netdb/lib_dnsdelserver.c: support delete the DNS server address

by index or address

 - dns_del_nameserver()
 - dns_del_nameserver_by_index()

Update the "DNS function" section in 11_network.rst, and create
the netlib API documentation in netlib/index.rst

Signed-off-by: nuttxs <zhaoqing.zhang@sony.com>

Documentation/reference/user/11_network.rst

@@ -413,3 +413,114 @@ the following paragraphs.
   -  ``NOBUFS``. Insufficient resources are available in the system to
      complete the call.
 
+=============
+DNS Functions
+=============
+
+NuttX provides DNS resolver functions for configuring and managing DNS
+servers. These functions are defined in ``nuttx/net/dns.h`` and allow
+applications to add, remove, and query DNS nameservers.
+
+  - :c:func:`dns_add_nameserver`
+  - :c:func:`dns_del_nameserver`
+  - :c:func:`dns_del_nameserver_by_index`
+  - :c:func:`dns_default_nameserver`
+  - :c:func:`dns_foreach_nameserver`
+  - :c:func:`dns_register_notify`
+  - :c:func:`dns_unregister_notify`
+  - :c:func:`dns_set_queryfamily`
+
+.. c:function:: int dns_add_nameserver(const struct sockaddr *addr, socklen_t addrlen);
+
+  Configure a DNS server to use for queries. Set the port number to zero
+  to use the default DNS server port (53).
+
+  :param addr: Address of the DNS server (sockaddr_in or sockaddr_in6).
+  :param addrlen: Length of the address structure.
+
+  :return: 0 on success; -1 on error with ``errno`` set appropriately:
+
+    -  ``EINVAL``. Invalid argument.
+    -  ``ENOMEM``. Insufficient memory to add the new DNS server.
+
+.. c:function:: int dns_del_nameserver(const struct sockaddr *addr, socklen_t addrlen);
+
+  Remove a DNS server from the list by address.
+
+  :param addr: Address of the DNS server to remove.
+  :param addrlen: Length of the address structure.
+
+  :return: 0 on success; -1 on error with ``errno`` set appropriately:
+
+    -  ``EINVAL``. Invalid argument.
+    -  ``ENOENT``. The specified DNS server was not found.
+
+.. c:function:: int dns_del_nameserver_by_index(int index);
+
+  Remove a DNS server from the list by index (0-based).
+
+  :param index: Index of the DNS server in the list (0-based).
+
+  :return: 0 on success; -1 on error with ``errno`` set appropriately:
+
+    -  ``EINVAL``. Invalid index.
+
+.. c:function:: int dns_default_nameserver(void);
+
+  Reset the resolver to use only the default DNS server, if any. This function
+  clears all added DNS servers and restores the default configuration.
+
+  :return: 0 on success; -1 on error.
+
+.. c:function:: int dns_foreach_nameserver(dns_callback_t callback, void *arg);
+
+  Traverse each nameserver entry and perform the provided callback.
+
+  :param callback: Callback function to invoke for each DNS server. The callback
+                   prototype is: ``int (*callback)(void *arg, struct sockaddr *addr, socklen_t addrlen)``
+  :param arg: User argument to pass to the callback function.
+
+  :return: 0 on success; -1 on error with ``errno`` set appropriately.
+           If the callback returns a non-zero value, traversal stops and that value is returned.
+
+    -  ``EINVAL``. Callback function pointer is NULL.
+
+.. c:function:: int dns_register_notify(dns_callback_t callback, void *arg);
+
+  Register a callback function to receive nameserver change notifications. When the
+  DNS server list changes (servers added or removed), registered callbacks will be invoked.
+
+  :param callback: Callback function to invoke on nameserver changes.
+  :param arg: User argument to pass to the callback function.
+
+  :return: 0 on success; -1 on error with ``errno`` set appropriately:
+
+    -  ``EINVAL``. Callback function pointer is NULL.
+    -  ``ENOMEM``. Insufficient memory to register the notification.
+
+.. c:function:: int dns_unregister_notify(dns_callback_t callback, void *arg);
+
+  Unsubscribe from nameserver change notifications.
+
+  :param callback: Callback function to unregister.
+  :param arg: User argument provided during registration.
+
+  :return: 0 on success; -1 on error with ``errno`` set appropriately:
+
+    -  ``EINVAL``. Callback function pointer is NULL.
+    -  ``ENOENT``. The specified callback was not found.
+
+.. c:function:: int dns_set_queryfamily(sa_family_t family);
+
+  Configure the address family to be used for queries.
+
+  :param family: Address family, can be:
+
+    -  ``AF_INET``: Use IPv4 for DNS queries.
+    -  ``AF_INET6``: Use IPv6 for DNS queries.
+    -  ``AF_UNSPEC``: Automatic selection (prefer IPv6, fallback to IPv4).
+
+  :return: 0 on success; -1 on error with ``errno`` set appropriately:
+
+    -  ``EINVAL``. Unsupported address family.
+

