added cookie store and retrieve API

api/src/main/java/net/md_5/bungee/api/connection/ProxiedPlayer.java

@@ -3,6 +3,7 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
 import net.md_5.bungee.api.Callback;
 import net.md_5.bungee.api.ChatMessageType;
 import net.md_5.bungee.api.CommandSender;
@@ -339,4 +340,26 @@ public enum MainHand
      */
     @Deprecated
     Scoreboard getScoreboard();
+
+    /**
+     * Retrieves a cookie from this player.
+     *
+     * @param cookie the resource location of the cookie, for example "bungeecord:my_cookie"
+     *
+     * @return a {@link CompletableFuture} that will be completed when the Cookie response is received
+     * @apiNote Only useable for 1.20.5 clients or newer,
+     * if the cookie is not set in the client, the {@link CompletableFuture} will complete with a null value
+     */
+    CompletableFuture<byte[]> retrieveCookie(String cookie);
+
+
+    /**
+     * Stores a cookie in this player's client.
+     *
+     * @param cookie the resource location of the cookie, for example "bungeecord:my_cookie"
+     * @param data the data to store in the cookie
+     *
+     * @apiNote Only useable for 1.20.5 clients or newer
+     */
+    void storeCookie(String cookie, byte[] data);
 }

proxy/src/main/java/net/md_5/bungee/UserConnection.java

@@ -20,6 +20,7 @@
 import java.util.Objects;
 import java.util.Queue;
 import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.logging.Level;
 import lombok.Getter;
@@ -771,4 +772,16 @@ public Scoreboard getScoreboard()
     {
         return serverSentScoreboard;
     }
+
+    @Override
+    public CompletableFuture<byte[]> retrieveCookie(String cookie)
+    {
+        return pendingConnection.retrieveCookie( cookie );
+    }
+
+    @Override
+    public void storeCookie(String cookie, byte[] data)
+    {
+        pendingConnection.storeCookie( cookie, data );
+    }
 }

proxy/src/main/java/net/md_5/bungee/connection/InitialHandler.java

@@ -11,12 +11,19 @@
 import java.security.MessageDigest;
 import java.time.Instant;
 import java.util.HashSet;
+import java.util.Queue;
 import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.logging.Level;
 import javax.crypto.SecretKey;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.EqualsAndHashCode;
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
+import lombok.ToString;
 import net.md_5.bungee.BungeeCord;
 import net.md_5.bungee.BungeeServerInfo;
 import net.md_5.bungee.EncryptionUtil;
@@ -51,6 +58,8 @@
 import net.md_5.bungee.protocol.PlayerPublicKey;
 import net.md_5.bungee.protocol.Protocol;
 import net.md_5.bungee.protocol.ProtocolConstants;
+import net.md_5.bungee.protocol.packet.CookieRequest;
+import net.md_5.bungee.protocol.packet.CookieResponse;
 import net.md_5.bungee.protocol.packet.EncryptionRequest;
 import net.md_5.bungee.protocol.packet.EncryptionResponse;
 import net.md_5.bungee.protocol.packet.Handshake;
@@ -64,6 +73,7 @@
 import net.md_5.bungee.protocol.packet.PluginMessage;
 import net.md_5.bungee.protocol.packet.StatusRequest;
 import net.md_5.bungee.protocol.packet.StatusResponse;
+import net.md_5.bungee.protocol.packet.StoreCookie;
 import net.md_5.bungee.util.AllowedCharacters;
 import net.md_5.bungee.util.BufUtil;
 import net.md_5.bungee.util.QuietException;
@@ -86,6 +96,18 @@ public class InitialHandler extends PacketHandler implements PendingConnection
     @Getter
     private final Set<String> registeredChannels = new HashSet<>();
     private State thisState = State.HANDSHAKE;
+    private final Queue<CookieFuture> requestedCookies = new ConcurrentLinkedQueue<>();
+
+    @Data
+    @ToString
+    @EqualsAndHashCode
+    @AllArgsConstructor
+    public static class CookieFuture
+    {
+        private String cookie;
+        private CompletableFuture<byte[]> future;
+    }
+
     private final Unsafe unsafe = new Unsafe()
     {
         @Override
@@ -653,6 +675,19 @@ public void handle(LoginPayloadResponse response) throws Exception
         disconnect( "Unexpected custom LoginPayloadResponse" );
     }
 
+    @Override
+    public void handle(CookieResponse cookieResponse)
+    {
+        // be careful spigot could also make the client send a cookie response
+        CookieFuture future = requestedCookies.peek();
+        if ( future != null && future.cookie.equals( cookieResponse.getCookie() ) )
+        {
+            requestedCookies.remove();
+            future.getFuture().complete( cookieResponse.getData() );
+            throw CancelSendSignal.INSTANCE;
+        }
+    }
+
     @Override
     public void disconnect(String reason)
     {
@@ -785,4 +820,26 @@ public void relayMessage(PluginMessage input) throws Exception
             brandMessage = input;
         }
     }
+
+    public CompletableFuture<byte[]> retrieveCookie(String cookie)
+    {
+        Preconditions.checkState( getVersion() >= ProtocolConstants.MINECRAFT_1_20_5, "Cookies are only supported in 1.20.5 and above" );
+        Preconditions.checkState( loginRequest != null, "Cannot retrieve cookies for Status or legacy connections" );
+        if ( cookie.indexOf( ':' ) == -1 )
+        {
+            // if we request an invalid resource location (no prefix) the client will respond with minecraft: prefix
+            cookie = "minecraft:" + cookie;
+        }
+        CompletableFuture<byte[]> future = new CompletableFuture<>();
+        requestedCookies.add( new CookieFuture( cookie, future ) );
+        unsafe.sendPacket( new CookieRequest( cookie ) );
+        return future;
+    }
+
+    public void storeCookie(String cookie, byte[] data)
+    {
+        Preconditions.checkState( getVersion() >= ProtocolConstants.MINECRAFT_1_20_5, "Cookies are only supported in 1.20.5 and above" );
+        Preconditions.checkState( loginRequest != null, "Cannot retrieve cookies for Status or legacy connections" );
+        unsafe().sendPacket( new StoreCookie( cookie, data ) );
+    }
 }

proxy/src/main/java/net/md_5/bungee/connection/UpstreamBridge.java

@@ -32,6 +32,7 @@
 import net.md_5.bungee.protocol.packet.ClientChat;
 import net.md_5.bungee.protocol.packet.ClientCommand;
 import net.md_5.bungee.protocol.packet.ClientSettings;
+import net.md_5.bungee.protocol.packet.CookieResponse;
 import net.md_5.bungee.protocol.packet.FinishConfiguration;
 import net.md_5.bungee.protocol.packet.KeepAlive;
 import net.md_5.bungee.protocol.packet.LoginAcknowledged;
@@ -363,6 +364,12 @@ public void handle(FinishConfiguration finishConfiguration) throws Exception
         con.sendQueuedPackets();
     }
 
+    @Override
+    public void handle(CookieResponse cookieResponse) throws Exception
+    {
+        con.getPendingConnection().handle( cookieResponse );
+    }
+
     @Override
     public String toString()
     {