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<?xml version="1.0" encoding="UTF-8"?>
<chapter xml:id="writing-you-own-guacamole-app" xmlns="http://docbook.org/ns/docbook" version="5.0"
xml:lang="en" xmlns:xi="http://www.w3.org/2001/XInclude">
<title>Writing your own Guacamole application</title>
<indexterm xmlns:xl="http://www.w3.org/1999/xlink">
<primary>custom application</primary>
</indexterm>
<indexterm xmlns:xl="http://www.w3.org/1999/xlink">
<primary>application</primary>
<secondary>development</secondary>
</indexterm>
<para>As Guacamole is an API, one of the best ways to put Guacamole to use is by building your
own Guacamole-driven web application, integrating HTML5 remote desktop into whatever you
think needs it.</para>
<para>The Guacamole project provides an example of doing this called "guacamole-example", but
this example is already completed for you, and from a quick glance at this example, it may
not be obvious just how easy it is to integrate remote access into a web application. This
tutorial will walk you through the basic steps of building an HTML5 remote desktop
application using the Guacamole API and Maven.</para>
<section xml:id="basic-guacamole-architecture">
<title>The basics</title>
<para>Guacamole's architecture is made up of many components, but it's actually
straightforward, especially from the perspective of the web application.</para>
<para>Guacamole has a proxy daemon, guacd, which handles communication using remote desktop
protocols, exposing those to whatever connects to it (in this case, the web application)
using the Guacamole protocol. From where the web application is standing, it doesn't
really matter that guacd dynamically loads protocol plugins or that it shares a common
library allowing this; all that matters is that the web application just has to connect
to port 4822 (where guacd listens by default) and use the Guacamole protocol. The
architecture will take care of the rest.</para>
<para>Thankfully, the Java side of the Guacamole API provides simple classes which already
implement the Guacamole protocol with the intent of tunneling it between guacd and the
JavaScript half of your web application. A typical web application leveraging these
classes needs only the following:<orderedlist>
<listitem>
<para>A class which extends <classname>GuacamoleHTTPTunnelServlet</classname>,
providing the tunnel between the JavaScript client (presumably using
guacamole-common-js) and guacd.</para>
<para><classname>GuacamoleHTTPTunnelServlet</classname> is an abstract class
which is provided by the Guacamole API and already implements a fully
functional, HTTP-based tunnel which the tunneling objects already part of
guacamole-common-js are written to connect to. This class exists to make it
easy for you to use Guacamole's existing and robust HTTP tunnel
implementation.</para>
<para>If you want to not use this class and instead use your own tunneling
mechanism, perhaps WebSocket, this is fine; the JavaScript object mentioned
above implements a common interface which you can also implement, and the
Guacamole JavaScript client which is also part of guacamole-common-js will
happily use your implementation as long as it provides that
interface.</para>
</listitem>
<listitem>
<para>A web page which includes JavaScript files from guacamole-common-js and
uses the client and tunnel objects to connect back to the web
application.</para>
<para>The JavaScript API provided by the Guacamole project includes a full
implementation of the Guacamole protocol as a client, implementations of
HTTP and WebSocket-based tunnels, and mouse/keyboard/touch input
abstraction. Again, as the Guacamole protocol and all parts of the
architecture are documented here, you don't absolutely need to use these
objects, but it will make your life easier. Mouse and keyboard support in
JavaScript is finicky business, and the Guacamole client provided is
well-known to work with other components in the API, being the official
client of the project.</para>
</listitem>
</orderedlist></para>
<para>That's really all there is to it.</para>
<para>If you want authentication, the place to implement that would be in your extended
version of <classname>GuacamoleHTTPTunnelServlet</classname>; this is what the Guacamole
web application does. Besides authentication, there are many other things you could wrap
around your remote desktop application, but ultimately the base of all this is simple:
you have a tunnel which allows the JavaScript client to communicate with guacd, and you
have the JavaScript client itself, with the hard part already provided within
guacamole-common-js.</para>
</section>
<section xml:id="web-app-skeleton">
<title>Web application skeleton</title>
<para>As with most tutorials, this tutorial begins with creating a project skeleton that
establishes a minimal base for the tutorial to enhance in subsequent steps.</para>
<para>This tutorial will use Maven, which is the same build system used by the upstream
Guacamole project. As the Guacamole project has a Maven repository for both the Java and
JavaScript APIs, writing a Guacamole-based application using Maven is much easier; Maven
will download and use the Guacamole API automatically.</para>
<section>
<title><filename>pom.xml</filename></title>
<para>All Maven projects must have a project descriptor, the
<filename>pom.xml</filename> file, in the root directory of the project. This
file describes project dependencies and specific build requirements. Unlike other
build tools like Apache Ant or GNU Autotools, Maven chooses convention over
configuration: files within the project must be placed in specific locations, and
the project dependencies must be fully described in the pom.xml. If this is done,
