socket DF flag on UDP socket via IP_MTU_DISCOVER on Linux and IP_DONTFRAGMENT on FreeBSD for path MTU discovery purpose.

idea proposal via ml :
https://marc.info/?l=php-internals&m=167329288509393&w=2

Close GH-10282

Author: devnexen

NEWS

@@ -86,6 +86,7 @@ PHP                                                                        NEWS
   . Added socket_atmark if send/recv needs using MSG_OOB. (David Carlier)
   . Added TCP_QUICKACK constant, to give tigher control over
     ACK delays. (David Carlier)
+  . Added DONTFRAGMENT support for path MTU discovery purpose. (David Carlier)
 
 - Standard:
   . E_NOTICEs emitted by unserialize() have been promoted to E_WARNING. (timwolla)

UPGRADING

@@ -117,6 +117,14 @@ PHP 8.3 UPGRADE NOTES
 - Sockets:
   . SO_ATTACH_REUSEPORT_CBPF (Linux only).
   . TCP_QUICKACK (Linux only).
+  . IP_DONTFRAG (FreeBSD only).
+  . IP_MTU_DISCOVER (Linux only).
+  . IP_PMTUDISC_DO (Linux only).
+  . IP_PMTUDISC_DONT (Linux only).
+  . IP_PMTUDISC_WANT (Linux only).
+  . IP_PMTUDISC_PROBE (Linux only).
+  . IP_PMTUDISC_INTERFACE (Linux only).
+  . IP_PMTUDISC_OMIT (Linux only).
 
 ========================================
 11. Changes to INI File Handling

ext/sockets/sockets.stub.php

@@ -1706,6 +1706,62 @@
  */
 const TCP_QUICKACK = UNKNOWN;
 #endif
+#if defined(IP_DONTFRAG)
+/**
+ * @var int
+ * @cvalue IP_DONTFRAG
+ */
+const IP_DONTFRAG = UNKNOWN;
+#endif
+#if defined(IP_MTU_DISCOVER)
+/**
+ * @var int
+ * @cvalue IP_MTU_DISCOVER
+ */
+const IP_MTU_DISCOVER = UNKNOWN;
+#endif
+#if defined(IP_PMTUDISC_DO)
+/**
+ * @var int
+ * @cvalue IP_PMTUDISC_DO
+ */
+const IP_PMTUDISC_DO = UNKNOWN;
+#endif
+#if defined(IP_PMTUDISC_DONT)
+/**
+ * @var int
+ * @cvalue IP_PMTUDISC_DONT
+ */
+const IP_PMTUDISC_DONT = UNKNOWN;
+#endif
+#if defined(IP_PMTUDISC_WANT)
+/**
+ * @var int
+ * @cvalue IP_PMTUDISC_WANT
+ */
+const IP_PMTUDISC_WANT = UNKNOWN;
+#endif
+#if defined(IP_PMTUDISC_PROBE)
+/**
+ * @var int
+ * @cvalue IP_PMTUDISC_PROBE
+ */
+const IP_PMTUDISC_PROBE = UNKNOWN;
+#endif
+#if defined(IP_PMTUDISC_INTERFACE)
+/**
+ * @var int
+ * @cvalue IP_PMTUDISC_INTERFACE
+ */
+const IP_PMTUDISC_INTERFACE = UNKNOWN;
+#endif
+#if defined(IP_PMTUDISC_OMIT)
+/**
+ * @var int
+ * @cvalue IP_PMTUDISC_OMIT
+ */
+const IP_PMTUDISC_OMIT = UNKNOWN;
+#endif
 
 /**
  * @strict-properties

ext/sockets/sockets_arginfo.h

@@ -0,0 +1,19 @@
+--TEST--
+IP_MTU_DISCOVER test
+--EXTENSIONS--
+sockets
+--SKIPIF--
+<?php
+if (PHP_OS != 'Linux') {
+    die('skip For Linux only');
+}
+?>
+--FILE--
+<?php
+$socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
+socket_bind($socket, '127.0.0.1', 5557);
+$ret = socket_set_option($socket, IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_DO);
+var_dump($ret);
+?>
+--EXPECT--
+bool(true)

ext/sockets/tests/socket_dontfragment.phpt

@@ -0,0 +1,19 @@
+--TEST--
+IP_DONTFRAG test
+--EXTENSIONS--
+sockets
+--SKIPIF--
+<?php
+if (PHP_OS != 'FreeBSD') {
+    die('skip For FreeBSD only');
+}
+?>
+--FILE--
+<?php
+$socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
+socket_bind($socket, '127.0.0.1', 5557);
+$ret = socket_set_option($socket, IPPROTO_IP, IP_DONTFRAG, 1);
+var_dump($ret);
+?>
+--EXPECT--
+bool(true)