C# .Net 8 - UDP Socket: receiver address missing (IPPacketInformation - n/a)

[rinor]

Intro

While trying to test/package https://github.com/TechnitiumSoftware/DnsServer encountered some issues in some places.
https://github.com/TechnitiumSoftware/DnsServer/blob/3a7636ac3b1c221521f4031bb185277bbc85f068/DnsServerCore/Dns/DnsServer.cs#L429 - being one of them causing

[2025-04-28 13:25:15 UTC] [10.0.2.2:43112] [UDP] System.ArgumentNullException: Value cannot be null. (Parameter 'address')
   at System.ArgumentNullException.Throw(String paramName)
   at System.ArgumentNullException.ThrowIfNull(Object argument, String paramName)
   at System.Net.IPEndPoint..ctor(IPAddress address, Int32 port)
   at DnsServerCore.Dns.DnsServer.ReadUdpRequestAsync(Socket udpListener, DnsTransportProtocol protocol) in /usr/local/src/Technitium/DnsServer/DnsServerCore/Dns/DnsServer.cs:line 429

upon investigation it turned out that on Nanos - https://learn.microsoft.com/en-us/dotnet/api/system.net.sockets.ippacketinformation?view=net-8.0 looks like is not available.

• C# - Program.cs - code to reproduce the "issue":

   using System;
   using System.Net;
   using System.Net.Sockets;
   using System.Threading.Tasks;

   class Program
   {
       static async Task Main()
       {
           Console.WriteLine($"Task.Delay(3000) - Start");
           await Task.Delay(3000);
           Console.WriteLine($"Task.Delay(3000) - Done");

           // Define the local endpoint (IP address and port)

           IPAddress ipAddress = IPAddress.Any; // same issue when we test with a specific ip
           // IPAddress ipAddress = IPAddress.Parse("10.0.2.15");

           IPEndPoint localEP = new IPEndPoint(ipAddress, 53);
           Console.WriteLine($"Local Endpoint: {localEP}");

           // Create a UDP socket
           Socket udpListener = new Socket(localEP.AddressFamily, SocketType.Dgram, ProtocolType.Udp);

           // Set the PacketInformation option - ReceiveMessageFromAsync sets this also, but try it early
           udpListener.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.PacketInformation, true);

           // Bind the socket to the local endpoint
           udpListener.Bind(localEP);
           Console.WriteLine("DNS Server was bound successfully");

           // Prepare to receive messages
           var buffer = new byte[512]; // Adjust buffer size as needed
           var remoteEP = new IPEndPoint(IPAddress.Any, 0); // Placeholder for remote endpoint
           var result = new SocketReceiveMessageFromResult();


           // Receive the message
           result = await udpListener.ReceiveMessageFromAsync(new ArraySegment<byte>(buffer), SocketFlags.None, remoteEP);

           // Check if PacketInformation data is avalable - linux it is ok, nanos is not available
           if (result.PacketInformation.Address != null)
           {
               Console.WriteLine($"Received packet from: {result.PacketInformation.Address}"); // linux
           }
           else
           {
               Console.WriteLine("No valid PacketInformation.Address available."); // nanos
           }
       }
   }

.Net build instructions

• dotnet --version 8.0.408

# 1. create new project
dotnet new console -n DnsTest

# 2. replace the code at Program.cs

# 3. update DnsTest.cproj with
<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <PublishSingleFile>true</PublishSingleFile>
    <SelfContained>true</SelfContained>
    <RuntimeIdentifier>linux-x64</RuntimeIdentifier>
  </PropertyGroup>

</Project>

# 4. build it
dotnet publish DnsTest.csproj -c Release --self-contained --runtime linux-x64 -p:PublishSingleFile=true

ops nanos

• config_dnstest.json

{
    "Files": [
        "usr/lib/x86_64-linux-gnu/libicuuc.so.72",
        "usr/lib/x86_64-linux-gnu/libicudata.so.72",
        "usr/lib/x86_64-linux-gnu/libicui18n.so.72"
    ],
    "RunConfig": {
        "UDPPorts": [
            "53"
        ]
    }
}

• ops run

ops run DnsTest -c config_dnstest.json -f --smp=1   
running local instance
booting /home/rinor/.ops/images/DnsTest ...
[0.134084] en1: assigned 10.0.2.15
Task.Delay(3000) - Start
[2.108918] en1: assigned FE80::3CEC:28FF:FEDD:9CFD
Task.Delay(3000) - Done
Local Endpoint: 0.0.0.0:53
DNS Server was bound successfully

test it

• dig example.com @127.0.0.1 - you will get No valid PacketInformation.Address available. on ops logs
• test_trace.log

While on linux, from the same binary, you get the proper receiver interface address.

[eyberg]

i didn't look at this too much but perhaps the any interface is causing issues w/ReceiveMessageFromAsync

re-writing your recvfrom using BeginReceiveFrom (taken from https://gist.github.com/darkguy2008/413a6fea3a5b4e67e5e0d96f750088a9) gives me an address:

         udpListener.BeginReceiveFrom(state.buffer, 0, bufSize, SocketFlags.None, ref epFrom, recv = (ar) =>
            {
                State so = (State)ar.AsyncState;
                int bytes = udpListener.EndReceiveFrom(ar, ref epFrom);
                udpListener.BeginReceiveFrom(so.buffer, 0, bufSize, SocketFlags.None, ref epFrom, recv, so);
                Console.WriteLine("RECV: {0}:", epFrom.ToString());
            }, state);