initial work on DisconnectMessage; it's pretty straightforward, I think

common/src/main/scala/net/psforever/packet/GamePacketOpcode.scala

@@ -535,7 +535,7 @@ object GamePacketOpcode extends Enumeration {
     case 0xb4 => game.BattleExperienceMessage.decode
     case 0xb5 => noDecoder(TargetingImplantRequest)
     case 0xb6 => game.ZonePopulationUpdateMessage.decode
-    case 0xb7 => noDecoder(DisconnectMessage)
+    case 0xb7 => game.DisconnectMessage.decode
     // 0xb8
     case 0xb8 => noDecoder(ExperienceAddedMessage)
     case 0xb9 => game.OrbitalStrikeWaypointMessage.decode

common/src/main/scala/net/psforever/packet/game/DisconnectMessage.scala

@@ -0,0 +1,36 @@
+// Copyright (c) 2016 PSForever.net to present
+package net.psforever.packet.game
+
+import net.psforever.packet.{GamePacketOpcode, Marshallable, PacketHelpers, PlanetSideGamePacket}
+import scodec.Codec
+import scodec.codecs._
+
+/**
+  * Dispatched to the client to force a disconnect.<br>
+  * <br>
+  * The client's render will fade and be centered with a system textbox with the given message.
+  * Using the button on the textbox will drop the current world session and return the player to the world select screen.
+  * Being disconnected like this has no client-based consequences on its own.<br>
+  * <br>
+  * Exploration:<br>
+  * When do the other two messages appear, if at all?
+  * @param msg the displayed message
+  * @param unk2 na
+  * @param unk3 na
+  */
+final case class DisconnectMessage(msg : String,
+                                   unk2 : String = "",
+                                   unk3 : String = "")
+  extends PlanetSideGamePacket {
+  type Packet = DisconnectMessage
+  def opcode = GamePacketOpcode.DisconnectMessage
+  def encode = DisconnectMessage.encode(this)
+}
+
+object DisconnectMessage extends Marshallable[DisconnectMessage] {
+  implicit val codec : Codec[DisconnectMessage] = (
+    ("msg" | PacketHelpers.encodedString) ::
+      ("unk2" | PacketHelpers.encodedString) ::
+      ("unk3" | PacketHelpers.encodedString)
+    ).as[DisconnectMessage]
+}

common/src/test/scala/GamePacketTest.scala

@@ -1492,6 +1492,28 @@ class GamePacketTest extends Specification {
       }
     }
 
+    "DisconnectMessage" should {
+      val string = hex"B7 85 46 69 72 73 74 86 53 65 63 6F 6E 64 8E 46 69 72 73 74 20 26 20 73 65 63 6F 6E 64"
+
+      "decode" in {
+        PacketCoding.DecodePacket(string).require match {
+          case DisconnectMessage(unk1, unk2, unk3) =>
+            unk1 mustEqual "First"
+            unk2 mustEqual "Second"
+            unk3 mustEqual "First & second"
+          case default =>
+            ko
+        }
+      }
+
+      "encode" in {
+        val msg = DisconnectMessage("First", "Second", "First & second")
+        val pkt = PacketCoding.EncodePacket(msg).require.toByteVector
+
+        pkt mustEqual string
+      }
+    }
+
     "OrbitalStrikeWaypointMessage" should {
       val string_on = hex"B9 46 0C AA E3 D2 2A 92 00"
       val string_off = hex"B9 46 0C 00"