/*
Technitium DNS Server
Copyright (C) 2024 Shreyas Zare (shreyas@technitium.com)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see .
*/
using DnsServerCore.ApplicationCommon;
using System;
using System.Collections.Generic;
using System.Net;
using System.Security.Cryptography;
using System.Text.Json;
using System.Threading.Tasks;
using TechnitiumLibrary.Net.Dns;
using TechnitiumLibrary.Net.Dns.ResourceRecords;
namespace WeightedRoundRobin
{
public sealed class Address : IDnsApplication, IDnsAppRecordRequestHandler
{
#region IDisposable
public void Dispose()
{
//do nothing
}
#endregion
#region public
public Task InitializeAsync(IDnsServer dnsServer, string config)
{
return Task.CompletedTask;
}
public Task ProcessRequestAsync(DnsDatagram request, IPEndPoint remoteEP, DnsTransportProtocol protocol, bool isRecursionAllowed, string zoneName, string appRecordName, uint appRecordTtl, string appRecordData)
{
DnsQuestionRecord question = request.Question[0];
if (!question.Name.Equals(appRecordName, StringComparison.OrdinalIgnoreCase) && !appRecordName.StartsWith('*'))
return Task.FromResult(null);
string jsonPropertyName;
switch (question.Type)
{
case DnsResourceRecordType.A:
jsonPropertyName = "ipv4Addresses";
break;
case DnsResourceRecordType.AAAA:
jsonPropertyName = "ipv6Addresses";
break;
default:
return Task.FromResult(null);
}
List addresses;
int totalWeight = 0;
using (JsonDocument jsonDocument = JsonDocument.Parse(appRecordData))
{
JsonElement jsonAppRecordData = jsonDocument.RootElement;
if (!jsonAppRecordData.TryGetProperty(jsonPropertyName, out JsonElement jsonAddresses) || (jsonAddresses.ValueKind == JsonValueKind.Null))
return Task.FromResult(null);
addresses = new List(jsonAddresses.GetArrayLength());
foreach (JsonElement jsonAddressEntry in jsonAddresses.EnumerateArray())
{
if (jsonAddressEntry.TryGetProperty("enabled", out JsonElement jsonEnabled) && (jsonEnabled.ValueKind != JsonValueKind.Null) && !jsonEnabled.GetBoolean())
continue;
if (!jsonAddressEntry.TryGetProperty("address", out JsonElement jsonAddress) || (jsonAddress.ValueKind == JsonValueKind.Null) || !IPAddress.TryParse(jsonAddress.GetString(), out IPAddress address))
continue;
if (!jsonAddressEntry.TryGetProperty("weight", out JsonElement jsonWeight) || (jsonWeight.ValueKind == JsonValueKind.Null))
continue;
int weight = jsonWeight.GetInt32();
if (weight < 1)
continue;
addresses.Add(new WeightedAddress() { Address = address, Weight = weight });
totalWeight += weight;
}
}
if (addresses.Count == 0)
return Task.FromResult(null);
int randomSelection = RandomNumberGenerator.GetInt32(1, 101);
int rangeFrom;
int rangeTo = 0;
DnsResourceRecord answer = null;
for (int i = 0; i < addresses.Count; i++)
{
rangeFrom = rangeTo + 1;
if (i == addresses.Count - 1)
rangeTo = 100;
else
rangeTo += addresses[i].Weight * 100 / totalWeight;
if ((rangeFrom <= randomSelection) && (randomSelection <= rangeTo))
{
switch (question.Type)
{
case DnsResourceRecordType.A:
answer = new DnsResourceRecord(question.Name, question.Type, DnsClass.IN, appRecordTtl, new DnsARecordData(addresses[i].Address));
break;
case DnsResourceRecordType.AAAA:
answer = new DnsResourceRecord(question.Name, question.Type, DnsClass.IN, appRecordTtl, new DnsAAAARecordData(addresses[i].Address));
break;
default:
throw new InvalidOperationException();
}
break;
}
}
if (answer is null)
throw new InvalidOperationException();
return Task.FromResult(new DnsDatagram(request.Identifier, true, request.OPCODE, true, false, request.RecursionDesired, isRecursionAllowed, false, false, DnsResponseCode.NoError, request.Question, new DnsResourceRecord[] { answer }));
}
#endregion
#region properties
public string Description
{ get { return "Returns an A or AAAA record using weighted round-robin load balancing."; } }
public string ApplicationRecordDataTemplate
{
get
{
return @"{
""ipv4Addresses"": [
{
""address"": ""1.1.1.1"",
""weight"": 5,
""enabled"": true
},
{
""address"": ""2.2.2.2"",
""weight"": 3,
""enabled"": true
}
],
""ipv6Addresses"": [
{
""address"": ""::1"",
""weight"": 2,
""enabled"": true
},
{
""address"": ""::2"",
""weight"": 3,
""enabled"": true
}
]
}";
}
}
#endregion
struct WeightedAddress
{
public IPAddress Address;
public int Weight;
}
}
}