<?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.apache.guacamole&lt;/groupId>
    &lt;artifactId>guacamole-tutorial&lt;/artifactId>
    &lt;packaging>war&lt;/packaging>
    &lt;version>1.2.0&lt;/version>
    &lt;name>guacamole-tutorial&lt;/name>

    &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. This file, as well as any other future static files, belongs within
                    <filename>src/main/webapp</filename>.</para>
            <para>For now, this file can contain anything, since the other parts of our
                Guacamole-driven web application are not written yet. It is a placeholder which we
                will replace 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-1.2.0.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;version>3.3&lt;/version>
                &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;version>2.6&lt;/version>
                &lt;configuration>
                    &lt;overlays>
                        &lt;overlay>
                            &lt;groupId>org.apache.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.apache.guacamole&lt;/groupId>
            &lt;artifactId>guacamole-common&lt;/artifactId>
            &lt;version>1.1.0&lt;/version>
            &lt;scope>compile&lt;/scope>
        &lt;/dependency>

        &lt;!-- Guacamole JavaScript library -->
        &lt;dependency>
            &lt;groupId>org.apache.guacamole&lt;/groupId>
            &lt;artifactId>guacamole-common-js&lt;/artifactId>
            &lt;version>1.2.0&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>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-1.2.0/guacamole-common-js/all.min.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.apache.guacamole.net.example;

import javax.servlet.http.HttpServletRequest;
import org.apache.guacamole.GuacamoleException;
import org.apache.guacamole.net.GuacamoleSocket;
import org.apache.guacamole.net.GuacamoleTunnel;
import org.apache.guacamole.net.InetGuacamoleSocket;
import org.apache.guacamole.net.SimpleGuacamoleTunnel;
import org.apache.guacamole.protocol.ConfiguredGuacamoleSocket;
import org.apache.guacamole.protocol.GuacamoleConfiguration;
import org.apache.guacamole.servlet.GuacamoleHTTPTunnelServlet;

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
        );

        // Return a new tunnel which uses the connected socket
        return new SimpleGuacamoleTunnel(socket);;

    }

}</programlisting>
            </informalexample>
            <para>Place this file in the
                    <filename>src/main/java/org/apache/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.apache.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-1.2.0/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;!-- Guacamole -->
        &lt;script type="text/javascript"
            src="guacamole-common-js/all.min.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().getElement());
            
            // 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;!-- Init -->
        &lt;script type="text/javascript"> /* &lt;![CDATA[ */

            ...

            // Mouse
            var mouse = new Guacamole.Mouse(guac.getDisplay().getElement());

            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>