Fix #81302: Stream position after stream filter removed

When flushing the stream filters actually causes data to be written to
the stream, we need to update its position, because that is not done by
the streams' write methods.

Closes GH-7354.

NEWS

@@ -2,6 +2,8 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 7.4.24
 
+- Core:
+  . Fixed bug #81302 (Stream position after stream filter removed). (cmb)
 
 26 Aug 2021, PHP 7.4.23
 

ext/standard/tests/filters/bug81302.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Bug #81302 (Stream position after stream filter removed)
+--SKIPIF--
+<?php
+if (!extension_loaded('zlib')) die("skip zlib extension not available");
+?>
+--FILE--
+<?php
+$f = fopen("php://memory", "w+b");
+$z = stream_filter_append($f, "zlib.deflate", STREAM_FILTER_WRITE, 6);
+fwrite($f, "Testing");
+stream_filter_remove($z);
+$pos = ftell($f);
+fseek($f, 0);
+$count = strlen(fread($f, 1024));
+fclose($f);
+var_dump($count === $pos);
+?>
+--EXPECT--
+bool(true)

main/streams/filter.c

@@ -470,7 +470,10 @@ PHPAPI int _php_stream_filter_flush(php_stream_filter *filter, int finish)
 	} else if (chain == &(stream->writefilters)) {
 		/* Send flushed data to the stream */
 		while ((bucket = inp->head)) {
-			stream->ops->write(stream, bucket->buf, bucket->buflen);
+			ssize_t count = stream->ops->write(stream, bucket->buf, bucket->buflen);
+			if (count > 0) {
+				stream->position += count;
+			}
 			php_stream_bucket_unlink(bucket);
 			php_stream_bucket_delref(bucket);
 		}