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// Copyright 2024 Michael Conrad.
// Licensed under the Apache License, Version 2.0.
// See LICENSE file for details.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Threading.Tasks;
using DnsClient.Protocol;
namespace DnsClient
{
/// <summary>
/// Extension methods for the <see cref="IDnsQuery"/> contract.
/// <para>
/// The methods implement common queries which are more complex and have some business logic.
/// </para>
/// </summary>
public static class DnsQueryExtensions
{
/// <summary>
/// The <c>GetHostEntry</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="GetHostEntry(IDnsQuery, string)"/> method to resolve an IP address or hostname to an <see cref="IPHostEntry"/> instance.
/// <code>
/// <![CDATA[
/// public static void PrintHostEntry(string hostOrIp)
/// {
/// var lookup = new LookupClient();
/// IPHostEntry hostEntry = lookup.GetHostEntry(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="DnsQueryOptions.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="DnsQueryOptions.ThrowDnsErrors"/> is set to true and a DNS error occurs.</exception>
public static IPHostEntry GetHostEntry(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.GetHostEntry(address);
}
return GetHostEntryFromName(query, hostNameOrAddress);
}
/// <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="DnsQueryOptions.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="DnsQueryOptions.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);
}
/// <summary>
/// The <c>GetHostEntry</c> method does a reverse lookup on the IP <paramref name="address"/>,
/// and queries a DNS server for the IP addresses and aliases associated with the resolved 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 of the <paramref name="address"/>.
/// </para>
/// </summary>
/// <example>
/// The following code example uses the <see cref="GetHostEntry(IDnsQuery, IPAddress)"/> method to resolve an IP address to an <see cref="IPHostEntry"/> instance.
/// <code>
/// <![CDATA[
/// public static void PrintHostEntry(IPAddress address)
/// {
/// var lookup = new LookupClient();
/// IPHostEntry hostEntry = lookup.GetHostEntry(address);
/// 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="address">The <see cref="IPAddress"/> to query for.</param>
/// <returns>
/// An <see cref="IPHostEntry"/> instance that contains address information about the host specified in <paramref name="address"/>.
/// In case the <paramref name="address"/> could not be resolved to a domain name, this method returns <c>null</c>,
/// unless <see cref="DnsQueryOptions.ThrowDnsErrors"/> is set to true, then it might throw a <see cref="DnsResponseException"/>.
/// </returns>
/// <exception cref="ArgumentNullException">If <paramref name="address"/> is null.</exception>
/// <exception cref="DnsResponseException">In case <see cref="DnsQueryOptions.ThrowDnsErrors"/> is set to true and a DNS error occurs.</exception>
public static IPHostEntry GetHostEntry(this IDnsQuery query, IPAddress address)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (address == null)
{
throw new ArgumentNullException(nameof(address));
}
var hostName = query.GetHostName(address);
if (string.IsNullOrWhiteSpace(hostName))
{
return null;
}
return GetHostEntryFromName(query, hostName);
}
/// <summary>
/// The <c>GetHostEntryAsync</c> method does a reverse lookup on the IP <paramref name="address"/>,
/// and queries a DNS server for the IP addresses and aliases associated with the resolved 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 of the <paramref name="address"/>.
/// </para>
/// </summary>
/// <example>
/// The following code example uses the <see cref="GetHostEntryAsync(IDnsQuery, IPAddress)"/> method to resolve an IP address to an <see cref="IPHostEntry"/> instance.
/// <code>
/// <![CDATA[
/// public static async Task PrintHostEntry(IPAddress address)
/// {
/// var lookup = new LookupClient();
/// IPHostEntry hostEntry = await lookup.GetHostEntryAsync(address);
/// 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="address">The <see cref="IPAddress"/> to query for.</param>
/// <returns>
/// An <see cref="IPHostEntry"/> instance that contains address information about the host specified in <paramref name="address"/>.
