SOExtendedAttributes is a category on NSURL providing methods for manipulating extended attributes on a file system object.
The implementation uses listxattr(2), getxattr(2), setxattr(2), and removexattr(2).
Introspection
- (BOOL) hasExtendedAttributeWithName:(NSString *)name;
Accessing attributes individually
- (id) valueOfExtendedAttributeWithName:(NSString *)name error:(NSError * __autoreleasing *)outError;
- (BOOL) setExtendedAttributeValue:(id)value forName:(NSString *)name error:(NSError * __autoreleasing *)outError;
Accessing attributes in batch
- (NSDictionary *) extendedAttributesWithError:(NSError * __autoreleasing *)outError;
- (BOOL) setExtendedAttributes:(NSDictionary *)attributes error:(NSError * __autoreleasing *)outError;
Removing an extended attribute
- (BOOL) removeExtendedAttributeWithName:(NSString *)name error:(NSError * __autoreleasing *)outError;
Use with iCloud Backup
Note 2013-06-03: see Apple Tech QA 1719 for the recommended way to mark a file for exclusion from iCloud backup. Hint: don't use the @"com.apple.MobileMeBackup" extended attribute.
Extended Attribute Values
An extended attribute value can be any Foundation object that can be serialized into a property list:
- NSData
- NSString
- NSNumber
- NSArray
- NSDictionary
- NSDate
##Known Issues, Stuff & Bother
Maximum Value Size
The maximum size of an extended attribute value? I'm not sure, but I believe it is a function of the node size in the HFS+ catalog or attributes tree. The Internet says anywhere from 3802 bytes to 128 KB. So the standard disclaimers apply: Your mileage may vary. Void where prohibited. Do not operate heavy machinery.
Refs: Google Search
Non-file URLs
An NSInternalInconsistencyException is thrown if these methods are invoked on a non-file URL.
Resolving Symbolic links
These methods act on the explicitly given URL. If that URL points to a symbolic link, you'll be manipulating extended attributes on the symlink, not its original file. Use -URLByResolvingSymlinksInPath to get a URL pointing to the original file system item.
ARC
If your project is not using ARC, you will need to set a per-file build flag in Xcode on NSURL+SOExtendedAttributes.m:
-fobc-arc
For either Mac OS X or iOS projects, add these files:
NSURL+SOExtendedAttributes.h
NSURL+SOExtendedAttributes.m
SOExtendedAttributes is compatible with Mac OS X 10.6+ and iOS 5. The clang compiler is required. The source file NSURL+SOExtendedAttributes.m must be compiled with ARC enabled.
For an alternate Cocoa implementation compatible with Mac OS X 10.4 and greater, see UKXattrMetadataStore.
Bill Garrison, initial creation. @github, @bitbucket
Uli Kusterer, for UKXattrMetadataStore.
Simon Tännler, for starting a Cocoapods spec. @github.