Add API to get ipv6 link local address.

Protocols like mdns requires IPv6 link local address to be advertised in its
records (AAAA record). LWIP::Interface::bringup() API is creating IPv6 link
local address;But as of now there is no API exposed by mbed-os to get the
IPv6 link local address.

This new API is required to deliver mDNS library support on mbed-os for Cypress
platforms. Unit tested it by invoking get_ipv6_link_local_address with a simple
application.

Author: Jayasankar Nara

features/lwipstack/LWIPInterface.cpp

@@ -273,6 +273,21 @@ char *LWIP::Interface::get_interface_name(char *buf)
     return buf;
 }
 
+char *LWIP::Interface::get_ipv6_link_local_address(char *buf, nsapi_size_t buflen)
+{
+    const ip_addr_t *addr = LWIP::get_ipv6_link_local_addr(&netif);
+
+    if (!addr) {
+        return NULL;
+    }
+#if LWIP_IPV6
+    if (IP_IS_V6(addr)) {
+        return ip6addr_ntoa_r(ip_2_ip6(addr), buf, buflen);
+    }
+#endif
+    return NULL;
+}
+
 char *LWIP::Interface::get_ip_address(char *buf, nsapi_size_t buflen)
 {
     const ip_addr_t *addr = LWIP::get_ip_addr(true, &netif);

features/lwipstack/LWIPStack.h

@@ -100,6 +100,14 @@ class LWIP : public OnboardNetworkStack, private mbed::NonCopyable<LWIP> {
          */
         virtual char *get_ip_address(char *buf, nsapi_size_t buflen);
 
+        /** Copies IPv6 link local address of the network interface to user supplied buffer
+         *
+         * @param    buf        buffer to which IP address will be copied as "W:X:Y:Z"
+         * @param    buflen     size of supplied buffer
+         * @return              Pointer to a buffer, or NULL if the buffer is too small
+         */
+        char *get_ipv6_link_local_address(char *buf, nsapi_size_t buflen);
+
         /** Copies IP address of the name based network interface to user supplied buffer
          *
          * @param    buf        buffer to which IP address will be copied as "W:X:Y:Z"
@@ -548,6 +556,7 @@ class LWIP : public OnboardNetworkStack, private mbed::NonCopyable<LWIP> {
     static const ip_addr_t *get_ip_addr(bool any_addr, const struct netif *netif);
     static const ip_addr_t *get_ipv4_addr(const struct netif *netif);
     static const ip_addr_t *get_ipv6_addr(const struct netif *netif);
+    static const ip_addr_t *get_ipv6_link_local_addr(const struct netif *netif);
 
     static void add_dns_addr(struct netif *lwip_netif, const char *interface_name);
 

features/lwipstack/lwip_tools.cpp

@@ -74,6 +74,23 @@ const ip_addr_t *LWIP::get_ipv4_addr(const struct netif *netif)
     return NULL;
 }
 
+const ip_addr_t *LWIP::get_ipv6_link_local_addr(const struct netif *netif)
+{
+#if LWIP_IPV6
+    if (!netif_is_up(netif)) {
+        return NULL;
+    }
+
+    for (int i = 0; i < LWIP_IPV6_NUM_ADDRESSES; i++) {
+        if (ip6_addr_isvalid(netif_ip6_addr_state(netif, i)) &&
+                ip6_addr_islinklocal(netif_ip6_addr(netif, i))) {
+            return netif_ip_addr6(netif, i);
+        }
+    }
+#endif
+    return NULL;
+}
+
 const ip_addr_t *LWIP::get_ipv6_addr(const struct netif *netif)
 {
 #if LWIP_IPV6

features/netsocket/EMACInterface.cpp

@@ -95,6 +95,15 @@ const char *EMACInterface::get_ip_address()
     return NULL;
 }
 
+const char *EMACInterface::get_ipv6_link_local_address()
+{
+    if (_interface && _interface->get_ipv6_link_local_address(_ip_address, sizeof(_ip_address))) {
+        return _ip_address;
+    }
+
+    return NULL;
+}
+
 const char *EMACInterface::get_netmask()
 {
     if (_interface && _interface->get_netmask(_netmask, sizeof(_netmask))) {

features/netsocket/EMACInterface.h

@@ -102,6 +102,7 @@ class EMACInterface : public virtual NetworkInterface {
      *                  or null if no IP address has been received
      */
     virtual const char *get_ip_address();
+    virtual const char *get_ipv6_link_local_address();
 
     /** Get the local network mask
      *

features/netsocket/NetworkInterface.cpp

@@ -37,6 +37,11 @@ const char *NetworkInterface::get_ip_address()
     return 0;
 }
 
+const char *NetworkInterface::get_ipv6_link_local_address()
+{
+    return 0;
+}
+
 const char *NetworkInterface::get_netmask()
 {
     return 0;

features/netsocket/NetworkInterface.h

@@ -106,6 +106,8 @@ class NetworkInterface: public DNS {
      */
     virtual const char *get_ip_address();
 
+    virtual const char *get_ipv6_link_local_address();
+
     /** Get the local network mask.
      *
      *  @return         Null-terminated representation of the local network mask

features/netsocket/OnboardNetworkStack.h

@@ -118,6 +118,19 @@ class OnboardNetworkStack : public NetworkStack {
 
         virtual char *get_ip_address(char *buf, nsapi_size_t buflen) = 0;
 
+        /** Copies IPv6 link local address of the network interface to user supplied buffer
+         *
+         * @param    buf        buffer to which IP address will be copied as "W:X:Y:Z"
+         * @param    buflen     size of supplied buffer
+         * @param    interface_name  Network interface name
+         * @return              Pointer to a buffer, or NULL if the buffer is too small
+         */
+
+        virtual char *get_ipv6_link_local_address(char *buf, nsapi_size_t buflen)
+        {
+            return NULL;
+        }
+
         /** Copies IP address of the network interface to user supplied buffer
          *
          * @param    buf        buffer to which IP address will be copied as "W:X:Y:Z"