ipv6: Add support for RFC5014 for Linux

Linux has a sockopt flag defined by RFC5014 that informs IPv6 systems with
SLAAC config to prefer to bind the socket to a public address instead of
any temporary private address.

This patch adds a client info flag LCCSCF_IPV6_PREFER_PUBLIC_ADDR that lets
the user indicate the client socket should be prepared with the public
address binding preference.

Currently it's only implemented on Linux.

CMakeLists.txt

@@ -658,6 +658,7 @@ CHECK_C_SOURCE_COMPILES("#include <malloc.h>\nvoid main(void) { while(1) ; } voi
 CHECK_C_SOURCE_COMPILES("#include <pthread.h>\nvoid main(void) { while(1) ; } void xxexit(void){}" LWS_HAVE_PTHREAD_H)
 CHECK_C_SOURCE_COMPILES("#include <inttypes.h>\nvoid main(void) { while(1) ; } void xxexit(void){}" LWS_HAVE_INTTYPES_H)
 CHECK_C_SOURCE_COMPILES("#include <sys/resource.h>\nvoid main(void) { while(1) ; } void xxexit(void){}" LWS_HAVE_SYS_RESOURCE_H)
+CHECK_C_SOURCE_COMPILES("#include <linux/ipv6.h>\nvoid main(void) { while(1) ; } void xxexit(void){}" LWS_HAVE_LINUX_IPV6_H)
 
 if (LWS_EXT_PTHREAD_INCLUDE_DIR)
 	set(LWS_HAVE_PTHREAD_H 1)

cmake/lws_config.h.in

@@ -258,4 +258,4 @@
 #cmakedefine LWS_WITH_PLUGINS_API
 #cmakedefine LWS_HAVE_RTA_PREF
 #cmakedefine PICO_SDK_PATH
-
+#cmakedefine LWS_HAVE_LINUX_IPV6_H

include/libwebsockets/lws-client.h

@@ -56,6 +56,11 @@ enum lws_client_connect_ssl_connection_flags {
 	 * then it is not possible to bind to this port for any local address
 	 */
 
+	LCCSCF_IPV6_PREFER_PUBLIC_ADDR				= (1 << 15),
+	/**< RFC5014 - For IPv6 systems with SLAAC config, allow for preference
+	 * to bind a socket to public address vs temporary private address
+	 */
+
 	LCCSCF_PIPELINE				= (1 << 16),
 		/**< Serialize / pipeline multiple client connections
 		 * on a single connection where possible.

lib/plat/unix/unix-sockets.c

@@ -1,7 +1,7 @@
 /*
  * libwebsockets - small server side websockets and web server implementation
  *
- * Copyright (C) 2010 - 2019 Andy Green <andy@warmcat.com>
+ * Copyright (C) 2010 - 2023 Andy Green <andy@warmcat.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to
@@ -27,6 +27,10 @@
 #endif
 #include "private-lib-core.h"
 
+#if defined(LWS_HAVE_LINUX_IPV6_H)
+#include <linux/ipv6.h>
+#endif
+
 #include <sys/ioctl.h>
 
 #if !defined(LWS_DETECTED_PLAT_IOS)
@@ -273,6 +277,26 @@ lws_plat_set_socket_options_ip(lws_sockfd_type fd, uint8_t pri, int lws_flags)
 	}
 
 
+	if (lws_flags & LCCSCF_IPV6_PREFER_PUBLIC_ADDR) {
+#if defined(LWS_WITH_IPV6) && defined(IPV6_PREFER_SRC_PUBLIC)
+		optval = IPV6_PREFER_SRC_PUBLIC;
+
+		if (setsockopt(fd, IPPROTO_IPV6, IPV6_ADDR_PREFERENCES,
+						(const void *)&optval, optlen) < 0) {
+				#if (_LWS_ENABLED_LOGS & LLL_WARN)
+					en = errno;
+					lwsl_warn("%s: unable to set IPV6_PREFER_SRC_PUBLIC: errno %d\n",
+						__func__, en);
+				#endif
+				ret = 1;
+		} else
+			lwsl_notice("%s: set IPV6_PREFER_SRC_PUBLIC\n", __func__);
+#else
+		lwsl_err("%s: IPV6_PREFER_SRC_PUBLIC UNIMPLEMENTED on this platform\n", __func__);
+#endif
+	}
+
+
 #if !defined(__NuttX__)
 	for (n = 0; n < 4; n++) {
 		if (!(lws_flags & ip_opt_lws_flags[n]))

lib/plat/windows/windows-sockets.c

@@ -193,6 +193,16 @@ lws_plat_set_socket_options_ip(lws_sockfd_type fd, uint8_t pri, int lws_flags)
 		} else
 			lwsl_notice("%s: set use exclusive addresses\n", __func__);
 	}
+
+
+#if defined(LWS_WITH_IPV6)
+	/* I do not believe Microsoft supports RFC5014
+	 * Instead, you must set lws_client_connect_info::iface */
+	if (lws_flags & LCCSCF_IPV6_PREFER_PUBLIC_ADDR) {
+		lwsl_err("%s: UNIMPLEMENTED on this platform\n", __func__);
+	}
+#endif
+
 
 
 	return ret;