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<h1>Groovy API Manual</h1>
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<div>
<div class="toc">
<ul>
<li><a href="#writing-verticles">Writing Verticles</a><ul>
<li><a href="#compiled-groovy-verticles">Compiled Groovy verticles</a></li>
<li><a href="#asynchronous-start">Asynchronous start</a></li>
<li><a href="#verticle-clean-up">Verticle clean-up</a></li>
<li><a href="#the-container-object">The container object</a></li>
<li><a href="#the-vertx-object">The vertx object</a></li>
<li><a href="#getting-configuration-in-a-verticle">Getting Configuration in a Verticle</a></li>
<li><a href="#logging-from-a-verticle">Logging from a Verticle</a></li>
<li><a href="#accessing-environment-variables-from-a-verticle">Accessing environment variables from a Verticle</a></li>
<li><a href="#causing-the-container-to-exit">Causing the container to exit</a></li>
</ul>
</li>
<li><a href="#deploying-and-undeploying-verticles-programmatically">Deploying and Undeploying Verticles Programmatically</a><ul>
<li><a href="#deploying-a-simple-verticle">Deploying a simple verticle</a></li>
<li><a href="#deploying-worker-verticles">Deploying Worker Verticles</a></li>
<li><a href="#deploying-a-module-programmatically">Deploying a module programmatically</a></li>
<li><a href="#passing-configuration-to-a-verticle-programmatically">Passing configuration to a verticle programmatically</a></li>
<li><a href="#using-a-verticle-to-co-ordinate-loading-of-an-application">Using a Verticle to co-ordinate loading of an application</a></li>
<li><a href="#specifying-number-of-instances">Specifying number of instances</a></li>
<li><a href="#getting-notified-when-deployment-is-complete">Getting Notified when Deployment is complete</a></li>
<li><a href="#undeploying-a-verticle-or-module">Undeploying a Verticle or Module</a></li>
</ul>
</li>
<li><a href="#scaling-your-application">Scaling your application</a></li>
<li><a href="#the-event-bus">The Event Bus</a><ul>
<li><a href="#the-theory">The Theory</a><ul>
<li><a href="#addressing">Addressing</a></li>
<li><a href="#handlers">Handlers</a></li>
<li><a href="#publish-subscribe-messaging">Publish / subscribe messaging</a></li>
<li><a href="#point-to-point-and-request-response-messaging">Point to point and Request-Response messaging</a></li>
<li><a href="#transient">Transient</a></li>
<li><a href="#types-of-messages">Types of messages</a></li>
</ul>
</li>
<li><a href="#event-bus-api">Event Bus API</a><ul>
<li><a href="#registering-and-unregistering-handlers">Registering and Unregistering Handlers</a></li>
<li><a href="#publishing-messages">Publishing messages</a></li>
<li><a href="#sending-messages">Sending messages</a></li>
<li><a href="#replying-to-messages">Replying to messages</a></li>
<li><a href="#message-types">Message types</a></li>
</ul>
</li>
<li><a href="#distributed-event-bus">Distributed event bus</a></li>
</ul>
</li>
<li><a href="#shared-data">Shared Data</a><ul>
<li><a href="#shared-maps">Shared Maps</a></li>
<li><a href="#shared-sets">Shared Sets</a></li>
</ul>
</li>
<li><a href="#buffers">Buffers</a></li>
<li><a href="#buffers_1">Buffers</a><ul>
<li><a href="#creating-buffers">Creating Buffers</a></li>
<li><a href="#writing-to-a-buffer">Writing to a Buffer</a><ul>
<li><a href="#appending-to-a-buffer">Appending to a Buffer</a></li>
<li><a href="#random-access-buffer-writes">Random access buffer writes</a></li>
</ul>
</li>
<li><a href="#reading-from-a-buffer">Reading from a Buffer</a></li>
<li><a href="#other-buffer-methods">Other buffer methods:</a></li>
</ul>
</li>
<li><a href="#delayed-and-periodic-tasks">Delayed and Periodic Tasks</a><ul>
<li><a href="#one-shot-timers">One-shot Timers</a></li>
<li><a href="#periodic-timers">Periodic Timers</a></li>
<li><a href="#cancelling-timers">Cancelling timers</a></li>
</ul>
</li>
<li><a href="#writing-tcp-servers-and-clients">Writing TCP Servers and Clients</a><ul>
<li><a href="#net-server">Net Server</a><ul>
<li><a href="#creating-a-net-server">Creating a Net Server</a></li>
<li><a href="#start-the-server-listening">Start the Server Listening</a></li>
<li><a href="#getting-notified-of-incoming-connections">Getting Notified of Incoming Connections</a></li>
<li><a href="#closing-a-net-server">Closing a Net Server</a></li>
<li><a href="#netserver-properties">NetServer Properties</a></li>
<li><a href="#handling-data">Handling Data</a><ul>
<li><a href="#reading-data-from-the-socket">Reading Data from the Socket</a></li>
<li><a href="#writing-data-to-a-socket">Writing Data to a Socket</a></li>
</ul>
</li>
<li><a href="#socket-remote-address">Socket Remote Address</a></li>
<li><a href="#closing-a-socket">Closing a socket</a></li>
<li><a href="#closed-handler">Closed Handler</a></li>
<li><a href="#exception-handler">Exception handler</a></li>
<li><a href="#event-bus-write-handler">Event Bus Write Handler</a></li>
<li><a href="#read-and-write-streams">Read and Write Streams</a></li>
</ul>
</li>
<li><a href="#scaling-tcp-servers">Scaling TCP Servers</a></li>
<li><a href="#netclient">NetClient</a><ul>
<li><a href="#creating-a-net-client">Creating a Net Client</a></li>
<li><a href="#making-a-connection">Making a Connection</a></li>
<li><a href="#configuring-reconnection">Configuring Reconnection</a></li>
<li><a href="#netclient-properties">NetClient Properties</a></li>
</ul>
</li>
<li><a href="#ssl-servers">SSL Servers</a></li>
<li><a href="#ssl-clients">SSL Clients</a></li>
</ul>
</li>
<li><a href="#flow-control-streams-and-pumps">Flow Control - Streams and Pumps</a><ul>
<li><a href="#readstream">ReadStream</a></li>
<li><a href="#writestream">WriteStream</a></li>
<li><a href="#pump">Pump</a></li>
</ul>
</li>
<li><a href="#writing-http-servers-and-clients">Writing HTTP Servers and Clients</a><ul>
<li><a href="#writing-http-servers">Writing HTTP servers</a><ul>
<li><a href="#creating-an-http-server">Creating an HTTP Server</a></li>
<li><a href="#start-the-server-listening_1">Start the Server Listening</a></li>
<li><a href="#getting-notified-of-incoming-requests">Getting Notified of Incoming Requests</a></li>
<li><a href="#handling-http-requests">Handling HTTP Requests</a><ul>
<li><a href="#request-method">Request Method</a></li>
<li><a href="#request-uri">Request URI</a></li>
<li><a href="#request-path">Request Path</a></li>
<li><a href="#request-query">Request Query</a></li>
<li><a href="#request-headers">Request Headers</a></li>
<li><a href="#request-params">Request params</a></li>
<li><a href="#remote-address">Remote Address</a></li>
<li><a href="#absolute-uri">Absolute URI</a></li>
<li><a href="#reading-data-from-the-request-body">Reading Data from the Request Body</a></li>
<li><a href="#handling-multipart-form-uploads">Handling Multipart Form Uploads</a></li>
<li><a href="#handling-multipart-form-attributes">Handling Multipart Form Attributes</a></li>
</ul>
</li>
<li><a href="#http-server-responses">HTTP Server Responses</a></li>
<li><a href="#setting-status-code-and-message">Setting Status Code and Message</a><ul>
<li><a href="#writing-http-responses">Writing HTTP responses</a></li>
