Close Chrome process pipes before termination to prevent loop hang

library/Pdfexport/HeadlessChrome.php

@@ -191,7 +191,7 @@
 
         foreach ($arguments as $name => $value) {
             if ($value !== null) {
                 $value = escapeshellarg($value);
 
                 if (! is_int($name)) {
                     if (substr($name, -1) === '=') {
@@ -247,18 +247,18 @@
      *
      * @return PromiseInterface
      */
     public function asyncToPdf(): PromiseInterface
     {
         $deferred = new Promise\Deferred();
         Loop::futureTick(function () use ($deferred) {
             switch (true) {
                 case $this->remote !== null:
                     try {
                         $result = $this->jsonVersion($this->remote[0], $this->remote[1]);
                         if (is_array($result)) {
                             $parts = explode('/', $result['webSocketDebuggerUrl']);
                             $pdf = $this->printToPDF(
                                 join(':', $this->remote),
                                 end($parts),
                                 ! $this->document->isEmpty() ? $this->document->getPrintParameters() : []
                             );
@@ -313,7 +313,7 @@
                     }
 
                     $killer = Loop::addTimer(10, function (TimerInterface $timer) use ($chrome, $deferred) {
-                        $chrome->terminate(6); // SIGABRT
+                        $this->terminateProcess($chrome, 6); // SIGABRT
 
                         Logger::error(
                             'Browser timed out after %d seconds without the expected output',
@@ -330,10 +330,10 @@
 
                     $chrome->start();
 
                     $chrome->stderr->on('data', function ($chunk) use ($chrome, $deferred, $killer) {
                         Logger::debug('Caught browser output: %s', $chunk);
 
                         if (preg_match(self::DEBUG_ADDR_PATTERN, trim($chunk), $matches)) {
                             Loop::cancelTimer($killer);
 
                             try {
@@ -346,7 +346,7 @@
                                 Logger::error('Failed to print PDF. An error occurred: %s', $e);
                             }
 
-                            $chrome->terminate();
+                            $this->terminateProcess($chrome);
 
                             if (! empty($pdf)) {
                                 $deferred->resolve($pdf);
@@ -689,6 +689,26 @@
         return $params;
     }
 
+    /**
+     * Terminate a process and close pipes inherited by subprocesses
+     *
+     * Chrome spawns sub-processes that inherit open pipes. Close them before termination
+     * so the event loop is not kept alive by inherited file descriptors.
+     *
+     * @param Process $process The process to terminate
+     * @param ?int $signal The signal passed to Process::terminate()
+     *
+     * @return void
+     */
+    private function terminateProcess(Process $process, ?int $signal = null): void
+    {
+        foreach ($process->pipes as $pipe) {
+            $pipe->close();
+        }
+
+        $process->terminate($signal);
+    }
+
     /**
      * Get the major version number of Chrome or false on failure
      *