/// In case the <paramref name="address"/> could not be resolved to a domain name, this method returns <c>null</c>,
/// unless <see cref="DnsQueryOptions.ThrowDnsErrors"/> is set to true, then it might throw a <see cref="DnsResponseException"/>.
/// </returns>
/// <exception cref="ArgumentNullException">If <paramref name="address"/> is null.</exception>
/// <exception cref="DnsResponseException">In case <see cref="DnsQueryOptions.ThrowDnsErrors"/> is set to true and a DNS error occurs.</exception>
public static async Task<IPHostEntry> GetHostEntryAsync(this IDnsQuery query, IPAddress address)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (address == null)
{
throw new ArgumentNullException(nameof(address));
}
var hostName = await query.GetHostNameAsync(address).ConfigureAwait(false);
if (string.IsNullOrWhiteSpace(hostName))
{
return null;
}
return await GetHostEntryFromNameAsync(query, hostName).ConfigureAwait(false);
}
private static IPHostEntry GetHostEntryFromName(IDnsQuery query, string hostName)
{
if (string.IsNullOrWhiteSpace(hostName))
{
throw new ArgumentNullException(nameof(hostName));
}
var hostString = DnsString.FromResponseQueryString(hostName);
var ipv4Result = query.Query(hostString, QueryType.A);
var ipv6Result = query.Query(hostString, QueryType.AAAA);
var allRecords = ipv4Result
.Answers.Concat(ipv6Result.Answers)
.ToArray();
return GetHostEntryProcessResult(hostString, allRecords);
}
private static async Task<IPHostEntry> GetHostEntryFromNameAsync(IDnsQuery query, string hostName)
{
if (string.IsNullOrWhiteSpace(hostName))
{
throw new ArgumentNullException(nameof(hostName));
}
var hostString = DnsString.FromResponseQueryString(hostName);
var ipv4Result = query.QueryAsync(hostString, QueryType.A);
var ipv6Result = query.QueryAsync(hostString, QueryType.AAAA);
await Task.WhenAll(ipv4Result, ipv6Result).ConfigureAwait(false);
#pragma warning disable CA1849 // We did.
var allRecords = ipv4Result.Result
.Answers.Concat(ipv6Result.Result.Answers)
.ToArray();
#pragma warning restore CA1849 // Call async methods when in an async method
return GetHostEntryProcessResult(hostString, allRecords);
}
private static IPHostEntry GetHostEntryProcessResult(DnsString hostString, DnsResourceRecord[] allRecords)
{
var addressRecords = allRecords
.OfType<AddressRecord>()
.Select(p => new
{
p.Address,
Alias = DnsString.FromResponseQueryString(p.DomainName)
})
.ToArray();
var hostEntry = new IPHostEntry()
{
Aliases = new string[0],
AddressList = addressRecords
.Select(p => p.Address)
.ToArray()
};
if (addressRecords.Length > 1)
{
if (addressRecords.Any(p => !p.Alias.Equals(hostString)))
{
hostEntry.Aliases = addressRecords
.Select(p => p.Alias.ToString())
.Select(p => p.Substring(0, p.Length - 1))
.Distinct()
.ToArray();
}
}
else if (addressRecords.Length == 1)
{
if (allRecords.Any(p => !DnsString.FromResponseQueryString(p.DomainName).Equals(hostString)))
{
hostEntry.Aliases = allRecords
.Select(p => p.DomainName.ToString())
.Select(p => p.Substring(0, p.Length - 1))
.Distinct()
.ToArray();
}
}
hostEntry.HostName = hostString.Value.Substring(0, hostString.Value.Length - 1);
return hostEntry;
}
/// <summary>
/// The <c>GetHostName</c> method queries a DNS server to resolve the hostname of the <paramref name="address"/> via reverse lookup.
/// </summary>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="address">The <see cref="IPAddress"/> to resolve.</param>
/// <returns>
/// The hostname if the reverse lookup was successful or <c>null</c>, in case the host was not found.
