1 files changed, 135 insertions, 0 deletions
diff --git a/doc/platform-requirements/multicast-local-addr.c b/doc/platform-requirements/multicast-local-addr.c
new file mode 100644
index 0000000..222b291
--- /dev/null
+++ b/doc/platform-requirements/multicast-local-addr.c
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/* multicast-local-addr.c
+ *
+ * Check behaviour of local address assignment when sending to multicast
+ * destinations.
+ *
+ * Copyright Red Hat
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ */
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "common.h"
+
+static struct sockaddr_in6 sa6_from_str(const char *addr, in_port_t port)
+{
+	struct sockaddr_in6 sa = {
+		.sin6_family = AF_INET6,
+		.sin6_port = htons(port),
+	};
+
+	if (!inet_pton(AF_INET6, addr, &sa.sin6_addr))
+		die("Couldn't parse address %s\n", addr);
+
+	return sa;
+}
+
+#define INET6_SADDRSTRLEN	(INET6_ADDRSTRLEN + 7)
+
+static const char *str_from_sa6(const struct sockaddr_in6 *sa,
+				char *buf, size_t size)
+{
+	char astr[INET6_ADDRSTRLEN];
+
+	if (!sa) {
+		if (snprintf(buf, size, "[*]:?") >= size)
+			die("Failed to format address");
+		return buf;
+	}
+
+	if (!inet_ntop(AF_INET6, &sa->sin6_addr, astr, sizeof(astr)))
+		die("Failed to format address");
+
+	if (snprintf(buf, size, "[%s]:%hu", astr, ntohs(sa->sin6_port)) >= size)
+		die("Failed to format address");
+
+	return buf;
+}
+
+/* Address used by bittorrent for local peer discovery
+ * This is a site-local multicast address.
+ */
+#define BITTORRENT_PORT		6771
+#define BITTORRENT_MC		sa6_from_str("ff15::efc0:988f", BITTORRENT_PORT)
+
+static void test_one(const struct sockaddr_in6 local,
+		     const struct sockaddr_in6 remote,
+		     int do_connect)
+{
+	char lstr[INET6_SADDRSTRLEN], rstr[INET6_SADDRSTRLEN];
+	struct sockaddr_in6 la;
+	socklen_t addrlen = sizeof(la);
+	const char data[] = "TEST";
+	int s;
+
+	printf("Testing %s -> %s %s\n", str_from_sa6(&local, lstr, sizeof(lstr)),
+	       str_from_sa6(&remote, rstr, sizeof(rstr)),
+	       do_connect ? "(connected)" : "");
+
+	s = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
+	if (s < 0)
+		die("socket() failed: %s\n", strerror(errno));
+	
+	if (bind(s, (const struct sockaddr *)&local, sizeof(local)))
+		die("bind() to %s failed: %s\n", lstr, strerror(errno));
+	if (do_connect &&
+	    connect(s, (const struct sockaddr *)&remote, sizeof(remote)))
+		die("connect() to %s failed: %s\n", rstr, strerror(errno));
+
+	if (do_connect) {
+		if (send(s, data, sizeof(data), 0) < 0)
+			die("send() failed: %s\n", strerror(errno));
+	} else {
+		if (sendto(s, data, sizeof(data), 0,
+			   (const struct sockaddr *)&remote, sizeof(remote)) < 0)
+			die("sendto() failed: %s\n", strerror(errno));
+	}
+
+	if (getsockname(s, (struct sockaddr *)&la, &addrlen))
+		die("getsockname() failed: %s\n", strerror(errno));
+
+	printf("Final local address: %s\n",
+	       str_from_sa6(&la, lstr, sizeof(lstr)));
+	close(s);
+}
+
+static void test_dest(const struct sockaddr_in6 remote)
+{
+	in_port_t rport = ntohs(remote.sin6_port);
+	const char *srcaddr[] = {"::", "::1"};
+	const in_port_t srcport[] = {0, rport};
+	int i, j, k;
+
+	for (i = 0; i < ARRAY_SIZE(srcaddr); i++) {
+		for (j = 0; j < ARRAY_SIZE(srcport); j++) {
+			struct sockaddr_in6 local;
+
+			local = sa6_from_str(srcaddr[i], srcport[j]);
+
+			for (k = 0; k <= 1; k++)
+				test_one(local, remote, k);
+		}
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	(void)argc;
+	(void)argv;
+
+	test_dest(BITTORRENT_MC);
+
+	printf("So far so good\n");
+	exit(0);
+}