Add small multicast server demo for mongoose

PUBLISHED_FROM=c5f6b0c64bc1e43030743b6aae5d06ae231df5dc

examples/mcast_udp_server/Makefile

+PROG = mcast_udp_server
+
+ifeq ($(OS),Windows_NT)
+all:
+	@echo "This example is not yet supported on $(OS)"
+else
+include ../examples.mk
+endif
+
+clean:

examples/mcast_udp_server/mcast_udp_server.c

+// Copyright (c) 2016 Cesanta Software Limited
+// All rights reserved
+//
+// This software is dual-licensed: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License version 2 as
+// published by the Free Software Foundation. For the terms of this
+// license, see <http://www.gnu.org/licenses/>.
+//
+// You are free to use this software under the terms of the GNU General
+// Public License, but WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU General Public License for more details.
+//
+// Alternatively, you can license this software under a commercial
+// license, as set out in <https://www.cesanta.com/license>.
+//
+// This demo shows how to configure a mongoose UDP connection to receive
+// multicast traffic.
+
+#include <netinet/in.h>
+
+#include "mongoose.h"
+
+#define MCAST_GROUP "224.0.22.1"
+#define DEFAULT_PORT "1234"
+
+static void ev_handler(struct mg_connection *nc, int ev, void *p) {
+  struct mbuf *io = &nc->recv_mbuf;
+  (void) p;
+  switch (ev) {
+    case MG_EV_RECV:
+      printf("Received (%zu bytes): '%.*s'\n", io->len, (int) io->len, io->buf);
+      mbuf_remove(io, io->len);
+      nc->flags |= MG_F_SEND_AND_CLOSE;
+      break;
+    default:
+      break;
+  }
+}
+
+void usage(char **argv) {
+  fprintf(stderr, "%s: -i address_of_mcast_interface [ -g %s ] [ -p %s ]\n",
+          argv[0], MCAST_GROUP, DEFAULT_PORT);
+  exit(1);
+}
+
+int main(int argc, char **argv) {
+  struct mg_mgr mgr;
+  const char *port = "1234";
+  struct mg_connection *nc;
+  struct ip_mreq group;
+  const char *interface = NULL;
+  const char *mcast_group = MCAST_GROUP;
+  int i;
+
+  /* Parse command line arguments */
+  for (i = 1; i < argc; i++) {
+    // IP address of the interface where to join a multicast group.
+    if (strcmp(argv[i], "-i") == 0) {
+      interface = argv[++i];
+    } else if (strcmp(argv[i], "-g") == 0) {
+      mcast_group = argv[++i];
+    } else if (strcmp(argv[i], "-p") == 0) {
+      port = argv[++i];
+    }
+  }
+
+  if (interface == NULL) {
+    usage(argv);
+  }
+
+  mg_mgr_init(&mgr, NULL);
+  {
+    char listen[256];
+    sprintf(listen, "udp://%s", port);
+    nc = mg_bind(&mgr, listen, ev_handler);
+  }
+
+  if (nc == NULL) {
+    perror("cannot bind\n");
+    exit(1);
+  }
+
+  group.imr_multiaddr.s_addr = inet_addr(mcast_group);
+  group.imr_interface.s_addr = inet_addr(interface);
+  if (setsockopt(nc->sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *) &group,
+                 sizeof(group)) < 0) {
+    perror("Adding multicast group error");
+    exit(1);
+  }
+
+  printf("Starting mcast server on port %s listening to group %s\n", port,
+         mcast_group);
+  for (;;) {
+    mg_mgr_poll(&mgr, 1000);
+  }
+  mg_mgr_free(&mgr);
+
+  return 0;
+}