NSFileManager+BKExtensions.h

//
//  NSFileManager+BKExtensions.h
//  BlocksKit
//
//  Created by Steve Streza on 10/3/10.
//  Copyright 2010 Steve Streza. All rights reserved.
//

#import <Foundation/Foundation.h>


@interface NSFileManager (BKExtensions)

-(void)BK_getContentsAtPath:(NSString *)path handler:(void (^)(NSData *data, NSError *error))handler;

@end

NSFileManager+BKExtensions.m

//
//  NSFileManager+BKExtensions.m
//  BlocksKit
//
//  Created by Steve Streza on 10/3/10.
//  Copyright 2010 Steve Streza. All rights reserved.
//

#import "NSFileManager+BKExtensions.h"
#import <dispatch/dispatch.h>

#define DISPATCH_GET_DEFAULT_GLOBAL_QUEUE() dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)

@implementation NSFileManager (BKExtensions)

-(void)BK_getContentsAtPath:(NSString *)path handler:(void (^)(NSData *, NSError *))handler{
	dispatch_queue_t queue = DISPATCH_GET_DEFAULT_GLOBAL_QUEUE();
	dispatch_async(queue, ^{
		NSFileHandle *fh = [[NSFileHandle fileHandleForReadingAtPath:path] retain];
		NSError *error = nil;
		
		NSMutableData *data = [[NSMutableData data] retain];
		
		// create a GCD source using the file descriptor, which will respond whenever the descriptor fires
		dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ, [fh fileDescriptor], 0, queue);
		dispatch_source_set_event_handler(source, ^{
			BOOL eof = NO;

			// if we get less than this much, we hit end of file, so we can file the callback
			NSUInteger max = 65536;
			NSData *newData = [fh readDataOfLength:max];
			if(!newData || newData.length < max){
				eof = YES;
			}
			[data appendData:newData];
			
			if(eof){
				dispatch_async(dispatch_get_main_queue(), ^{
					handler(data, error);
					[data release];
				});
				
				dispatch_source_cancel(source);
				[fh release];
			}
		});
		dispatch_resume(source);
	});
}

@end