Table of Contents ***************** GNU WebSocket4J 1 WebSocket 2 Accepting connections 3 Connecting to server 4 Using an established socket Appendix A Example echo server Appendix B Example echo client 3 GNU Free Documentation License Index GNU WebSocket4J *************** This manual is for GNU WebSocket4J, version 1.3. 1 WebSocket *********** This chapter describes WebSocket protocol and it's GNU WebSocket4J implementation. WebSocket protocol ================== WebSocket is a protocol that provides bi-directional communication over a TCP socket, designed to be implemented in web browsers for use in HTML5 applications. While main use of this protocol is to allow a stable communication channel between a web server and JavaScript running in a web browser the protocol can be used by any application. JavaScript WebSocket API is being standardised by W3C (latest draft can be obtained from ). WebSocket protocol is being standardised by the IETF. Latest standard can be downloaded from . GNU WebSocket4J implementation ============================== GNU WebSocket4J is an implementation of WebSocket protocol in Java. GNU WebSocket4J tries to provide a simple API for both client and server sockets that would be as easy to use, as the WebSocket JavaScript API, or TCP sockets in Java standard library. *Note Accepting connections::, if you want to create a WebSocket server application. *Note Connecting to server::, if you want to create a WebSocket client application talking to a WebSocket server. 2 Accepting connections *********************** This chapter tells how to use GNU WebSocket4J in a server application. Naming convention ================= Throughout this chapter `WebServerSocket' will refer to `websocket4j.server.WebServerSocket' class and `WebSocket' will refer to `websocket4j.server.WebSocket' class. General idea ============ Accepting WebSocket connections is similar to using TCP sockets from the standard library. You have to create an instance of `WebServerSocket' (modelled after `java.net.ServerSocket'), and then you can use `accept() : WebSocket' method to get incoming connections. Accepted sockets have successfully completed an opening handshake and are ready to use (*note Using an established socket::). Creating a WebServerSocket instance =================================== `websocket4j.server.WebServerSocket' has two constructors, first without any parameters and second taking an `Integer'. Second one creates a new socket listening on port specified as an argument, and the first one chooses a random free port. If you create a socket listening on a random port, you can use `getLocalPort() : Integer' method to get that port number. Accepting new connnections ========================== `accept() : WebSocket' works similar to method, of `java.net.ServerSocket' class, of the same name. It waits until someone connects and returns an established socket. You can limit the time for which `accept' will block with `setSoTimeout(Integer) : void' method (provided `Integer' is time in milliseconds) -- if no client connects in this much time a `java.io.IOException' will be thrown. After you've accepted a socket, you can use `getRequestUri() : String' method of `WebSocket' to get URI requested by client, so you can decide what to do next with this socket. Closing the socket ================== Both `WebServerSocket' and `WebSocket' have `close() : void' method that closes the socket and ends connection in case of `WebSocket', or stops listening for new connections in case of `WebServerSocket'. `isClosed() : Boolean' method can be used to determine if socket is already closed. 3 Connecting to server ********************** This chapter tells how to use GNU WebSocket4J in a client application. Naming convention ================= Throughout this chapter `WebSocket' will refer to `websocket4j.client.WebSocket' class. General idea ============ `WebSocket' class works similar to `java.net.Socket' -- you have to create an instance providing information where it should connect to and you get back a socket that is ready to use (*note Using an established socket::). Creating a WebSocket instance ============================= `WebSocket' has two constructors, first one takes a `String', `Integer' and `String', second one takes an additional `Integer'. First `String' is the host name of the server you want to connect to, first `Integer' is port on which the server listens for incoming connections. Second `String' is URI that should be requested when connecting -- just as HTTP servers, WebSocket servers can handle multiple kinds of connections over one port. For example `new WebSocket("localhost", 5432, "/echo")' would connect to localhost on port 5432 and request /echo URI. In JavaScript API you'd use `ws://localhost:5432/echo' URI to connect to the same server. Fourth, optional, argument of the constructor is timeout in milliseconds, if the opening handshake takes more time than this, an IOException will be thrown. Closing the socket ================== Just like the server socket, client sockets have `close() : void' method that ends the connection. Also you can use `isClosed() : Boolean' method to check if the socket is already closed. 