Handle unexpected disconnects without a reason.

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java

@@ -6,6 +6,7 @@ import com.velocitypowered.api.proxy.messages.MessageHandler;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.VelocityConstants;
 import com.velocitypowered.proxy.connection.client.ClientPlaySessionHandler;
+import com.velocitypowered.proxy.connection.util.ConnectionMessages;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
 import com.velocitypowered.proxy.protocol.ProtocolConstants;
 import com.velocitypowered.proxy.protocol.packet.*;
@@ -44,6 +45,7 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
             connection.getPlayer().getConnection().write(packet);
         } else if (packet instanceof Disconnect) {
             Disconnect original = (Disconnect) packet;
+            connection.disconnect();
             connection.getPlayer().handleConnectionException(connection.getServerInfo(), original);
         } else if (packet instanceof JoinGame) {
             playerHandler.handleBackendJoinGame((JoinGame) packet);
@@ -113,6 +115,18 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
         connection.getPlayer().handleConnectionException(connection.getServerInfo(), throwable);
     }
 
+    public VelocityServer getServer() {
+        return server;
+    }
+
+    @Override
+    public void disconnected() {
+        if (connection.isGracefulDisconnect()) {
+            return;
+        }
+        connection.getPlayer().handleConnectionException(connection.getServerInfo(), Disconnect.create(ConnectionMessages.UNEXPECTED_DISCONNECT));
+    }
+
     private boolean canForwardPluginMessage(PluginMessage message) {
         ClientPlaySessionHandler playerHandler =
                 (ClientPlaySessionHandler) connection.getPlayer().getConnection().getSessionHandler();

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/VelocityServerConnection.java

@@ -44,6 +44,7 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
     private MinecraftConnection minecraftConnection;
     private boolean legacyForge = false;
     private boolean hasCompletedJoin = false;
+    private boolean gracefulDisconnect = false;
 
     public VelocityServerConnection(ServerInfo target, ConnectedPlayer proxyPlayer, VelocityServer server) {
         this.serverInfo = target;
@@ -148,6 +149,7 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
         if (minecraftConnection != null) {
             minecraftConnection.close();
             minecraftConnection = null;
+            gracefulDisconnect = true;
         }
     }
 
@@ -181,4 +183,8 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
     public void setHasCompletedJoin(boolean hasCompletedJoin) {
         this.hasCompletedJoin = hasCompletedJoin;
     }
+
+    public boolean isGracefulDisconnect() {
+        return gracefulDisconnect;
+    }
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -205,14 +205,19 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
         String plainTextReason = PASS_THRU_TRANSLATE.serialize(disconnectReason);
         if (connectedServer != null && connectedServer.getServerInfo().equals(info)) {
             logger.error("{}: kicked from server {}: {}", this, info.getName(), plainTextReason);
+            handleConnectionException(info, disconnectReason, TextComponent.builder()
+                    .content("Kicked from " + info.getName() + ": ")
+                    .color(TextColor.RED)
+                    .append(disconnectReason)
+                    .build());
         } else {
             logger.error("{}: disconnected while connecting to {}: {}", this, info.getName(), plainTextReason);
+            handleConnectionException(info, disconnectReason, TextComponent.builder()
+                    .content("Unable to connect to " + info.getName() + ": ")
+                    .color(TextColor.RED)
+                    .append(disconnectReason)
+                    .build());
         }
-        handleConnectionException(info, disconnectReason, TextComponent.builder()
-                .content("Unable to connect to " + info.getName() + ": ")
-                .color(TextColor.RED)
-                .append(disconnectReason)
-                .build());
     }
 
     private void handleConnectionException(ServerInfo info, @Nullable Component kickReason, Component friendlyReason) {

proxy/src/main/java/com/velocitypowered/proxy/connection/util/ConnectionMessages.java

@@ -7,6 +7,7 @@ public class ConnectionMessages {
     public static final TextComponent ALREADY_CONNECTED = TextComponent.of("You are already connected to this server!", TextColor.RED);
     public static final TextComponent IN_PROGRESS = TextComponent.of("You are already connecting to a server!", TextColor.RED);
     public static final TextComponent INTERNAL_SERVER_CONNECTION_ERROR = TextComponent.of("Internal server connection error");
+    public static final TextComponent UNEXPECTED_DISCONNECT = TextComponent.of("Unexpectedly disconnected from server - crash?");
 
     private ConnectionMessages() {
         throw new AssertionError();