Fwd: [PHP] proc_open and buffer limit?

My guess at first look is that you fill the stdout buffer because you don't
read from it untill you stop piping data to stdin.

I asked this last night on the general mailing list and also have
asked around about it. Nobody seems to know. I normally wouldn't ask a
support quesiton on a developers mailing list, but nobody else seems to
know so I thought that perhaps a developer knows.

Why would I be running into this STDIN data size limit when using
proc_open?

I've tried setting the limits for apache to unlimited in
/etc/security/limits.conf just to see if its a system limit.

----- Forwarded message from Mark Krenz mark@suso.org -----

Date: Sun, 22 Jan 2006 00:25:33 +0000
From: Mark Krenz mark@suso.org
To: php-general@lists.php.net
Subject: [PHP] proc_open and buffer limit?

I'm using PHP 5.1.1 on Apache 2.0.54 on Gentoo Linux. I've been trying
to write a program to pass information to a program using proc_open,
however when I do, it only passes the first 65536 bytes of the stream
and then cuts off the rest. To make sure its not the program I'm trying
to send to, I tries using /bin/cat instead and get the same problem.

Below, I've included the code that I'm using, which for the most part is
from the proc_open documentation page. For testing, I'm reading from a
word dictionary which is over 2MB in size. Is there something I'm
missing about using proc_open?

---

$program = "/bin/cat";

$descriptorspec = array(
0 => array("pipe", "r"),
1 => array("pipe", "w"),
2 => array("file", "/tmp/error-output.txt", "a")
);

$cwd = '/var/www';
$env = array('HOME' => '/var/www');

$process = proc_open($program, $descriptorspec, $pipes, $cwd, $env);

if (is_resource($process)) {

stream_set_blocking($pipes[0], FALSE);
stream_set_blocking($pipes[1], FALSE);

$handle = fopen("/usr/share/dict/words", "r");
while (!feof($handle)) {
    $input .= fread($handle, 8192);
}

fwrite($pipes[0], $input);
fclose($handle);
fclose($pipes[0]);

while (!feof($pipes[1])) {
   $output .= fgets($pipes[1], 8192);
}
fclose($pipes[1]);

 print "<PRE>$output</PRE><BR><BR>\n";

$return_value = proc_close($process);

echo "command returned $return_value\n";

}

--
Mark S. Krenz
IT Director
Suso Technology Services, Inc.
http://suso.org/

--
PHP General Mailing List (http://www.php.net/)

----- End forwarded message -----

--
Mark S. Krenz
IT Director
Suso Technology Services, Inc.
http://suso.org/

--

--
Nicolas Bérard Nault (nicobn@gmail.com)
Étudiant D.E.C. Sciences, Lettres & Arts
Cégep de Sherbrooke

Site web: http://www.lapsus-engineer.org

"La liberté est un bagne aussi longtemps qu'un seul homme est asservi sur la
terre." - Albert Camus, Les Justes.

There are quite a few bad streams usages there.

I'd rewrite your code like this:

$words = fopen('/usr/share/dict/words', 'r');
stream_copy_to_stream($words, $pipes[0]);
fclose($pipes[0]);
fclose($words);
$output = stream_get_contents($pipes[1]);
fclose($pipes[1]);
proc_close($process);

My guess at the cause of the problem was that you're tying to write
2MB into a pipe, and the underlying write() syscall could only write
64k; since you're ignoring the return code from fwrite(), you're
missing this vital fact.

Using the streams functions in PHP 5 helps you to write code that
"does what I mean", and makes for shorter, more readable code.

--Wez.

PS: http://netevil.org/talks/PHP-Streams-Lucky-Dip.pdf
has some tips and insider knowledge on using streams in PHP.

stream_set_blocking($pipes[0], FALSE);
stream_set_blocking($pipes[1], FALSE);

$handle = fopen("/usr/share/dict/words", "r");
while (!feof($handle)) {
    $input .= fread($handle, 8192);
}

fwrite($pipes[0], $input);
fclose($handle);
fclose($pipes[0]);

while (!feof($pipes[1])) {
   $output .= fgets($pipes[1], 8192);
}
fclose($pipes[1]);

 print "<PRE>$output</PRE><BR><BR>\n";

$return_value = proc_close($process);

echo "command returned $return_value\n";

}