Re: convert password from SecKeychainFindGenericPassword to NSString
Re: convert password from SecKeychainFindGenericPassword to NSString
- Subject: Re: convert password from SecKeychainFindGenericPassword to NSString
- From: Stuart Malin <email@hidden>
- Date: Mon, 1 Feb 2010 06:58:53 -0500
On Jan 31, 2010, at 9:53 PM, Jens Alfke wrote:
> No. You don't want to pass a null terminated string to anything but the methods that explicitly take a C string. Anything else just wants the characters, with no nulls.
>
> --Jens {via iPhone}
NSString's +stringWithCString:encoding: does require a NULL terminated C string [1].
My code worked fine with NSString's +stringWithCString:length: even though the string was not NULL terminated. When I changed that to +stringWithCString:encoding: I would *sometimes* get incorrect results. When I added the code to copy the suppled non-null terminated string to a new buffer with a null termination (prior to calling +stringWithCString:encoding:), the results were made proper again.
[1] from the NSString documentation <http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html#//apple_ref/occ/clm/NSString/stringWithCString:encoding:>
+ (id)stringWithCString:(const char *)cString encoding:(NSStringEncoding)enc
Parameters
cString: A C array of bytes. The array must end with a NULL character; intermediate NULL characters are not allowed.
>
> On Jan 31, 2010, at 6:28 PM, Stuart Malin <email@hidden> wrote:
>
>>
>> On Jan 31, 2010, at 9:12 PM, Kyle Sluder wrote:
>>
>>> On Sun, Jan 31, 2010 at 5:51 PM, Stuart Malin <email@hidden> wrote:
>>>> I acquire a password from a keychain using SecKeychainFindGenericPassword. That provides a non null terminated c string and a length. I had been using [NSString stringWithCString: length:] to get an NSString instance of the password. However, the +stringWithCString:length: method was deprecated way back, so I thought I'd clean up my code and use +stringWithCString:encoding: -- however that doesn't work because the supplied C string isn't null terminated. I did a bit of searching, and found in the archives on CocoaBuilder [1] someone's solution back in September of 2005, which was to copy the acquired password to a new buffer of 1 additional byte and create a new null terminated C string there:
>>>
>>> You could wrap the provided buffer with an NSData and use -[NSString initWithData:encoding:].
>>
>>
>> If I use +dataWithBytes:length: then I need to specify a length 1 greater, and that additional byte must be set to 0 (to null terminate the string). So, I could use NSMutableData, then -resetBytesInRange: to zero out the last byte, which requires creating an NSRange struct, and that all seems heavier than just using the C code. But then, the processor is fast, and this is code that is run rarely, so optimizing isn't important. I guess it is just a question of style...
>>
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