note 88911 added to function.fread

fread has a bug than can cause large memory leaks if you're storing separate strings from multiple reads, or even just a single string if the length parameter is large. The strings returned always allocate *length* bytes (the parameter in the call), even if the total amount of returned data is tiny. E.g.,: <?php file_put_contents('temp.txt', 'a few bytes'); $fp = fopen('temp.txt', 'rb'); echo 'Memory usage: ' . number_format(memory_get_usage(), null, null, ' ') . "\n"; $x = fread($fp, 1024 * 1024); fclose($fp); echo 'Memory usage: ' . number_format(memory_get_usage(), null, null, ' ') . "\n"; echo 'String length: ' . strlen($x); ?> Example output: Memory usage: 67 520 Memory usage: 1 117 056 String length: 11 After just one fread call, the string $x now takes over 1 MB of memory for 11 bytes of data, and will stay that way until you unset or release it. This affects network streams too. The bug was apparently dismissed as "won't fix" (or "wont fix" actually): http://bugs.php.net/bug.php?id=34471 If you want to avoid it, re-alloc the string before storing it, and the wasted memory will disappear. Specifying a smaller length value avoids creating the large buffer in the first place too. E.g.: <?php $x = substr(fread($fp, 65536), 0); ?> ---- Server IP: 193.95.141.37 Probable Submitter: 89.100.60.13 ---- Manual Page -- http://www.php.net/manual/en/function.fread.php Edit -- https://master.php.net/note/edit/88911 Del: integrated -- https://master.php.net/note/delete/88911/integrated Del: useless -- https://master.php.net/note/delete/88911/useless Del: bad code -- https://master.php.net/note/delete/88911/bad+code Del: spam -- https://master.php.net/note/delete/88911/spam Del: non-english -- https://master.php.net/note/delete/88911/non-english Del: in docs -- https://master.php.net/note/delete/88911/in+docs Del: other reasons-- https://master.php.net/note/delete/88911 Reject -- https://master.php.net/note/reject/88911 Search -- https://master.php.net/manage/user-notes.php