/// If <see cref="DnsQueryOptions.ThrowDnsErrors"/> is set to <c>true</c>, this method will throw an <see cref="DnsResponseException"/> instead of returning <c>null</c>!
/// </returns>
/// <exception cref="ArgumentNullException">If <paramref name="address"/>is null.</exception>
/// <exception cref="DnsResponseException">If no host has been found and <see cref="DnsQueryOptions.ThrowDnsErrors"/> is <c>true</c>.</exception>
public static string GetHostName(this IDnsQuery query, IPAddress address)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (address == null)
{
throw new ArgumentNullException(nameof(address));
}
var result = query.QueryReverse(address);
return GetHostNameAsyncProcessResult(result);
}
/// <summary>
/// The <c>GetHostNameAsync</c> method queries a DNS server to resolve the hostname of the <paramref name="address"/> via reverse lookup.
/// </summary>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="address">The <see cref="IPAddress"/> to resolve.</param>
/// <returns>
/// The hostname if the reverse lookup was successful or <c>null</c>, in case the host was not found.
/// If <see cref="DnsQueryOptions.ThrowDnsErrors"/> is set to <c>true</c>, this method will throw an <see cref="DnsResponseException"/> instead of returning <c>null</c>!
/// </returns>
/// <exception cref="ArgumentNullException">If <paramref name="address"/>is null.</exception>
/// <exception cref="DnsResponseException">If no host has been found and <see cref="DnsQueryOptions.ThrowDnsErrors"/> is <c>true</c>.</exception>
public static async Task<string> GetHostNameAsync(this IDnsQuery query, IPAddress address)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (address == null)
{
throw new ArgumentNullException(nameof(address));
}
var result = await query.QueryReverseAsync(address).ConfigureAwait(false);
return GetHostNameAsyncProcessResult(result);
}
private static string GetHostNameAsyncProcessResult(IDnsQueryResponse result)
{
if (result.HasError)
{
return null;
}
var hostName = result.Answers.PtrRecords().FirstOrDefault()?.PtrDomainName;
if (string.IsNullOrWhiteSpace(hostName))
{
return null;
}
// removing the . at the end
return hostName.Value.Substring(0, hostName.Value.Length - 1);
}
/// <summary>
/// The <c>ResolveService</c> method does a <see cref="QueryType.SRV"/> lookup for <c>_{<paramref name="serviceName"/>}[._{<paramref name="protocol"/>}].{<paramref name="baseDomain"/>}</c>
/// and aggregates the result (hostname, port and list of <see cref="IPAddress"/>s) to a <see cref="ServiceHostEntry"/>.
/// <para>
/// This method expects matching A or AAAA records to populate the <see cref="IPHostEntry.AddressList"/>,
/// and/or a <see cref="ResourceRecordType.CNAME"/> record to populate the <see cref="IPHostEntry.HostName"/> property of the result.
/// </para>
/// </summary>
/// <remarks>
/// The returned list of <see cref="IPAddress"/>s and/or the hostname can be empty if no matching additional records are found.
/// </remarks>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="baseDomain">The base domain, which will be appended to the end of the query string.</param>
/// <param name="serviceName">The name of the service to look for. Must not have any <c>_</c> prefix.</param>
/// <param name="protocol">
/// The protocol of the service to query for.
/// Set it to <see cref="ProtocolType.Unknown"/> or <see cref="ProtocolType.Unspecified"/> to not pass any protocol.
/// </param>
/// <returns>A collection of <see cref="ServiceHostEntry"/>s.</returns>
/// <exception cref="ArgumentNullException">If <paramref name="baseDomain"/> or <paramref name="serviceName"/> are null.</exception>
/// <seealso href="https://tools.ietf.org/html/rfc2782">RFC 2782</seealso>
public static ServiceHostEntry[] ResolveService(this IDnsQuery query, string baseDomain, string serviceName, ProtocolType protocol)
{
if (protocol == ProtocolType.Unspecified || protocol == ProtocolType.Unknown)
{
return ResolveService(query, baseDomain, serviceName, null);
}
return ResolveService(query, baseDomain, serviceName, protocol.ToString());
}
/// <summary>
/// The <c>ResolveServiceAsync</c> method does a <see cref="QueryType.SRV"/> lookup for <c>_{<paramref name="serviceName"/>}[._{<paramref name="protocol"/>}].{<paramref name="baseDomain"/>}</c>
/// and aggregates the result (hostname, port and list of <see cref="IPAddress"/>s) to a <see cref="ServiceHostEntry"/>.
