ios - 调度队列和异步RNCryptor

这是Asynchronously decrypt a large file with RNCryptor on iOS的后续

我设法用本文中描述的方法异步解密了一个较大的下载文件(60Mb)，由Calman在他的回答中进行了纠正。

它基本上是这样的:

int blockSize = 32 * 1024;
NSInputStream *cryptedStream = [NSInputStream inputStreamWithFileAtPath:...];
NSOutputStream *decryptedStream = [NSOutputStream output...];

[cryptedStream open];
[decryptedStream open];

RNDecryptor *decryptor = [[RNDecryptor alloc] initWithPassword:@"blah" handler:^(RNCryptor *cryptor, NSData *data) {
    NSLog("Decryptor recevied %d bytes", data.length);
    [decryptedStream write:data.bytes maxLength:data.length];
    if (cryptor.isFinished) {
        [decryptedStream close];
        // call my delegate that I'm finished with decrypting
    }
}];

while (cryptedStream.hasBytesAvailable) {
    uint8_t buf[blockSize];
    NSUInteger bytesRead = [cryptedStream read:buf maxLength:blockSize];
    NSData *data = [NSData dataWithBytes:buf length:bytesRead];

    [decryptor addData:data];
    NSLog("Sent %d bytes to decryptor", bytesRead);
}

[cryptedStream close];
[decryptor finish];

但是，我仍然面临一个问题:整个数据在解密之前先加载到内存中。我可以看到一堆“发送X字节给解密器”，然后，在控制台中，当我想看到“发送，接收，发送，接收，..”时，也看到了同一堆“解密器已恢复X字节”。 ”。

对于小型(2Mb)文件或模拟器上的大型(60Mb)文件来说，这很好。但是在真正的iPad1上，由于内存限制，它崩溃了，因此很明显我无法在我的生产应用程序中保留此过程。

我觉得我需要通过使用dispatch_async将数据发送到解密器，而不是在while循环中盲目发送它，但是我完全迷失了。我试过了:

在while之前创建自己的队列，并使用dispatch_async(myQueue, ^{ [decryptor addData:data]; });

相同，但是在while循环

内部调度整个代码

相同，但调度整个while循环

使用RNCryptor提供的responseQueue代替我自己的队列

在这4个变体中，没有任何作用。

我还没有对调度队列的完整了解。我觉得问题出在这里。我很高兴有人能对此有所启发。

最佳答案

如果您一次只想处理一个块，则仅在第一个块回叫您时才处理一个块。您不需要信号量就可以了，您只需要在回调内执行下一个读取。您可能需要在@autoreleasepool内添加一个readStreamBlock块，但我认为您不需要它。

有空的时候，我可能会直接将其包装到RNCryptor中。我为此打开了Issue#47。我愿意提出要求。

// Make sure that this number is larger than the header + 1 block.
// 33+16 bytes = 49 bytes. So it shouldn't be a problem.
int blockSize = 32 * 1024;

NSInputStream *cryptedStream = [NSInputStream inputStreamWithFileAtPath:@"C++ Spec.pdf"];
NSOutputStream *decryptedStream = [NSOutputStream outputStreamToFileAtPath:@"/tmp/C++.crypt" append:NO];

[cryptedStream open];
[decryptedStream open];

// We don't need to keep making new NSData objects. We can just use one repeatedly.
__block NSMutableData *data = [NSMutableData dataWithLength:blockSize];
__block RNEncryptor *decryptor = nil;

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

decryptor = [[RNEncryptor alloc] initWithSettings:kRNCryptorAES256Settings
                                         password:@"blah"
                                          handler:^(RNCryptor *cryptor, NSData *data) {
                                            NSLog(@"Decryptor recevied %ld bytes", (unsigned long)data.length);
                                            [decryptedStream write:data.bytes maxLength:data.length];
                                            if (cryptor.isFinished) {
                                              [decryptedStream close];
                                              // call my delegate that I'm finished with decrypting
                                            }
                                            else {
                                              // Might want to put this in a dispatch_async(), but I don't think you need it.
                                              readStreamBlock();
                                            }
                                          }];

// Read the first block to kick things off
readStreamBlock();