DNS Domain Name System

Functions
uint32_t	gethostbyname (char *hostname, int32_t *timeout)
	Get the ip address of clients specified by name. More...

Detailed Description

DNS Domain Name System

To enable the DNS lookup system net_init() must be called with parameter DNS_ENABLE and a DNS server address (ref. Software Initialization):

DNS server = 192.168.1.1

net_init ("192.168.1.100", "255.255.255.0", NULL, NULL, "192.168.1.1", DNS_ENABLE);

A hostname is automatically resolved when specified with socket_open(). E.g.:

tcp_socket = socket_open ("www.dsignt.de",
                          ANY_PORT,
                          5031,
                          DATATYPE_CHAR,
                          TCP_INIT_FUNC);

Also gethostbyname() can be used to determine the destination IP address:

int32_t timeout = 1000000;
uint32_t host_address;
int8_t buffer[20];

host_address = gethostbyname ("www.dsignt.de", &timeout);

if (host_address)
{
  tcp_socket = socket_open (inet_ntoa (host_address, buffer),
                            ANY_PORT,
                            5031,
                            DATATYPE_CHAR,
                            TCP_INIT_FUNC);
}
else
{
  printf ("www.dsignt.de can not be resolved\r\n");
}

Function Documentation

uint32_t gethostbyname	(	char *	hostname,
		int32_t *	timeout
	)

Parameters

hostname	- host name string
timeout	- maximum loop count for this blocking function

Returns

• FALSE - address resolution not possible
• host address on successful name resolution

Get the ip address of clients specified by name

Library:

net.lib

Prototype:

net.h

//****************************************************************************
//
//    @brief      perform DNS lookup
//
//    @param      hostname  - name to resolve
//    @param      max_retry - number of retries (useful on dial-up connection)
//    @return     resolved IP-address on success or zero (0) on error
//    @sa         gethostbyname() - netlib
//
//****************************************************************************
uint32_t resolve_name ( char *hostname, int max_retry )
{
  //**************************************************************************
  // locals
  //**************************************************************************
  uint32_t ret = 0;
  int32_t timeout;
  int i;

  for ( i = 0; i < max_retry ; i++ )
  {
    CPrintf (".");

    //************************************************************************
    //  configure timeout value to stop the loop if name resolution is not
    //  possible
    //************************************************************************
    timeout = 500000;

    //************************************************************************
    //  resolve address:
    //************************************************************************
    ret = gethostbyname (hostname, &timeout);

    if ( ret ) // on success stop loop
    {
      break;
    }
  }

  return (ret);
}

Examples:

DNSTest.c.