Add method in Connection API for transferring connections (#2891)

api/base/src/main/java/org/geysermc/api/session/Connection.java

@@ -26,6 +26,7 @@
 package org.geysermc.api.session;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.common.value.qual.IntRange;
 
 import java.util.UUID;
 
@@ -55,5 +56,13 @@ public interface Connection {
      */
     String xuid();
 
-
+    /**
+     * Transfer the connection to a server. A Bedrock player can successfully transfer to the same server they are
+     * currently playing on.
+     *
+     * @param address The address of the server
+     * @param port The port of the server
+     * @return true if the transfer was a success
+     */
+    boolean transfer(@NonNull String address, @IntRange(from = 0, to = 65535) int port);
 }

core/src/main/java/org/geysermc/geyser/session/GeyserSession.java

@@ -78,6 +78,7 @@ import lombok.AccessLevel;
 import lombok.Getter;
 import lombok.NonNull;
 import lombok.Setter;
+import org.checkerframework.common.value.qual.IntRange;
 import org.geysermc.common.PlatformType;
 import org.geysermc.cumulus.Form;
 import org.geysermc.cumulus.util.FormBuilder;
@@ -1310,6 +1311,21 @@ public class GeyserSession implements GeyserConnection, CommandSender {
         return authData.xuid();
     }
 
+    @SuppressWarnings("ConstantConditions") // Need to enforce the parameter annotations
+    @Override
+    public boolean transfer(@NonNull String address, @IntRange(from = 0, to = 65535) int port) {
+        if (address == null || address.isBlank()) {
+            throw new IllegalArgumentException("Server address cannot be null or blank");
+        } else if (port < 0 || port > 65535) {
+            throw new IllegalArgumentException("Server port must be between 0 and 65535, was " + port);
+        }
+        TransferPacket transferPacket = new TransferPacket();
+        transferPacket.setAddress(address);
+        transferPacket.setPort(port);
+        sendUpstreamPacket(transferPacket);
+        return true;
+    }
+
     @Override
     public void sendMessage(String message) {
         TextPacket textPacket = new TextPacket();