From 8827cc34cf8c77828330182ee1e6d0b9438d489c Mon Sep 17 00:00:00 2001
From: Anatol Belski <ab@php.net>
Date: Tue, 30 Oct 2018 20:42:00 +0100
Subject: [PATCH] Fixed bug #77081 ftruncate() changes seek pointer in c mode

---
 NEWS                                          |  3 +++
 .../tests/file/ftruncate_bug77081.phpt        | 24 +++++++++++++++++++
 main/streams/plain_wrapper.c                  |  7 +++---
 3 files changed, 31 insertions(+), 3 deletions(-)
 create mode 100644 ext/standard/tests/file/ftruncate_bug77081.phpt

diff --git a/NEWS b/NEWS
index 17dbea657db..34533b88725 100644
--- a/NEWS
+++ b/NEWS
@@ -13,6 +13,9 @@ PHP                                                                        NEWS
   . Fixed bug #50675 (SoapClient can't handle object references correctly).
     (Cameron Porter)
 
+- Standard:
+  . Fixed bug #77081 (ftruncate() changes seek pointer in c mode). (cmb, Anatol)
+
 - XML:
   . Fixed bug 71592 (External entity processing never fails). (cmb)
 
diff --git a/ext/standard/tests/file/ftruncate_bug77081.phpt b/ext/standard/tests/file/ftruncate_bug77081.phpt
new file mode 100644
index 00000000000..7a9aa691fb3
--- /dev/null
+++ b/ext/standard/tests/file/ftruncate_bug77081.phpt
@@ -0,0 +1,24 @@
+--TEST--
+Bug #77081 ftruncate() changes seek pointer in c mode
+--FILE--
+<?php
+
+$filename = dirname(__FILE__) . DIRECTORY_SEPARATOR . "test77081";
+
+file_put_contents($filename, 'foo');
+$stream = fopen($filename, 'c');
+ftruncate($stream, 0);
+var_dump(ftell($stream));
+fwrite($stream, 'bar');
+fclose($stream);
+var_dump(file_get_contents($filename));
+
+?>
+--CLEAN--
+<?php
+$fn = dirname(__FILE__) . DIRECTORY_SEPARATOR . "test77081";
+unlink($fn);
+?>
+--EXPECT--
+int(0)
+string(3) "bar"
diff --git a/main/streams/plain_wrapper.c b/main/streams/plain_wrapper.c
index fdfc7b4f634..d8e1f517b47 100644
--- a/main/streams/plain_wrapper.c
+++ b/main/streams/plain_wrapper.c
@@ -858,12 +858,13 @@ static int php_stdiop_set_option(php_stream *stream, int option, int value, void
 						return PHP_STREAM_OPTION_RETURN_ERR;
 					}
 
-					LARGE_INTEGER old_sz;
-					if (!GetFileSizeEx(h, &old_sz)) {
+					LARGE_INTEGER sz, old_sz;
+					sz.QuadPart = 0;
+
+					if (!SetFilePointerEx(h, sz, &old_sz, FILE_CURRENT)) {
 						return PHP_STREAM_OPTION_RETURN_ERR;
 					}
 
-					LARGE_INTEGER sz;
 #if defined(_WIN64)
 					sz.HighPart = (new_size >> 32);
 					sz.LowPart = (new_size & 0xffffffff);