include/nuttx/net/dns.h

@@ -2,7 +2,10 @@
  * include/nuttx/net/dns.h
  *
  * SPDX-License-Identifier: BSD-3-Clause
- * SPDX-FileCopyrightText: 2007-2009, 2011-2012, 2014-2015, 2018 Gregory Nutt. All rights reserved.
+ * SPDX-FileCopyrightText: 2018 Gregory Nutt. All rights reserved.
+ * SPDX-FileCopyrightText: 2014-2015 Gregory Nutt. All rights reserved.
+ * SPDX-FileCopyrightText: 2011-2012 Gregory Nutt. All rights reserved.
+ * SPDX-FileCopyrightText: 2007-2009 Gregory Nutt. All rights reserved.
  * SPDX-FileCopyrightText: 2002-2003, Adam Dunkels. All rights reserved.
  * SPDX-FileContributor: Gregory Nutt <gnutt@nuttx.org>
  * SPDX-FileContributor: Adam Dunkels <adam@dunkels.com>
@@ -203,6 +206,26 @@ extern "C"
 
 int dns_add_nameserver(FAR const struct sockaddr *addr, socklen_t addrlen);
 
+/****************************************************************************
+ * Name: dns_del_nameserver
+ *
+ * Description:
+ *   Remove a DNS server from the list by address.
+ *
+ ****************************************************************************/
+
+int dns_del_nameserver(FAR const struct sockaddr *addr, socklen_t addrlen);
+
+/****************************************************************************
+ * Name: dns_del_nameserver_by_index
+ *
+ * Description:
+ *   Remove a DNS server from the list by index (0-based).
+ *
+ ****************************************************************************/
+
+int dns_del_nameserver_by_index(int index);
+
 /****************************************************************************
  * Name: dns_default_nameserver
  *

libs/libc/netdb/CMakeLists.txt

@@ -59,7 +59,8 @@ if(CONFIG_LIBC_NETDB)
 
   if(CONFIG_NETDB_DNSCLIENT)
     list(APPEND SRCS lib_dnsinit.c lib_dnsbind.c lib_dnsquery.c)
-    list(APPEND SRCS lib_dnsaddserver.c lib_dnsdefaultserver.c)
+    list(APPEND SRCS lib_dnsaddserver.c lib_dnsdelserver.c
+         lib_dnsdefaultserver.c)
     list(APPEND SRCS lib_dnsforeach.c lib_dnsnotify.c)
     list(APPEND SRCS lib_dnsqueryfamily.c)
 

libs/libc/netdb/Make.defs

@@ -44,7 +44,7 @@ endif
 
 ifeq ($(CONFIG_NETDB_DNSCLIENT),y)
 CSRCS += lib_dnsinit.c lib_dnsbind.c lib_dnsquery.c
-CSRCS += lib_dnsaddserver.c lib_dnsdefaultserver.c
+CSRCS += lib_dnsaddserver.c lib_dnsdelserver.c lib_dnsdefaultserver.c
 CSRCS += lib_dnsforeach.c lib_dnsnotify.c
 CSRCS += lib_dnsqueryfamily.c
 

