Re: is_prefix() - checking wheather $A is prefix for $B

In case you haven't realized it, I have already written two functions to check for a prefix !! The question is: Which function is better? (is_prefix1() or is_prefix2()) On 12/29/07, Zoltán Németh <znemeth@alterationx.hu> wrote: > > 2007. 12. 29, szombat keltezéssel 13.39-kor AmirBehzad Eslami ezt írta: > > I want to write a function to check > > whether string $A is a prefix for string $B or not. > > if (strpos($B, $A) === 0) { > echo '$B begins with $A'; > } else { > echo '$B does not begin with $A'; > } > > greets > Zoltán Németh > > > > > I writing this function in order to prevent directory traversal > > during a download request. (e.g., download.php?file=..\index.php) > > > > I want to make sure that the realpath() of the requested file is > > within the realpath() of the download-directory. Trying to make > > sure that the the $download_dir is a prefix for $filepath. > > > > @see: http://en.wikipedia.org/wiki/Directory_traversal > > ** > > *TWO FUNCTIONS:* > > > > function is_prefix1($prefix, $str) { > > return (0 == strncasecmp($prefix, $str, strlen($prefix))); > > } > > > > function is_prefix2($prefix, $str) { > > return (0 === stripos($str, $prefix)); > > } > > *USAGE:* > > if (is_prefix1('a', 'abcdef')) > > echo 'prefix1 returned True!', '<br />'; > > > > if (is_prefix2('a', 'abcdef')) > > echo 'prefix2 returned True!', '<br />'; > > > > ------------------------ > > Do these functions do the same job? > > Which one provides better performance? > > > > -behzad > >