iOS how to fetch all available users from xmpp

Question

I integrated XMPP chat server in my iOS application. Kindly help me is there any way to fetch users list from roaster? I have used below code and still no response. .

- (void)getAllRegisteredUsers {

NSError *error = [[NSError alloc] init];
NSXMLElement *query = [[NSXMLElement alloc] initWithXMLString:@"<query xmlns='http://jabber.org/protocol/disco#items' node='all users'/>"
                                                        error:&error];
XMPPIQ *iq = [XMPPIQ iqWithType:@"get"
                             to:[XMPPJID jidWithString:@"DOMAIN"]
                      elementID:[xmppStream generateUUID] child:query];
[xmppStream sendElement:iq];
}

- (BOOL)xmppStream:(XMPPStream *)sender didReceiveIQ:(XMPPIQ *)iq
{ 
 NSXMLElement *queryElement = [iq elementForName: @"query" xmlns: @"http://jabber.org/protocol/disco#items"];

if (queryElement) {
    NSArray *itemElements = [queryElement elementsForName: @"item"];
    NSMutableArray *mArray = [[NSMutableArray alloc] init];
    for (int i=0; i<[itemElements count]; i++) {

        NSString *jid=[[[itemElements objectAtIndex:i] attributeForName:@"jid"] stringValue];
        [mArray addObject:jid];
    }
}