Add methods for setting hostname

In the same ways it is done for setting user MAC address, add methods
for setting hostname. The underlying network stack can then request this
to the local DNS through DHCP.

Author: guilhermerc

connectivity/netsocket/include/netsocket/EMACInterface.h

@@ -86,6 +86,12 @@ class EMACInterface : public virtual NetworkInterface {
     /** @copydoc NetworkInterface::disconnect */
     nsapi_error_t disconnect() override;
 
+    /** @copydoc NetworkInterface::get_hostname */
+    const char *get_hostname() override;
+
+    /** @copydoc NetworkInterface::set_hostname */
+    nsapi_error_t set_hostname(const char *hostname) override;
+
     /** @copydoc NetworkInterface::get_mac_address */
     const char *get_mac_address() override;
 
@@ -149,6 +155,8 @@ class EMACInterface : public virtual NetworkInterface {
     OnboardNetworkStack::Interface *_interface = nullptr;
     bool _dhcp = true;
     bool _blocking = true;
+    bool _hostname_set = false;
+    char _hostname[NSAPI_HOSTNAME_SIZE];
     bool _hw_mac_addr_set = false;
     char _mac_address[NSAPI_MAC_SIZE];
     char _ip_address[NSAPI_IPv6_SIZE] {};

connectivity/netsocket/include/netsocket/NetworkInterface.h

@@ -90,6 +90,24 @@ class NetworkInterface: public DNS {
      */
     virtual void set_as_default();
 
+    /** Get hostname.
+     *
+     *  @return         Hostname if configured, null otherwise
+     */
+    virtual const char *get_hostname();
+
+    /** Set hostname.
+     *
+     *  @param          hostname Hostname string
+     *  @retval         NSAPI_ERROR_OK on success
+     *  @retval         NSAPI_ERROR_UNSUPPORTED if this feature is not supported
+     *  @retval         NSAPI_ERROR_PARAMETER if hostname is not valid
+     *  @retval         NSAPI_ERROR_BUSY if hostname couldn't be set (e.g. for
+     *                  LwIP stack, hostname can only be set before calling
+     *                  \c EthernetInterface::connect method)
+     */
+    virtual nsapi_error_t set_hostname(const char *hostname);
+
     /** Get the local MAC address.
      *
      *  Provided MAC address is intended for info or debug purposes and

connectivity/netsocket/include/netsocket/nsapi_types.h

@@ -196,6 +196,16 @@ typedef enum nsapi_security {
  */
 #define NSAPI_IP_BYTES NSAPI_IPv6_BYTES
 
+/** Maximum size of hostname
+ *
+ *  According to RFC 1034 [1], Section 3.1 "Name space specifications and
+ *  terminology", 63 is the maximum size of a hostname. +1 for the string
+ *  terminator.
+ *
+ *  [1] https://www.rfc-editor.org/rfc/rfc1034
+ */
+#define NSAPI_HOSTNAME_SIZE 64
+
 /** Maximum size of MAC address representation
  */
 #define NSAPI_MAC_SIZE 18

connectivity/netsocket/source/EMACInterface.cpp

@@ -88,6 +88,32 @@ nsapi_error_t EMACInterface::disconnect()
     return NSAPI_ERROR_NO_CONNECTION;
 }
 
+const char *EMACInterface::get_hostname()
+{
+    if (_hostname_set) {
+        return _hostname;
+    }
+    return nullptr;
+}
+
+nsapi_error_t EMACInterface::set_hostname(const char *hostname)
+{
+    if (!hostname || strlen(hostname) > NSAPI_HOSTNAME_SIZE-1) {
+        return NSAPI_ERROR_PARAMETER;
+    }
+
+    if (_interface) {
+        // can't set hostname once initialized
+        return NSAPI_ERROR_BUSY;
+    }
+
+    memset(_hostname, 0, NSAPI_HOSTNAME_SIZE);
+    strncpy(_hostname, hostname, NSAPI_HOSTNAME_SIZE-1);
+    _hostname_set = true;
+
+    return NSAPI_ERROR_OK;
+}
+
 const char *EMACInterface::get_mac_address()
 {
     if (_interface && _interface->get_mac_address(_mac_address, sizeof(_mac_address))) {

connectivity/netsocket/source/NetworkInterface.cpp

@@ -29,6 +29,16 @@ void NetworkInterface::set_as_default()
 
 }
 
+const char *NetworkInterface::get_hostname()
+{
+    return 0;
+}
+
+nsapi_error_t NetworkInterface::set_hostname(const char *hostname)
+{
+    return NSAPI_ERROR_UNSUPPORTED;
+}
+
 const char *NetworkInterface::get_mac_address()
 {
     return 0;