Added support for Proxy Protocol (#72)

* Added support for proxy protocol

Other SMTP servers support proxy protocol [1] allowing load balancers
like HAProxy to tell the server the "real" address of the client making
the request.
[1] http://www.haproxy.org/download/1.8/doc/proxy-protocol.txt

* Added (missing) new properties to interface.

* Megred with default for latest updates. Fixed a few changes in the branch code resulting from merge

* Update to store proxy protocol addresses the same way as Local / Remote Endpoints are stored since the merge.

* Removed now redundant unit test

Co-authored-by: Nic Colledge <nic@imperialmetric.net>

Author: slick-nic

Src/SmtpServer.Tests/SmtpParserTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Net;
 using System.Text;
 using SmtpServer.Mail;
 using SmtpServer.Protocol;
@@ -245,6 +246,42 @@ public void CanMakeRcpt(string email, string user, string host)
             Assert.Equal(host, ((RcptCommand)command).Address.Host);
         }
 
+        [Fact]
+        public void CanMakeProxyIpV4()
+        {
+            // arrange
+            var parser = CreateParser("PROXY TCP4 192.168.1.1 192.168.1.2 1234 16789");
+
+            // act
+            var result = parser.TryMakeProxy(out SmtpCommand command, out SmtpResponse errorResponse);
+
+            // assert
+            Assert.True(result);
+            Assert.True(command is ProxyProtocolCommand);
+            Assert.Equal("192.168.1.1", ((ProxyProtocolCommand)command).SourceEndpoint.Address.ToString());
+            Assert.Equal("192.168.1.2", ((ProxyProtocolCommand)command).DestinationEndpoint.Address.ToString());
+            Assert.Equal(1234, ((ProxyProtocolCommand)command).SourceEndpoint.Port);
+            Assert.Equal(16789, ((ProxyProtocolCommand)command).DestinationEndpoint.Port);
+        }
+
+        [Fact]
+        public void CanMakeProxyIpV6()
+        {
+            // arrange
+            var parser = CreateParser("PROXY TCP6 2001:1234:abcd::0001 3456:2e76:66d8:f84:abcd:abef:ffff:1234 1234 16789");
+
+            // act
+            var result = parser.TryMakeProxy(out SmtpCommand command, out SmtpResponse errorResponse);
+
+            // assert
+            Assert.True(result);
+            Assert.True(command is ProxyProtocolCommand);
+            Assert.Equal(IPAddress.Parse("2001:1234:abcd::0001").ToString(), ((ProxyProtocolCommand)command).SourceEndpoint.Address.ToString());
+            Assert.Equal(IPAddress.Parse("3456:2e76:66d8:f84:abcd:abef:ffff:1234").ToString(), ((ProxyProtocolCommand)command).DestinationEndpoint.Address.ToString());
+            Assert.Equal(1234, ((ProxyProtocolCommand)command).SourceEndpoint.Port);
+            Assert.Equal(16789, ((ProxyProtocolCommand)command).DestinationEndpoint.Port);
+        }
+
         [Fact]
         public void CanMakeAtom()
         {
@@ -578,7 +615,7 @@ public void CanMakeIpv6AddressLiteral(string input)
             var parser = CreateParser("IPv6:" + input);
 
             // act
-            var result = parser.TryMakeIpv6AddressLiteral(out var address);
+            var result = parser.TryMakeIpv6AddressLiteralWithPrefix(out var address);
 
             // assert
             Assert.True(result);
@@ -597,7 +634,7 @@ public void CanNotMakeIpv6AddressLiteral(string input)
             var parser = CreateParser("IPv6:" + input);
 
             // act
-            var result = parser.TryMakeIpv6AddressLiteral(out var address);
+            var result = parser.TryMakeIpv6AddressLiteralWithPrefix(out var address);
 
             // assert
             Assert.False(result);

Src/SmtpServer/ISessionContext.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Net;
 using SmtpServer.IO;
 
 namespace SmtpServer

Src/SmtpServer/Protocol/ProxyProtocolCommand.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Net;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace SmtpServer.Protocol
+{
+    /// <summary>
+    /// Support for proxy protocol version 1 header for use with HAProxy.
+    /// Documented at http://www.haproxy.org/download/1.8/doc/proxy-protocol.txt
+    /// This should always (and only ever) be the first command seen on a new connection from HAProxy
+    /// </summary>
+    public sealed class ProxyProtocolCommand : SmtpCommand
+    {
+        public const string ProxySourceEndpointKey = "ProxyProtocol:ProxySourceEndpoint";
+        public const string ProxyDestinationEndpointKey = "ProxyProtocol:ProxyDestinationEndpoint";
+
+        public const string Command = "PROXY";
+
+        public IPEndPoint SourceEndpoint { get; }
+        public IPEndPoint DestinationEndpoint { get; }
+
+        public ProxyProtocolCommand(ISmtpServerOptions options, IPEndPoint sourceEndpoint, IPEndPoint destinationEndpoint) : base(options)
+        {
+            SourceEndpoint = sourceEndpoint;
+            DestinationEndpoint = destinationEndpoint;
+        }
+
+        internal override Task<bool> ExecuteAsync(SmtpSessionContext context, CancellationToken cancellationToken)
+        {
+            context.Properties.Add(ProxySourceEndpointKey, SourceEndpoint);
+            context.Properties.Add(ProxyDestinationEndpointKey, DestinationEndpoint);
+            
+            // Do not transition smtp protocol state for these commands.
+            return Task.FromResult(false);
+        }
+    }
+}

Src/SmtpServer/Protocol/SmtpCommandVisitor.cs

@@ -46,6 +46,12 @@ public void Visit(SmtpCommand command)
                 return;
             }
 
+            if (command is ProxyProtocolCommand)
+            {
+                Visit((ProxyProtocolCommand)command);
+                return;
+            }
+
             if (command is QuitCommand)
             {
                 Visit((QuitCommand)command);
@@ -109,6 +115,13 @@ protected virtual void Visit(MailCommand command) { }
         /// <param name="command">The command that is being visited.</param>
         protected virtual void Visit(NoopCommand command) { }
 
+        /// <summary>
+        /// Visit an PROXY command.
+        /// </summary>
+        /// <param name="command">The command that is being visited.</param>
+        protected virtual void Visit(ProxyProtocolCommand command) { }
+
+
         /// <summary>
         /// Visit an QUIT command.
         /// </summary>