the build will be handled automatically.</para>
<para>The basis of this Guacamole-driven web application will be a simple HTML file
which will ultimately become the client. While the finished product will have an
HTTP tunnel written in Java, we don't need this yet for our skeleton. We will create
a very basic, barebones Maven project containing only
<filename>index.html</filename> and a web application descriptor file,
<filename>web.xml</filename>. Once these files are in place, the project can be
packaged into a <filename>.war</filename> file which can be deployed to your servlet
container of choice (such as Apache Tomcat).</para>
<para>As this skeleton will contain no Java code, it has no dependencies, and no build
requirements beyond the metadata common to any Maven project. The
<filename>pom.xml</filename> is thus very simple for the time being:</para>
<informalexample>
<programlisting>&lt;project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/maven-v4_0_0.xsd">
&lt;modelVersion>4.0.0&lt;/modelVersion>
&lt;groupId>org.glyptodon.guacamole&lt;/groupId>
&lt;artifactId>guacamole-tutorial&lt;/artifactId>
&lt;packaging>war&lt;/packaging>
&lt;version>0.8.0&lt;/version>
&lt;name>guacamole-tutorial&lt;/name>
&lt;url>http://guac-dev.org/&lt;/url>
&lt;properties>
&lt;project.build.sourceEncoding>UTF-8&lt;/project.build.sourceEncoding>
&lt;/properties>
&lt;/project></programlisting>
</informalexample>
</section>
<section>
<title><filename>WEB-INF/web.xml</filename></title>
<para>Before the project will build, there needs to be a web application deployment
descriptor, <filename>web.xml</filename>. This file is required by the Java EE
standard for building the <filename>.war</filename> file which will contain the web
application, and will be read by the servlet container when the application is
actually deployed. For Maven to find and use this file when building the
<filename>.war</filename>, it must be placed in the
<filename>src/main/webapp/WEB-INF/</filename> directory.</para>
<informalexample>
<programlisting>&lt;?xml version="1.0" encoding="UTF-8"?>
&lt;web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
&lt;!-- Basic config -->
&lt;welcome-file-list>
&lt;welcome-file>index.html&lt;/welcome-file>
&lt;/welcome-file-list>
&lt;/web-app></programlisting>
</informalexample>
</section>
<section>
<title><filename>index.html</filename></title>
<para>With the <filename>web.xml</filename> file in place and the skeleton
<filename>pom.xml</filename> written, the web application will now build
successfully. However, as the <filename>web.xml</filename> refers to a "welcome
file" called <filename>index.html</filename> (which will ultimately contain our
client), we need to put this in place so the servlet container will have something
to serve. For now, this can be anything - we will replace it later:</para>
<informalexample>
<programlisting>&lt;!DOCTYPE HTML>
&lt;html>
&lt;head>
&lt;title>Guacamole Tutorial&lt;/title>
&lt;/head>
&lt;body>
&lt;p>Hello World&lt;/p>
&lt;/body>
&lt;/html></programlisting>
</informalexample>
</section>
<section>
<title>Building the skeleton</title>
<para>Once all three of the above files are in place, the web application will build,
and can even be deployed to your servlet container. It won't do anything yet other
than serve the <filename>index.html</filename> file, but it's good to at least try
building the web application to make sure nothing is missing and all steps were
followed correctly before proceeding:</para>
<informalexample>
<screen><prompt>$</prompt> mvn package
<computeroutput>[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Building guacamole-tutorial
[INFO] task-segment: [package]
[INFO] ------------------------------------------------------------------------
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4 seconds
[INFO] Finished at: Fri Jan 11 13:04:11 PST 2013
[INFO] Final Memory: 18M/128M
[INFO] ------------------------------------------------------------------------</computeroutput>
<prompt>$</prompt></screen>
</informalexample>
<para>Assuming you see the "<computeroutput>BUILD SUCCESSFUL</computeroutput>" message
when you build the web application, there will be a new file,
<filename>target/guacamole-tutorial-0.7.0.war</filename>, which can be deployed
to your servlet container and tested. If you changed the name or version of the
project in the <filename>pom.xml</filename> file, the name of this new
<filename>.war</filename> file will be different, but it can still be found
within <filename>target/</filename>.</para>
</section>
</section>
<section xml:id="guacamole-skeleton">
<title>Adding Guacamole</title>
<para>Once we have a functional web application built, the next step is to actually add the
references to the Guacamole API and integrate a Guacamole client into the
application.</para>
<section xml:id="adding-guac-to-pom">
<title>Updating <filename>pom.xml</filename></title>
<para>Now that we're adding Guacamole components to our project, we need to modify
<filename>pom.xml</filename> to specify which components are being used, and
where they can be obtained. With this information in place, Maven will automatically
resolve dependencies and download them as necessary during the build.</para>
<para>Regarding the build process itself, there are two main changes: we are now going
to be using Java, and we need the JavaScript files from guacamole-common-js included
automatically inside the <filename>.war</filename>.</para>
<para>Guacamole requires at least Java 1.6, thus we must add a section to the
<filename>pom.xml</filename> which describes the source and target Java
versions:</para>
<informalexample>
<programlisting> ...
