Re: Analyzer in error?
Re: Analyzer in error?
- Subject: Re: Analyzer in error?
- From: Greg Parker <email@hidden>
- Date: Wed, 13 Jan 2010 18:09:56 -0800
On Jan 13, 2010, at 5:54 PM, Graham Cox wrote:
> @implementation NSData (SHA1Hash)
>
> - (NSData*) sha1Hash
> {
> // calculates the 160 bit SHA-1 digest of the given data
>
> unsigned char* digest = (unsigned char*) malloc(20);
> SHA1([self bytes], [self length], digest);
>
> return [[self class] dataWithBytesNoCopy:digest length:20];
> }
>
> @end
>
> The static analyzer reports this:
>
> Potential leak of an object allocated on line 622
>
> Method returns an Objective-C object with a +1 retain count (owning reference)
> Object returned to caller as an owning reference (single retain count transferred to caller)
> Object allocated on line 622 is returned from a method whose name ('sha1Hash') does not contain 'copy' or otherwise starts with 'new' or 'alloc'. This violates the naming convention rules given in the Memory Management Guide for Cocoa (object leaked)
>
> But I think this is wrong - [NSData dataWithBytesNoCopy] returns an object I don't own, and it in turn takes ownership of <digest>. So where's the leak? Is clang simply mistaking the fact that +dataWithBytesNoCopy CONTAINS 'copy' and not STARTS WITH copy?
Yes, the static analyzer is wrong here.
The Official Rule is '... contains "copy" ...'. This is a case where a mechanical interpretation of the Official Rule isn't quite right.
The static analyzer does have a special case for +[NSData dataWithBytesNoCopy:length:].
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20090511/017258.html
But your code sends the message to [self class] instead of NSData, so perhaps the special case is not recognized. Alternatively, perhaps your Xcode isn't the newest available.
Try this to suppress the complaint:
return [(NSData *)[self class] dataWithBytesNoCopy:digest length:20];
--
Greg Parker email@hidden Runtime Wrangler
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