<li><a href="#ending-http-responses">Ending HTTP responses</a></li>
<li><a href="#closing-the-underlying-connection">Closing the underlying connection</a></li>
<li><a href="#response-headers">Response headers</a></li>
<li><a href="#chunked-http-responses-and-trailers">Chunked HTTP Responses and Trailers</a></li>
</ul>
</li>
<li><a href="#serving-files-directly-from-disk">Serving files directly from disk</a></li>
<li><a href="#pumping-responses">Pumping Responses</a></li>
</ul>
</li>
<li><a href="#writing-http-clients">Writing HTTP Clients</a><ul>
<li><a href="#creating-an-http-client">Creating an HTTP Client</a></li>
<li><a href="#pooling-and-keep-alive">Pooling and Keep Alive</a></li>
<li><a href="#closing-the-client">Closing the client</a></li>
<li><a href="#making-requests">Making Requests</a><ul>
<li><a href="#handling-exceptions">Handling exceptions</a></li>
<li><a href="#writing-to-the-request-body">Writing to the request body</a></li>
<li><a href="#ending-http-requests">Ending HTTP requests</a></li>
<li><a href="#writing-request-headers">Writing Request Headers</a></li>
<li><a href="#request-timeouts">Request timeouts</a></li>
<li><a href="#http-chunked-requests">HTTP chunked requests</a></li>
</ul>
</li>
<li><a href="#http-client-responses">HTTP Client Responses</a><ul>
<li><a href="#reading-data-from-the-response-body">Reading Data from the Response Body</a></li>
<li><a href="#reading-cookies">Reading cookies</a></li>
</ul>
</li>
<li><a href="#100-continue-handling">100-Continue Handling</a></li>
</ul>
</li>
<li><a href="#pumping-requests-and-responses">Pumping Requests and Responses</a></li>
<li><a href="#https-servers">HTTPS Servers</a></li>
<li><a href="#https-clients">HTTPS Clients</a></li>
<li><a href="#scaling-http-servers">Scaling HTTP servers</a></li>
</ul>
</li>
<li><a href="#routing-http-requests-with-pattern-matching">Routing HTTP requests with Pattern Matching</a><ul>
<li><a href="#specifying-matches">Specifying matches</a></li>
<li><a href="#extracting-parameters-from-the-path">Extracting parameters from the path</a></li>
<li><a href="#extracting-params-using-regular-expressions">Extracting params using Regular Expressions</a></li>
<li><a href="#handling-requests-where-nothing-matches">Handling requests where nothing matches</a></li>
</ul>
</li>
<li><a href="#websockets">WebSockets</a><ul>
<li><a href="#websockets-on-the-server">WebSockets on the server</a><ul>
<li><a href="#reading-from-and-writing-to-websockets">Reading from and Writing to WebSockets</a></li>
<li><a href="#rejecting-websockets">Rejecting WebSockets</a></li>
<li><a href="#headers-on-the-websocket">Headers on the websocket</a></li>
</ul>
</li>
<li><a href="#websockets-on-the-http-client">WebSockets on the HTTP client</a></li>
<li><a href="#websockets-in-the-browser">WebSockets in the browser</a></li>
</ul>
</li>
<li><a href="#sockjs">SockJS</a><ul>
<li><a href="#sockjs-server">SockJS Server</a></li>
<li><a href="#reading-and-writing-data-from-a-sockjs-server">Reading and writing data from a SockJS server</a></li>
<li><a href="#sockjs-client">SockJS client</a></li>
</ul>
</li>
<li><a href="#sockjs-eventbus-bridge">SockJS - EventBus Bridge</a><ul>
<li><a href="#setting-up-the-bridge">Setting up the Bridge</a></li>
<li><a href="#using-the-event-bus-from-client-side-javascript">Using the Event Bus from client side JavaScript</a></li>
<li><a href="#securing-the-bridge">Securing the Bridge</a></li>
<li><a href="#messages-that-require-authorisation">Messages that require authorisation</a></li>
</ul>
</li>
<li><a href="#file-system">File System</a><ul>
<li><a href="#synchronous-forms">Synchronous forms</a></li>
<li><a href="#copy">copy</a></li>
<li><a href="#move">move</a></li>
<li><a href="#truncate">truncate</a></li>
<li><a href="#chmod">chmod</a></li>
<li><a href="#props">props</a></li>
<li><a href="#lprops">lprops</a></li>
<li><a href="#link">link</a></li>
<li><a href="#symlink">symlink</a></li>
<li><a href="#unlink">unlink</a></li>
<li><a href="#readsymlink">readSymLink</a></li>
<li><a href="#delete">delete</a></li>
<li><a href="#mkdir">mkdir</a></li>
<li><a href="#readdir">readDir</a></li>
<li><a href="#readfile">readFile</a></li>
<li><a href="#writefile">writeFile</a></li>
<li><a href="#createfile">createFile</a></li>
<li><a href="#exists">exists</a></li>
<li><a href="#fsprops">fsProps</a></li>
<li><a href="#open">open</a></li>
<li><a href="#asyncfile">AsyncFile</a><ul>
<li><a href="#random-access-writes">Random access writes</a></li>
<li><a href="#random-access-reads">Random access reads</a></li>
<li><a href="#flushing-data-to-underlying-storage">Flushing data to underlying storage.</a></li>
<li><a href="#using-asyncfile-as-readstream-and-writestream">Using AsyncFile as ReadStream and WriteStream</a></li>
<li><a href="#closing-an-asyncfile">Closing an AsyncFile</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#dns-client">DNS Client</a><ul>
<li><a href="#lookup">lookup</a></li>
<li><a href="#lookup4">lookup4</a></li>
<li><a href="#lookup6">lookup6</a></li>
<li><a href="#resolvea">resolveA</a></li>
<li><a href="#resolveaaaa">resolveAAAA</a></li>
<li><a href="#resolvecname">resolveCNAME</a></li>
<li><a href="#resolvemx">resolveMX</a></li>
<li><a href="#resolvetxt">resolveTXT</a></li>
<li><a href="#resolvens">resolveNS</a></li>
<li><a href="#resolvesrv">resolveSRV</a></li>
<li><a href="#resolveptr">resolvePTR</a></li>
<li><a href="#reverselookup">reverseLookup</a></li>
<li><a href="#error-handling">Error handling</a><ul>
<li><a href="#noerror">NOERROR</a></li>
<li><a href="#formerror">FORMERROR</a></li>
<li><a href="#servfail">SERVFAIL</a></li>
<li><a href="#nxdomain">NXDOMAIN</a></li>
<li><a href="#notimpl">NOTIMPL</a></li>
<li><a href="#refused">REFUSED</a></li>
<li><a href="#yxdomain">YXDOMAIN</a></li>
<li><a href="#yxrrset">YXRRSET</a></li>
<li><a href="#nxrrset">NXRRSET</a></li>
<li><a href="#notzone">NOTZONE</a></li>
<li><a href="#badver">BADVER</a></li>
<li><a href="#badsig">BADSIG</a></li>
<li><a href="#badkey">BADKEY</a></li>
<li><a href="#badtime">BADTIME</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<h1 id="writing-verticles">Writing Verticles</h1><br/>
<p>As was described in the <a href="manual.html#verticle">main manual</a>, a verticle is the execution unit of Vert.x.</p>
<p>To recap, Vert.x is a container which executes packages of code called Verticles, and it ensures that the code in the verticle is never executed concurrently by more than one thread. You can write your verticles in any of the languages that Vert.x supports, and Vert.x supports running many verticle instances concurrently in the same Vert.x instance.</p>
<p>All the code you write in a Vert.x application runs inside a Verticle instance.</p>
<p>For simple prototyping and trivial tasks you can write raw verticles and run them directly on the command line, but in most cases you will always wrap your verticles inside Vert.x <a href="mods_manual.html">modules</a>.</p>
<p>For now, let's try writing a simple raw verticle.</p>
<p>As an example we'll write a simple TCP echo server. The server just accepts connections and any data received by it is echoed back on the connection.</p>
