Merge branch 'PHP-7.4'

* PHP-7.4:
  Fixed bug #78902
  Add unit test for bug #78902

Author: nikic

ext/standard/tests/streams/bug78902.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Bug #78902: Memory leak when using stream_filter_append
+--INI--
+memory_limit=512k
+--FILE--
+<?php
+
+/** create temporary file 2mb file */
+$tmp_file_name = tempnam(sys_get_temp_dir(), 'test_');
+$fp = fopen($tmp_file_name, 'w+');
+$size = 1024 * 1024 * 2; // 2mb
+$chunk = 1024;
+while ($size > 0) {
+    fputs($fp, str_pad('', min($chunk,$size)));
+    $size -= $chunk;
+}
+fclose($fp);
+
+$fp = fopen($tmp_file_name, 'r');
+stream_filter_append($fp, "string.toupper");
+while (!feof($fp)) {
+    fread($fp, 1);
+}
+fclose($fp);
+var_dump(true);
+?>
+--EXPECT--
+bool(true)

main/streams/streams.c

@@ -588,8 +588,15 @@ PHPAPI int _php_stream_fill_read_buffer(php_stream *stream, size_t size)
 					 * stream read buffer */
 					while (brig_inp->head) {
 						bucket = brig_inp->head;
-						/* grow buffer to hold this bucket
-						 * TODO: this can fail for persistent streams */
+						/* reduce buffer memory consumption if possible, to avoid a realloc */
+						if (stream->readbuf && stream->readbuflen - stream->writepos < bucket->buflen) {
+							if (stream->writepos > stream->readpos) {
+								memmove(stream->readbuf, stream->readbuf + stream->readpos, stream->writepos - stream->readpos);
+							}
+							stream->writepos -= stream->readpos;
+							stream->readpos = 0;
+						}
+						/* grow buffer to hold this bucket */
 						if (stream->readbuflen - stream->writepos < bucket->buflen) {
 							stream->readbuflen += bucket->buflen;
 							stream->readbuf = perealloc(stream->readbuf, stream->readbuflen,