DNS: Add POSIX DNS implementation

Kerberos.NET/Dns/DnsQuery.cs

@@ -23,6 +23,8 @@ static DnsQuery()
             {
                 QueryImplementation = new WindowsDnsQuery();
             }
+            //for now assume it's POSIX
+            QueryImplementation = new POSIXDnsQuery();
         }
 
         public static bool Debug

Kerberos.NET/Dns/DnsQueryPOSIX.cs

@@ -0,0 +1,232 @@
+// -----------------------------------------------------------------------
+// Licensed to The .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// -----------------------------------------------------------------------
+
+using System;
+using System.Buffers;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Net;
+using System.Net.NetworkInformation;
+using System.Runtime.InteropServices;
+using System.Text;
+
+namespace Kerberos.NET.Dns
+{
+    public unsafe class DnsQueryPOSIX
+    {
+        private const int NS_PACKETSZ = 512;
+        private const int NS_MAXDNAME = 1025;
+
+        private const string LIBC = "libc.so";
+
+        [DllImport(LIBC, EntryPoint = "res_query")]
+        private static extern short ResQuery(
+            [MarshalAs(UnmanagedType.LPStr)] string dname,
+            NsClass @class,
+            DnsRecordType type,
+            char[] answer,
+            int anslen
+        );
+
+        [DllImport(LIBC, EntryPoint = "ns_initparse")]
+        private static extern short NsInitParse(
+            // [MarshalAs(UnmanagedType.LPStr)] string msg,
+            char[] msg,
+            short msglen,
+            NsMsg* handle
+        );
+
+        [DllImport(LIBC, EntryPoint = "ns_msg_count")]
+        private static extern ushort NsMsgCount(
+            NsMsg handle,
+            NsSect section
+        );
+
+        [DllImport(LIBC, EntryPoint = "ns_parserr")]
+        private static extern short NsParserr(
+            NsMsg* handle,
+            NsSect section,
+            short rrnum,
+            NsRr* rr
+        );
+
+        [DllImport(LIBC, EntryPoint = "ns_rr_type")]
+        private static extern DnsRecordType NsRrType(
+            NsRr rr
+        );
+
+        [DllImport(LIBC, EntryPoint = "ns_msg_base")]
+        private static extern string NsMsgBase(
+            NsMsg handle
+        );
+
+        [DllImport(LIBC, EntryPoint = "ns_msg_end")]
+        private static extern string NsMsgEnd(
+            NsMsg handle
+        );
+
+        [DllImport(LIBC, EntryPoint = "ns_rr_rdata")]
+        private static extern string NsRrRdata(
+            NsRr rr
+        );
+
+        [DllImport(LIBC, EntryPoint = "dn_expand")]
+        private static extern short DnExpand(
+            [MarshalAs(UnmanagedType.LPStr)] string msg,
+            [MarshalAs(UnmanagedType.LPStr)] string eomorig,
+            [MarshalAs(UnmanagedType.LPStr)] string comp_dn,
+            StringBuilder exp_dn,
+            short length
+        );
+
+        [DllImport(LIBC, EntryPoint = "ns_rr_name")]
+        private static extern string NsRrName(
+            NsRr rr
+        );
+
+        [DllImport(LIBC, EntryPoint = "inet_ntoa")]
+        private static extern string InetNToA(
+            InAddr @in
+        );
+
+        public static IReadOnlyCollection<DnsRecord> QuerySrvRecord(
+            string query,
+            DnsRecordType type,
+            DnsQueryOptions options = DnsQueryOptions.BypassCache)
+        {
+            var list = new List<DnsRecord>();
+            var buffer = new char[NS_PACKETSZ];
+
+            short respLen = -1;
+            if ((respLen = ResQuery(query, NsClass.NsCIn, type, buffer, NS_PACKETSZ)) < 0)
+                throw new Exception($"Query for {query} failed!");
+
+            NsMsg handle;
+            if (NsInitParse(buffer, respLen, &handle) < 0)
+                throw new Exception("Failed to parse response buffer!");
+
+            var count = NsMsgCount(handle, NsSect.NsSAn);
+            Debug.WriteLine($"{count} records returned in the answer section.");
+
+            for (short i = 0; i < count; i++)
+            {
+                NsRr rr;
+                if (NsParserr(&handle, NsSect.NsSAn, i, &rr) < 0)
+                    throw new Exception("ns_parserr: TODO strerror");
+
+                if (NsRrType(rr) != DnsRecordType.SRV) continue;
+
+                var name = new StringBuilder(1025);
+                short ret;
+                if ((ret = DnExpand(NsMsgBase(handle),
+                        NsMsgEnd(handle),
+                        NsRrRdata(rr) + 6,
+                        name,
+                        1025)) < 0)
