/// <summary>
/// The <c>GetHostEntryAsync</c> method queries a DNS server for the IP addresses and aliases associated with the <paramref name="hostNameOrAddress"/>.
/// In case <paramref name="hostNameOrAddress"/> is an <see cref="IPAddress"/>, <c>GetHostEntry</c> does a reverse lookup on that first to determine the hostname.
/// <para>
/// IP addresses found are returned in <see cref="IPHostEntry.AddressList"/>.
/// <see cref="ResourceRecordType.CNAME"/> records are used to populate the <see cref="IPHostEntry.Aliases"/>.<br/>
/// The <see cref="IPHostEntry.HostName"/> property will be set to the resolved hostname or <paramref name="hostNameOrAddress"/>.
/// </para>
/// </summary>
/// <example>
/// The following code example uses the <see cref="GetHostEntryAsync(IDnsQuery, string)"/> method to resolve an IP address or hostname to an <see cref="IPHostEntry"/> instance.
/// <code>
/// <![CDATA[
/// public static async Task PrintHostEntry(string hostOrIp)
/// {
/// var lookup = new LookupClient();
/// IPHostEntry hostEntry = await lookup.GetHostEntryAsync(hostOrIp);
/// Console.WriteLine(hostEntry.HostName);
/// foreach (var ip in hostEntry.AddressList)
/// {
/// Console.WriteLine(ip);
/// }
/// foreach (var alias in hostEntry.Aliases)
/// {
/// Console.WriteLine(alias);
/// }
/// }
/// ]]>
/// </code>
/// </example>
/// <remarks>
/// The method has some logic to populate the <see cref="IPHostEntry.Aliases"/> list:
/// <list type="bullet">
/// <item>
/// <term>
/// In case of sub-domain queries or similar, there might be multiple <see cref="ResourceRecordType.CNAME"/> records for one <see cref="IPAddress"/>,
/// </term>
/// </item><item>
/// <term>
/// If only one <see cref="IPAddress"/> is in the result set, all the aliases found will be returned.
/// </term>
/// </item><item>
/// <term>
/// If more than one <see cref="IPAddress"/> is in the result set, aliases are returned only if at least one doesn't match the queried hostname.
/// </term>
/// </item>
/// </list>
/// </remarks>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="hostNameOrAddress">The <see cref="IPAddress"/> or host name to query for.</param>
/// <returns>
/// An <see cref="IPHostEntry"/> instance that contains address information about the host specified in <paramref name="hostNameOrAddress"/>.
/// In case the <paramref name="hostNameOrAddress"/> could not be resolved to a domain name, this method returns <c>null</c>,
/// unless <see cref="ILookupClient.ThrowDnsErrors"/> is set to true, then it might throw a <see cref="DnsResponseException"/>.
/// </returns>
/// <exception cref="ArgumentNullException">If <paramref name="hostNameOrAddress"/> is null.</exception>
/// <exception cref="DnsResponseException">In case <see cref="ILookupClient.ThrowDnsErrors"/> is set to true and a DNS error occurs.</exception>
public static Task <IPHostEntry> GetHostEntryAsync(this IDnsQuery query, string hostNameOrAddress)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (string.IsNullOrWhiteSpace(hostNameOrAddress))
{
throw new ArgumentNullException(nameof(hostNameOrAddress));
}
if (IPAddress.TryParse(hostNameOrAddress, out IPAddress address))
{
return(query.GetHostEntryAsync(address));
}
return(GetHostEntryFromNameAsync(query, hostNameOrAddress));
}