Merge branch 'PHP-8.1'

* PHP-8.1:
  Fix #81659: stream_get_contents() may unnecessarily overallocate

Author: cmb69

ext/standard/tests/streams/bug81659.phpt

@@ -0,0 +1,24 @@
+--TEST--
+Bug #81659 (stream_get_contents() may unnecessarily overallocate)
+--FILE--
+<?php
+$stream = fopen(__DIR__ . "/81659.txt", "w+");
+
+for ($i = 0; $i < 1024; $i++) {
+    fwrite($stream, str_repeat("*", 1024));
+}
+
+fseek($stream, 1023 * 1024);
+
+$m0 = memory_get_peak_usage();
+var_dump(strlen(stream_get_contents($stream)));
+$m1 = memory_get_peak_usage();
+var_dump($m1 < $m0 + 512 * 1024);
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . "/81659.txt");
+?>
+--EXPECT--
+int(1024)
+bool(true)

main/streams/streams.c

@@ -1506,9 +1506,9 @@ PHPAPI zend_string *_php_stream_copy_to_mem(php_stream *src, size_t maxlen, int
 	 * result may be inaccurate, as the filter may inflate or deflate the
 	 * number of bytes that we can read.  In order to avoid an upsize followed
 	 * by a downsize of the buffer, overestimate by the step size (which is
-	 * 2K).  */
+	 * 8K).  */
 	if (php_stream_stat(src, &ssbuf) == 0 && ssbuf.sb.st_size > 0) {
-		max_len = ssbuf.sb.st_size + step;
+		max_len = MAX(ssbuf.sb.st_size - src->position, 0) + step;
 	} else {
 		max_len = step;
 	}