Add CustomPayloadDecoder (dotpcap#144)

yyl-20020115 · Sep 30, 2021 · 01affc1 · 01affc1
1 parent 56e7140
commit 01affc1
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Showing 4 changed files with 75 additions and 3 deletions.
diff --git a/PacketDotNet/TcpPacket.cs b/PacketDotNet/TcpPacket.cs
@@ -85,7 +85,16 @@ public TcpPacket(ByteArraySegment byteArraySegment)
             // store the payload bytes
             PayloadPacketOrData = new LazySlim<PacketOrByteArraySegment>(() =>
             {
-                var result = new PacketOrByteArraySegment { ByteArraySegment = Header.NextSegment() };
+                PacketOrByteArraySegment result;
+                var payload = Header.NextSegment();
+
+                if (CustomPayloadDecoder != null && (result = CustomPayloadDecoder(payload, this)) != null)
+                {
+                    Log.Debug("Use CustomPayloadDecoder");
+                    return result;
+                }
+
+                result = new PacketOrByteArraySegment { ByteArraySegment = payload };
                 return result;
             });
         }
@@ -117,7 +126,16 @@ public TcpPacket
             // store the payload bytes
             PayloadPacketOrData = new LazySlim<PacketOrByteArraySegment>(() =>
             {
-                var result = new PacketOrByteArraySegment { ByteArraySegment = Header.NextSegment() };
+                PacketOrByteArraySegment result;
+                var payload = Header.NextSegment();
+
+                if (CustomPayloadDecoder != null && (result = CustomPayloadDecoder(payload, this)) != null)
+                {
+                    Log.Debug("Use CustomPayloadDecoder");
+                    return result;
+                }
+
+                result = new PacketOrByteArraySegment { ByteArraySegment = payload };
 
                 // if the parent packet is an IPv4Packet we need to adjust
                 // the payload length because it is possible for us to have

diff --git a/PacketDotNet/TransportPacket.cs b/PacketDotNet/TransportPacket.cs
@@ -6,6 +6,7 @@ This Source Code Form is subject to the terms of the Mozilla Public
 file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */
 
+using System;
 using PacketDotNet.Utils;
 
 #if DEBUG
@@ -20,6 +21,14 @@ namespace PacketDotNet
     /// </summary>
     public abstract class TransportPacket : Packet
     {
+        /// <summary>
+        /// Callback function for TransportPacket Payload decoding.
+        /// First parameter is the payload, second parameter if the TransportPacket itself
+        /// returned value is the decoded payload as PacketOrByteArraySegment or null if payload is invalid or not supported
+        /// then internal decoding will continue
+        /// </summary>
+        public static Func<ByteArraySegment, TransportPacket, PacketOrByteArraySegment> CustomPayloadDecoder;
+
 #if DEBUG
         private static readonly ILog Log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
 #else

diff --git a/PacketDotNet/UdpPacket.cs b/PacketDotNet/UdpPacket.cs
@@ -80,11 +80,19 @@ public UdpPacket(ByteArraySegment byteArraySegment)
                 const int wakeOnLanPort7 = 7;
                 const int wakeOnLanPort9 = 9;
                 
-                var result = new PacketOrByteArraySegment();
+                PacketOrByteArraySegment result;
                 var destinationPort = DestinationPort;
                 var sourcePort = SourcePort;
                 var payload = Header.NextSegment();
 
+                if (CustomPayloadDecoder != null && (result = CustomPayloadDecoder(payload, this)) != null)
+                {
+                    Log.Debug("Use CustomPayloadDecoder");
+                    return result;
+                }
+
+                result = new PacketOrByteArraySegment();
+
                 // If this packet is going to port 0, 7 or 9, then it might be a WakeOnLan packet.
                 if (destinationPort == wakeOnLanPort0 || destinationPort == wakeOnLanPort7 || destinationPort == wakeOnLanPort9)
                 {

diff --git a/Test/PacketType/L2tpPacketTest.cs b/Test/PacketType/L2tpPacketTest.cs
@@ -9,6 +9,7 @@ This Source Code Form is subject to the terms of the Mozilla Public
 using System;
 using NUnit.Framework;
 using PacketDotNet;
+using PacketDotNet.Utils;
 using SharpPcap;
 using SharpPcap.LibPcap;
 
@@ -37,5 +38,41 @@ public void L2tpParsing()
             Assert.AreEqual(l2tp.SessionID, 54110);
             Console.WriteLine(l2tp.GetType());
         }
+
+        [Test]
+        public void L2tpParsingWithUdpCustomDecoder()
+        {
+            TransportPacket.CustomPayloadDecoder = UdpPayloadCustomDecoderFunc;
+            var dev = new CaptureFileReaderDevice(NUnitSetupClass.CaptureDirectory + "l2tp.pcap");
+            dev.Open();
+            PacketCapture c;
+            dev.GetNextPacket(out c);
+            var rawCapture = c.GetPacket();
+            dev.Close();
+
+            var p = Packet.ParsePacket(rawCapture.GetLinkLayers(), rawCapture.Data);
+
+            Assert.IsNotNull(p);
+
+            var l2tp = p.Extract<L2tpPacket>();
+            Assert.AreEqual(l2tp.TunnelID, 18994);
+            Assert.AreEqual(l2tp.SessionID, 54110);
+            Console.WriteLine(l2tp.GetType());
+        }
+
+        private PacketOrByteArraySegment UdpPayloadCustomDecoderFunc(ByteArraySegment payload, TransportPacket udpPacket)
+        {
+            if (udpPacket is UdpPacket)
+            {
+                Console.WriteLine($"Udp Packet from {udpPacket.SourcePort} to {udpPacket.DestinationPort}");
+                if (udpPacket.DestinationPort == L2tpFields.Port || udpPacket.SourcePort == L2tpFields.Port)
+                {
+
+                    return new PacketOrByteArraySegment { Packet = new L2tpPacket(payload, udpPacket) };
+                }
+            }
+
+            return null;
+        }
     }
 }