<p>Copy the following into a text editor and save it as <code>Server.groovy</code></p>
<pre class="prettyprint">import static org.vertx.groovy.core.streams.Pump.createPump
vertx.createNetServer().connectHandler { socket ->
createPump(socket, socket).start()
}.listen(1234)
</pre>
<p>Now run it:</p>
<pre class="prettyprint">vertx run Server.groovy
</pre>
<p>The server will now be running. Connect to it using telnet:</p>
<pre class="prettyprint">telnet localhost 1234
</pre>
<p>And notice how data you send (and hit enter) is echoed back to you. </p>
<p>Congratulations! You've written your first verticle.</p>
<p>A Groovy script verticle is simply a Groovy script that is executed when the verticle is deployed.</p>
<p><em>In the rest of this manual we'll assume the code snippets are running inside a verticle.</em></p>
<h2 id="compiled-groovy-verticles">Compiled Groovy verticles</h2><br/>
<p>You can also write Vert.x verticles as compiled Groovy classes. Here's an example of the source for a compiled Groovy verticle:</p>
<pre class="prettyprint">package examples
import org.vertx.groovy.platform.Verticle
import static org.vertx.groovy.core.streams.Pump.createPump
import org.vertx.groovy.core.Vertx
class EchoServer extends Verticle {
def start() {
vertx.createNetServer().connectHandler { socket ->
createPump(socket, socket).start()
}.listen(1234)
}
def stop() {
}
}
</pre>
<p>Once you've compiled it, you run it by specifing the classname prefixed with <code>groovy:</code>. We need the prefix to tell Vert.x to treat it as a Groovy class, not a Java class.</p>
<pre class="prettyprint">vertx run groovy:examples.EchoServer
</pre>
<h2 id="asynchronous-start">Asynchronous start</h2><br/>
<p>In some cases your Verticle has to do some other stuff asynchronous in its <code>start()</code> method, e.g. start other verticles, and the verticle shouldn't be considered started until those other actions are complete.</p>
<p>If this is the case for your compiled Groovy verticle you can override the asynchronous version of the <code>start()</code> method:</p>
<pre class="prettyprint">def start(Future<Void> startedResult) {
// For example - deploy some other verticle
container.deployVerticle("foo.js") { deployResult ->
if (deployResult.succeeded) {
startedResult.setResult(null)
} else {
startedResult.setFailure(deployResult.cause)
}
}
}
</pre>
<h2 id="verticle-clean-up">Verticle clean-up</h2><br/>
<p>Servers, clients, event bus handlers and timers will be automatically closed / cancelled when the verticle is stopped. However, if you have any other clean-up logic that you want to execute when the verticle is stopped, you can override the <code>stop</code> method in your compiled Groovy verticle or implement a top level <code>vertxStop</code> method in your Groovy script verticle which will be called when the verticle is undeployed. </p>
<pre class="prettyprint">import static org.vertx.groovy.core.streams.Pump.createPump
vertx.createNetServer().connectHandler { socket ->
createPump(socket, socket).start()
}.listen(1234)
def vertxStop() {
println 'Verticle has been undeployed'
}
</pre>
<h2 id="the-container-object">The <code>container</code> object</h2><br/>
<p>Each verticle instance has a property called <code>container</code>. This represents the Verticle's view of the container in which it is running.</p>
<p>The container object contains methods for deploying and undeploying verticle and modules, and also allows config, environment variables and a logger to be accessed.</p>
<h2 id="the-vertx-object">The <code>vertx</code> object</h2><br/>
<p>Each verticle instance has a property called <code>vertx</code>. This provides access to the Vert.x core API. You'll use the Core API to do most things in Vert.x including TCP, HTTP, file system access, event bus, timers etc.</p>
<h2 id="getting-configuration-in-a-verticle">Getting Configuration in a Verticle</h2><br/>
<p>You can pass configuration to a module or verticle from the command line using the <code>-conf</code> option, for example:</p>
<pre class="prettyprint">vertx runmod com.mycompany~my-mod~1.0 -conf myconf.json
</pre>
<p>or for a raw verticle</p>
<pre class="prettyprint">vertx run foo.js -conf myconf.json
</pre>
<p>The argument to <code>-conf</code> is the name of a text file containing a valid JSON object.</p>
<p>That configuration is available as a Map inside your verticle via the <code>config</code> property on the container:</p>
<pre class="prettyprint">def config = container.config
</pre>
<p>You can use this config to configure the verticle. Allowing verticles to be configured in a consistent way like this allows configuration to be easily passed to them irrespective of the language.</p>
<h2 id="logging-from-a-verticle">Logging from a Verticle</h2><br/>
<p>Each verticle is given its own logger. To get a reference to it use the <code>logger</code> property on the container instance:</p>
<pre class="prettyprint">def logger = container.logger
logger.info "I am logging something"
</pre>
<p>The logger is an instance of the class <code>org.vertx.core.logging.Logger</code> and has the following methods</p>
<ul>
<li>trace</li>
<li>debug</li>
<li>info</li>
<li>warn</li>
<li>error</li>
<li>fatal</li>
</ul>
<p>Which have the normal meanings you would expect.</p>
<p>The log files by default go in a file called <code>vertx.log</code> in the system temp directory. On my Linux box this is <code>\tmp</code>.</p>
<p>For more information on configuring logging, please see the main manual.</p>
<h2 id="accessing-environment-variables-from-a-verticle">Accessing environment variables from a Verticle</h2><br/>
<p>You can access the map of environment variables from a Verticle with the <code>env</code> property on the <code>container</code> object.</p>
<h2 id="causing-the-container-to-exit">Causing the container to exit</h2><br/>
<p>You can call the <code>exit()</code> method of the container to cause the Vert.x instance to make a clean shutdown.</p>
<h1 id="deploying-and-undeploying-verticles-programmatically">Deploying and Undeploying Verticles Programmatically</h1><br/>
<p>You can deploy and undeploy verticles programmatically from inside another verticle. Any verticles deployed this way will be able to see resources (classes, scripts, other files) of the main verticle.</p>
<h2 id="deploying-a-simple-verticle">Deploying a simple verticle</h2><br/>
<p>To deploy a verticle programmatically call the function <code>deployVerticle</code> on the <code>container</code> object. </p>
<p>To deploy a single instance of a verticle :</p>
<pre class="prettyprint">container.deployVerticle(main)
</pre>
<p>Where <code>main</code> is the name of the Verticle (i.e. the name of the script or FQCN of the class).</p>
<p>See the chapter on <a href="manual.html#running-vertx">"running Vert.x"</a> in the main manual for a description of what a main is.</p>
<h2 id="deploying-worker-verticles">Deploying Worker Verticles</h2><br/>
<p>The <code>deployVerticle</code> method deploys standard (non worker) verticles. If you want to deploy worker verticles use the <code>deployWorkerVerticle</code> method. This method takes the same parameters as <code>deployVerticle</code> with the same meanings.</p>
