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243 lines
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<html lang="en"><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><link href="../images/docs-stylesheet.css" rel="stylesheet" type="text/css"><title>Apache Tomcat 9 Configuration Reference (9.0.76) - The HTTP2 Upgrade Protocol</title></head><body><div id="wrapper"><header><div id="header"><div><div><div class="logo noPrint"><a href="https://tomcat.apache.org/"><img alt="Tomcat Home" src="../images/tomcat.png"></a></div><div style="height: 1px;"></div><div class="asfLogo noPrint"><a href="https://www.apache.org/" target="_blank"><img src="../images/asf-logo.svg" alt="The Apache Software Foundation" style="width: 266px; height: 83px;"></a></div><h1>Apache Tomcat 9 Configuration Reference</h1><div class="versionInfo">
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Version 9.0.76,
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<time datetime="2023-06-05">Jun 5 2023</time></div><div style="height: 1px;"></div><div style="clear: left;"></div></div></div></div></header><div id="middle"><div><div id="mainLeft" class="noprint"><div><nav><div><h2>Links</h2><ul><li><a href="../index.html">Docs Home</a></li><li><a href="index.html">Config Ref. Home</a></li><li><a href="https://cwiki.apache.org/confluence/display/TOMCAT/FAQ">FAQ</a></li><li><a href="#comments_section">User Comments</a></li></ul></div><div><h2>Top Level Elements</h2><ul><li><a href="server.html">Server</a></li><li><a href="service.html">Service</a></li></ul></div><div><h2>Executors</h2><ul><li><a href="executor.html">Executor</a></li></ul></div><div><h2>Connectors</h2><ul><li><a href="http.html">HTTP/1.1</a></li><li><a href="http2.html">HTTP/2</a></li><li><a href="ajp.html">AJP</a></li></ul></div><div><h2>Containers</h2><ul><li><a href="context.html">Context</a></li><li><a href="engine.html">Engine</a></li><li><a href="host.html">Host</a></li><li><a href="cluster.html">Cluster</a></li></ul></div><div><h2>Nested Components</h2><ul><li><a href="cookie-processor.html">CookieProcessor</a></li><li><a href="credentialhandler.html">CredentialHandler</a></li><li><a href="globalresources.html">Global Resources</a></li><li><a href="jar-scanner.html">JarScanner</a></li><li><a href="jar-scan-filter.html">JarScanFilter</a></li><li><a href="listeners.html">Listeners</a></li><li><a href="loader.html">Loader</a></li><li><a href="manager.html">Manager</a></li><li><a href="realm.html">Realm</a></li><li><a href="resources.html">Resources</a></li><li><a href="sessionidgenerator.html">SessionIdGenerator</a></li><li><a href="valve.html">Valve</a></li></ul></div><div><h2>Cluster Elements</h2><ul><li><a href="cluster.html">Cluster</a></li><li><a href="cluster-manager.html">Manager</a></li><li><a href="cluster-channel.html">Channel</a></li><li><a href="cluster-membership.html">Channel/Membership</a></li><li><a href="cluster-sender.html">Channel/Sender</a></li><li><a href="cluster-receiver.html">Channel/Receiver</a></li><li><a href="cluster-interceptor.html">Channel/Interceptor</a></li><li><a href="cluster-valve.html">Valve</a></li><li><a href="cluster-deployer.html">Deployer</a></li><li><a href="cluster-listener.html">ClusterListener</a></li></ul></div><div><h2>web.xml</h2><ul><li><a href="filter.html">Filter</a></li></ul></div><div><h2>Other</h2><ul><li><a href="systemprops.html">System properties</a></li><li><a href="jaspic.html">JASPIC</a></li></ul></div></nav></div></div><div id="mainRight"><div id="content"><h2>The HTTP2 Upgrade Protocol</h2><h3 id="Table_of_Contents">Table of Contents</h3><div class="text">
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<ul><li><a href="#Introduction">Introduction</a></li><li><a href="#Attributes">Attributes</a><ol><li><a href="#Common_Attributes">Common Attributes</a></li><li><a href="#Standard_Implementation">Standard Implementation</a></li></ol></li><li><a href="#Nested_Components">Nested Components</a></li><li><a href="#Special_Features">Special Features</a></li></ul>
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</div><h3 id="Introduction">Introduction</h3><div class="text">
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<p>The <strong>HTTP Upgrade Protocol</strong> element represents an
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<strong>Upgrade Protocol</strong> component that supports the HTTP/2 protocol.
