Fixed bug #76803 ftruncate changes file pointer

ext/standard/tests/file/ftruncate_bug76803.phpt

@@ -0,0 +1,38 @@
+--TEST--
+Bug #76803 ftruncate changes file pointer
+--FILE--
+<?php
+
+$fn = dirname(__FILE__) . DIRECTORY_SEPARATOR . "test76803";
+
+$f = fopen($fn, "w");
+fwrite($f, "Hello");
+ftruncate($f, 2);
+fwrite($f, "World");
+fclose($f);
+var_dump(addslashes(file_get_contents($fn)));
+
+$f = fopen($fn, "w");
+fwrite($f, "Hello");
+ftruncate($f, 2);
+fclose($f);
+var_dump(addslashes(file_get_contents($fn)));
+
+$f = fopen('php://memory', 'w+');
+fwrite($f, 'Hello');
+ftruncate($f, 2); // in 7.3 changes file pointer to 2
+fwrite($f, 'World');
+rewind($f);
+var_dump(addslashes(stream_get_contents($f)));
+fclose($f);
+
+?>
+--CLEAN--
+<?php
+$fn = dirname(__FILE__) . DIRECTORY_SEPARATOR . "test76803";
+unlink($fn);
+?>
+--EXPECT--
+string(13) "He\0\0\0World"
+string(2) "He"
+string(7) "HeWorld"

main/streams/plain_wrapper.c

@@ -857,6 +857,12 @@ static int php_stdiop_set_option(php_stream *stream, int option, int value, void
 					if (INVALID_HANDLE_VALUE == h) {
 						return PHP_STREAM_OPTION_RETURN_ERR;
 					}
+
+					LARGE_INTEGER old_sz;
+					if (!GetFileSizeEx(h, &old_sz)) {
+						return PHP_STREAM_OPTION_RETURN_ERR;
+					}
+
 					LARGE_INTEGER sz;
 #if defined(_WIN64)
 					sz.HighPart = (new_size >> 32);
@@ -871,6 +877,9 @@ static int php_stdiop_set_option(php_stream *stream, int option, int value, void
 					if (0 == SetEndOfFile(h)) {
 						return PHP_STREAM_OPTION_RETURN_ERR;
 					}
+					if (INVALID_SET_FILE_POINTER == SetFilePointerEx(h, old_sz, NULL, FILE_BEGIN) && NO_ERROR != GetLastError()) {
+						return PHP_STREAM_OPTION_RETURN_ERR;
+					}
 					return PHP_STREAM_OPTION_RETURN_OK;
 #else
 					return ftruncate(fd, new_size) == 0 ? PHP_STREAM_OPTION_RETURN_OK : PHP_STREAM_OPTION_RETURN_ERR;