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<?xml version="1.0" encoding="UTF-8"?>
<!--
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The ASF licenses this file to You under the Apache License, Version 2.0
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<!DOCTYPE document [
<!ENTITY project SYSTEM "project.xml">
]>
<document url="web-socket-howto.html">
&project;
<properties>
<title>WebSocket How-To</title>
</properties>
<body>
<section name="Table of Contents">
<toc/>
</section>
<section name="Overview">
<p>Tomcat provides support for WebSocket as defined by
<a href="https://tools.ietf.org/html/rfc6455">RFC 6455</a>.</p>
</section>
<section name="Application development">
<p>Tomcat implements the Java WebSocket 1.1 API defined by <a
href="https://www.jcp.org/en/jsr/detail?id=356">JSR-356</a>.</p>
<p>There are several example applications that demonstrate how the WebSocket API
can be used. You will need to look at both the client side <a
href="https://svn.apache.org/viewvc/tomcat/trunk/webapps/examples/websocket/">
HTML</a> and the server side <a
href="https://svn.apache.org/viewvc/tomcat/trunk/webapps/examples/WEB-INF/classes/websocket/">
code</a>.</p>
</section>
<section name="Tomcat WebSocket specific configuration">
<p>Tomcat provides a number of Tomcat specific configuration options for
WebSocket. It is anticipated that these will be absorbed into the WebSocket
specification over time.</p>
<p>The write timeout used when sending WebSocket messages in blocking mode
defaults to 20000 milliseconds (20 seconds). This may be changed by setting
the property <code>org.apache.tomcat.websocket.BLOCKING_SEND_TIMEOUT</code>
in the user properties collection attached to the WebSocket session. The
value assigned to this property should be a <code>Long</code> and represents
the timeout to use in milliseconds. For an infinite timeout, use
<code>-1</code>.</p>
<p>If the application does not define a <code>MessageHandler.Partial</code> for
incoming binary messages, any incoming binary messages must be buffered so
the entire message can be delivered in a single call to the registered
<code>MessageHandler.Whole</code> for binary messages. The default buffer
size for binary messages is 8192 bytes. This may be changed for a web
application by setting the servlet context initialization parameter
<code>org.apache.tomcat.websocket.binaryBufferSize</code> to the desired
value in bytes.</p>
<p>If the application does not define a <code>MessageHandler.Partial</code> for
incoming text messages, any incoming text messages must be buffered so the
entire message can be delivered in a single call to the registered
<code>MessageHandler.Whole</code> for text messages. The default buffer size
for text messages is 8192 bytes. This may be changed for a web application by
setting the servlet context initialization parameter
<code>org.apache.tomcat.websocket.textBufferSize</code> to the desired value
in bytes.</p>
<p>The Java WebSocket specification 1.0 does not permit programmatic deployment
after the first endpoint has started a WebSocket handshake. By default,
Tomcat continues to permit additional programmatic deployment. This
behavior is controlled by the
<code>org.apache.tomcat.websocket.noAddAfterHandshake</code> servlet context
initialization parameter. The default may be changed by setting the
<code>org.apache.tomcat.websocket.STRICT_SPEC_COMPLIANCE</code> system
property to <code>true</code> but any explicit setting on the servlet context
will always take priority.</p>
<p>When using the WebSocket client to connect to server endpoints, the timeout
for IO operations while establishing the connection is controlled by the
<code>userProperties</code> of the provided
<code>javax.websocket.ClientEndpointConfig</code>. The property is
<code>org.apache.tomcat.websocket.IO_TIMEOUT_MS</code> and is the
timeout as a <code>String</code> in milliseconds. The default is 5000 (5
seconds).</p>
<p>When using the WebSocket client to connect to secure server endpoints, the
client SSL configuration is controlled by the <code>userProperties</code>
of the provided <code>javax.websocket.ClientEndpointConfig</code>. The
following user properties are supported:</p>
<ul>
<li><code>org.apache.tomcat.websocket.SSL_CONTEXT</code></li>
<li><code>org.apache.tomcat.websocket.SSL_PROTOCOLS</code></li>
<li><code>org.apache.tomcat.websocket.SSL_TRUSTSTORE</code></li>
<li><code>org.apache.tomcat.websocket.SSL_TRUSTSTORE_PWD</code></li>
</ul>
<p>The default truststore password is <code>changeit</code>.</p>
<p>If the <code>org.apache.tomcat.websocket.SSL_CONTEXT</code> property is
set then the <code>org.apache.tomcat.websocket.SSL_TRUSTSTORE</code> and
<code>org.apache.tomcat.websocket.SSL_TRUSTSTORE_PWD</code> properties
will be ignored.</p>
<p>For secure server end points, host name verification is enabled by default.
To bypass this verification (not recommended), it is necessary to provide a
custom <code>SSLContext</code> via the
<code>org.apache.tomcat.websocket.SSL_CONTEXT</code> user property. The
custom <code>SSLContext</code> must be configured with a custom
<code>TrustManager</code> that extends
<code>javax.net.ssl.X509ExtendedTrustManager</code>. The desired verification
(or lack of verification) can then be controlled by appropriate
implementations of the individual abstract methods.</p>
<p>When using the WebSocket client to connect to server endpoints, the number of
HTTP redirects that the client will follow is controlled by the
<code>userProperties</code> of the provided
<code>javax.websocket.ClientEndpointConfig</code>. The property is
<ocde>org.apache.tomcat.websocket.MAX_REDIRECTIONS</ocde>. The default value
is 20. Redirection support can be disabled by configuring a value of zero.</p>
</section>
</body>
</document>