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To tag functions as WebSocket functions you have to use [[XQuery 3.0#Annotations|annotations]]. The annotation is written after the keyword ''declare'' and before the keyword ''function''. For the context of WebSockets there are some annotations listed below. Functions which are annotated with a WebSocket annotation will be called if the appropriate event occurs. For example, the function annotated with <code>ws:connect('/')</code> will be executed if a client establishes a connection with the WebSocket root path (which is, by default, <code>ws/</code>). By using annotations, it’s easy to provide an API for your WebSocket connection. You just have to specify what to do when a WebSocket Event occurs, annotate it with the corresponding annotation and the Servlet will do the rest for you.

Called directly after a successful WebSocket handshake. The <code>path</code> specifies the path which a client is connected to. You can specify here how to handle your users, f.e. save a name as a WebSocket attribute. Furthermore, you can check here some of the header-params for validity. :

<syntaxhighlight lang=="xquery">declare %ws:messageconnect('/') function local:connect(path,message)=={ };</syntaxhighlight>

You can specify here how to handle your users, e. g. save a name as a WebSocket attribute. Furthermore, you can check header parameters for validity.  ==ws:message(path, message)== Called when a <code>client message</code> arrives at the server. The <code>path</code> specifies the path which a client is connected to. The <code>message</code> is string contains the name of the variable to which the message will be bound: <syntaxhighlight lang="xquery">declare %ws:message('/', '{$info}') function local:message($info) { };</syntaxhighlight> The value will be of type <code>xs:string</code>messageor <code>xs:base64Binary</code> sent by . As there is no fixed message protocol, the clientneeds to take care of the message syntax. Could be a text- ==ws:error(path, message or )== Called when an error occurs. The <code>path</code> specifies the path which a binary-client is connected to. The <code>message. It should be ensured that </code> string contains the format name of the variable to which the message is correctwill be bound: <syntaxhighlight lang="xquery">declare %ws:error('/', '{$error}') function local:error($error) { };</syntaxhighlight> Usually, errors happen because of bad/malformed incoming packets. The WebSocket connection gets closed after the error handling.

Called when the WebSocket closes. The <code>path</code> specifies the path which a client is connected to.: <syntaxhighlight lang="xquery">declare %ws:close('/') function local:connect() { };</syntaxhighlight> 

==ws:errorheader-param(name, variable[, default])== For accessing connection-specific properties like the HTTP version. The value will be bound to the specified <code>variable</code>. If the property has no value, an optional <code>default</code> value will be assigned instead: <syntaxhighlight lang="xquery">declare %ws:close('host', '{$host}') %ws:header-param(path'host', message'{$host}')function local:close($host) { admin:write-log('Connection was closed: ' || $host)};</syntaxhighlight> The following parameters are available: {| class="wikitable" |- valign="top"! Name! Description|- valign="top"| <code>host</code>| The host of the request URI.|- valign="top"| <code>http-version</code>| The HTTP version used for the request.|- valign="top"| <code>is-secure</code>| Indicates if the connection is secure.|- valign="top"| <code>origin</code>| The WebSocket origin.|- valign="top"| <code>protocol-version</code>| The version of the used protocol.|- valign="top"| <code>query-string</code>| The query string of the request URI.|- valign="top"| <code>request-uri</code>| The Request URI to use for this request.|- valign="top"| <code>sub-protocols</code>| List of configured sub-protocols.|} General information on the request can be retrieved via the [[Request Module]]. =Writing Applications= The [[WebSocket Module]] contains functions for interacting with other clients or manage specific clients. For example, you can store and access client-specific properties for a WebSocket connection or close the connection of clients. Note that one WebSocket connection can be opened per browser tab. In contrast, only one HTTP session exists for multiple tabs in in a browser. If you want to keep client-specific data on the web server, you can either store them in HTTP sessions or in the WebSocket connection. Note further that the results of functions annotated with <code>%ws:close</code> or <code>%ws:error</code> will not be transmitted to the client. Both annotations have rather been designed to gracefully close connections, write log data, remove clients from session data, etc.