&lt;build>
&lt;plugins>
&lt;!-- Compile using Java 1.6 -->
&lt;plugin>
&lt;groupId>org.apache.maven.plugins&lt;/groupId>
&lt;artifactId>maven-compiler-plugin&lt;/artifactId>
&lt;configuration>
&lt;source>1.6&lt;/source>
&lt;target>1.6&lt;/target>
&lt;/configuration>
&lt;/plugin>
&lt;/plugins>
&lt;/build>
...</programlisting>
</informalexample>
<para>Including the JavaScript files from an external project like guacamole-common-js
requires using a feature of the maven war plugin called overlays. To add an overlay
containing guacamole-common-js, we add a section describing the configuration of the
Maven war plugin, listing guacamole-common-js as an overlay:</para>
<informalexample>
<programlisting> ...
&lt;build>
&lt;plugins>
...
&lt;!-- Overlay guacamole-common-js (zip) -->
&lt;plugin>
&lt;groupId>org.apache.maven.plugins&lt;/groupId>
&lt;artifactId>maven-war-plugin&lt;/artifactId>
&lt;configuration>
&lt;overlays>
&lt;overlay>
&lt;groupId>org.glyptodon.guacamole&lt;/groupId>
&lt;artifactId>guacamole-common-js&lt;/artifactId>
&lt;type>zip&lt;/type>
&lt;/overlay>
&lt;/overlays>
&lt;/configuration>
&lt;/plugin>
&lt;/plugins>
&lt;/build>
...</programlisting>
</informalexample>
<para>With the build now configured, we still need to add dependencies and list the
repositories those dependencies can be downloaded from.</para>
<para>As this is a web application which will use the Java Servlet API, we must
explicitly include this as a dependency, as well as the Guacamole Java and
JavaScript APIs:</para>
<informalexample>
<programlisting> ...
&lt;dependencies>
&lt;!-- Servlet API -->
&lt;dependency>
&lt;groupId>javax.servlet&lt;/groupId>
&lt;artifactId>servlet-api&lt;/artifactId>
&lt;version>2.5&lt;/version>
&lt;scope>provided&lt;/scope>
&lt;/dependency>
&lt;!-- Main Guacamole library -->
&lt;dependency>
&lt;groupId>org.glyptodon.guacamole&lt;/groupId>
&lt;artifactId>guacamole-common&lt;/artifactId>
&lt;version>0.8.0&lt;/version>
&lt;scope>compile&lt;/scope>
&lt;/dependency>
&lt;!-- Guacamole JavaScript library -->
&lt;dependency>
&lt;groupId>org.glyptodon.guacamole&lt;/groupId>
&lt;artifactId>guacamole-common-js&lt;/artifactId>
&lt;version>0.7.1&lt;/version>
&lt;type>zip&lt;/type>
&lt;scope>runtime&lt;/scope>
&lt;/dependency>
&lt;/dependencies>
...</programlisting>
</informalexample>
<para>The Java Servlet API will be provided by your servlet container, so Maven does not
need to download it during the build, and it need not exist in any Maven
repository.</para>
<para>The Guacamole APIs <emphasis>are</emphasis> required, and are
<emphasis>not</emphasis> in any standard Maven repository, thus we must add the
URL of the upstream Maven repository exposed by the Guacamole project. This
repository will always have all stable releases of the Guacamole APIs:</para>
<informalexample>
<programlisting> ...
