Class DnsUtils

Namespace

VpnHood.Net.Toolkit.Utils

Assembly

VpnHood.Net.Toolkit.dll

Provides DNS helpers: the network's resolvers, and a minimal A-record lookup over UDP.

public static class DnsUtils

Inheritance

object

DnsUtils

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Methods

BuildDnsQuery(ushort, string)

Builds a DNS query for a host's A records, recursion desired.

public static byte[] BuildDnsQuery(ushort queryId, string host)

Parameters

queryId ushort

The query's ID.

host string

The host name. A dot at its end is left out, and a label with Unicode letters goes in its ASCII form.

Returns

byte[]

The query's bytes.

Exceptions

ArgumentException

host is empty, or no host name: a label of it is empty or longer than 63 characters, or the name longer than 253.

GetHostEntry(string, IPEndPoint, UdpClient, TimeSpan, CancellationToken)

Looks up a host's IPv4 addresses with one query to a resolver, over a given UDP client: the IN A records of the answer section; the names and the other sections are not checked.

public static Task<IPHostEntry> GetHostEntry(string host, IPEndPoint dnsEndPoint, UdpClient udpClient, TimeSpan timeout, CancellationToken cancellationToken)

Parameters

host string

The host name.

dnsEndPoint IPEndPoint

The resolver.

udpClient UdpClient

The UDP client, which this call connects to the resolver; the caller keeps owning it.

timeout TimeSpan

How long the send and the answer may take.

cancellationToken CancellationToken

The token to monitor for cancellation requests.

Returns

Task<IPHostEntry>

A task whose result is the host's addresses.

Exceptions

ArgumentException

host is empty or white space, or no host name.

ArgumentNullException

dnsEndPoint is null.

OperationCanceledException

The timeout passed, or cancellationToken was canceled.

InvalidOperationException

The answer is not this query's, not a response, truncated, or an error.

Exception

The answer has no A record.

EndOfStreamException

The answer ends early.

ArgumentOutOfRangeException

The timeout is negative, other than infinite, or too long.

GetHostEntry(string, IPEndPoint, TimeSpan, CancellationToken)

Looks up a host's IPv4 addresses with one query to a resolver, over a UDP client of its own: the IN A records of the answer section; the names and the other sections are not checked.

public static Task<IPHostEntry> GetHostEntry(string host, IPEndPoint dnsEndPoint, TimeSpan timeout, CancellationToken cancellationToken)

Parameters

host string

The host name.

dnsEndPoint IPEndPoint

The resolver.

timeout TimeSpan

How long the send and the answer may take.

cancellationToken CancellationToken

The token to monitor for cancellation requests.

Returns

Task<IPHostEntry>

A task whose result is the host's addresses.

Exceptions

ArgumentException

host is empty or white space, or no host name.

ArgumentNullException

dnsEndPoint is null.

OperationCanceledException

The timeout passed, or cancellationToken was canceled.

InvalidOperationException

The answer is not this query's, not a response, truncated, or an error.

Exception

The answer has no A record.

EndOfStreamException

The answer ends early.

ArgumentOutOfRangeException

The timeout is negative, other than infinite, or too long.

GetNetworkDnsServers()

Gets the resolvers of the networks the machine reaches beyond itself by: adapters that are up with a gateway, not loopback or tunnel ones.

public static IReadOnlyList<IPAddress> GetNetworkDnsServers()

Returns

IReadOnlyList<IPAddress>

The resolvers' addresses; none where there are none.

Remarks

IPv6 site-local addresses, as Windows' fec0:0:0:ffff:: placeholders, and loopback ones, as a stub on this machine, are left out. On Linux, when none is left, as where it names only systemd-resolved's stub, the upstream list it writes, /run/systemd/resolve/resolv.conf, stands in.

ParseDnsResponse(byte[], ushort)

Reads the IN A records of a DNS response's answer section, after checking its ID and flags: a response, not truncated, as a truncated one may lack some of the name's addresses, and without an error. The names and the other sections are not checked.

public static IPHostEntry ParseDnsResponse(byte[] response, ushort queryId)

Parameters

response byte[]

The response's bytes.

queryId ushort

The query's ID.

Returns

IPHostEntry

The addresses, with an empty host name.

Exceptions

InvalidOperationException

The answer is not this query's, not a response, truncated, or an error.

EndOfStreamException

The response ends early.

Exception

The response has no A record.