webapps/docs/web-socket-howto.xml - tomcat80 - Git at Google

 <?xml version="1.0" encoding="UTF-8"?>
 <!--
   Licensed to the Apache Software Foundation (ASF) under one or more
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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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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="Production usage">
 <p>Although the WebSocket implementation does work with any of the HTTP
 connectors, it is not recommended to the WebSocket with the BIO HTTP connector
 as the typical uses of WebSocket (large numbers of mostly idle connections) is
 not a good fit for the HTTP BIO connector which requires that one thread is
 allocated per connection regardless of whether or not the connection is idle.
 </p>

 <p>It has been reported (<bug>56304</bug>) that Linux can take large numbers of
 minutes to report dropped connections. When using WebSocket with the BIO HTTP
 connector this can result in threads blocking on writes for this period. This is
 likely to be undesirable. The time taken for the connection to be reported as
 dropped can be reduced by using the kernel network parameter
 <code>/proc/sys/net/ipv4/tcp_retries2</code>. Alternatively, one of the other
 HTTP connectors may be used as they utilise non-blocking IO enabling Tomcat to
 implement its own timeout mechanism to handle these cases.</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>The Java WebSocket 1.0 specification requires that callbacks for
    asynchronous writes are performed on a different thread to the thread that
    initiated the write. Since the container thread pool is not exposed via the
    Servlet API, the WebSocket implementation has to provide its own thread pool.
    This thread pool is controlled by the following servlet context
    initialization parameters:</p>
    <ul>
      <li><code>org.apache.tomcat.websocket.executorCoreSize</code>: The core
          size of the executor thread pool. If not set, the default of 0 (zero)
          is used. Note that the maximum permitted size of the executor thread
          pool is hard coded to <code>Integer.MAX_VALUE</code> which effectively
          means it is unlimited.</li>
      <li><code>org.apache.tomcat.websocket.executorKeepAliveTimeSeconds</code>:
          The maximum time an idle thread will remain in the executor thread pool
          until it is terminated. If not specified, the default of 60 seconds is
          used.</li>
    </ul>

 <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>
	<?xml version="1.0" encoding="UTF-8"?>
	<!--
	Licensed to the Apache Software Foundation (ASF) under one or more
	contributor license agreements. See the NOTICE file distributed with
	this work for additional information regarding copyright ownership.
	The ASF licenses this file to You under the Apache License, Version 2.0
	(the "License"); you may not use this file except in compliance with
	the License. You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->
	<!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="Production usage">
	<p>Although the WebSocket implementation does work with any of the HTTP
	connectors, it is not recommended to the WebSocket with the BIO HTTP connector
	as the typical uses of WebSocket (large numbers of mostly idle connections) is
	not a good fit for the HTTP BIO connector which requires that one thread is
	allocated per connection regardless of whether or not the connection is idle.
	</p>

	<p>It has been reported (<bug>56304</bug>) that Linux can take large numbers of
	minutes to report dropped connections. When using WebSocket with the BIO HTTP
	connector this can result in threads blocking on writes for this period. This is
	likely to be undesirable. The time taken for the connection to be reported as
	dropped can be reduced by using the kernel network parameter
	<code>/proc/sys/net/ipv4/tcp_retries2</code>. Alternatively, one of the other
	HTTP connectors may be used as they utilise non-blocking IO enabling Tomcat to
	implement its own timeout mechanism to handle these cases.</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>The Java WebSocket 1.0 specification requires that callbacks for
	asynchronous writes are performed on a different thread to the thread that
	initiated the write. Since the container thread pool is not exposed via the
	Servlet API, the WebSocket implementation has to provide its own thread pool.
	This thread pool is controlled by the following servlet context
	initialization parameters:</p>
	<ul>
	<li><code>org.apache.tomcat.websocket.executorCoreSize</code>: The core
	size of the executor thread pool. If not set, the default of 0 (zero)
	is used. Note that the maximum permitted size of the executor thread
	pool is hard coded to <code>Integer.MAX_VALUE</code> which effectively
	means it is unlimited.</li>
	<li><code>org.apache.tomcat.websocket.executorKeepAliveTimeSeconds</code>:
	The maximum time an idle thread will remain in the executor thread pool
	until it is terminated. If not specified, the default of 60 seconds is
	used.</li>
	</ul>

	<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>