PDFTK with php://memory

Question

Question: Is it possible to use php://memory on a exec or passthru command?

I can use php variables in the exec or passthru with no problem, but I am having trouble with php://memory

background: I am trying to eliminate all of my temporary pdf file writing with PDFTK.
1)I am writing an temporary fdf file
2) form-fill a temporary pdf file using #1
3) repeat #1 and #2 for all the pdfs
4) merge all pdf's together.

This currently works - but it creates a lot of files, and is the bottleneck.

I would like to speed things up with pdftk by making use of the virtual file php://memory

First, I am trying to just virtualize the fdf file used in #1.
Answering this alone is enough for a 'correct answer'.   :)

The code is as follows:

$fdf = 'fdf file contents here';
$tempFdfVirtual= fopen("php://memory", 'r+');
if(  $tempFdfVirtual ) {
  fwrite(  $tempFdfVirtual, $fdf);
} else {
    echo "Failure to open temporary fdf file";
    exit;
}
rewind( $tempFdfVirtual);
$url = "unfilled.pdf";
$temppdf_fn = "output.pdf"; 
$command = "pdftk $url fill_form  $tempFdfVirtual output $temppdf_fn flatten"; 
$error="";   
exec( $command, $error );
if ($error!="") {
    $_SESSION['err'] = $error;       
} else {
    $_SESSION['err'] = 0;
}

I am getting an errorcode #1. If I do a stream_get_contents($tempFdfVirtual), it shows the contents.

Thanks for looking!

Answer 1

php://memory and php://temp (and in fact any file descriptor) are only available to the currently-running php process. Besides, $tempFdfVirtual is a resource handle so it makes no sense to put it in a string.

You should pass the data from your resource handle to the process through its standard-in. You can do this with proc-open, which gives you more control over input and output to the child process than exec.

Note that for some reason, you can't pass a 'php://memory' file descriptor to a process. PHP will complain:

Warning: proc_open(): cannot represent a stream of type MEMORY as a File Descriptor

Use php://temp instead, which is supposed to be exactly the same except it will use a temporary file once the stream gets big enough.

This is a tested example that illustrates the general pattern of code that uses proc_open(). This should be wrapped up in a function or other abstraction:

$testinput = "THIS IS A TEST STRING\n";

$fp = fopen('php://temp', 'r+');
fwrite($fp, $testinput);
rewind($fp);

$cmd = 'cat';
$dspec = array(
    0 => $fp,
    1 => array('pipe', 'w'),
);
$pp = proc_open($cmd, $dspec, $pipes);

// busywait until process is finished running.
do {
    usleep(10000);
    $stat = proc_get_status($pp);
} while($stat and $stat['running']);

if ($stat['exitcode']===0) {
    // index in $pipes will match index in $dspec
    // note only descriptors created by proc_open will be in $pipes
    // i.e. $dspec indexes with an array value.
    $output = stream_get_contents($pipes[1]);
    if ($output == $testinput) {
        echo "TEST PASSED!!";
    } else {
        echo "TEST FAILED!! Output does not match input.";
    }
} else {
    echo "TEST FAILED!! Process has non-zero exit status.";
}

// cleanup
// close pipes first, THEN close process handle.
foreach ($pipes as $pipe) {
    fclose($pipe);
}
// Only file descriptors created by proc_open() will be in $pipes.
// We still need to close file descriptors we created ourselves and
// passed to it.
// We can do this before or after proc_close().
fclose($fp);
proc_close($pp);

Untested Example specific to your use of PDFTK:

// Command takes input from STDIN
$command = "pdftk unfilled.pdf fill_form - output tempfile.pdf flatten"; 
$descriptorspec = array(
    0 => $tempFdfVirtual, // feed stdin of process from this file descriptor
//    1 => array('pipe', 'w'), // Note you can also grab stdout from a pipe, no need for temp file
);
$prochandle = proc_open($command, $descriptorspec, $pipes);
// busy-wait until it finishes running
do {
    usleep(10000);
    $stat = proc_get_status($prochandle);
} while ($stat and $stat['running']);

if ($stat['exitcode']===0) {
    // ran successfully
    // output is in that filename
    // or in the file handle in $pipes if you told the command to write to stdout.
}

// cleanup
foreach ($pipes as $pipe) {
   fclose($pipe);
}
proc_close($prochandle);

Answer 2

It's not just that you're using php://memory, it's any file handle. File handles only exist for the current process. For all intents and purposes, the handle you get back from fopen cannot be transferred to any other place outside of your script.

As long as you're working with an outside application, you're pretty much stuck using temporary files. Your only other option is to try and pass the data to pdftk on stdin, and retrieve the output on stdout (if it supports that). As far as I know the only way to invoke an external process with that kind of access to its descriptors (stdin/stdout) is using the proc_ family of functions, specifically proc_open.