/// <para>
/// This method expects matching A or AAAA records to populate the <see cref="IPHostEntry.AddressList"/>,
/// and/or a <see cref="ResourceRecordType.CNAME"/> record to populate the <see cref="IPHostEntry.HostName"/> property of the result.
/// </para>
/// </summary>
/// <remarks>
/// The returned list of <see cref="IPAddress"/>s and/or the hostname can be empty if no matching additional records are found.
/// </remarks>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="baseDomain">The base domain, which will be appended to the end of the query string.</param>
/// <param name="serviceName">The name of the service to look for. Must not have any <c>_</c> prefix.</param>
/// <param name="protocol">
/// The protocol of the service to query for.
/// Set it to <see cref="ProtocolType.Unknown"/> or <see cref="ProtocolType.Unspecified"/> to not pass any protocol.
/// </param>
/// <returns>A collection of <see cref="ServiceHostEntry"/>s.</returns>
/// <exception cref="ArgumentNullException">If <paramref name="baseDomain"/> or <paramref name="serviceName"/> are null.</exception>
/// <seealso href="https://tools.ietf.org/html/rfc2782">RFC 2782</seealso>
public static Task<ServiceHostEntry[]> ResolveServiceAsync(this IDnsQuery query, string baseDomain, string serviceName, ProtocolType protocol)
{
if (protocol == ProtocolType.Unspecified || protocol == ProtocolType.Unknown)
{
return ResolveServiceAsync(query, baseDomain, serviceName, null);
}
return ResolveServiceAsync(query, baseDomain, serviceName, protocol.ToString());
}
/// <summary>
/// The <c>ResolveService</c> method does a <see cref="QueryType.SRV"/> lookup for <c>_{<paramref name="serviceName"/>}[._{<paramref name="tag"/>}].{<paramref name="baseDomain"/>}</c>
/// and aggregates the result (hostname, port and list of <see cref="IPAddress"/>s) to a <see cref="ServiceHostEntry"/>.
/// <para>
/// This method expects matching A or AAAA records to populate the <see cref="IPHostEntry.AddressList"/>,
/// and/or a <see cref="ResourceRecordType.CNAME"/> record to populate the <see cref="IPHostEntry.HostName"/> property of the result.
/// </para>
/// </summary>
/// <remarks>
/// The returned list of <see cref="IPAddress"/>s and/or the hostname can be empty if no matching additional records are found.
/// </remarks>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="baseDomain">The base domain, which will be appended to the end of the query string.</param>
/// <param name="serviceName">The name of the service to look for. Must not have any <c>_</c> prefix.</param>
/// <param name="tag">An optional tag. Must not have any <c>_</c> prefix.</param>
/// <returns>A collection of <see cref="ServiceHostEntry"/>s.</returns>
/// <exception cref="ArgumentNullException">If <paramref name="baseDomain"/> or <paramref name="serviceName"/> are null.</exception>
/// <seealso href="https://tools.ietf.org/html/rfc2782">RFC 2782</seealso>
public static ServiceHostEntry[] ResolveService(this IDnsQuery query, string baseDomain, string serviceName, string tag = null)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (baseDomain == null)
{
throw new ArgumentNullException(nameof(baseDomain));
}
if (string.IsNullOrWhiteSpace(serviceName))
{
throw new ArgumentNullException(nameof(serviceName));
}
var queryString = ConcatServiceName(baseDomain, serviceName, tag);
var result = query.Query(queryString, QueryType.SRV);
return ResolveServiceProcessResult(result);
}
/// <summary>
/// The <c>ResolveService</c> method does a <see cref="QueryType.SRV"/> lookup for <c>{<paramref name="service"/>}</c>
/// and aggregates the result (hostname, port and list of <see cref="IPAddress"/>s) to a <see cref="ServiceHostEntry"/>.
