Uri.IdnHost Property

Definition

Namespace:

System

Assemblies:

netstandard.dll, System.Runtime.dll

Source:

Uri.cs

Gets the RFC 3490 compliant International Domain Name of the host, using Punycode as appropriate. This string, after being unescaped if necessary, is safe to use for DNS resolution.

public:
 property System::String ^ IdnHost { System::String ^ get(); };

public string IdnHost { get; }

member this.IdnHost : string

Public ReadOnly Property IdnHost As String

Property Value

String

The hostname, formatted with Punycode according to the IDN standard.

Exceptions

InvalidOperationException

This instance represents a relative URI, and this property is valid only for absolute URIs.

Examples

The following example shows how Host and IdnHost differ across DNS, IDN, IPv4, and IPv6 inputs:

// Demonstrate differences between Host, IdnHost, and DnsSafeHost.

// Example 1: Regular hostname (ASCII).
Console.WriteLine("Example 1: Regular ASCII hostname");
Uri uri1 = new Uri("http://www.contoso.com:8080/path");
Console.WriteLine($"  Host:        {uri1.Host}");        // www.contoso.com
Console.WriteLine($"  IdnHost:     {uri1.IdnHost}");     // www.contoso.com
Console.WriteLine($"  DnsSafeHost: {uri1.DnsSafeHost}"); // www.contoso.com
Console.WriteLine();

// Example 2: International domain name (non-ASCII).
Console.WriteLine("Example 2: International domain name");
Uri uri2 = new Uri("http://münchen.de/path");
Console.WriteLine($"  Host:        {uri2.Host}");        // münchen.de (original)
Console.WriteLine($"  IdnHost:     {uri2.IdnHost}");     // xn--mnchen-3ya.de (punycode)
Console.WriteLine($"  DnsSafeHost: {uri2.DnsSafeHost}"); // münchen.de or xn--mnchen-3ya.de, depending on configuration.
Console.WriteLine();

// Example 3: International domain name already in punycode (encoded) form.
Console.WriteLine("Example 3: Already-encoded international domain name");
Uri uri2Encoded = new Uri("http://xn--mnchen-3ya.de/path");
Console.WriteLine($"  Host:        {uri2Encoded.Host}");        // xn--mnchen-3ya.de (as provided)
Console.WriteLine($"  IdnHost:     {uri2Encoded.IdnHost}");     // xn--mnchen-3ya.de (already punycode)
Console.WriteLine($"  DnsSafeHost: {uri2Encoded.DnsSafeHost}"); // xn--mnchen-3ya.de
Console.WriteLine();

// Example 4: IPv6 address without zone ID.
Console.WriteLine("Example 4: IPv6 address without zone ID");
Uri uri3 = new Uri("http://[::1]:8080/path");
Console.WriteLine($"  Host:        {uri3.Host}");        // [::1] (with brackets)
Console.WriteLine($"  IdnHost:     {uri3.IdnHost}");     // ::1 (without brackets)
Console.WriteLine($"  DnsSafeHost: {uri3.DnsSafeHost}"); // ::1 (without brackets)
Console.WriteLine();

// Example 5: IPv6 link-local address with zone ID.
Console.WriteLine("Example 5: IPv6 link-local address with zone ID");
Uri uri4 = new Uri("http://[fe80::1%10]:8080/path");
Console.WriteLine($"  Host:        {uri4.Host}");        // [fe80::1] (with brackets, no zone ID)
Console.WriteLine($"  IdnHost:     {uri4.IdnHost}");     // fe80::1%10 (without brackets, with zone ID)
Console.WriteLine($"  DnsSafeHost: {uri4.DnsSafeHost}"); // fe80::1%10 (without brackets, with zone ID)
Console.WriteLine();

// Example 6: IPv4 address.
Console.WriteLine("Example 6: IPv4 address");
Uri uri5 = new Uri("http://192.168.1.1:8080/path");
Console.WriteLine($"  Host:        {uri5.Host}");        // 192.168.1.1
Console.WriteLine($"  IdnHost:     {uri5.IdnHost}");     // 192.168.1.1
Console.WriteLine($"  DnsSafeHost: {uri5.DnsSafeHost}"); // 192.168.1.1

Remarks

This property is provided for the use of lower-level networking protocols that require the domain name in Punycode form. If your code does not require that specific format, use Host for the hostname.

The value returned by this property depends on the host type:

• For DNS host names: For valid international domain names, non-ASCII characters are punycode encoded (for example, münchen.de becomes xn--mnchen-3ya.de). Hostnames that aren't valid IDNs might be returned as-is and include non-ASCII characters.
• For IPv6 addresses: Returns the address without the surrounding brackets, and includes the zone ID (scope) if one was specified (for example, ::1 or fe80::1%18).
• For IPv4 addresses: Returns the dotted-decimal notation (for example, 192.168.1.1).

IdnHost is the preferred alternative to the legacy DnsSafeHost property, because its behavior doesn't depend on app.config settings and it's designed to produce a value suitable for DNS resolution. Note that for IPv6 results that include a zone ID, callers might still need to strip the zone ID before passing the value to APIs that don't accept it.

If you used an escaped string to construct this instance (for example, "http://[fe80::200:39ff:fe36:1a2d%254]/temp/example.htm"), then IdnHost returns an escaped string. You should unescape any escaped string returned from IdnHost before using that string for DNS resolution. Be aware that if you used an invalid unescaped string to construct this instance (for example, "http://[fe80::200:39ff:fe36:1a2d%4]/temp/example.htm"), then IdnHost returns an unescaped string.