examples/mdnsd: Create an event-based starter for mDNS daemon

Start the mDNS daemon based on the event of getting a new IP
address for any of the system's network interfaces. This allows
DHCP client to trigger the mDNS daemon after getting a new IP
address, for instance.

Signed-off-by: Tiago Medicci <tiago.medicci@espressif.com>

examples/mdnsd/Makefile

@@ -26,11 +26,11 @@ include $(APPDIR)/Make.defs
 
 CSRCS = mdnsd_daemon.c
 
-MAINSRC = mdnsd_start.c mdnsd_stop.c
+MAINSRC = mdnsd_start.c mdnsd_stop.c mdnsd_event.c
 
 # MDNSD built-in application info
 
-PROGNAME = mdnsd_start mdnsd_stop
+PROGNAME = mdnsd_start mdnsd_stop mdnsd_event
 PRIORITY = SCHED_PRIORITY_DEFAULT
 STACKSIZE = $(CONFIG_DEFAULT_TASK_STACKSIZE)
 MODULE = $(CONFIG_EXAMPLES_MDNSD)

examples/mdnsd/mdnsd_event.c

@@ -0,0 +1,244 @@
+/****************************************************************************
+ * apps/examples/mdnsd/mdnsd_event.c
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <netpacket/if_addr.h>
+#include <netpacket/netlink.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#include "netutils/mdnsd.h"
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#define MDNSD_EVENT_BUFSIZE   512
+#define MDNSD_EVENT_SETTLE_MS 500
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: mdnsd_event_has_ipv4addr
+ *
+ * Description:
+ *   Check whether any network interface already has a non-zero IPv4
+ *   address.  Uses SIOCGIFCONF to enumerate interfaces.
+ *
+ * Returned Value:
+ *   true if at least one interface has a non-zero IPv4 address,
+ *   false otherwise.
+ *
+ ****************************************************************************/
+
+static bool mdnsd_event_has_ipv4addr(void)
+{
+  struct ifconf ifc;
+  char buf[sizeof(struct ifreq) * 4];
+  int sd;
+  int i;
+
+  sd = socket(AF_INET, SOCK_DGRAM, 0);
+  if (sd < 0)
+    {
+      return false;
+    }
+
+  ifc.ifc_len = sizeof(buf);
+  ifc.ifc_buf = buf;
+  if (ioctl(sd, SIOCGIFCONF, &ifc) < 0)
+    {
+      close(sd);
+      return false;
+    }
+
+  close(sd);
+
+  for (i = 0; i < ifc.ifc_len; i += sizeof(struct ifreq))
+    {
+      FAR struct ifreq *ifr = (FAR struct ifreq *)&buf[i];
+      FAR struct sockaddr_in *sin;
+
+      if (ifr->ifr_addr.sa_family != AF_INET)
+        {
+          continue;
+        }
+
+      sin = (FAR struct sockaddr_in *)&ifr->ifr_addr;
+      if (sin->sin_addr.s_addr != INADDR_ANY &&
+          sin->sin_addr.s_addr != htonl(INADDR_LOOPBACK))
+        {
+          return true;
+        }
+    }
+
+  return false;
+}
+
+/****************************************************************************
+ * Name: mdnsd_event_is_newaddr
+ *
+ * Description:
+ *   Checks whether the given Netlink message header represents a new
+ *   IPv4 or IPv6 address event (RTM_NEWADDR).
+ *
+ * Input Parameters:
+ *   hdr - Pointer to the Netlink message header to inspect.
+ *
+ * Returned Value:
+ *   true if the message is a new IPv4 or IPv6 address notification,
+ *   false otherwise.
+ *
+ ****************************************************************************/
+
+static bool mdnsd_event_is_newaddr(FAR struct nlmsghdr *hdr)
+{
+  FAR struct ifaddrmsg *addr;
+
+  if (hdr->nlmsg_type != RTM_NEWADDR)
+    {
+      return false;
+    }
+
+  if (hdr->nlmsg_len < NLMSG_LENGTH(sizeof(struct ifaddrmsg)))
+    {
+      return false;
+    }
+
+  addr = (FAR struct ifaddrmsg *)NLMSG_DATA(hdr);
+  return addr->ifa_family == AF_INET || addr->ifa_family == AF_INET6;
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: main
+ *
+ * Description:
+ *   Entry point for the mdnsd_event application.  Listens for Netlink
+ *   address events and starts the mDNS daemon when an IP address is
+ *   assigned to a network interface.
+ *
+ * Input Parameters:
+ *   argc - Number of command-line arguments.
+ *   argv - Array of command-line argument strings.
+ *
+ * Returned Value:
+ *   EXIT_SUCCESS on success, EXIT_FAILURE on error.
+ *
+ ****************************************************************************/
+
+int main(int argc, FAR char *argv[])
+{
+#ifdef CONFIG_NETLINK_ROUTE
+  struct sockaddr_nl addr;
+  uint8_t buffer[MDNSD_EVENT_BUFSIZE];
+  int sd;
+  int ret;
+
+  /* If an interface already has an IP (DHCP finished before we started),
+   * skip the netlink wait and start mDNS right away.
+   */
+
+  if (mdnsd_event_has_ipv4addr())
+    {
+      printf("mdnsd_event: address already set, starting mDNS\n");
+      usleep(MDNSD_EVENT_SETTLE_MS * 1000);
+      ret = mdnsd_start(CONFIG_EXAMPLES_MDNS_SERVICE,
+                         CONFIG_EXAMPLES_MDNS_SERVICE_PORT);
+      return ret < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+    }
+
+  sd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+  if (sd < 0)
+    {
+      fprintf(stderr, "mdnsd_event: socket failed: %d\n", errno);
+      return EXIT_FAILURE;
+    }
+
+  memset(&addr, 0, sizeof(addr));
+  addr.nl_family = AF_NETLINK;
+  addr.nl_groups = RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR;
+
+  ret = bind(sd, (FAR struct sockaddr *)&addr, sizeof(addr));
+  if (ret < 0)
+    {
+      fprintf(stderr, "mdnsd_event: bind failed: %d\n", errno);
+      close(sd);
+      return EXIT_FAILURE;
+    }
+
+  printf("mdnsd_event: waiting for network address event\n");
+
+  for (; ; )
+    {
+      FAR struct nlmsghdr *hdr;
+      ssize_t nread;
+      int remaining;
+
+      nread = recv(sd, buffer, sizeof(buffer), 0);
+      if (nread < 0)
+        {
+          fprintf(stderr, "mdnsd_event: recv failed: %d\n", errno);
+          close(sd);
+          return EXIT_FAILURE;
+        }
+
+      remaining = nread;
+      for (hdr = (FAR struct nlmsghdr *)buffer;
+           NLMSG_OK(hdr, remaining);
+           hdr = NLMSG_NEXT(hdr, remaining))
+        {
+          if (mdnsd_event_is_newaddr(hdr))
+            {
+              printf("mdnsd_event: address set, starting mDNS\n");
+              usleep(MDNSD_EVENT_SETTLE_MS * 1000);
+              ret = mdnsd_start(CONFIG_EXAMPLES_MDNS_SERVICE,
+                                CONFIG_EXAMPLES_MDNS_SERVICE_PORT);
+              close(sd);
+              return ret < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+            }
+        }
+    }
+#else
+  fprintf(stderr, "mdnsd_event: CONFIG_NETLINK_ROUTE is required\n");
+  return EXIT_FAILURE;
+#endif
+}