PHP Function Timeout

Question

I'm not an expert with PHP. I have a function which uses EXEC to run WINRS whcih then runs commands on remote servers. The problem is this function is placed into a loop which calls getservicestatus function dozens of times. Sometimes the WINRS command can get stuck or take longer than expected causing the PHP script to time out and throw a 500 error.

Temporarily I've lowered the set timeout value in PHP and created a custom 500 page in IIS and if the referring page is equal to the script name then reload the page (else, throw an error). But this is messy. And obviously it doesn't apply to each time the function is called as it's global. So it only avoids the page stopping at the HTTP 500 error.

What I'd really like to do is set a timeout of 5 seconds on the function itself. I've been searching quite a bit and have been unable to find an answer, even on stackoverflow. Yes, there are similar questions but I have not been able to find any that relate to my function. Perhaps there's a way to do this when executing the command such as an alternative to exec()? I don't know. Ideally I'd like the function to timeout after 5 seconds and return $servicestate as 0.

Code is commented to explain my spaghetti mess. And I'm sorry you have to see it...

function getservicestatus($servername, $servicename, $username, $password)
{
//define start so that if an invalid result is reached the function can be restarted using goto.
start:

//Define command to use to get service status.
$command = 'winrs /r:' . $servername . ' /u:' . $username . ' /p:' . $password . ' sc query ' . $servicename . ' 2>&1';
exec($command, $output);

//Defines the server status as $servicestate which is stored in the fourth part of the command array.
//Then the string "STATE" and any number is stripped from $servicestate. This will leave only the status of the service (e.g. RUNNING or STOPPED).
$servicestate = $output[3];
$strremove = array('/STATE/','/:/','/[0-9]+/','/\s+/');
$servicestate = preg_replace($strremove, '', $servicestate);

//Define an invalid output. Sometimes the array is invalid. Catch this issue and restart the function for valid output. 
//Typically this can be caught when the string "SERVICE_NAME" is found in $output[3].
$badservicestate = "SERVICE_NAME" . $servicename;
if($servicestate == $badservicestate) {
    goto start;
}

//Service status (e.g. Running, Stopped Disabled) is returned as $servicestate.
return $servicestate;
}

Answer 1

The most straightforward solution, since you are calling an external process, and you actually need its output in your script, is to rewrite exec in terms of proc_open and non-blocking I/O:

function exec_timeout($cmd, $timeout, &$output = '') {
    $fdSpec = [
        0 => ['file', '/dev/null', 'r'], //nothing to send to child process
        1 => ['pipe', 'w'], //child process's stdout
        2 => ['file', '/dev/null', 'a'], //don't care about child process stderr
    ];
    $pipes = [];
    $proc = proc_open($cmd, $fdSpec, $pipes);
    stream_set_blocking($pipes[1], false);

    $stop = time() + $timeout;
    while(1) {
        $in = [$pipes[1]];
        $out = [];
        $err = [];
        stream_select($in, $out, $err, min(1, $stop - time()));

        if($in) {
            while(!feof($in[0])) {
                $output .= stream_get_contents($in[0]);
                break;
            }

            if(feof($in[0])) {
                break;
            }
        } else if($stop <= time()) {
            break;
        }
    }

    fclose($pipes[1]); //close process's stdout, since we're done with it 
    $status = proc_get_status($proc);
    if($status['running']) {
        proc_terminate($proc); //terminate, since close will block until the process exits itself

        return -1;
    } else {
        proc_close($proc);

        return $status['exitcode'];
    }
}

$returnValue = exec_timeout('YOUR COMMAND HERE', $timeout, $output);

This code:

• uses proc_open to open a child process. We only specify the pipe for the child's stdout, since we have nothing to send to it, and don't care about its stderr output. if you do, you'll have to adjust the following code accordingly.
• Loops on stream_select(), which will block for a period up to the $timeout set ($stop - time()).
• If there is input, it will var_dump() the contents of the input buffer. This won't block, because we have stream_set_blocking($pipe[1], false) on the pipe. You will likely want to save the content into a variable (appending it rather than overwriting it), rather than printing out.
• When we have read the entire file, or we have exceeded our timeout, stop.
• Cleanup by closing the process we have opened.
• Output is stored in the pass-by-reference string $output. The process's exit code is returned, or -1 in the case of a timeout.