} // GetHostName
/*****************************************************************************
* Function : resolve
*
* Abstract: Converts IP/hostnames to IP numerical address using DNS
* Additional methods provided for convenience
* (These methods will resolve strings and hostnames. In case of
* multiple IP addresses, the address returned is chosen arbitrarily.)
*
* Input Parameters: host/IP
*
* Returns: IPAddress
******************************************************************************/
/// <include file='doc\DNS.uex' path='docs/doc[@for="Dns.Resolve"]/*' />
/// <devdoc>
/// <para>Creates an <see cref='System.Net.IPAddress'/>
/// instance from a DNS hostname.</para>
/// </devdoc>
// UEUE
public static IPHostEntry Resolve(string hostName)
{
//
// demand Unrestricted DnsPermission for this call
//
s_DnsPermission.Demand();
//This is a perf optimization, this method call others that will demand and we already did that.
s_DnsPermission.Assert();
IPHostEntry ipHostEntry = null;
try {
if (hostName == null)
{
throw new ArgumentNullException("hostName");
}
GlobalLog.Print("Dns.Resolve: " + hostName);
//
// as a minor perf improvement, we'll look at the first character
// in the hostName and if that's a digit, call GetHostByAddress() first.
// note that GetHostByAddress() will succeed ONLY if the first character is a digit.
// hence if this is not the case, below, we will only call GetHostByName()
// specifically, on Win2k, only the following are valid:
// "11.22.33.44" - success
// "0x0B16212C" - success
// while these will fail or return bogus data (note the prepended spaces):
// " 11.22.33.44" - bogus data
// " 0x0B16212C" - bogus data
// " 0B16212C" - bogus data
// "0B16212C" - failure
//
// IPv6 support: added ':' as a legal character in IP addresses so that
// we can attempt gethostbyaddress first.
//
if (hostName.Length > 0 &&
((hostName[0] >= '0' && hostName[0] <= '9') || // Possible IPv4 or IPv6 numeric
(hostName.IndexOf(':') >= 0))) // Possible IPv6 numeric
{
try {
ipHostEntry = GetHostByAddress(hostName);
}
catch {
//
// this can fail for weird hostnames like 3com.com
//
}
}
if (ipHostEntry == null)
{
ipHostEntry = GetHostByName(hostName);
}
}
finally {
DnsPermission.RevertAssert();
}
return(ipHostEntry);
}
