nodeForXPath leaks memory

FROM : Lorenzo Thurman
DATE : Thu Nov 22 03:58:01 2007

I posted this on usenet, but still could not solve the problem. Maybe
someone here can help me:

I have a subclass of NSXMLDocument that I use as an XMLParser. While
running my program through MallocDebug and Leaks, I see that I am
leaking blocks of memory in one of my methods. The function returns the
data I expect, but I'm at a loss to understand why it leaks. Here is the
function in question:

-(NSArray*)itemsForElement:(NSString*)el{
    NSError* err = nil;
    NSString* searchString = [NSString stringWithFormat:@".//%@", el];
    NSArray* nodes = [self nodesForXPath:searchString error:&err];
    int i = 0;
    if([nodes count] == 0)
        return nil;

    NSMutableArray* values = [[NSMutableArray alloc] init];

    for(i; i < [nodes count]; i++){
        [values addObject:[[[nodes objectAtIndex:i] objectValue]
stringByTrimmingCharactersInSet:[NSCharacterSet
whitespaceAndNewlineCharacterSet]]];
    }

    return [values autorelease];

}

I don't call this function in a loop, only one time for a single
element, but as you can see from the stack trace, I'm leaking 11 XQuery
blocks although there can never be more than 7 items in the array. I
searched Google looking for memory problems with nodesForXPath, but
found nothing indicating an inherent problem with nodesForXPath. I found
this in the archives though:
http://lists.apple.com/archives/cocoa-dev/2005/Sep/msg01565.html
The usage there is similar to mine, so assuming that's the correct way
to use it, I should be OK.  I've included a portion of the MallocDebug
dump file in case that helps.
TIA

STACK
Address /098ca730/size/00000010
0x0006a4f0  / 0x6a4f0 / libMallocDebug.A.dylib
0x90c585d0  / _internal_class_createInstanceFromZone / libobjc.A.dylib
0x94316b88  / +[NSObject allocWithZone:] / CoreFoundation
0x0964b7d4  / 0x964b7d4 / XQuery
0x09653278  / 0x9653278 / XQuery
0x0963546c  / 0x963546c / XQuery
0x09635d40  / 0x9635d40 / XQuery
0x09635f60  / 0x9635f60 / XQuery
0x09636dc8  / 0x9636dc8 / XQuery
0x09635fcc  / 0x9635fcc / XQuery
0x09636dc8  / 0x9636dc8 / XQuery
0x09635c60  / 0x9635c60 / XQuery
0x09645d84  / 0x9645d84 / XQuery
0x09651bfc  / 0x9651bfc / XQuery
0x92a43364  / -[NSXMLNode objectsForXQuery:constants:error:] / Foundation
0x92a43024  / -[NSXMLNode nodesForXPath:error:] / Foundation
0x00004c20  / -[WeatherParser valueForElement:atIndex:] / Weather Vane
0x00007818  / -[WeatherVane tooltipData] / Weather Vane
0x00007004  / -[WeatherVane parseData] / Weather Vane
0x00006724  / -[WeatherVane parseAndUpdateData] / Weather Vane
0x000022a8  / -[WeatherVane(WVURLConnection)
connectionDidFinishLoading:] / Weather Vane
0x929ff590  / _NSURLConnectionDidFinishLoading / Foundation
0x963f9218  / sendDidFinishLoadingCallback / CFNetwork
0x96414ee0  / handleCacheResponseIsValid / CFNetwork
0x963f5e6c  / _CFURLConnectionSendCallbacks / CFNetwork
0x963f5914  / muxerSourcePerform / CFNetwork
0x942a239c  / CFRunLoopRunSpecific / CoreFoundation
0x93d39ab8  / RunCurrentEventLoopInMode / HIToolbox
0x93d398dc  / ReceiveNextEventCommon / HIToolbox
0x93d3971c  / BlockUntilNextEventMatchingListInMode / HIToolbox
0x90eac7a4  / _DPSNextEvent / AppKit
0x90eac1f4  / -[NSApplication
nextEventMatchingMask:untilDate:inMode:dequeue:] / AppKit
0x90ea5eb0  / -[NSApplication run] / AppKit
0x90e76930  / NSApplicationMain / AppKit
0x00004054  / main / Weather Vane
0x00001f64  / _start / Weather Vane
0x00001c40  / start / Weather Vane
ENDSTACK