+                    throw new Exception($"Failed to uncompress name ({ret})");
+
+                Debug.WriteLine(name);
+
+                var p = NsRrRdata(rr);
+                var ip = new InAddr
+                {
+                    s_addr = ((uint) p[3] << 24) | ((uint) p[2] << 16) | ((uint) p[1] << 8) | p[0]
+                };
+
+                list.Add(new DnsRecord
+                {
+                    Target = InetNToA(ip),
+                    Name = rr.name.ToString(),
+                    //Port =
+                    //Priority =
+                    TimeToLive = (int) rr.ttl,
+                    Type = rr.type,
+                    //Weight = rr.
+                });
+            }
+
+            for (short i = 0; i < NsMsgCount(handle, NsSect.NsSAr); i++)
+            {
+                NsRr rr;
+                if (NsParserr(&handle, NsSect.NsSAr, i, &rr) < 0)
+                    throw new Exception("ns_parserr: TODO strerror");
+
+                if (NsRrType(rr) != DnsRecordType.A) continue;
+
+                var p = NsRrRdata(rr);
+                var ip = new InAddr
+                {
+                    s_addr = ((uint) p[3] << 24) | ((uint) p[2] << 16) | ((uint) p[1] << 8) | p[0]
+                };
+
+                Debug.WriteLine($"{NsRrName(rr)} has address {InetNToA(ip)}");
+
+                list.Add(new DnsRecord
+                {
+                    Type = rr.type,
+                    Name = rr.name.ToString(),
+                    Target = InetNToA(ip)
+                });
+            }
+
+            return list;
+        }
+
+        private struct InAddr
+        {
+            public uint s_addr;
+        }
+
+        private struct NsRr
+        {
+            [MarshalAs(UnmanagedType.LPArray, SizeConst = NS_PACKETSZ)]
+            public char[] name;
+            public DnsRecordType type;
+            public ushort rr_class;
+            public uint ttl;
+            public ushort rdlength;
+            [MarshalAs(UnmanagedType.LPStr)]
+            public string rdata;
+        }
+
+        private enum NsSect
+        {
+            NsSQd = 0, /*%< Query: Question. */
+            NsSZn = 0, /*%< Update: Zone. */
+            NsSAn = 1, /*%< Query: Answer. */
+            NsSPr = 1, /*%< Update: Prerequisites. */
+            NsSNs = 2, /*%< Query: Name servers. */
+            NsSUd = 2, /*%< Update: Update. */
+            NsSAr = 3, /*%< Query|Update: Additional records. */
+            NsSMax = 4
+        }
+
+        private struct NsMsg
+        {
+            [MarshalAs(UnmanagedType.LPStr)] public string _msg, _eom;
+            public ushort _id, _flags;
+            [MarshalAs(UnmanagedType.ByValArray, SizeConst = (int) NsSect.NsSMax)]
+            public ushort[] _counts;
+            [MarshalAs(UnmanagedType.ByValArray, SizeConst = (int) NsSect.NsSMax)]
+            public string[] _sections;
+            public NsSect _sect;
+            public short _rrnum;
+            [MarshalAs(UnmanagedType.LPStr)]
+            public string _msg_ptr;
+        }
+
+        private enum NsClass : ushort
+        {
+            NsCInvalid,
+            NsCIn,
+            NsC2,
+            NsCChaos,
+            NsCHs,
+            NsCNone = 254,
+            NsCAny,
+            NsCMax = 65535
+        }
+    }
+}

Kerberos.NET/Dns/POSIXDnsQuery.cs

@@ -0,0 +1,31 @@
+// -----------------------------------------------------------------------
+// Licensed to The .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// -----------------------------------------------------------------------
+
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace Kerberos.NET.Dns
+{
+    public class POSIXDnsQuery : IKerberosDnsQuery
+    {
+        public bool Debug { get; set; }
+
+        public bool IsSupported => OSPlatform.IsLinux;
+
+        public Task<IReadOnlyCollection<DnsRecord>> Query(string query, DnsRecordType type)
+        {
+            if (!IsSupported)
+            {
+                throw new InvalidOperationException(
+                    "The POSIX DNS query implementation is not supported outside of POSIX-compliant systems");
+            }
+
+            var result = DnsQueryWin32.QuerySrvRecord(query, type);
+
+            return Task.FromResult(result);
+        }
+    }
+}

Kerberos.NET/Kerberos.NET.csproj

@@ -5,6 +5,7 @@
     <Description>A cross-platform, managed-code Kerberos Ticket parsing, validation, and authentication library.</Description>
     <PackageTags>security kerberos</PackageTags>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
   <PropertyGroup>