/// <para>
/// This method expects matching A or AAAA records to populate the <see cref="IPHostEntry.AddressList"/>,
/// and/or a <see cref="ResourceRecordType.CNAME"/> record to populate the <see cref="IPHostEntry.HostName"/> property of the result.
/// </para>
/// </summary>
/// <remarks>
/// The returned list of <see cref="IPAddress"/>s and/or the hostname can be empty if no matching additional records are found.
/// </remarks>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="service">The name of the service to look for. Must have <c>_</c> prefix and domain and protocol.</param>
/// <returns>A collection of <see cref="ServiceHostEntry"/>s.</returns>
/// <exception cref="ArgumentNullException">If <paramref name="service"/> are null.</exception>
/// <seealso href="https://tools.ietf.org/html/rfc2782">RFC 2782</seealso>
public static ServiceHostEntry[] ResolveService(this IDnsQuery query, string service)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (string.IsNullOrWhiteSpace(service))
{
throw new ArgumentNullException(nameof(service));
}
var result = query.Query(service, QueryType.SRV);
return ResolveServiceProcessResult(result);
}
/// <summary>
/// The <c>ResolveServiceAsync</c> method does a <see cref="QueryType.SRV"/> lookup for <c>_{<paramref name="serviceName"/>}[._{<paramref name="tag"/>}].{<paramref name="baseDomain"/>}</c>
/// and aggregates the result (hostname, port and list of <see cref="IPAddress"/>s) to a <see cref="ServiceHostEntry"/>.
/// <para>
/// This method expects matching A or AAAA records to populate the <see cref="IPHostEntry.AddressList"/>,
/// and/or a <see cref="ResourceRecordType.CNAME"/> record to populate the <see cref="IPHostEntry.HostName"/> property of the result.
/// </para>
/// </summary>
/// <remarks>
/// The returned list of <see cref="IPAddress"/>s and/or the hostname can be empty if no matching additional records are found.
/// </remarks>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="baseDomain">The base domain, which will be appended to the end of the query string.</param>
/// <param name="serviceName">The name of the service to look for. Must not have any <c>_</c> prefix.</param>
/// <param name="tag">An optional tag. Must not have any <c>_</c> prefix.</param>
/// <returns>A collection of <see cref="ServiceHostEntry"/>s.</returns>
/// <exception cref="ArgumentNullException">If <paramref name="baseDomain"/> or <paramref name="serviceName"/> are null.</exception>
/// <seealso href="https://tools.ietf.org/html/rfc2782">RFC 2782</seealso>
public static async Task<ServiceHostEntry[]> ResolveServiceAsync(this IDnsQuery query, string baseDomain, string serviceName, string tag = null)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (baseDomain == null)
{
throw new ArgumentNullException(nameof(baseDomain));
}
if (string.IsNullOrWhiteSpace(serviceName))
{
throw new ArgumentNullException(nameof(serviceName));
}
var queryString = ConcatServiceName(baseDomain, serviceName, tag);
var result = await query.QueryAsync(queryString, QueryType.SRV).ConfigureAwait(false);
return ResolveServiceProcessResult(result);
}
/// <summary>
/// The <c>ResolveServiceAsync</c> method does a <see cref="QueryType.SRV"/> lookup for <c>{<paramref name="service"/>}</c>
/// and aggregates the result (hostname, port and list of <see cref="IPAddress"/>s) to a <see cref="ServiceHostEntry"/>.
/// <para>
/// This method expects matching A or AAAA records to populate the <see cref="IPHostEntry.AddressList"/>,
/// and/or a <see cref="ResourceRecordType.CNAME"/> record to populate the <see cref="IPHostEntry.HostName"/> property of the result.
