Prevent sending disconnect if disposed

protocol.ts

@@ -13,6 +13,8 @@ export interface SocketOptions {
 }
 
 export class Protocol extends PersistentProtocol {
+	private disposed: boolean = false;
+
 	public constructor(
 		secWebsocketKey: string,
 		socket: net.Socket,
@@ -40,13 +42,22 @@ export class Protocol extends PersistentProtocol {
 		].join("\r\n") + "\r\n\r\n");
 	}
 
+	public sendDisconnect(): void {
+		if (!this.disposed) {
+			super.sendDisconnect();
+		}
+	}
+
 	public dispose(error?: Error): void {
+		if (!this.disposed) {
+			this.disposed = true;
 			if (error) {
 				this.sendMessage({ type: "error", reason: error.message });
 			}
 			super.dispose();
 			this.getSocket().dispose();
 		}
+	}
 
 	/**
 	 * Perform a handshake to get a connection request.