Preserve file-position when php://temp switches to temporary file

Closes GH-8333.

Author: bitbaendiger

NEWS

@@ -10,6 +10,10 @@ PHP                                                                        NEWS
   . Fixed bug GH-8267 (MySQLi uses unsupported format specifier on Windows).
     (cmb)
 
+- Streams:
+  . Fixed php://temp does not preserve file-position when switched to temporary
+    file. (Bernd Holzmüller)
+
 14 Apr 2022, PHP 8.0.18
 
 - Core:

ext/standard/tests/streams/temp_stream_seek.phpt

@@ -0,0 +1,20 @@
+--TEST--
+BUG: php://temp does not preserve file-pointer once it switches from memory to temporary file
+--FILE--
+<?php
+
+$f = fopen('php://temp/maxmemory:1024', 'r+');
+fwrite($f, str_repeat("1", 738));
+fseek($f, 0, SEEK_SET);
+fwrite($f, str_repeat("2", 512));
+
+fseek($f, 0, SEEK_SET);
+var_dump(fread($f, 16));
+
+fseek($f, 0, SEEK_END);
+var_dump(ftell($f));
+
+?>
+--EXPECT--
+string(16) "2222222222222222"
+int(738)

main/streams/memory.c

@@ -375,10 +375,11 @@ static ssize_t php_stream_temp_write(php_stream *stream, const char *buf, size_t
 		return -1;
 	}
 	if (php_stream_is(ts->innerstream, PHP_STREAM_IS_MEMORY)) {
-		size_t memsize;
-		char *membuf = php_stream_memory_get_buffer(ts->innerstream, &memsize);
-
-		if (memsize + count >= ts->smax) {
+		zend_off_t pos = php_stream_tell(ts->innerstream);
+		
+		if (pos + count >= ts->smax) {
+			size_t memsize;
+			char *membuf = php_stream_memory_get_buffer(ts->innerstream, &memsize);
 			php_stream *file = php_stream_fopen_temporary_file(ts->tmpdir, "php", NULL);
 			if (file == NULL) {
 				php_error_docref(NULL, E_WARNING, "Unable to create temporary file, Check permissions in temporary files directory.");
@@ -388,6 +389,7 @@ static ssize_t php_stream_temp_write(php_stream *stream, const char *buf, size_t
 			php_stream_free_enclosed(ts->innerstream, PHP_STREAM_FREE_CLOSE);
 			ts->innerstream = file;
 			php_stream_encloses(stream, ts->innerstream);
+			php_stream_seek(ts->innerstream, pos, SEEK_SET);
 		}
 	}
 	return php_stream_write(ts->innerstream, buf, count);