On 4 Jun 2010, at 00:49, Ken Thomases wrote:
> On Jun 3, 2010, at 8:46 AM, jonat...@mugginsoft.com wrote:
>
>> My app runs user supplied scripts.
>>
>> These scripts may contain RubyCocoa statements such as:
>> OSX::NSLog("task parameters are %@ and %@", a, b)
>>
>> These scripts may contain errors and the generated error reports may contain
>> the likes of:
>> syntax error, unexpected tIDENTIFIER, expecting $end OSX::NSLog("task
>> parameters are %@ and %@", a, b)
>>
>> When the error is logged the extra format specifiers trip the code.
>
>> All I need to do is sanitise those logging statements that derive from
>> script errors and escape % as %%.
>
> I don't think that's the route you should take. As I mentioned toward the
> very end of my reply, if you have a string that you need to write/log, and
> that string is not supposed to be treated as a format string, don't pass it
> as the format string. Pass it as a value. Pass something that you control
> as the format string.
>
> E.g.:
>
> NSLog(@"syntax error, unexpected tIDENTIFIER, expecting $end %...@\n",
> arbitrary_nsstring);
>
Thanks for persisting Ken.
You are of course quite right.
I was erroneously calling my log macro as:
MLog(RELEASELOG, logError);
which is fine until logError contains format specifiers.
The correct approach is, as you point out:
MLog(RELEASELOG, @"%@", logError);
In general it would seem that when a method/function has format + va_list
signature
invocations should not contain single variable argument lists.
NSLog(someStringVar);
is unsafe.
NSLog(@"%@", someStringVar);
is safe.
Needless to say I had committed the same mistake in several other locations, so
thanks again.
This was a frequent offender:
@try {
[whatever really];
}
@catch (NSException *e) {
NSLog([e reason]);
}
The following regex is reasonably effective at finding the issue:
NSLog\([...@]
Regards
Jonathan Mitchell
Developer
Mugginsoft LLP
http://www.mugginsoft.com
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