<h2 id="deploying-a-module-programmatically">Deploying a module programmatically</h2><br/>
<p>You should use <code>deployModule</code> to deploy a module, for example:</p>
<pre class="prettyprint">container.deployModule("io.vertx~mod-mailer~2.0.0-beta1", config)
</pre>
<p>Would deploy an instance of the <code>io.vertx~mod-mailer~2.0.0-beta1</code> module with the specified configuration. Please see the <a href="">modules manual</a> for more information about modules.</p>
<h2 id="passing-configuration-to-a-verticle-programmatically">Passing configuration to a verticle programmatically</h2><br/>
<p>JSON configuration can be passed to a verticle that is deployed programmatically. For example:</p>
<pre class="prettyprint">def config = [ foo: "wibble", bar: false]
container.deployVerticle("foo.ChildVerticle", config)
</pre>
<p>Then, in <code>ChildVerticle</code> you can access the config via the <code>config</code> property as previously explained.</p>
<h2 id="using-a-verticle-to-co-ordinate-loading-of-an-application">Using a Verticle to co-ordinate loading of an application</h2><br/>
<p>If you have an appplication that is composed of multiple verticles that all need to be started at application start-up, then you can use another verticle that maintains the application configuration and starts all the other verticles. You can think of this as your application starter verticle.</p>
<p>For example, you could create a verticle <code>AppStarter.groovy</code> as follows:</p>
<pre class="prettyprint">// Start the verticles that make up the app
container.deployVerticle("verticle1.js", appConfig["verticle1_conf"])
container.deployVerticle("verticle2.rb", appConfig["verticle2_conf"])
container.deployVerticle("foo.Verticle3", appConfig["verticle3_conf"])
container.deployWorkerVerticle("foo.Verticle4", appConfig["verticle4_conf"])
container.deployWorkerVerticle("verticle5.js", appConfig["verticle5_conf"], 10)
</pre>
<p>Then create a file 'config.json" with the actual JSON config in it</p>
<pre class="prettyprint">{
"verticle1_conf": {
"foo": "wibble"
},
"verticle2_conf": {
"age": 1234,
"shoe_size": 12,
"pi": 3.14159
},
"verticle3_conf": {
"strange": true
},
"verticle4_conf": {
"name": "george"
},
"verticle5_conf": {
"tel_no": "123123123"
}
}
</pre>
<p>Then set the <code>AppStarter.groovy</code> as the main of your module and then you can start your entire application by simply running:</p>
<pre class="prettyprint">vertx runmod com.mycompany~my-mod~1.0 -conf config.json
</pre>
<p>If your application is large and actually composed of multiple modules rather than verticles you can use the same technique.</p>
<h2 id="specifying-number-of-instances">Specifying number of instances</h2><br/>
<p>By default, when you deploy a verticle only one instance of the verticle is deployed. Verticles instances are strictly single threaded so this means you will use at most one core on your server.</p>
<p>Vert.x scales by deploying many verticle instances concurrently.</p>
<p>If you want more than one instance of a particular verticle or module to be deployed, you can specify the number of instances as follows:</p>
<pre class="prettyprint">container.deployVerticle("Foo.groovy", 10)
</pre>
<p>Or</p>
<pre class="prettyprint">container.deployModule("io.vertx~some-mod~1.0", 10)
</pre>
<p>The above examples would deploy 10 instances.</p>
<h2 id="getting-notified-when-deployment-is-complete">Getting Notified when Deployment is complete</h2><br/>
<p>The actual verticle deployment is asynchronous and might not complete until some time after the call to <code>deployVerticle</code> or <code>deployModule</code> has returned. If you want to be notified when the verticle has completed being deployed, you can pass a closure to <code>deployVerticle</code> or <code>deployModule</code>:</p>
<pre class="prettyprint">container.deployVerticle("Foo.groovy") { asyncResult ->
if (asyncResult.succeeded) {
println "The verticle has been deployed, deployment ID is ${asyncResult.result}"
} else {
asyncResult.cause.printStackTrace()
}
}
</pre>
<p>The handler will get passed an instance of <code>AsyncResult</code> when it completes. You can use the properties <code>succeeded</code> and <code>failed</code> on <code>AsyncResult</code> to see if the operation completed ok.</p>
<p>The property <code>result</code> provides the result of the async operation (if any) which in this case is the deployment ID - you will need this if you need to subsequently undeploy the verticle / module.</p>
<p>The property <code>cause</code> provides the <code>Throwable</code> if the action failed.</p>
<h2 id="undeploying-a-verticle-or-module">Undeploying a Verticle or Module</h2><br/>
<p>Any verticles or modules that you deploy programmatically from within a verticle, and all of their children are automatically undeployed when the parent verticle is undeployed, so in many cases you will not need to undeploy a verticle manually, however if you do need to do this, it can be done by calling the method <code>undeployVerticle</code> or <code>undeployModule</code> passing in the deployment id. </p>
<pre class="prettyprint">container.undeployVerticle(deploymentID)
</pre>
<p>You can also provide a handler to the undeploy method if you want to be informed when undeployment is complete.</p>
<h1 id="scaling-your-application">Scaling your application</h1><br/>
<p>A verticle instance is almost always single threaded (the only exception is multi-threaded worker verticles which are an advanced feature not intended for normal development), this means a single instance can at most utilise one core of your server.</p>
<p>In order to scale across cores you need to deploy more verticle instances. The exact numbers depend on your application - how many verticles there are and of what type.</p>
<p>You can deploy more verticle instances programmatically or on the command line when deploying your module using the <code>-instances</code> command line option.</p>
<h1 id="the-event-bus">The Event Bus</h1><br/>
<p>The event bus is the nervous system of Vert.x.</p>
<p>It allows verticles to communicate with each other irrespective of what language they are written in, and whether they're in the same Vert.x instance, or in a different Vert.x instance.</p>
<p>It even allows client side JavaScript running in a browser to communicate on the same event bus. (More on that later).</p>
<p>The event bus forms a distributed peer-to-peer network spanning multiple server nodes and multiple browsers.</p>
<p>The event bus API is incredibly simple. It basically involves registering handlers, unregistering handlers and sending and publishing messages.</p>
<p>First some theory:</p>
<h2 id="the-theory">The Theory</h2><br/>
<h3 id="addressing">Addressing</h3><br/>
<p>Messages are sent on the event bus to an <em>address</em>.</p>
<p>Vert.x doesn't bother with any fancy addressing schemes. In Vert.x an address is simply a string, any string is valid. However it is wise to use some kind of scheme, e.g. using periods to demarcate a namespace.</p>
