General file I/O reliability

I'm desperately trying to build a reliable stream bzip2 decompressor, but until now without much success. The problem is how to detect deconding errors, which seem to be impossible (more follows). In the meanwhile, I discovered several issues I was not aware of and that I wouls share with you, with the premise that all the samples of code below are run in a very safe environement where even the smallest E_NOTICE causes an exception: error_reporting(-1); ini_set("track_errors", "1"); function my_error_handler($errno, $message) { throw new ErrorException($message); } set_error_handler("my_error_handler"); 1. fread() succeeds reading an unreadable file. While fopen() complains immediately if it cannot read a file: fopen("/root/secret.txt", "r"); --> E_WARNING: fopen(/root/secret.txt): failed to open stream: Permission denied the fread() function seem much more tolerant reading an unreadable file. For example, the /proc/self/mem file can be opened, but its first 512 bytes block cannot be read and causes an error (credits for this trick: http://unix.stackexchange.com/a/6302): $ cat /proc/self/mem cat: /proc/self/mem: Input/output error Lets try with PHP what happens: $f = fopen("/proc/self/mem", "r"); $bytes = fread($f, 1000); echo "bytes="; var_dump($bytes); --> displays bytes=string(0) "", no error whatsoever The file seems empty, and no error whatsoever is shown. 2. Also the require*() and include*() family of functions seems very tolerant: require("/proc/self/mem"); echo "read myself!\n"; require("/root/secret.php"); # just to exsercise error reporting :-) --> read myself! E_WARNING: require(/root/secret.php): failed to open stream: Permission denied The first require() silently ignored. Bad feeling about safety. 3. Now back to the original question: BZIP2 stream decoding from a given input resource. Lets start creating a corrupted BZIP2 file: $plain = "The quick brown fox jumps over the lazy dog."; $fn = "test.bz2"; $compressed = bzcompress($plain); // Set a random byte in the middle of the compressed data $compressed[strlen($compressed) - 15] = 'X'; file_put_contents($fn, $compressed); Now I create the input resource filtered with the decompressor: $r = fopen($fn, "r"); stream_filter_append($r, 'bzip2.decompress', STREAM_FILTER_READ); and lets see what come back: do { $s = fread($r, 10); echo "read: "; var_dump($s); } while(! feof($r)); --> read: string(0) "" read: string(10) "bthes ohe " read: string(10) "rpujumr.bt" read: string(10) "hes ohe rp" read: string(10) "ujumr.bthe" read: string(3) "s o" What?! Why is fread() returning garbage? and why it does not fails with some E_WARNING telling me that the file is corrupted? And what if my program blindly processes these "data"? Now the big question is: can I trust file access under PHP anymore? If yes (and I hope so) how can my applications be made aware when something goes wrong? Regards, ___ /_|_\ Umberto Salsi \/_\/ www.icosaedro.it