Skip backup NSURL category for iOS.

NSDate+AGCategory.h

//
//  NSURL+AGCategory.m
//  AGFoundation
//
//  Created by Andrew Garn on 24/07/2012.
//  Copyright (c) 2012 Andrew Garn. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

@interface NSURL (AGCategory)

/**
 Adds the skip backup extended attribute to the receiver

 This requirement was added by apple with the introduction of iCloud. Files stored in the documents directory that have not been created by the user, or do not contain user data, must not be backed up. For more information see the following: http://developer.apple.com/library/ios/#qa/qa1719/_index.html
 @return `YES` if the operation was successful, otherwise `NO`.
*/
- (BOOL)addSkipBackupAttribute;

@end

NSDate+AGCategory.m

//
//  NSURL+AGCategory.m
//  AGFoundation
//
//  Created by Andrew Garn on 24/07/2012.
//  Copyright (c) 2012 Andrew Garn. All rights reserved.
//

#import "NSURL+AGCategory.h"
#include <sys/xattr.h>

@implementation NSURL (AGCategory)

- (BOOL)addSkipBackupAttribute
{
    NSString *systemVersion = [[UIDevice currentDevice] systemVersion];   
    
    if ([systemVersion floatValue] < 5.0 || [systemVersion isEqualToString:@"5.0.0"])
        return YES; // "do not backup" is not yet supported or required
    
    if ([systemVersion isEqualToString:@"5.0.1"])
    {
        const char *filePath = [[self path] fileSystemRepresentation];
        const char *attrName = "com.apple.MobileBackup";
        u_int8_t attrValue = 1;
        
        int result = setxattr(filePath, attrName, &attrValue, sizeof(attrValue), 0, 0);
        return result == 0;
    }
    else 
    {
        NSError *error = nil;
        BOOL success = [self setResourceValue:[NSNumber numberWithBool:YES]
                                      forKey:NSURLIsExcludedFromBackupKey error:&error];
        if(!success)
            NSLog(@"Error excluding %@ from backup %@", [self lastPathComponent], error);
        
        return success;
    }
    return NO;
}

@end