<p>Some examples of valid addresses are <code>europe.news.feed1</code>, <code>acme.games.pacman</code>, <code>sausages</code>, and <code>X</code>.</p>
<h3 id="handlers">Handlers</h3><br/>
<p>A handler is a thing that receives messages from the bus. You register a handler at an address.</p>
<p>Many different handlers from the same or different verticles can be registered at the same address. A single handler can be registered by the verticle at many different addresses.</p>
<h3 id="publish-subscribe-messaging">Publish / subscribe messaging</h3><br/>
<p>The event bus supports <em>publishing</em> messages. Messages are published to an address. Publishing means delivering the message to all handlers that are registered at that address. This is the familiar <em>publish/subscribe</em> messaging pattern.</p>
<h3 id="point-to-point-and-request-response-messaging">Point to point and Request-Response messaging</h3><br/>
<p>The event bus supports <em>point to point</em> messaging. Messages are sent to an address. Vert.x will then route it to just one of the handlers registered at that address. If there is more than one handler registered at the address, one will be chosen using a non-strict round-robin algorithm.</p>
<p>With point to point messaging, an optional reply handler can be specified when sending the message. When a message is received by a recipient, and has been handled, the recipient can optionally decide to reply to the message. If they do so that reply handler will be called.</p>
<p>When the reply is received back at the sender, it too can be replied to. This can be repeated ad-infinitum, and allows a dialog to be set-up between two different verticles. This is a common messaging pattern called the <em>Request-Response</em> pattern.</p>
<h3 id="transient">Transient</h3><br/>
<p><em>All messages in the event bus are transient, and in case of failure of all or parts of the event bus, there is a possibility messages will be lost. If your application cares about lost messages, you should code your handlers to be idempotent, and your senders to retry after recovery.</em></p>
<p>If you want to persist your messages you can use a persistent work queue module for that.</p>
<h3 id="types-of-messages">Types of messages</h3><br/>
<p>Messages that you send on the event bus can be as simple as a string, a number or a boolean. You can also send Vert.x buffers or JSON messages.</p>
<p>It's highly recommended you use JSON messages to communicate between verticles. JSON is easy to create and parse in all the languages that Vert.x supports.</p>
<h2 id="event-bus-api">Event Bus API</h2><br/>
<p>Let's jump into the API.</p>
<h3 id="registering-and-unregistering-handlers">Registering and Unregistering Handlers</h3><br/>
<p>To set a message handler on the address <code>test.address</code>, you do something like the following:</p>
<pre class="prettyprint">def eb = vertx.eventBus
eb.registerHandler("test.address") { message -> println "I received a message ${message.body}" }
</pre>
<p>It's as simple as that. The handler will then receive any messages sent to that address.</p>
<p>The return value of <code>registerHandler</code> is the Event Bus itself, i.e. we provide a <em>fluent</em> API so you can chain multiple calls together. </p>
<p>When you register a handler on an address and you're in a cluster it can take some time for the knowledge of that new handler to be propagated across the entire cluster. If you want to be notified when that has completed you can optionally specify another handler to the <code>registerHandler</code> method as the third argument. This handler will then be called once the information has reached all nodes of the cluster. E.g. :</p>
<pre class="prettyprint">def myHandler = { message -> println "I received a message ${message.body}" }
eb.registerHandler("test.address", myHandler) { println "The handler has been registered across the cluster" }
</pre>
<p>To unregister a handler it's just as straightforward. You simply call <code>unregisterHandler</code> passing in the address and the handler:</p>
<pre class="prettyprint">eb.unregisterHandler("test.address", myHandler)
</pre>
<p>A single handler can be registered multiple times on the same, or different, addresses so in order to identify it uniquely you have to specify both the address and the handler.</p>
<p>As with registering, when you unregister a handler and you're in a cluster it can also take some time for the knowledge of that unregistration to be propagated across the entire to cluster. If you want to be notified when that has completed you can optionally specify another function to the registerHandler as the third argument. E.g. :</p>
<pre class="prettyprint">eb.unregisterHandler("test.address", myHandler) { println "The handler has been unregistered across the cluster" }
</pre>
<p>If you want your handler to live for the full lifetime of your verticle there is no need to unregister it explicitly - Vert.x will automatically unregister any handlers when the verticle is stopped.</p>
<h3 id="publishing-messages">Publishing messages</h3><br/>
<p>Publishing a message is also trivially easy. Just publish it specifying the address, for example:</p>
<pre class="prettyprint">eb.publish("test.address", "hello world")
</pre>
<p>That message will then be delivered to all handlers registered against the address "test.address".</p>
<h3 id="sending-messages">Sending messages</h3><br/>
<p>Sending a message will result in only one handler registered at the address receiving the message. This is the point to point messaging pattern. The handler is chosen in a non strict round-robin fashion.</p>
<pre class="prettyprint">eb.publish("test.address", "hello world")
</pre>
<h3 id="replying-to-messages">Replying to messages</h3><br/>
<p>Sometimes after you send a message you want to receive a reply from the recipient. This is known as the <em>request-response pattern</em>.</p>
<p>To do this you send a message, and specify a reply handler as the third argument. When the receiver receives the message they can reply to it by calling the <code>reply</code> method on the message.. When this method is invoked it causes a reply to be sent back to the sender where the reply handler is invoked. An example will make this clear:</p>
<p>The receiver:</p>
<pre class="prettyprint">def myHandler = { message ->
println "I received a message ${message.body}"
message.reply "This is a reply" // Reply to it
}
eb.registerHandler("test.address", myHandler)
</pre>
<p>The sender:</p>
<pre class="prettyprint">eb.send("test.address", "This is a message") { message ->
println "I received a reply ${message.body}"
}
</pre>
<p>It is legal also to send an empty reply or a null reply.</p>
<p>The replies themselves can also be replied to so you can create a dialog between two different verticles consisting of multiple rounds.</p>
<h3 id="message-types">Message types</h3><br/>
<p>The message you send can be any of the following types (or their matching boxed type):</p>
<ul>
<li>boolean</li>
<li>byte[]</li>
<li>byte</li>
<li>char</li>
<li>double</li>
<li>float</li>
<li>int</li>
<li>long</li>
<li>short</li>
