Uri.CheckHostName(String) Method in C#

The Uri.CheckHostName() method in C# is used to determine the type of hostname specified in a string. It validates whether the given string represents a valid DNS name, IPv4 address, IPv6 address, or an unknown format.

Syntax

Following is the syntax −

public static UriHostNameType CheckHostName(string hostName);

Parameters

• hostName − A string that contains the hostname to validate.

Return Value

The method returns a UriHostNameType enumeration value that indicates the type of the hostname −

Using CheckHostName() with DNS Names

Example

using System;

public class Demo {
   public static void Main() {
      string hostname = "www.tutorialspoint.com";
      Console.WriteLine("Hostname = " + hostname);
      UriHostNameType result = Uri.CheckHostName(hostname);
      Console.WriteLine("Host type = " + result);
      
      string localhost = "localhost";
      Console.WriteLine("\nHostname = " + localhost);
      result = Uri.CheckHostName(localhost);
      Console.WriteLine("Host type = " + result);
   }
}

The output of the above code is −

Hostname = www.tutorialspoint.com
Host type = Dns

Hostname = localhost
Host type = Dns

Using CheckHostName() with IP Addresses

Example

using System;

public class Demo {
   public static void Main() {
      string ipv4 = "192.168.1.1";
      Console.WriteLine("IP Address = " + ipv4);
      UriHostNameType result = Uri.CheckHostName(ipv4);
      Console.WriteLine("Host type = " + result);
      
      string ipv6 = "2001:0db8:85a3:0000:0000:8a2e:0370:7334";
      Console.WriteLine("\nIP Address = " + ipv6);
      result = Uri.CheckHostName(ipv6);
      Console.WriteLine("Host type = " + result);
      
      string invalidHost = "http://localhost";
      Console.WriteLine("\nInvalid hostname = " + invalidHost);
      result = Uri.CheckHostName(invalidHost);
      Console.WriteLine("Host type = " + result);
   }
}

The output of the above code is −

IP Address = 192.168.1.1
Host type = IPv4

IP Address = 2001:0db8:85a3:0000:0000:8a2e:0370:7334
Host type = IPv6

Invalid hostname = http://localhost
Host type = Unknown

Practical Usage Example

Example

using System;

public class HostnameValidator {
   public static void ValidateHostname(string hostname) {
      UriHostNameType hostType = Uri.CheckHostName(hostname);
      
      switch (hostType) {
         case UriHostNameType.Dns:
            Console.WriteLine($"{hostname} is a valid DNS name");
            break;
         case UriHostNameType.IPv4:
            Console.WriteLine($"{hostname} is a valid IPv4 address");
            break;
         case UriHostNameType.IPv6:
            Console.WriteLine($"{hostname} is a valid IPv6 address");
            break;
         case UriHostNameType.Basic:
            Console.WriteLine($"{hostname} is a basic hostname");
            break;
         default:
            Console.WriteLine($"{hostname} is not a valid hostname");
            break;
      }
   }
   
   public static void Main() {
      ValidateHostname("google.com");
      ValidateHostname("127.0.0.1");
      ValidateHostname("::1");
      ValidateHostname("invalid..host");
   }
}

The output of the above code is −

google.com is a valid DNS name
127.0.0.1 is a valid IPv4 address
::1 is a valid IPv6 address
invalid..host is not a valid hostname

Conclusion

The Uri.CheckHostName() method is essential for validating hostname formats in network applications. It efficiently identifies DNS names, IPv4/IPv6 addresses, and invalid formats, making it useful for input validation and URL processing scenarios.