished with decrypting
                                                [self streamEncryptionDidFinish];
                                              }
                                              else {
                                                readStreamBlock();
                                              }
                                            }];

  // Read the first block to kick things off
  self.isFinished = NO;
  readStreamBlock();
}

When I profile using the Allocation Instrument, the allocation categories I see consistently growing are malloc 32.50 KB, malloc 4.00 KB, NSConcreteData and NSSubrangeData. Especially the malloc 32.50 KB grows big, over 1 GB. The responsible caller is [NSConcreteData initWithBytes:length:copy:freeWhenDone:bytesAreVM:] For NSConcreteData the responsible caller is -[NSData(NSData) copyWithZone:].

When I profile using the Leaks Instrument, no leaks are found.

I'm new to Objective-C, and from what I understood, the new ARC is supposed to handle allocation and deallocation of memory. When googling on anything memory related, all the information I find is assuming you don't use ARC (or it didn't exist at time of writing). I sure am using ARC, since I get compile errors saying so when I try to manually deallocate memory.

If anyone can help me with this, it would be greatly appreciated! If any more information is needed, I'll be happy to provide it :) Also, I'm new to StackOverflow, so if there's anything I've overlooked that I should have done, kindly inform me!