<li>java.lang.String</li>
<li>java.util.Map - representing a JSON object</li>
<li>org.vertx.java.groovy.buffer.Buffer</li>
</ul>
<p>Vert.x buffers and JSON objects are copied before delivery if they are delivered in the same JVM, so different verticles can't access the exact same object instance.</p>
<p>Here are some more examples:</p>
<p>Send some numbers:</p>
<pre class="prettyprint">eb.send("test.address", 1234)
eb.send("test.address", 3.14159)
</pre>
<p>Send a boolean:</p>
<pre class="prettyprint">eb.send("test.address", true)
</pre>
<p>Send a JSON object:</p>
<pre class="prettyprint">eb.send("test.address", ["foo": "wibble", "bar": "eek"])
</pre>
<p>Null messages can also be sent:</p>
<pre class="prettyprint">eb.send("test.address", null)
</pre>
<p>It's a good convention to have your verticles communicating using JSON -this is because JSON is easy to generate and parse for all the languages that Vert.x supports.</p>
<h2 id="distributed-event-bus">Distributed event bus</h2><br/>
<p>To make each Vert.x instance on your network participate on the same event bus, start each Vert.x instance with the <code>-cluster</code> command line switch.</p>
<p>See the chapter in the main manual on <a href=""><em>running Vert.x</em></a> for more information on this. </p>
<p>Once you've done that, any Vert.x instances started in cluster mode will merge to form a distributed event bus. </p>
<h1 id="shared-data">Shared Data</h1><br/>
<p>Sometimes it makes sense to allow different verticles instances to share data in a safe way. Vert.x allows simple <code>java.util.concurrent.ConcurrentMap</code> and <code>java.util.Set</code> data structures to be shared between verticles.</p>
<p>There is a caveat: To prevent issues due to mutable data, vert.x only allows simple immutable types such as number, boolean and string or Buffer to be used in shared data. With a Buffer, it is automatically copied when retrieved from the shared data, so different verticle instances never see the same object instance.</p>
<p>Currently data can only be shared between verticles in the <em>same vert.x instance</em>. In later versions of vert.x we aim to extend this to allow data to be shared by all vert.x instances in the cluster.</p>
<h2 id="shared-maps">Shared Maps</h2><br/>
<p>To use a shared map to share data between verticles first we get a reference to the map, and then use it like any other instance of <code>java.util.concurrent.ConcurrentMap</code></p>
<pre class="prettyprint">def map = vertx.sharedData.getMap('demo.mymap')
map["some-key"] = 123
</pre>
<p>And then, in a different verticle you can access it:</p>
<pre class="prettyprint">def map = vertx.sharedData.getMap('demo.mymap')
// etc
</pre>
<h2 id="shared-sets">Shared Sets</h2><br/>
<p>To use a shared set to share data between verticles first we get a reference to the set.</p>
<pre class="prettyprint">def set = vertx.sharedData.getMap('demo.myset')
set << "some-value"
</pre>
<p>And then, in a different verticle:</p>
<pre class="prettyprint">def set = vertx.sharedData.getMap('demo.myset')
// etc
</pre>
<h1 id="buffers">Buffers</h1><br/>
<p>Most data in vert.x is shuffled around using instances of <code>org.vertx.groovy.core.buffer.Buffer</code>.</p>
<p>A Buffer represents a sequence of zero or more bytes that can be written to or read from, and which expands automatically as necessary to accomodate any bytes written to it. You can perhaps think of a buffer as smart byte array.</p>
<h1 id="buffers_1">Buffers</h1><br/>
<p>Most data in vert.x is shuffled around using instances of <code>org.vertx.groovy.core.buffer.Buffer</code>.</p>
<p>A Buffer represents a sequence of zero or more bytes that can be written to or read from, and which expands automatically as necessary to accomodate any bytes written to it. You can perhaps think of a buffer as smart byte array.</p>
<h2 id="creating-buffers">Creating Buffers</h2><br/>
<p>Create a new empty buffer:</p>
<pre class="prettyprint">def buff = new Buffer()
</pre>
<p>Create a buffer from a String. The String will be encoded in the buffer using UTF-8.</p>
<pre class="prettyprint">def buff = new Buffer("some-string")
</pre>
<p>Create a buffer from a String: The String will be encoded using the specified encoding, e.g:</p>
<pre class="prettyprint">def buff = new Buffer("some-string", "UTF-16")
</pre>
<p>Create a buffer from a byte[]</p>
<pre class="prettyprint">def bytes = ...
def buff = new Buffer(bytes)
</pre>
<p>Create a buffer with an initial size hint. If you know your buffer will have a certain amount of data written to it you can create the buffer and specify this size. This makes the buffer initially allocate that much memory and is more efficient than the buffer automatically resizing multiple times as data is written to it.</p>
<p>Note that buffers created this way <em>are empty</em>. It does not create a buffer filled with zeros up to the specified size.</p>
<pre class="prettyprint">def buff = new Buffer(100000)
</pre>
<h2 id="writing-to-a-buffer">Writing to a Buffer</h2><br/>
<p>There are two ways to write to a buffer: appending, and random access. In either case buffers will always expand automatically to encompass the bytes. It's not possible to get an <code>IndexOutOfBoundsException</code> with a buffer.</p>
<h3 id="appending-to-a-buffer">Appending to a Buffer</h3><br/>
<p>To append to a buffer, you use the <code>appendXXX</code> methods or the leftShift (<<) operator. Append methods exist for appending other buffers, byte[], String and all primitive types.</p>
<p>The return value of the <code>appendXXX</code> methods is the buffer itself, so these can be chained:</p>
<pre class="prettyprint">def buff = new Buffer()
// You can use the appendXXX methods
buff.appendInt(123).appendString("hello\n")
// Or use the leftShift operator
buff << 123 << "hello" << '\n'
socket << buff
</pre>
<h3 id="random-access-buffer-writes">Random access buffer writes</h3><br/>
<p>You can also write into the buffer at a specific index, by using the <code>setXXX</code> methods. Set methods exist for other buffers, byte[], String and all primitive types. All the set methods take an index as the first argument - this represents the position in the buffer where to start writing the data.</p>
<p>The buffer will always expand as necessary to accomodate the data.</p>
<pre class="prettyprint">def buff = new Buffer()
buff.setInt(1000, 123)
buff.setBytes(0, "hello")
</pre>
<p>You can also use the subscript operator to set data in the buffer at a specific index, e.g.</p>
<pre class="prettyprint">def buff = new Buffer()
buff[1000] = 123
buff[0] = "hello"
</pre>
<h2 id="reading-from-a-buffer">Reading from a Buffer</h2><br/>
<p>Data is read from a buffer using the <code>getXXX</code> methods. Get methods exist for byte[], String and all primitive types. The first argument to these methods is an index in the buffer from where to get the data.</p>
<pre class="prettyprint">def buff = ...
for (i in 0 ..< buff.length) {
println "byte value at $i is ${buff.getByte(i)}"
}
</pre>
<p>You can also use the subscript operator to get a byte</p>
<pre class="prettyprint">def buff = ...
