Block per block file copying

Question

Is there a good way to copy some file or directory(with files and subdirectories) block per block in Mac OS with objective c?

Answer 1

You can copy a file per blocks by creating a NSInputStream and a NSOutputStream and scheduling them in a NSRunLoop. Then, when you get bytes from the input stream, you write them in a buffer and when the output stream is ready, you copy the contents of the buffer into it.

@synthesize numberOfBytesTransferred = _numberOfBytesTransferred;

static const NSUInteger blockSize = 65536; // should be adjusted

- (void)startWithSourcePath:(NSString *)srcPath
            destinationPath:(NSString *)dstPath
          completionHandler:(void (^)(NSUInteger, NSError *))completionHandler
{
    _buffer = malloc(blockSize);
    _numberOfBytesTransferred = _bufferLength = _bufferOffset = 0;
    _completionHandler = [completionHandler copy];
    _srcStream = [[NSInputStream alloc] initWithFileAtPath:srcPath];
    _dstStream = [[NSOutputStream alloc] initToFileAtPath:dstPath append:NO];
    _srcStream.delegate = self;
    _dstStream.delegate = self;
    [_srcStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
    [_dstStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
    [_srcStream open];
    [_dstStream open];
}

- (void)processStreams
{    
    if ( _srcStream.hasBytesAvailable && ! _bufferLength )
        _bufferLength = [_srcStream read:_buffer maxLength:blockSize];

    if ( _dstStream.hasSpaceAvailable && _bufferLength ) {
        NSInteger length = [_dstStream write:_buffer + _bufferOffset maxLength:_bufferLength];
        _bufferOffset += length;
        _bufferLength -= length;
    }

    if ( _bufferOffset && !_bufferLength ) {
        [self willChangeValueForKey:@"numberOfBytesTransferred"];
        _numberOfBytesTransferred += _bufferOffset;
        _bufferOffset = 0;
        [self didChangeValueForKey:@"numberOfBytesTransferred"];
    }

    if ( _dstStream.hasSpaceAvailable && NSStreamStatusAtEnd == _srcStream.streamStatus ) {
        [_srcStream close];
        [_dstStream close];
        _completionHandler(_numberOfBytesTransferred, nil);
    }
}

- (void)cancel
{
    [_srcStream close];
    [_dstStream close];
}

- (void)pause
{
    _paused = YES;
}

- (void)resume
{
    _paused = NO;
    [self processStreams];
}

- (void)stream:(NSStream *)stream handleEvent:(NSStreamEvent)eventCode
{
    if ( NSStreamEventErrorOccurred == eventCode ) {
        [_srcStream close];
        [_dstStream close];
        _completionHandler(_numberOfBytesTransferred, stream.streamError);
        return;
    }

    if ( ! _paused )
        [self processStreams];
}

Copying the contents of a directory will require to enumerate through the contents of the directory. You can create an instance of NSDirectoryEnumerator with -[NSFileManager enumeratorAtPath:].

Once you have the enumerator, you call nextObject then get the file attributes:

• If the file is a directory, you create a new directory in the destination directory
• If the file is a regular file, you start a file copy task and wait until the completion handler is called.