4 Using an established socket ***************************** Once a connection is established and you have an instance of either `websocket4j.client.WebSocket', or `websocket4j.server.WebSocket' you can use them in uniform way to send and receive messages. Naming convention ================= Throughout this chapter `WebSocket' will refer to both `websocket4j.client.WebSocket' and `websocket4j.server.WebSocket'. Sending messages ================ To send messages you can use `sendMessage(String) : void' method of WebSocket. This method immediately sends given string to the other party. Receiving ========= To receive messages you can use synchronous `getMessage(void) : String' method of WebSocket. This method waits until the other party sends a message and then returns it. Appendix A Example echo server ****************************** This chapter shows how to build a simple threaded echo server. This example is included in the distributed package in 'src/websocket4j/examples/EchoServer.java'. package websocket4j.examples; /** * This file is part of GNU WebSocket4J. * Copyright (C) 2010 Marek Aaron Sapota * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * As a special exception, the copyright holders of this library give you * permission to link this library with independent modules to produce an * executable, regardless of the license terms of these independent modules, * and to copy and distribute the resulting executable under terms of your choice, * provided that you also meet, for each linked independent module, the terms and * conditions of the license of that module. An independent module is a module * which is not derived from or based on this library. If you modify this library, * you may extend this exception to your version of the library, but you are not * obligated to do so. If you do not wish to do so, delete this exception * statement from your version. */ import java.io.IOException; import websocket4j.server.WebServerSocket; import websocket4j.server.WebSocket; /** * Example presenting an echo server using WebSocket4j. */ public class EchoServer extends Thread { private WebSocket ws; public EchoServer(WebSocket ws) { this.ws = ws; } private void handleConnection() { try { while (true) { String message = ws.getMessage(); ws.sendMessage(message); System.out.println("Received: " + message); if (message.equals("exit")) break; } } catch (IOException e) { }finally { try { ws.close(); } catch (IOException e) { } } } public void run() { handleConnection(); } public static void main(String[] args) throws IOException { WebServerSocket socket = new WebServerSocket(5555); try { while (true) { WebSocket ws = socket.accept(); System.out.println("GET " + ws.getRequestUri()); if (ws.getRequestUri().equals("/echo")) (new EchoServer(ws)).start(); else { System.out.println("Unsupported Request-URI"); try { ws.close(); } catch (IOException e) { } } } } finally { socket.close(); } } } Appendix B Example echo client ****************************** This chapter shows how to build a simple echo client reading from stdin. This example is included in the distributed package in 'src/websocket4j/examples/EchoClient.java'. package websocket4j.examples; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import websocket4j.client.WebSocket; /** * This file is part of GNU WebSocket4J. * Copyright (C) 2010 Marek Aaron Sapota * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * As a special exception, the copyright holders of this library give you * permission to link this library with independent modules to produce an * executable, regardless of the license terms of these independent modules, * and to copy and distribute the resulting executable under terms of your choice, * provided that you also meet, for each linked independent module, the terms and * conditions of the license of that module. An independent module is a module * which is not derived from or based on this library. If you modify this library, * you may extend this exception to your version of the library, but you are not * obligated to do so. If you do not wish to do so, delete this exception * statement from your version. */ /** * Example presenting an echo client using WebSocket4J. */ public class EchoClient { public static void main(String[] args) throws IOException { BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); WebSocket ws = new WebSocket("localhost", 5555, "/echo"); while (true) { String message = in.readLine(); ws.sendMessage(message); System.out.println("Response: " + ws.getMessage()); if (message.equals("exit")) break; } ws.close(); } } 3 GNU Free Documentation License ******************************** Version 1.3, 3 November 2008 Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. `http://fsf.org/' Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. 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The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing. ADDENDUM: How to use this License for your documents ==================================================== To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: Copyright (C) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with...Texts." line with this: with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation. If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software. Index ***** accepting WebSocket connections: See 2. (line 57) connecting to WebSocket server: See 3. (line 112) GNU WebSocket4J: See 1. (line 43) making a WebSocket client: See 3. (line 112) making a WebSocket server: See 2. (line 57) protocol: See 1. (line 29) receiving messages: See 4. (line 178) sending messages: See 4. (line 171) using an established socket: See 4. (line 158) WebSocket: See 1. (line 29) WebSocket protocol: See 1. (line 29) WebSocket4J: See 1. (line 43)