/// </para>
/// </summary>
/// <remarks>
/// The returned list of <see cref="IPAddress"/>s and/or the hostname can be empty if no matching additional records are found.
/// </remarks>
/// <param name="query">The <see cref="IDnsQuery"/> instance.</param>
/// <param name="service">The name of the service to look for. Must have <c>_</c> prefix and domain and protocol.</param>
/// <returns>A collection of <see cref="ServiceHostEntry"/>s.</returns>
/// <exception cref="ArgumentNullException">If <paramref name="service"/> are null.</exception>
/// <seealso href="https://tools.ietf.org/html/rfc2782">RFC 2782</seealso>
public static async Task<ServiceHostEntry[]> ResolveServiceAsync(this IDnsQuery query, string service)
{
if (query == null)
{
throw new ArgumentNullException(nameof(query));
}
if (string.IsNullOrWhiteSpace(service))
{
throw new ArgumentNullException(nameof(service));
}
var result = await query.QueryAsync(service, QueryType.SRV).ConfigureAwait(false);
return ResolveServiceProcessResult(result);
}
/// <summary>
/// Constructs a DNS <see cref="QueryType.SRV"/> query string from the constituent parts.
/// </summary>
/// <param name="baseDomain">The base domain, which will be appended to the end of the query string.</param>
/// <param name="serviceName">The name of the service to look for. Must not have any <c>_</c> prefix.</param>
/// <param name="tag">An optional tag. Must not have any <c>_</c> prefix.</param>
/// <returns>A service string that can be used in a DNS service query.</returns>
public static string ConcatServiceName(string baseDomain, string serviceName, string tag = null)
{
return string.IsNullOrWhiteSpace(tag) ?
$"{serviceName}.{baseDomain}." :
$"_{serviceName}._{tag}.{baseDomain}.";
}
/// <summary>
/// Transforms a DNS query result into a collection of <see cref="ServiceHostEntry"/> objects.
/// </summary>
/// <param name="result">The DNS </param>
/// <returns>A collection of <see cref="ServiceHostEntry"/>s.</returns>
public static ServiceHostEntry[] ResolveServiceProcessResult(IDnsQueryResponse result)
{
var hosts = new List<ServiceHostEntry>();
if (result == null || result.HasError)
{
return hosts.ToArray();
}
foreach (var entry in result.Answers.SrvRecords())
{
var addresses = result.Additionals
.OfType<AddressRecord>()
.Where(p => p.DomainName.Equals(entry.Target))
.Select(p => p.Address);
var hostName = result.Additionals
.OfType<CNameRecord>()
.Where(p => p.DomainName.Equals(entry.Target))
.Select(p => p.CanonicalName).FirstOrDefault()
?? entry.Target;
hosts.Add(new ServiceHostEntry()
{
AddressList = addresses.ToArray(),
HostName = hostName,
Port = entry.Port,
Priority = entry.Priority,
Weight = entry.Weight,
});
}
return hosts.ToArray();
}
}
/// <summary>
/// Extends <see cref="IPHostEntry"/> by the <see cref="Port"/> property.
/// </summary>
/// <seealso cref="IPHostEntry" />
public class ServiceHostEntry : IPHostEntry
{
/// <summary>
/// Gets or sets the port.
/// </summary>
/// <value>
/// The port of this entry.
/// </value>
public int Port { get; set; }
/// <summary>
/// Gets or sets priority of the original <see cref="ResourceRecordType.SRV"/> record.
/// Might be zero if not provided.
/// </summary>
/// <value>
/// The priority of this entry.
/// </value>
public int Priority { get; set; }
/// <summary>
/// Gets or sets weight of the original <see cref="ResourceRecordType.SRV"/> record.
/// Might be zero if not provided.
/// </summary>
/// <value>
/// The weight of this entry.
/// </value>
public int Weight { get; set; }
}
}