&lt;repositories>
&lt;!-- Main Guacamole repository -->
&lt;repository>
&lt;id>guac-dev&lt;/id>
&lt;url>http://guac-dev.org/repo&lt;/url>
&lt;/repository>
&lt;/repositories>
...</programlisting>
</informalexample>
<para>With these changes, the web application will still build at this point, even
though no Java code has been written yet. You may wish to verify that everything
still works.</para>
<para>If the <filename>pom.xml</filename> was updated properly as described above, the
web application should build successfully, and the Guacamole JavaScript API should
be accessible in the <filename>guacamole-common-js/</filename> subdirectory of your
web application after it is deployed. A quick check that you can access
<uri>/guacamole-tutorial-0.8.0/guacamole-common-js/guacamole.js</uri> is
probably worth the effort.</para>
</section>
<section xml:id="simple-tunnel">
<title>The simplest tunnel possible</title>
<para>As with the other tutorials in this book, we will keep this simple for the sake of
demonstrating the principles behind a Guacamole-based web application, and to give
developers a good idea of where to start looking when it's time to consult the API
documentation.</para>
<para>It is the duty of the class extending
<classname>GuacamoleHTTPTunnelServlet</classname> to implement a function called
<methodname>doConnect()</methodname>. This is the only function required to be
implemented, and in general it is the only function you should implement; the other
functions involved are already optimized for tunneling the Guacamole
protocol.</para>
<para>The <methodname>doConnect()</methodname> function returns a
<classname>GuacamoleTunnel</classname>, which provides a persistent
communication channel for <classname>GuacamoleHTTPTunnelServlet</classname> to use
when talking with guacd and initiating a connection with some arbitrary remote
desktop using some arbitrary remote desktop protocol. In our simple tunnel, this
configuration will be hard-coded, and no authentication will be attempted. Any user
accessing this web application will be immediately given a functional remote
desktop, no questions asked.</para>
<para>Create a new file, <filename>TutorialGuacamoleTunnelServlet.java</filename>,
defining a basic implementation of a tunnel servlet class:</para>
<informalexample>
<programlisting>
package org.glyptodon.guacamole.net.example;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import org.glyptodon.guacamole.GuacamoleException;
import org.glyptodon.guacamole.net.GuacamoleSocket;
import org.glyptodon.guacamole.net.GuacamoleTunnel;
import org.glyptodon.guacamole.net.InetGuacamoleSocket;
import org.glyptodon.guacamole.protocol.ConfiguredGuacamoleSocket;
import org.glyptodon.guacamole.protocol.GuacamoleConfiguration;
import org.glyptodon.guacamole.servlet.GuacamoleHTTPTunnelServlet;
import org.glyptodon.guacamole.servlet.GuacamoleSession;
public class TutorialGuacamoleTunnelServlet
extends GuacamoleHTTPTunnelServlet {
@Override
protected GuacamoleTunnel doConnect(HttpServletRequest request)
throws GuacamoleException {
// Create our configuration
GuacamoleConfiguration config = new GuacamoleConfiguration();
config.setProtocol("vnc");
config.setParameter("hostname", "localhost");
config.setParameter("port", "5901");
config.setParameter("password", "potato");
// Connect to guacd - everything is hard-coded here.
GuacamoleSocket socket = new ConfiguredGuacamoleSocket(
new InetGuacamoleSocket("localhost", 4822),
config
);
// Establish the tunnel using the connected socket
GuacamoleTunnel tunnel = new GuacamoleTunnel(socket);
// Attach tunnel to session
HttpSession httpSession = request.getSession(true);
GuacamoleSession session = new GuacamoleSession(httpSession);
session.attachTunnel(tunnel);
// Return pre-attached tunnel
return tunnel;
}
}</programlisting>
</informalexample>
<para>Place this file in the
<filename>src/main/java/net/sourceforge/guacamole/net/example</filename>
subdirectory of the project. The initial part of this subdirectory,
<filename>src/main/java</filename>, is the path required by Maven, while the
rest is the directory required by Java based on the package associated with the
class.</para>
<para>Once the class defining our tunnel is created, it must be added to the
<filename>web.xml</filename> such that the servlet container knows which URL
maps to it. This URL will later be given to the JavaScript client to establish the
connection back to the Guacamole server:</para>
<informalexample>
<programlisting> ...
