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

Question

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 befo…

Accepted Answer

I finally tried the solution given here, which uses semaphores instead of depending on the callback to wait for the stream. This works perfectly :) The memory usage hovers around 1.1 MB according to the Allocations Instrument. It may not look as neat because of the semaphore syntax, but at least it does what I need it to do.

Other suggestions are still welcome of course :)

```
- (void)encryptWithSemaphore:(NSURL *)url {
  dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);

__block int total = 0;
  int blockSize = 32 * 1024;

NSString *encryptedFile = [[url lastPathComponent] stringByDeletingPathExtension];
  NSURL *docsURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
  self.tempURL = [[docsURL URLByAppendingPathComponent:encryptedFile isDirectory:NO] URLByAppendingPathExtension:@"crypt"];

NSInputStream *inputStream = [NSInputStream inputStreamWithURL:url];
  __block NSOutputStream *outputStream = [NSOutputStream outputStreamWithURL:self.tempURL append:NO];
  __block NSError *encryptionError = nil;

[inputStream open];
  [outputStream open];

RNEncryptor *encryptor = [[RNEncryptor alloc] initWithSettings:kRNCryptorAES256Settings
                                                        password:self.password
                                                         handler:^(RNCryptor *cryptor, NSData *data) {
                                                           @autoreleasepool {
                                                             [outputStream write:data.bytes maxLength:data.length];
                                                             dispatch_semaphore_signal(semaphore);

data = nil;
                                                             if (cryptor.isFinished) {
                                                               [outputStream close];
                                                               encryptionError = cryptor.error;
                                                               // call my delegate that I'm finished with decrypting
                                                             }
                                                           }
                                                         }];
  while (inputStream.hasBytesAvailable) {
    @autoreleasepool {
      uint8_t buf[blockSize];
      NSUInteger bytesRead = [inputStream read:buf maxLength:blockSize];
      if (bytesRead > 0) {
        NSData *data = [NSData dataWithBytes:buf length:bytesRead];

total = total + bytesRead;
        [encryptor addData:data];

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
      }
    }
  }

[inputStream close];
  [encryptor finish];  
}
```

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

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