for (i in 0 ..< buff.length) {
println "byte value at $i is ${buff[i]}"
}
</pre>
<h2 id="other-buffer-methods">Other buffer methods:</h2><br/>
<ul>
<li><code>length()</code>: To obtain the length of the buffer. The length of a buffer is the index of the byte in the buffer with the largest index + 1.</li>
<li><code>copy()</code>: Copy the entire buffer</li>
</ul>
<p>See the GroovyDoc for more detailed method level documentation. </p>
<h1 id="delayed-and-periodic-tasks">Delayed and Periodic Tasks</h1><br/>
<p>It's very common in Vert.x to want to perform an action after a delay, or periodically.</p>
<p>In standard verticles you can't just make the thread sleep to introduce a delay, as that will block the event loop thread.</p>
<p>Instead you use Vert.x timers. Timers can be <em>one-shot</em> or <em>periodic</em>. We'll discuss both</p>
<h2 id="one-shot-timers">One-shot Timers</h2><br/>
<p>A one shot timer calls an event handler after a certain delay, expressed in milliseconds. </p>
<p>To set a timer to fire once you use the <code>setTimer</code> method passing in the delay and a handler</p>
<pre class="prettyprint">def timerID = vertx.setTimer(1000) { timerID -> println "And one second later this is displayed" }
println "First this is printed"
</pre>
<p>The return value is a unique timer id which can later be used to cancel the timer. The handler is also passed the timer id.</p>
<h2 id="periodic-timers">Periodic Timers</h2><br/>
<p>You can also set a timer to fire periodically by using the <code>setPeriodic</code> method. There will be an initial delay equal to the period. The return value of <code>setPeriodic</code> is a unique timer id (long). This can be later used if the timer needs to be cancelled. The argument passed into the timer event handler is also the unique timer id:</p>
<pre class="prettyprint">def timerID = vertx.setPeriodic(1000) { timerID -> println "Every second this is displayed" }
println 'First this is printed'
</pre>
<h2 id="cancelling-timers">Cancelling timers</h2><br/>
<p>To cancel a periodic timer, call the <code>cancelTimer</code> method specifying the timer id. For example:</p>
<pre class="prettyprint">long timerID = vertx.setPeriodic(1000) {}
// And immediately cancel it
vertx.cancelTimer(timerID)
</pre>
<p>Or you can cancel it from inside the event handler. The following example cancels the timer after it has fired 10 times.</p>
<pre class="prettyprint">def count = 0
long timerID = vertx.setPeriodic(1000) { timerID ->
println "In event handler $count"
if (++count == 10) {
vertx.cancelTimer(timerID)
}
}
</pre>
<h1 id="writing-tcp-servers-and-clients">Writing TCP Servers and Clients</h1><br/>
<p>Creating TCP servers and clients is very easy with Vert.x.</p>
<h2 id="net-server">Net Server</h2><br/>
<h3 id="creating-a-net-server">Creating a Net Server</h3><br/>
<p>To create a TCP server you call the <code>createNetServer</code> method on your <code>vertx</code> instance.</p>
<pre class="prettyprint">def server = vertx.createNetServer()
</pre>
<h3 id="start-the-server-listening">Start the Server Listening</h3><br/>
<p>To tell that server to listen for connections we do: </p>
<pre class="prettyprint">def server = vertx.createNetServer()
server.listen(1234, "myhost")
</pre>
<p>The first parameter to <code>listen</code> is the port. A wildcard port of <code>0</code> can be specified which means a random available port will be chosen to actually listen at. Once the server has completed listening you can then call the <code>port</code> property of the server to find out the real port it is using.</p>
<p>The second parameter is the hostname or ip address. If it is omitted it will default to <code>0.0.0.0</code> which means it will listen at all available interfaces.</p>
<p>The actual bind is asynchronous so the server might not actually be listening until some time <em>after</em> the call to listen has returned. If you want to be notified when the server is actually listening you can provide a closure to the <code>listen</code> call. For example:</p>
<pre class="prettyprint">server.listen(1234, "myhost") { asyncResult ->
println "Listen succeeded? ${asyncResult.succeeded}"
}
</pre>
<h3 id="getting-notified-of-incoming-connections">Getting Notified of Incoming Connections</h3><br/>
<p>To be notified when a connection occurs we need to call the <code>connectHandler</code> method of the server, passing in a handler. The handler will then be called when a connection is made:</p>
<pre class="prettyprint">def server = vertx.createNetServer()
server.connectHandler { sock -> println "A client has connected!" }
server.listen(1234, "localhost")
</pre>
<p>That's a bit more interesting. Now it displays 'A client has connected!' every time a client connects. </p>
<p>The return value of the <code>connectHandler</code> method is the server itself, so multiple invocations can be chained together. That means we can rewrite the above as:</p>
<pre class="prettyprint">def server = vertx.createNetServer()
server.connectHandler { sock -> println "A client has connected!" }.listen(1234, "localhost")
</pre>
<p>or just</p>
<pre class="prettyprint">vertx.createNetServer().connectHandler { sock -> println "A client has connected!" }.listen(1234, "localhost")
</pre>
<p>This is a common pattern throughout the Vert.x API. </p>
<h3 id="closing-a-net-server">Closing a Net Server</h3><br/>
<p>To close a net server just call the <code>close</code> function.</p>
<pre class="prettyprint">server.close()
</pre>
<p>The close is actually asynchronous and might not complete until some time after the <code>close</code> method has returned. If you want to be notified when the actual close has completed then you can specify a closure to the <code>close</code> method.</p>
<p>This closure will then be called when the close has fully completed.</p>
<pre class="prettyprint">server.close { asyncResult ->
println "close succeeded? ${asyncResult.succeeded}"
}
</pre>
<p>If you want your net server to last the entire lifetime of your verticle, you don't need to call <code>close</code> explicitly, the Vert.x container will automatically close any servers that you created when the verticle is undeployed. </p>
<h3 id="netserver-properties">NetServer Properties</h3><br/>
<p>NetServer has a set of properties you can set which affect its behaviour. Firstly there are bunch of properties used to tweak the TCP parameters, in most cases you won't need to set these:</p>
<ul>
<li>
<p><code>tcpNoDelay</code>: If <code>tcpNoDelay</code> is true then <a href="http://en.wikipedia.org/wiki/Nagle's_algorithm">Nagle's Algorithm</a> is disabled. If false then it is enabled.</p>
</li>
<li>
<p><code>sendBufferSize</code>: Sets the TCP send buffer size in bytes.</p>
</li>
<li>
<p><code>receiveBufferSize</code>: Sets the TCP receive buffer size in bytes.</p>
</li>
<li>
<p><code>TCPKeepAlive</code>: if <code>keepAlive</code> is true then <a href="http://en.wikipedia.org/wiki/Keepalive#TCP_keepalive">TCP keep alive</a> is enabled, if false it is disabled.</p>
</li>
<li>
<p><code>reuseAddress</code>: if <code>reuse</code> is true then addresses in TIME_WAIT state can be reused after they have been closed.</p>
</li>
<li>
<p><code>soLinger</code></p>
</li>
<li>
<p><code>trafficClass</code></p>
</li>
</ul>
<p>NetServer has a further set of properties which are used to configure SSL. We'll discuss those later on.</p>
<h3 id="handling-data">Handling Data</h3><br/>
<p>So far we have seen how to create a NetServer, and accept incoming connections, but not how to do anything interesting with the connections. Let's remedy that now.</p>
<p>When a connection is made, the connect handler is called passing in an instance of <code>NetSocket</code>. This is a socket-like interface to the actual connection, and allows you to read and write data as well as do various other things like close the socket.</p>
<h4 id="reading-data-from-the-socket">Reading Data from the Socket</h4><br/>
<p>To read data from the socket you need to set the <code>dataHandler</code> on the socket. This handler will be called with an
instance of <code>org.vertx.groovy.core.buffer.Buffer</code> every time data is received on the socket. You could try the following code and telnet to it to send some data:</p>
<pre class="prettyprint">def server = vertx.createNetServer()
server.connectHandler { sock ->
sock.dataHandler { buffer ->
println "I received ${buffer.length} bytes of data"
}
}.listen(1234, "localhost")
</pre>
<h4 id="writing-data-to-a-socket">Writing Data to a Socket</h4><br/>
<p>To write data to a socket, you invoke the <code>write</code> method or leftShift operator This method can be invoked in a few ways:</p>
<p>With a single buffer:</p>
<pre class="prettyprint">def myBuffer = new Buffer(...)
