P2P: fix UnknownCapabilityvalidation and maintainig

src/Neo/Network/P2P/Capabilities/UnknownCapability.cs

@@ -48,7 +48,7 @@ protected override void DeserializeWithoutType(ref MemoryReader reader)
 
         protected override void SerializeWithoutType(BinaryWriter writer)
         {
-            throw new InvalidOperationException("Unknown capability can't be serialized");
+            writer.WriteVarBytes(Data.Span);
         }
     }
 }

src/Neo/Network/P2P/Payloads/NetworkAddressWithTime.cs

@@ -75,7 +75,10 @@ void ISerializable.Deserialize(ref MemoryReader reader)
             Capabilities = new NodeCapability[reader.ReadVarInt(VersionPayload.MaxCapabilities)];
             for (int x = 0, max = Capabilities.Length; x < max; x++)
                 Capabilities[x] = NodeCapability.DeserializeFrom(ref reader);
-            if (Capabilities.Select(p => p.Type).Distinct().Count() != Capabilities.Length)
+            // Verify that no duplicating capabilities are included. Unknown capabilities are not
+            // taken into account but still preserved to be able to share through the network.
+            var capabilities = Capabilities.Where(c => c is not UnknownCapability);
+            if (capabilities.Select(p => p.Type).Distinct().Count() != capabilities.Count())
                 throw new FormatException();
         }
 

src/Neo/Network/P2P/Payloads/VersionPayload.cs

@@ -99,8 +99,8 @@ void ISerializable.Deserialize(ref MemoryReader reader)
             Capabilities = new NodeCapability[reader.ReadVarInt(MaxCapabilities)];
             for (int x = 0, max = Capabilities.Length; x < max; x++)
                 Capabilities[x] = NodeCapability.DeserializeFrom(ref reader);
-            Capabilities = Capabilities.Where(c => c is not UnknownCapability).ToArray();
-            if (Capabilities.Select(p => p.Type).Distinct().Count() != Capabilities.Length)
+            var capabilities = Capabilities.Where(c => c is not UnknownCapability);
+            if (capabilities.Select(p => p.Type).Distinct().Count() != capabilities.Count())
                 throw new FormatException();
         }
 

tests/Neo.UnitTests/Network/P2P/Capabilities/UT_UnknownCapability.cs

@@ -30,7 +30,7 @@ public void DeserializeUnknown()
             var capab = (NodeCapability)NodeCapability.DeserializeFrom(ref br);
 
             Assert.IsTrue(capab is UnknownCapability);
-            Assert.ThrowsException<InvalidOperationException>(() => capab.ToArray());
+            CollectionAssert.AreEqual(buffer, capab.ToArray());
         }
     }
 }

tests/Neo.UnitTests/Network/P2P/Payloads/UT_NetworkAddressWithTime.cs

@@ -10,6 +10,7 @@
 // modifications are permitted.
 
 using FluentAssertions;
+using FluentAssertions.Equivalency;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Neo.Extensions;
 using Neo.IO;
@@ -40,7 +41,7 @@ public void SizeAndEndPoint_Get()
         [TestMethod]
         public void DeserializeAndSerialize()
         {
-            var test = NetworkAddressWithTime.Create(IPAddress.Any, 1, new NodeCapability[] { new ServerCapability(NodeCapabilityType.TcpServer, 22) });
+            var test = NetworkAddressWithTime.Create(IPAddress.Any, 1, new NodeCapability[] { new ServerCapability(NodeCapabilityType.TcpServer, 22), new UnknownCapability(NodeCapabilityType.Extension0), new UnknownCapability(NodeCapabilityType.Extension0) });
             var clone = test.ToArray().AsSerializable<NetworkAddressWithTime>();
 
             CollectionAssert.AreEqual(test.Capabilities.ToByteArray(), clone.Capabilities.ToByteArray());

tests/Neo.UnitTests/Network/P2P/Payloads/UT_VersionPayload.cs

@@ -58,8 +58,8 @@ public void DeserializeAndSerialize()
             buf = buf.Concat(new byte[] { 0x10, 0x01, 0x00, 0x00, 0x00 }).ToArray(); // FullNode capability, 0x01 index.
 
             clone = buf.AsSerializable<VersionPayload>();
-            Assert.AreEqual(2, clone.Capabilities.Length);
-            Assert.AreEqual(0, clone.Capabilities.OfType<UnknownCapability>().Count());
+            Assert.AreEqual(4, clone.Capabilities.Length);
+            Assert.AreEqual(2, clone.Capabilities.OfType<UnknownCapability>().Count());
         }
     }
 }