NSFileManager + extended attributes

ExtendedAttributes.h

//
//  ExtendedAttributes.h
//  NSFileManager+Xattr
//
//  Created by Jesús A. Álvarez on 2008-12-17.
//  Copyright 2008-2009 namedfork.net. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <sys/xattr.h>

extern NSString * XAFinderInfo;
extern NSString * XAFinderComment;
extern NSString * XAResourceFork;

typedef enum XAMode {
    XAAnyMode = 0,
    XACreate = XATTR_CREATE,
    XAReplace = XATTR_REPLACE,
} XAMode;

@interface NSFileManager (ExtendedAttributes)
- (NSArray*)extendedAttributeNamesAtPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err;
- (BOOL)hasExtendedAttribute:(NSString*)name atPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err;
- (NSData*)extendedAttribute:(NSString*)name atPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err;
// extendedAttributesAtPath dictionary DOES NOT include resource fork
- (NSDictionary*)extendedAttributesAtPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err;
- (BOOL)setExtendedAttribute:(NSString*)name value:(NSData*)value atPath:(NSString*)path traverseLink:(BOOL)follow mode:(XAMode)mode error:(NSError**)err;
- (BOOL)removeExtendedAttribute:(NSString*)name atPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err;
// overwrite will delete attributes not in dictionary, except resource fork
- (BOOL)setExtendedAttributes:(NSDictionary*)attrs atPath:(NSString*)path traverseLink:(BOOL)follow overwrite:(BOOL)overwrite error:(NSError**)err;
@end

ExtendedAttributes.m

//
//  ExtendedAttributes.m
//  NSFileManager+Xattr
//
//  Created by Jesús A. Álvarez on 2008-12-17.
//  Copyright 2008-2009 namedfork.net. All rights reserved.
//

#import "ExtendedAttributes.h"
#import <string.h>

NSString * XAFinderInfo = @XATTR_FINDERINFO_NAME;
NSString * XAFinderComment = @"com.apple.metadata:kMDItemFinderComment";
NSString * XAResourceFork = @XATTR_RESOURCEFORK_NAME;

@implementation NSFileManager (ExtendedAttributes)

- (NSArray*)extendedAttributeNamesAtPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err {
    int flags = follow? 0 : XATTR_NOFOLLOW;
    
    // get size of name list
    ssize_t nameBuffLen = listxattr([path fileSystemRepresentation], NULL, 0, flags);
    if (nameBuffLen == -1) {
        if (err) *err = [NSError errorWithDomain:NSPOSIXErrorDomain code:errno userInfo:
            [NSDictionary dictionaryWithObjectsAndKeys:
             [NSString stringWithUTF8String:strerror(errno)], @"error",
             @"listxattr", @"function",
             path, @":path",
             [NSNumber numberWithBool:follow], @":traverseLink",
             nil]
            ];
        return nil;
    } else if (nameBuffLen == 0) return [NSArray array];
    
    // get name list
    NSMutableData *nameBuff = [NSMutableData dataWithLength:nameBuffLen];
    listxattr([path fileSystemRepresentation], [nameBuff mutableBytes], nameBuffLen, flags);
    
    // convert to array
    NSMutableArray * names = [NSMutableArray arrayWithCapacity:5];
    char *nextName, *endOfNames = [nameBuff mutableBytes] + nameBuffLen;
    for(nextName = [nameBuff mutableBytes]; nextName < endOfNames; nextName += 1+strlen(nextName))
        [names addObject:[NSString stringWithUTF8String:nextName]];
    return [NSArray arrayWithArray:names];
}

- (BOOL)hasExtendedAttribute:(NSString*)name atPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err {
    int flags = follow? 0 : XATTR_NOFOLLOW;
    
    // get size of name list
    ssize_t nameBuffLen = listxattr([path fileSystemRepresentation], NULL, 0, flags);
    if (nameBuffLen == -1) {
        if (err) *err = [NSError errorWithDomain:NSPOSIXErrorDomain code:errno userInfo:
            [NSDictionary dictionaryWithObjectsAndKeys:
             [NSString stringWithUTF8String:strerror(errno)], @"error",
             @"listxattr", @"function",
             path, @":path",
             [NSNumber numberWithBool:follow], @":traverseLink",
             nil]
            ];
        return NO;
    } else if (nameBuffLen == 0) return NO;
    
    // get name list
    NSMutableData *nameBuff = [NSMutableData dataWithLength:nameBuffLen];
    listxattr([path fileSystemRepresentation], [nameBuff mutableBytes], nameBuffLen, flags);
    
    // find our name
    NSMutableArray * names = [NSMutableArray arrayWithCapacity:5];
    char *nextName, *endOfNames = [nameBuff mutableBytes] + nameBuffLen;
    for(nextName = [nameBuff mutableBytes]; nextName < endOfNames; nextName += 1+strlen(nextName))
        if (strcmp(nextName, [name UTF8String]) == 0) return YES;
    return NO;
}

