add warning when trying to connect to the old websocket endpoints

LavalinkServer/src/main/java/lavalink/server/config/WebsocketConfig.kt

@@ -2,18 +2,32 @@ package lavalink.server.config
 
 import lavalink.server.io.HandshakeInterceptorImpl
 import lavalink.server.io.SocketServer
+import org.slf4j.LoggerFactory
 import org.springframework.context.annotation.Configuration
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.RestController
 import org.springframework.web.socket.config.annotation.EnableWebSocket
 import org.springframework.web.socket.config.annotation.WebSocketConfigurer
 import org.springframework.web.socket.config.annotation.WebSocketHandlerRegistry
 
 @Configuration
 @EnableWebSocket
+@RestController
 class WebsocketConfig(
     private val server: SocketServer,
     private val handshakeInterceptor: HandshakeInterceptorImpl,
 ) : WebSocketConfigurer {
+
+    companion object {
+        private val log = LoggerFactory.getLogger(WebsocketConfig::class.java)
+    }
+
     override fun registerWebSocketHandlers(registry: WebSocketHandlerRegistry) {
         registry.addHandler(server, "/v4/websocket").addInterceptors(handshakeInterceptor)
     }
+
+    @GetMapping("/", "/v3/websocket")
+    fun oldWebsocket() {
+        log.warn("This is the old Lavalink websocket endpoint. Please use /v4/websocket instead. If you are using a client library, please update it to a Lavalink v4 compatible version or use Lavalink v3 instead.")
+    }
 }