Improve platform support by checking all available FDs as fallback

If we can not read from /dev/fd (which is available on Linux, Mac and
many others), we otherwise try temporarily duplicating file descriptors
in the range 0-1024 (FD_SETSIZE) to see which one is currently in use.
This is known to work on more exotic platforms and also inside
chroot environments without /dev/fd. Causes many syscalls, but still
rather fast.

Author: clue

src/Io/functions.php

@@ -13,10 +13,24 @@
  */
 function fds($path = '/dev/fd')
 {
-    // try to get list of all open FDs (Linux/Mac and others) or simply assume range 0-1024 (FD_SETSIZE)
+    // Try to get list of all open FDs (Linux/Mac and others)
     $fds = @\scandir($path);
 
-    return $fds !== false ? $fds : \range(0, 1024);
+    // Otherwise try temporarily duplicating file descriptors in the range 0-1024 (FD_SETSIZE).
+    // This is known to work on more exotic platforms and also inside chroot
+    // environments without /dev/fd. Causes many syscalls, but still rather fast.
+    if ($fds === false) {
+        $fds = array();
+        for ($i = 0; $i <= 1024; ++$i) {
+            $copy = @\fopen('php://fd/' . $i, 'r');
+            if ($copy !== false) {
+                $fds[] = $i;
+                \fclose($copy);
+            }
+        }
+    }
+
+    return $fds;
 }
 
 /**

tests/Io/FunctionsTest.php

@@ -41,15 +41,29 @@ public function testFdsWithInvalidPathReturnsArray()
         $this->assertInternalType('array', $fds);
     }
 
+    public function testFdsWithInvalidPathReturnsSubsetOfFdsFromDevFd()
+    {
+        if (@scandir('/dev/fd') === false) {
+            $this->markTestSkipped('Unable to read /dev/fd');
+        }
+
+        $fds = Io\fds();
+        $second = Io\fds('/dev/null');
+
+        foreach ($second as $one) {
+            $this->assertContains($one, $fds);
+        }
+    }
+
     public function testProcessWithoutFdsReturnsProcessWithoutClosingDefaultHandles()
     {
         $process = Io\processWithoutFds('sleep 10');
 
         $this->assertInstanceOf('React\ChildProcess\Process', $process);
 
-        $this->assertNotContains('0>&-', $process->getCommand());
-        $this->assertNotContains('1>&-', $process->getCommand());
-        $this->assertNotContains('2>&-', $process->getCommand());
+        $this->assertNotContains(' 0>&-', $process->getCommand());
+        $this->assertNotContains(' 1>&-', $process->getCommand());
+        $this->assertNotContains(' 2>&-', $process->getCommand());
     }
 
     public function testProcessWithoutFdsReturnsProcessWithOriginalCommandPartOfActualCommandWhenDescriptorsNeedToBeClosed()