- (NSData*)extendedAttribute:(NSString*)name atPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err {
    int flags = follow? 0 : XATTR_NOFOLLOW;
    // get length
    ssize_t attrLen = getxattr([path fileSystemRepresentation], [name UTF8String], NULL, 0, 0, flags);
    if (attrLen == -1) {
        if (err) *err = [NSError errorWithDomain:NSPOSIXErrorDomain code:errno userInfo:
                         [NSDictionary dictionaryWithObjectsAndKeys:
                          [NSString stringWithUTF8String:strerror(errno)], @"error",
                          @"getxattr", @"function",
                          name, @":name",
                          path, @":path",
                          [NSNumber numberWithBool:follow], @":traverseLink",
                          nil]
                         ];
        return nil;
    }
    
    // get attribute data
    NSMutableData * attrData = [NSMutableData dataWithLength:attrLen];
    getxattr([path fileSystemRepresentation], [name UTF8String], [attrData mutableBytes], attrLen, 0, flags);
    return attrData;
}

- (NSDictionary*)extendedAttributesAtPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err {
    // get names
    NSArray * names = [self extendedAttributeNamesAtPath:path traverseLink:follow error:err];
    if (names == nil) return nil;
    
    NSMutableDictionary * attrs = [NSMutableDictionary dictionaryWithCapacity:[names count]];
    // get attributes
    for(NSString * name in names) if (![name isEqualToString:XAResourceFork]) {
        NSData * attr = [self extendedAttribute:name atPath:path traverseLink:follow error:err];
        if (attr == nil) return nil;
        [attrs setObject:attr forKey:name];
    }
    
    return [NSDictionary dictionaryWithDictionary:attrs];
}

- (BOOL)setExtendedAttribute:(NSString*)name value:(NSData*)value atPath:(NSString*)path traverseLink:(BOOL)follow mode:(XAMode)mode error:(NSError**)err {
    int flags = (follow? 0 : XATTR_NOFOLLOW) | mode;
    if (0 == setxattr([path fileSystemRepresentation], [name UTF8String], [value bytes], [value length], 0, flags)) return YES;
    // error
    if (err) *err = [NSError errorWithDomain:NSPOSIXErrorDomain code:errno userInfo:
                     [NSDictionary dictionaryWithObjectsAndKeys:
                      [NSString stringWithUTF8String:strerror(errno)], @"error",
                      @"setxattr", @"function",
                      name, @":name",
                      [NSNumber numberWithUnsignedInteger:[value length]], @":value.length",
                      path, @":path",
                      [NSNumber numberWithBool:follow], @":traverseLink",
                      [NSNumber numberWithInt:mode], @":mode",
                      nil]
                     ];
    return NO;
}

- (BOOL)removeExtendedAttribute:(NSString*)name atPath:(NSString*)path traverseLink:(BOOL)follow error:(NSError**)err {
    int flags = (follow? 0 : XATTR_NOFOLLOW);
    if (0 == removexattr([path fileSystemRepresentation], [name UTF8String], flags)) return YES;
    // error
    if (err) *err = [NSError errorWithDomain:NSPOSIXErrorDomain code:errno userInfo:
                     [NSDictionary dictionaryWithObjectsAndKeys:
                      [NSString stringWithUTF8String:strerror(errno)], @"error",
                      @"removexattr", @"function",
                      name, @":name",
                      path, @":path",
                      [NSNumber numberWithBool:follow], @":traverseLink",
                      nil]
                     ];
    return NO;
}

- (BOOL)setExtendedAttributes:(NSDictionary*)attrs atPath:(NSString*)path traverseLink:(BOOL)follow overwrite:(BOOL)overwrite error:(NSError**)err {
    NSArray * oldNames = [self extendedAttributeNamesAtPath:path traverseLink:follow error:err];
    if (oldNames == nil) return NO;
    NSArray * newNames = [attrs allKeys];
    BOOL success = YES;
    
    // remove attributes
    if (overwrite) {
        NSMutableSet * attrsToRemove = [NSMutableSet setWithArray:oldNames];
        [attrsToRemove minusSet:[NSSet setWithArray:newNames]];
        [attrsToRemove removeObject:XAResourceFork];
        for(NSString * name in attrsToRemove)
            if (NO == [self removeExtendedAttribute:name atPath:path traverseLink:follow error:err]) success = NO;
        if (success == NO) return NO;
    }   
    
    // set attributes
    for (NSString * name in newNames)
        if (NO == [self setExtendedAttribute:name value:[attrs objectForKey:name] atPath:path traverseLink:follow mode:0 error:err]) success = NO;
    
    return success;
}

@end

Thank you. Such nice code it makes me wonder why Apple not yet introduced it as an official extension to NSFileManager. really! they have this rather big "MetaData" thing going on, important and all, but no Cocoa API for it. What do they think? will normal developers of iOS and Mac apps use/update/consult the Metadata without a proper API?

I think it worth to go yet another step in converting actual specific extended attributes (those documented by Apple here: to actual Obj-C objects (according to their definition) automatically, thus making this API even more usable. Extended attributes not documented/supported can still be returned as NSData object for the user's further parsing. What do you say?