From e49be5f8e2903dbefa262847f1494c8e4c86004e Mon Sep 17 00:00:00 2001
From: Jakub Zelenka <bukka@php.net>
Date: Thu, 20 Nov 2025 17:18:35 +0100
Subject: [PATCH] Allow filtered streams to be casted as fd for select

This removes the artificial limitation that is not necessary. The fact
that some streams can have some data buffered is not a problem because
the similar situation is already present for OpenSSL streams where
OpenSSL can internally buffer data for the unprocessed part of the
record.

Closes GH-20540
---
 NEWS                                          |  1 +
 UPGRADING                                     |  1 +
 .../stream_select_filtered_base64_basic.phpt  | 32 ++++++++++
 ...tream_select_filtered_base64_buffered.phpt | 59 +++++++++++++++++++
 main/streams/cast.c                           |  2 +-
 5 files changed, 94 insertions(+), 1 deletion(-)
 create mode 100644 ext/standard/tests/streams/stream_select_filtered_base64_basic.phpt
 create mode 100644 ext/standard/tests/streams/stream_select_filtered_base64_buffered.phpt

diff --git a/NEWS b/NEWS
index 3b20cbb026c44..14b47a44d3863 100644
--- a/NEWS
+++ b/NEWS
@@ -79,6 +79,7 @@ PHP                                                                        NEWS
     address resuse.
   . Fixed bug GH-20370 (User stream filters could violate typed property
     constraints). (alexandre-daubois)
+  . Allowed filtered streams to be casted as fd for select. (Jakub Zelenka)
 
 - Zip:
   . Fixed ZipArchive callback being called after executor has shut down.
diff --git a/UPGRADING b/UPGRADING
index f9e506235197a..85cad750f0866 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -49,6 +49,7 @@ PHP 8.6 UPGRADE NOTES
   . Added stream socket context options so_keepalive, tcp_keepidle,
     tcp_keepintvl and tcp_keepcnt that allow setting socket keepalive
     options.
+  . Allowed casting casting filtered streams as file descriptor for select.
 
 ========================================
 3. Changes in SAPI modules
diff --git a/ext/standard/tests/streams/stream_select_filtered_base64_basic.phpt b/ext/standard/tests/streams/stream_select_filtered_base64_basic.phpt
new file mode 100644
index 0000000000000..f7ec2b6a4b542
--- /dev/null
+++ b/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($file);
+?>
+--EXPECT--
+stream_select succeeded
+Hello World
diff --git a/ext/standard/tests/streams/stream_select_filtered_base64_buffered.phpt b/ext/standard/tests/streams/stream_select_filtered_base64_buffered.phpt
new file mode 100644
index 0000000000000..4d11bf718a1bd
--- /dev/null
+++ b/ext/standard/tests/streams/stream_select_filtered_base64_buffered.phpt
@@ -0,0 +1,59 @@
+--TEST--
+stream_select() base64-decode filter buffered data usage
+--FILE--
+<?php
+$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
diff --git a/main/streams/cast.c b/main/streams/cast.c
index 4b7183024571b..4dc8ddb5f6a30 100644
--- a/main/streams/cast.c
+++ b/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");
 		}