res_rtp: Fix regression when IPv6 is not available.

The latest Release candidate fails to create RTP streams when IPv6
is not available. Due to the changes made in September the ast_sockaddr
structure passed around to create these streams is always of AF_INET6
type, causing failure when used for IPv4. This patch adds a utility
function to check for availability of IPv6 and applies such check
at startup to determine how to create the ast_sockaddr structures.

ASTERISK-26617 #close

Change-Id: I627a4e91795e821111e1cda523f083a40d0e0c3e

include/asterisk/utils.h

@@ -1127,4 +1127,13 @@ int ast_file_is_readable(const char *filename);
  */
 int ast_compare_versions(const char *version1, const char *version2);
 
+/*
+ * \brief Test that an OS supports IPv6 Networking.
+ * \since 13.14.0
+ *
+ * \return True (non-zero) if the IPv6 supported.
+ * \return False (zero) if the OS doesn't support IPv6.
+ */
+int ast_check_ipv6(void);
+
 #endif /* _ASTERISK_UTILS_H */

main/utils.c

@@ -2425,6 +2425,18 @@ char *ast_utils_which(const char *binary, char *fullpath, size_t fullpath_size)
 	return NULL;
 }
 
+int ast_check_ipv6(void)
+{
+	int udp6_socket = socket(AF_INET6, SOCK_DGRAM, 0);
+
+	if (udp6_socket < 0) {
+		return 0;
+	}
+
+	close(udp6_socket);
+	return 1;
+}
+
 void DO_CRASH_NORETURN ast_do_crash(void)
 {
 #if defined(DO_CRASH)

res/res_pjsip_sdp_rtp.c

@@ -51,6 +51,7 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/acl.h"
 #include "asterisk/sdp_srtp.h"
 #include "asterisk/dsp.h"
+#include "asterisk/utils.h"
 
 #include "asterisk/res_pjsip.h"
 #include "asterisk/res_pjsip_session.h"
@@ -1493,7 +1494,11 @@ static int load_module(void)
 {
 	CHECK_PJSIP_SESSION_MODULE_LOADED();
 
-	ast_sockaddr_parse(&address_rtp, "::", 0);
+	if (ast_check_ipv6()) {
+		ast_sockaddr_parse(&address_rtp, "::", 0);
+	} else {
+		ast_sockaddr_parse(&address_rtp, "0.0.0.0", 0);
+	}
 
 	if (!(sched = ast_sched_context_create())) {
 		ast_log(LOG_ERROR, "Unable to create scheduler context.\n");

res/res_pjsip_t38.c

@@ -44,6 +44,7 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/netsock2.h"
 #include "asterisk/channel.h"
 #include "asterisk/acl.h"
+#include "asterisk/utils.h"
 
 #include "asterisk/res_pjsip.h"
 #include "asterisk/res_pjsip_session.h"
@@ -918,7 +919,11 @@ static int load_module(void)
 {
 	CHECK_PJSIP_SESSION_MODULE_LOADED();
 
-	ast_sockaddr_parse(&address, "::", 0);
+	if (ast_check_ipv6()) {
+		ast_sockaddr_parse(&address, "::", 0);
+	} else {
+		ast_sockaddr_parse(&address, "0.0.0.0", 0);
+	}
 
 	if (ast_sip_session_register_supplement(&t38_supplement)) {
 		ast_log(LOG_ERROR, "Unable to register T.38 session supplement\n");