Allow filtered streams to be casted as fd for select

ext/standard/tests/streams/stream_select_filtered_base64_basic.phpt

@@ -0,0 +1,32 @@
+--TEST--
+stream_select() base64-decode filter basic usage
+--FILE--
+<?php
+$file = fopen('php://temp', 'r+');
+
+// Write complete base64 "Hello World"
+fwrite($file, 'SGVsbG8gV29ybGQ=');
+
+stream_filter_append($file, 'convert.base64-decode');
+rewind($file);
+
+$read = [$file];
+$write = null;
+$except = null;
+
+$result = stream_select($read, $write, $except, 0);
+
+if ($result !== false) {
+    echo "stream_select succeeded\n";
+    if (count($read) > 0) {
+        echo fread($file, 1024) . "\n";
+    }
+} else {
+    echo "stream_select failed\n";
+}
+
+fclose($file);
+?>
+--EXPECT--
+stream_select succeeded
+Hello World

ext/standard/tests/streams/stream_select_filtered_base64_buffered.phpt

@@ -0,0 +1,59 @@
+--TEST--
+stream_select() base64-decode filter buffered data usage
+--FILE--
+<?php
+$domain = (strtoupper(substr(PHP_OS, 0, 3) == 'WIN') ? STREAM_PF_INET : STREAM_PF_UNIX);
+$pipes = stream_socket_pair($domain, STREAM_SOCK_STREAM, 0);
+if ($pipes === false) {
+    die("Failed to create socket pair");
+}
+
+list($read_pipe, $write_pipe) = $pipes;
+
+stream_set_blocking($read_pipe, false);
+stream_filter_append($read_pipe, 'convert.base64-decode');
+
+// Write incomplete base64 data: "SGVs" decodes to "Hel" but "SGVs" is incomplete
+fwrite($write_pipe, 'SGVs');
+fflush($write_pipe);
+
+$read = [$read_pipe];
+$write = null;
+$except = null;
+
+$result = fread($read_pipe, 1024);
+echo "Decoded content (before select): " . $result . "\n";
+
+// Should succeed but stream should NOT be readable yet (data buffered in filter)
+$result = stream_select($read, $write, $except, 0, 1000);
+echo "After incomplete data - select result: " . $result . "\n";
+echo "After incomplete data - readable streams: " . count($read) . "\n";
+
+// Now complete the base64 sequence: "SGVsbG8=" decodes to "Hello"
+fwrite($write_pipe, 'bG8=');
+fflush($write_pipe);
+
+$read = [$read_pipe];
+$write = null;
+$except = null;
+
+// Now stream should be readable
+$result = stream_select($read, $write, $except, 0, 1000);
+echo "After complete data - select result: " . $result . "\n";
+echo "After complete data - readable streams: " . count($read) . "\n";
+
+if (count($read) > 0) {
+    $content = fread($read_pipe, 1024);
+    echo "Decoded content: " . $content . "\n";
+}
+
+fclose($read_pipe);
+fclose($write_pipe);
+?>
+--EXPECT--
+Decoded content (before select): Hel
+After incomplete data - select result: 0
+After incomplete data - readable streams: 0
+After complete data - select result: 1
+After complete data - readable streams: 1
+Decoded content: lo

main/streams/cast.c

@@ -297,7 +297,7 @@ PHPAPI zend_result _php_stream_cast(php_stream *stream, int castas, void **ret,
 		}
 	}
 
-	if (php_stream_is_filtered(stream)) {
+	if (php_stream_is_filtered(stream) && castas != PHP_STREAM_AS_FD_FOR_SELECT) {
 		if (show_err) {
 			php_error_docref(NULL, E_WARNING, "Cannot cast a filtered stream on this system");
 		}