Fix wkhtmltopdf crash on large PDF

CHANGES.md

@@ -1,6 +1,10 @@
 # CHANGES
 ## RosarioSIS Student Information System
 
+Changes in 5.6.4
+----------------
+- Fix wkhtmltopdf crash on large PDF in Wkhtmltopdf.php
+
 Changes in 5.6.3
 ----------------
 - Accessibility HTML format Input in MassAssignFees.php & MassAssignPayments.php

classes/Wkhtmltopdf.php

@@ -192,19 +192,59 @@ public function getFilePath()
 	protected function _exec($cmd, $input = "")
 	{
 		$result = array('stdout' => '', 'stderr' => '', 'return' => '');
-
 		$proc = proc_open($cmd, array(0 => array('pipe', 'r'), 1 => array('pipe', 'w'), 2 => array('pipe', 'w')), $pipes);
-		fwrite($pipes[0], $input);
-		fclose($pipes[0]);
-
-		$result['stdout'] = stream_get_contents($pipes[1]);
-		fclose($pipes[1]);
-
-		$result['stderr'] = stream_get_contents($pipes[2]);
-		fclose($pipes[2]);
-
+		/**
+		 * We need to asynchronously process streams, as simple sequential stream_get_contents() risks deadlocking if the 2nd pipe's OS pipe buffer fills up before the 1st is fully consumed.
+		 * The input is probably subject to the same risk.
+		 */
+		foreach ($pipes as $pipe) {
+			stream_set_blocking($pipe, 0);
+		}
+		$indexPipes = function(array $pipes) { return array_combine(array_map('intval', $pipes), $pipes); };
+		$allWritables = $indexPipes(array($pipes[0]));
+		$allReadables = $indexPipes(array($pipes[1], $pipes[2]));
+		$readablesNames = array((int)$pipes[1] => 'stdout', (int)$pipes[2] => 'stderr');
+		do {
+			$readables = $allReadables;
+			$writables = $allWritables;
+			$exceptables = null;
+			$selectTime = microtime(true);
+			$nStreams = stream_select($readables, $writables, $exceptables, null, null);
+			$selectTime = microtime(true) - $selectTime;
+			if ($nStreams === false) {
+				throw new \Exception('Error reading/writing to WKHTMLTOPDF');
+			}
+			foreach ($writables as $writable) {
+				$nBytes = fwrite($writable, $input);
+				if ($nBytes === false) {
+					throw new \Exception('Error writing to WKHTMLTOPDF');
+				}
+				if ($nBytes == strlen($input)) {
+					fclose($writable);
+					unset($allWritables[(int)$writable]);
+					$input = '';
+				} else {
+					$input = substr($input, $nBytes);
+				}
+			}
+			if (count($readables) > 0) {
+				if ($selectTime < 30e3) {
+					usleep(30e3 - $selectTime); // up to 30ms padding, so we don't burn so much time/CPU reading just 1 byte at a time.
+				}
+				foreach ($readables as $readable) {
+					$in = fread($readable, 0x10000);
+					if ($in === false) {
+						throw new \Exception('Error reading from WKHTMLTOPDF '.$readablesNames[$readable]);
+					}
+					$result[$readablesNames[(int)$readable]] .= $in;
+					if (feof($readable)) {
+						fclose($readable);
+						unset($allReadables[(int)$readable]);
+					}
+				}
+			}
+		} while (count($allReadables) > 0 || count($allWritables) > 0);
 		$result['return'] = proc_close($proc);
-
 		return $result;
 	}