Working Objective-C keychain library

gistfile1.m

NSString *const kKeychainErrorDomain = @"kKeychainErrorDomain"

NSString * ServiceName = @"My Service";

+ (NSError *) errorWithStatus:(OSStatus) status {
    if (errSecSuccess == status) return nil;
#if __has_feature(objc_arc)
    NSString *message = (__bridge_transfer NSString *)SecCopyErrorMessageString(status, NULL);
#else
    NSString *message = [(id) SecCopyErrorMessageString(status, NULL) autorelease];
#endif
    NSDictionary *userInfo = [NSDictionary dictionaryWithObject:message
                                                         forKey:NSLocalizedDescriptionKey];
    return [NSError errorWithDomain:kKeychainErrorDomain
                               code:status
                           userInfo:userInfo];
}

+ (NSString *) keychainAccountNameForUserName:(NSString *) userName serverName:(NSString *) serverName {
    return [NSString stringWithFormat:@"%@@%@", userName, serverName];
}

+ (NSString *) passwordForUserName:(NSString *) userName serverName:(NSString *) serverName error:(NSError * __autoreleasing *) error {
    NSString *accountName = [self.class keychainAccountNameForUserName:userName serverName:serverName];
    void * resultBytes = NULL; UInt32 resultLength = 0;
    OSStatus status = SecKeychainFindGenericPassword(NULL,
                                                     (UInt32)ServiceName.length,
                                                     [ServiceName cStringUsingEncoding:NSUTF8StringEncoding],
                                                     (UInt32)accountName.length,
                                                     [accountName cStringUsingEncoding:NSUTF8StringEncoding],
                                                     &resultLength,
                                                     &resultBytes,
                                                     NULL);
    if (errSecItemNotFound == status) {
        return nil;
    } else if (errSecSuccess != status) {
        if (error) *error = [self errorWithStatus:status];
        return nil;
    }
    
    NSString *result = [[NSString alloc] initWithBytes:resultBytes
                                                length:resultLength
                                              encoding:NSUTF8StringEncoding];
    SecKeychainItemFreeContent(NULL, resultBytes);
    return result;
}

+ (BOOL) savePassword:(NSString *) password forUserName:(NSString *) userName serverName:(NSString *) serverName error:(NSError * __autoreleasing *) error {
    NSString *accountName = [self.class keychainAccountNameForUserName:userName serverName:serverName];
    if (!password || !accountName) return NO;
    OSStatus status = SecKeychainAddGenericPassword(NULL,
                                                    (UInt32)ServiceName.length,
                                                    [ServiceName cStringUsingEncoding:NSUTF8StringEncoding],
                                                    (UInt32)accountName.length,
                                                    [accountName cStringUsingEncoding:NSUTF8StringEncoding],
                                                    (UInt32)password.length,
                                                    [password cStringUsingEncoding:NSUTF8StringEncoding],
                                                    NULL);
    if (errSecSuccess == status) return YES;
    
    if (errSecDuplicateItem == status) {
        SecKeychainItemRef keyChainItem;
        status = SecKeychainFindGenericPassword(NULL,
                                                (UInt32)ServiceName.length,
                                                [ServiceName cStringUsingEncoding:NSUTF8StringEncoding],
                                                (UInt32)accountName.length,
                                                [accountName cStringUsingEncoding:NSUTF8StringEncoding],
                                                NULL,
                                                NULL,
                                                &keyChainItem);
        if (errSecSuccess == status) {
            status = SecKeychainItemModifyAttributesAndData(keyChainItem,
                                                            NULL,
                                                            (UInt32)password.length,
                                                            [password cStringUsingEncoding:NSUTF8StringEncoding]);
            CFRelease(keyChainItem);
            if (errSecSuccess == status) return YES;
        }
    }
    
    if (error) *error = [self errorWithStatus:status];
    return NO;
}

+ (BOOL) clearPasswordForUserName:(NSString *) userName serverName:(NSString *) serverName error:(NSError * __autoreleasing *) error {
    NSString *accountName = [self.class keychainAccountNameForUserName:userName serverName:serverName];
    if (!accountName) return NO;
    
    SecKeychainItemRef keyChainItem;
    OSStatus status = SecKeychainFindGenericPassword(NULL,
                                            (UInt32)ServiceName.length,
                                            [ServiceName cStringUsingEncoding:NSUTF8StringEncoding],
                                            (UInt32)accountName.length,
                                            [accountName cStringUsingEncoding:NSUTF8StringEncoding],
                                            NULL,
                                            NULL,
                                            &keyChainItem);
    if (errSecSuccess == status) {
        status = SecKeychainItemDelete(keyChainItem);        
        CFRelease(keyChainItem);
        if (errSecSuccess == status) return YES;
    }
    
    if (error) *error = [self errorWithStatus:status];
    return NO;
}