Called when an error has occurred. Usually, this happens because of bad/malformed incoming packets. The <code>path</code> specifies For keeping the path which a client connection alive it is connected recommendable to use heart-beats, and send regular pings tothe server. The <code>message</code> There is the error message. The WebSocket connection gets closed after the error handlingno ideal timespan for sending pings: It should not be sent too often, but you should also consider possible network latencies.

==If your HTTP connection is secure, you should use the <code>wss</code> instead of the <code>ws:header-param(name,variable[,default])==</code> scheme.

For accessing specific parameters like If you get the Http<code>[basex:ws] WebSocket connection required</code> error, you may be attempting to call WebSocket functions from a non-Version or WebSocket context. If you use a proxy server, check in the Sec-WebSocket-Versionconfiguration if WebSockets are enabled.

=Examples==Parameters===The following list shows the parameters of a WebSocket. You can access the parameters via the annotation <code>%ws:header-param(name,variable[,default])</code>* Http-Version -> f.e.: <code>%ws:param("Http-Version", "{$version}")</code>* Origin* Protocol-Version* QueryString* IsSecure* RequestURI* Host* Sec-WebSocket-Version* offset -> just for binary-Messages* len -> just for binary-Messages

=Tipps=Basic Example==

* For interacting The following chapter explains how to create a simple basic web application with other clients or manage specific clients you should check out the [[WebSocket Module]] as wellWebSockets.* The results of functions annotated with <code>%ws:close</code> or <code>%ws:error</code> will not be transmitted to You can find another example in the client* For keeping the connection alive it is possible to implement heart-beats * Use <BaseX source code>wss</code> instead of <code>ws</code> for a secure WebSocket connection* If you use a proxy server, check its configuration if WebSocket support is enabled.

=Example=The following chapter explains how to create a simple basic webapplication with websockets. You can find another example in the BaseX source code. First of all , you have to ensure that the <code>WsServlet </code> is enabled in your <code>web.xml</code>file. It will be enabled if you use the standard <code>web.xml</code>configuration of BaseX.

For establishing a connection to the WebSocket server , it is necessary that the server provides at least one function annotated with a WebSocket annotation. Lets Let’s start by using the annotation <code>%ws:connect('/')</code>.In the connect function, specific WebSocket a bidirectional communication with the client can be initialized: attributes like such as the id and nameof a client can be set, emit or a welcome message can be emitted to other connected users, write database entries, do nothing, ... can be setand so on.

<pre classsyntaxhighlight lang="brush:xquery">

</presyntaxhighlight> The connect function is sufficient for creating the persistent client/server connection. In order to something sensible with the connection, you should implement a function annotated with <code>%ws:message("/")</code>:

With the state until now you can create a connection between client and server. For doing sth. senseful with the WebSocket connection you should implement a function annotated with <code>%ws:message("/")</code>.<pre classsyntaxhighlight lang="brush:xquery">

$message as xs:string

</presyntaxhighlight> In the function above , the [[WebSocket Module]] is imported, and the WebSocketModule function <code>ws:emit</code> is used for forwarding the message to all connected clients. Notice that you have to import  The following client-side code demonstrates a basic application of the [[WebSocket Module]] before using it. connection:

With the code above it is possible to implement client-side functionality to connect to a <syntaxhighlight lang="javascript">var ws = new WebSocket and send("ws://receive messages via the WebSocket.Following client-side code shows basic usage of the WebSocket connectionlocalhost:8984/ws");

</presyntaxhighlight> The <code>send</code> function can be called to pass on a string to the server. There are no heart-beats in this example. This means that the connection is terminated if nothing happens for 5 minutes (standard timeout). It will also be closed if you send a message that exceeds the standard text size. ==Chat Application== In the full distributions of BaseX, you will find a little self-contained chat application that demonstrates how WebSockets can be used in practice. =Changelog=

There are no heartbeats in this exampleWebSockets werre introduced with Version 9. This means that the connection is terminated if nothing happens for 5 minutes (standard timeout).If you send a message which exceeds the textsize of 3kb defined in the <code>web.xml</code> the connection gets closed too1.