libs/libc/netdb/lib_dnsdelserver.c

@@ -0,0 +1,227 @@
+/****************************************************************************
+ * libs/libc/netdb/lib_dnsdelserver.c
+ *
+ * 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 <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <debug.h>
+
+#include <nuttx/net/ip.h>
+#include <nuttx/net/dns.h>
+
+#include "netdb/lib_dns.h"
+
+#ifdef CONFIG_NETDB_DNSCLIENT
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+#ifndef CONFIG_NETDB_RESOLVCONF
+
+static int dns_find_nameserver_index(FAR const struct sockaddr *addr,
+                                     socklen_t addrlen)
+{
+  size_t cmplen = 0;
+  int i;
+
+#ifdef CONFIG_NET_IPv4
+  if (addr->sa_family == AF_INET)
+    {
+      cmplen = sizeof(struct sockaddr_in);
+    }
+#endif
+
+#ifdef CONFIG_NET_IPv6
+  if (addr->sa_family == AF_INET6)
+    {
+      cmplen = sizeof(struct sockaddr_in6);
+    }
+#endif
+
+  if (cmplen == 0)
+    {
+      /* Unsupported address family */
+
+      return -ENOSYS;
+    }
+
+  if (addrlen < cmplen)
+    {
+      return -EINVAL;
+    }
+
+  dns_lock();
+
+  /* Search for the matching nameserver in the array */
+
+  for (i = 0; i < g_dns_nservers; i++)
+    {
+      if (g_dns_servers[i].addr.sa_family == addr->sa_family)
+        {
+#ifdef CONFIG_NET_IPv4
+          if (addr->sa_family == AF_INET)
+            {
+              FAR struct sockaddr_in *in1 =
+                  (FAR struct sockaddr_in *)&g_dns_servers[i].addr;
+              FAR struct sockaddr_in *in2 =
+                  (FAR struct sockaddr_in *)addr;
+
+              /* Compare only the IP address part, ignore port and padding */
+
+              if (net_ipv4addr_cmp(in1->sin_addr.s_addr,
+                                   in2->sin_addr.s_addr))
+                {
+                  dns_unlock();
+                  return i;
+                }
+            }
+#endif
+
+#ifdef CONFIG_NET_IPv6
+          if (addr->sa_family == AF_INET6)
+            {
+              FAR struct sockaddr_in6 *in6_1 =
+                  (FAR struct sockaddr_in6 *)&g_dns_servers[i].addr;
+              FAR struct sockaddr_in6 *in6_2 =
+                  (FAR struct sockaddr_in6 *)addr;
+
+              /* Compare only the IPv6 address part */
+
+              if (net_ipv6addr_cmp(in6_1->sin6_addr.s6_addr,
+                                   in6_2->sin6_addr.s6_addr))
+                {
+                  dns_unlock();
+                  return i;
+                }
+            }
+#endif
+        }
+    }
+
+  dns_unlock();
+  return -ENOENT;
+}
+
+#endif /* !CONFIG_NETDB_RESOLVCONF */
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: dns_del_nameserver
+ *
+ * Description:
+ *   Remove a DNS server from the list by matching the address
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDB_RESOLVCONF
+
+int dns_del_nameserver(FAR const struct sockaddr *addr, socklen_t addrlen)
+{
+  /* Not implemented for CONFIG_NETDB_RESOLVCONF */
+
+  return -ENOSYS;
+}
+
+int dns_del_nameserver_by_index(int index)
+{
+  /* For resolv.conf mode, removing requires rewriting the file */
+
+  return -ENOSYS;
+}
+
+#else /* !CONFIG_NETDB_RESOLVCONF */
+
+int dns_del_nameserver(FAR const struct sockaddr *addr, socklen_t addrlen)
+{
+  int index;
+
+  if (addr == NULL)
+    {
+      return -EINVAL;
+    }
+
+  /* Find the nameserver in the array */
+
+  index = dns_find_nameserver_index(addr, addrlen);
+  if (index < 0)
+    {
+      return index;  /* Return the error code */
+    }
+
+  /* Remove the server by index */
+
+  return dns_del_nameserver_by_index(index);
+}
+
+int dns_del_nameserver_by_index(int index)
+{
+  int i;
+
+  if (index < 0 || index >= CONFIG_NETDB_DNSSERVER_NAMESERVERS)
+    {
+      return -EINVAL;
+    }
+
+  dns_lock();
+
+  if (index >= g_dns_nservers)
+    {
+      dns_unlock();
+      return -ENOENT;
+    }
+
+  /* Shift all subsequent entries down by one position */
+
+  for (i = index; i < g_dns_nservers - 1; i++)
+    {
+      memcpy(&g_dns_servers[i], &g_dns_servers[i + 1],
+             sizeof(union dns_addr_u));
+    }
+
+  memset(&g_dns_servers[g_dns_nservers - 1], 0, sizeof(union dns_addr_u));
+
+  /* Decrement the server count */
+
+  g_dns_nservers--;
+
+  dns_unlock();
+
+#if CONFIG_NETDB_DNSCLIENT_ENTRIES > 0
+  /* Clear the DNS cache after removing a server */
+
+  dns_clear_answer();
+#endif
+
+  return OK;
+}
+
+#endif /* CONFIG_NETDB_RESOLVCONF */
+#endif /* CONFIG_NETDB_DNSCLIENT */