&lt;!-- Guacamole Tunnel Servlet -->
&lt;servlet>
&lt;description>Tunnel servlet.&lt;/description>
&lt;servlet-name>Tunnel&lt;/servlet-name>
&lt;servlet-class>
org.glyptodon.guacamole.net.example.TutorialGuacamoleTunnelServlet
&lt;/servlet-class>
&lt;/servlet>
&lt;servlet-mapping>
&lt;servlet-name>Tunnel&lt;/servlet-name>
&lt;url-pattern>/tunnel&lt;/url-pattern>
&lt;/servlet-mapping>
...</programlisting>
</informalexample>
<para>The first section assigns a unique name, "Tunnel", to the servlet class we just
defined. The second section maps the servlet class by it's servlet name ("Tunnel")
to the URL we wish to use when making HTTP requests to the servlet:
<uri>/tunnel</uri>. This URL is relative to the context root of the web
application. In the case of this web application, the final absolute URL will be
<uri>/guacamole-tutorial-0.8.0/tunnel</uri>.</para>
</section>
<section xml:id="simple-client">
<title>Adding the client</title>
<para>As the Guacamole JavaScript API already provides functional client and tunnel
implementations, as well as mouse and keyboard input objects, the coding required
for the "web" side of the web application is very minimal.</para>
<para>We must create a <classname>Guacamole.HTTPTunnel</classname>, connect it to our
previously-implemented tunnel servlet, and pass that tunnel to a new
<classname>Guacamole.Client</classname>. Once that is done, and the
<methodname>connect()</methodname> function of the client is called,
communication will immediately ensue, and your remote desktop will be
visible:</para>
<informalexample>
<programlisting> ...
&lt;body>
&lt;!-- Client core scripts -->
&lt;script type="text/javascript"
src="guacamole-common-js/layer.js">&lt;/script>
&lt;script type="text/javascript"
src="guacamole-common-js/tunnel.js">&lt;/script>
&lt;script type="text/javascript"
src="guacamole-common-js/guacamole.js">&lt;/script>
&lt;!-- Display -->
&lt;div id="display">&lt;/div>
&lt;!-- Init -->
&lt;script type="text/javascript"> /* &lt;![CDATA[ */
// Get display div from document
var display = document.getElementById("display");
// Instantiate client, using an HTTP tunnel for communications.
var guac = new Guacamole.Client(
new Guacamole.HTTPTunnel("tunnel")
);
// Add client to display div
display.appendChild(guac.getDisplay());
// Error handler
guac.onerror = function(error) {
alert(error);
};
// Connect
guac.connect();
// Disconnect on close
window.onunload = function() {
guac.disconnect();
}
/* ]]&gt; */ &lt;/script>
&lt;/body>
...</programlisting>
</informalexample>
<para>If you build and deploy the web application now, it will work, but mouse and
keyboard input will not. This is because input is not implemented by the client
directly. The Guacamole.Client object only decodes the Guacamole protocol and
handles the display, providing an element which you can add manually to the DOM.
While it will also send keyboard and mouse events for you, you need to call the
respective functions manually. The Guacamole API provides keyboard and mouse
abstraction objects which make this easy.</para>
<para>We need only create a <classname>Guacamole.Mouse</classname> and
<methodname>Guacamole.Keyboard</methodname>, and add event handlers to handle
their corresponding input events, calling whichever function of the Guacamole client
is appropriate to send the input event through the tunnel to guacd:</para>
<informalexample>
<programlisting> ...
&lt;!-- Input abstractions -->
&lt;script type="text/javascript"
src="guacamole-common-js/keyboard.js">&lt;/script>
&lt;script type="text/javascript"
src="guacamole-common-js/mouse.js">&lt;/script>
...
&lt;!-- Init -->
&lt;script type="text/javascript"> /* &lt;![CDATA[ */
...
// Mouse
var mouse = new Guacamole.Mouse(guac.getDisplay());
mouse.onmousedown =
mouse.onmouseup =
mouse.onmousemove = function(mouseState) {
guac.sendMouseState(mouseState);
};
// Keyboard
var keyboard = new Guacamole.Keyboard(document);
keyboard.onkeydown = function (keysym) {
guac.sendKeyEvent(1, keysym);
};
keyboard.onkeyup = function (keysym) {
guac.sendKeyEvent(0, keysym);
};
/* ]]&gt; */ &lt;/script></programlisting>
</informalexample>
</section>
</section>
<section xml:id="next-steps">
<title>Where to go from here</title>
<para>At this point, we now have a fully functional Guacamole-based web application. This
web application inherits all the core functionality present in the official Guacamole
web application, including sound and video, without very much coding.</para>
<para>Extending this application to provide authentication, multiple connections per user,
or a spiffy interface which is compatible with mobile is not too much of a stretch. This
is exactly how the Guacamole web application is written. Integrating Guacamole into an
existing application would be similar.</para>
</section>
</chapter>