sock.write(myBuffer)
// Or
sock << myBuffer
</pre>
<p>A string. In this case the string will encoded using UTF-8 and the result written to the wire.</p>
<pre class="prettyprint">sock.write("hello")
// Or
sock << "hello"
</pre>
<p>A string and an encoding. In this case the string will encoded using the specified encoding and the result written to the wire.</p>
<pre class="prettyprint">sock.write("hello", "UTF-16")
</pre>
<p>The <code>write</code> method or leftShift is asynchronous and always returns immediately after the write has been queued.</p>
<p>The actual write might occur some time later. </p>
<p>Let's put it all together.</p>
<p>Here's an example of a simple TCP echo server which simply writes back (echoes) everything that it receives on the socket:</p>
<pre class="prettyprint">def server = vertx.createNetServer()
server.connectHandler { sock ->
sock.dataHandler { buffer -> sock << buffer }
}.listen(1234, "localhost")
</pre>
<h3 id="socket-remote-address">Socket Remote Address</h3><br/>
<p>You can find out the remote address of the socket (i.e. the address of the other side of the TCP IP connection) with the property <code>remoteAddress</code>.</p>
<h3 id="closing-a-socket">Closing a socket</h3><br/>
<p>You can close a socket by invoking the <code>close</code> method. This will close the underlying TCP connection.</p>
<h3 id="closed-handler">Closed Handler</h3><br/>
<p>If you want to be notified when a socket is closed, you can set the `closedHandler':</p>
<pre class="prettyprint">def server = vertx.createNetServer()
server.connectHandler { sock ->
sock.closedHandler { println "The socket is now closed" }
}.listen(1234, "localhost")
</pre>
<p>The closed handler will be called irrespective of whether the close was initiated by the client or server.</p>
<h3 id="exception-handler">Exception handler</h3><br/>
<p>You can set an exception handler on the socket that will be called if an exception occurs asynchronously on the connection:</p>
<pre class="prettyprint">def server = vertx.createNetServer()
server.connectHandler { sock ->
sock.exceptionHandler { e -> println "Oops! $e" }
}.listen(1234, "localhost")
</pre>
<h3 id="event-bus-write-handler">Event Bus Write Handler</h3><br/>
<p>Every NetSocket automatically registers a handler on the event bus, and when any buffers are received in this handler, it writes them to itself. This enables you to write data to a NetSocket which is potentially in a completely different verticle or even in a different Vert.x instance by sending the buffer to the address of that handler.</p>
<p>The address of the handler is given by the <code>writeHandlerID</code> property.</p>
<p>For example to write some data to the NetSocket from a completely different verticle you could do:</p>
<pre class="prettyprint">def writeHandlerID = ... // E.g. retrieve the ID from shared data
vertx.eventBus.send(writeHandlerID, buffer)
</pre>
<h3 id="read-and-write-streams">Read and Write Streams</h3><br/>
<p>NetSocket also implements <code>org.vertx.groovy.core.streams.ReadStream</code> and <code>org.vertx.groovy.core.streams.WriteStream</code>. This allows flow control to occur on the connection and the connection data to be pumped to and from other object such as HTTP requests and responses, WebSockets and asynchronous files.</p>
<p>This will be discussed in depth in the chapter on <a href="#flow-control">streams and pumps</a>.</p>
<h2 id="scaling-tcp-servers">Scaling TCP Servers</h2><br/>
<p>A verticle instance is strictly single threaded.</p>
<p>If you create a simple TCP server and deploy a single instance of it then all the handlers for that server are always executed on the same event loop (thread).</p>
<p>This means that if you are running on a server with a lot of cores, and you only have this one instance deployed then you will have at most one core utilised on your server! </p>
<p>To remedy this you can simply deploy more instances of the module in the server, e.g.</p>
<pre class="prettyprint">vertx runmod com.mycompany~my-mod~1.0 -instances 20
</pre>
<p>Or for a raw verticle</p>
<pre class="prettyprint">vertx run Foo.groovy-instances 20
</pre>
<p>The above would run 20 instances of the module/verticle in the same Vert.x instance.</p>
<p>Once you do this you will find the echo server works functionally identically to before, but, <em>as if by magic</em>, all your cores on your server can be utilised and more work can be handled.</p>
<p>At this point you might be asking yourself <em>'Hold on, how can you have more than one server listening on the same host and port? Surely you will get port conflicts as soon as you try and deploy more than one instance?'</em></p>
<p><em>Vert.x does a little magic here</em>.</p>
<p>When you deploy another server on the same host and port as an existing server it doesn't actually try and create a new server listening on the same host/port.</p>
<p>Instead it internally maintains just a single server, and, as incoming connections arrive it distributes them in a round-robin fashion to any of the connect handlers set by the verticles.</p>
<p>Consequently Vert.x TCP servers can scale over available cores while each Vert.x verticle instance remains strictly single threaded, and you don't have to do any special tricks like writing load-balancers in order to scale your server on your multi-core machine.</p>
<h2 id="netclient">NetClient</h2><br/>
<p>A NetClient is used to make TCP connections to servers.</p>
<h3 id="creating-a-net-client">Creating a Net Client</h3><br/>
<p>To create a TCP client you call the <code>createNetClient</code> method on your <code>vertx</code> instance.</p>
<pre class="prettyprint">def client = vertx.createNetClient()
</pre>
<h3 id="making-a-connection">Making a Connection</h3><br/>
<p>To actually connect to a server you invoke the <code>connect</code> method:</p>
<pre class="prettyprint">def client = vertx.createNetClient()
client.connect(1234, "localhost") { asyncResult ->
if (asyncResult.succeeded) {
println "We have connected!"
} else {
asyncResult.cause.printStackTrace
}
}
</pre>
<p>The connect method takes the port number as the first parameter, followed by the hostname or ip address of the server. The third parameter is a closure. This closure will be called when the connection actually occurs.</p>
<p>The argument passed into the connect handler is an <code>AsyncResult<NetSocket></code>, and the <code>NetSocket</code> can be retrieved from the <code>result()</code> method. You can read and write data from the socket in exactly the same way as you do on the server side.</p>
<p>You can also close it, set the closed handler, set the exception handler and use it as a <code>ReadStream</code> or <code>WriteStream</code> exactly the same as the server side <code>NetSocket</code>.</p>
<h3 id="configuring-reconnection">Configuring Reconnection</h3><br/>
<p>A NetClient can be configured to automatically retry connecting or reconnecting to the server in the event that it cannot connect or has lost its connection. This is done by setting the properties <code>reconnectAttempts</code> and <code>reconnectInterval</code>:</p>
<pre class="prettyprint">def client = vertx.createNetClient()
client.reconnectAttempts = 1000
client.reconnectInterval = 500
</pre>
<p><code>reconnectAttempts</code> determines how many times the client will try to connect to the server before giving up. A value of <code>-1</code> represents an infinite number of times. The default value is <code>0</code> - i.e. no reconnection is attempted.</p>
<p><code>reconnectInterval</code> detemines how long, in milliseconds, the client will wait between reconnect attempts. The default
value is <code>1000</code>.</p>
<p>If an exception handler is set on the client, and reconnect attempts is not equal to <code>0</code>. Then the exception handler will not be called until the client gives up reconnecting.</p>
<h3 id="netclient-properties">NetClient Properties</h3><br/>
<p>Just like <code>NetServer</code>, <code>NetClient</code> also has a set of TCP properties you can set which affect its behaviour. They have the same meaning as those on <code>NetServer</code>.</p>
<p><code>NetClient</code> also has a further set of properties which are used to configure SSL. We'll discuss those later on.</p>
<h2 id="ssl-servers">SSL Servers</h2><br/>
<p>NNet servers can also be configured to work with <a href="http://en.wikipedia.org/wiki/Transport_Layer_Security">Transport Layer Security</a> (previously known as SSL).</p>
<p>When a <code>NetServer</code> is working as an SSL Server the API of the <code>NetServer</code> and <code>NetSocket</code> is identical compared to when it working with standard sockets. Getting the server to use SSL is just a matter of configuring the <code>NetServer</code> before <code>listen</code> is called.</p>
<p>To enable SSL the property <code>SSL</code> to <code>true</code> on the Net Server.</p>
<p>The server must also be configured with a <em>key store</em> and an optional <em>trust store</em>.</p>
<p>These are both <em>Java keystores</em> which can be managed using the <a href="http://docs.oracle.com/javase/6/docs/technotes/tools/solaris/keytool.html">keytool</a> utility which ships with the JDK.</p>
<p>The keytool command allows you to create keystores, and import and export certificates from them.</p>