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An instance of this component must be associated with an existing
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<a href="http.html">HTTP/1.1 Connector</a>.</p>
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<p>HTTP/2 connectors use non-blocking I/O, only utilising a container thread
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from the thread pool when there is data to read and write. However, because
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the Servlet API is fundamentally blocking, each HTTP/2 stream requires a
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dedicated container thread for the duration of that stream.</p>
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<p>Requests processed using HTTP/2 will have the following additional request
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attributes available:</p>
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<ul>
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<li><code>org.apache.coyote.connectionID</code> will return the HTTP/2
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connection ID</li>
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<li><code>org.apache.coyote.streamID</code> will return the HTTP/2 stream
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ID</li>
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</ul>
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</div><h3 id="Attributes">Attributes</h3><div class="text">
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<div class="subsection"><h4 id="Common_Attributes">Common Attributes</h4><div class="text">
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<p>All implementations of <strong>Upgrade Protocol</strong> support the
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following attributes:</p>
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<table class="defaultTable"><tr><th style="width: 15%;">
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Attribute
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</th><th style="width: 85%;">
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Description
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</th></tr><tr><td><strong><code class="attributeName">className</code></strong></td><td>
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<p>This must be <code>org.apache.coyote.http2.Http2Protocol</code>.</p>
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</td></tr></table>
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</div></div>
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<div class="subsection"><h4 id="Standard_Implementation">Standard Implementation</h4><div class="text">
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<p>The HTTP/2 <strong>Upgrade Protocol</strong> implementation supports the
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following attributes in addition to the common attributes listed above.</p>
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<table class="defaultTable"><tr><th style="width: 15%;">
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Attribute
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</th><th style="width: 85%;">
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Description
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</th></tr><tr><td><code class="attributeName">allowedTrailerHeaders</code></td><td>
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<p>By default Tomcat will ignore all trailer headers when processing
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HTTP/2 connections. For a header to be processed, it must be added to this
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comma-separated list of header names.</p>
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</td></tr><tr><td><code class="attributeName">compressibleMimeType</code></td><td>
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<p>The value is a comma separated list of MIME types for which HTTP
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compression may be used.
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The default value is
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<code>
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text/html,text/xml,text/plain,text/css,text/javascript,application/javascript,application/json,application/xml
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</code>.
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</p>
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</td></tr><tr><td><code class="attributeName">compression</code></td><td>
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<p>The HTTP/2 protocol may use compression in an attempt to save server
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bandwidth. The acceptable values for the parameter is "off" (disable
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compression), "on" (allow compression, which causes text data to be
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compressed), "force" (forces compression in all cases), or a numerical
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integer value (which is equivalent to "on", but specifies the minimum
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amount of data before the output is compressed). If the content-length is
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not known and compression is set to "on" or more aggressive, the output
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will also be compressed. If not specified, this attribute is set to
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"off".</p>
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<p><em>Note</em>: There is a tradeoff between using compression (saving
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your bandwidth) and using the sendfile feature (saving your CPU cycles).
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If the connector supports the sendfile feature, e.g. the NIO2 connector,
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using sendfile will take precedence over compression. The symptoms will
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be that static files greater that 48 Kb will be sent uncompressed.
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You can turn off sendfile by setting <code>useSendfile</code> attribute
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of the protocol, as documented below, or change the sendfile usage
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threshold in the configuration of the
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<a href="../default-servlet.html">DefaultServlet</a> in the default
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<code>conf/web.xml</code> or in the <code>web.xml</code> of your web
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application.
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</p>
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</td></tr><tr><td><code class="attributeName">compressionMinSize</code></td><td>
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<p>If <strong>compression</strong> is set to "on" then this attribute
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may be used to specify the minimum amount of data before the output is
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compressed. If not specified, this attribute is defaults to "2048".</p>
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</td></tr><tr><td><code class="attributeName">initialWindowSize</code></td><td>
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<p>Controls the initial size of the flow control window for streams that
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Tomcat advertises to clients. If not specified, the default value of
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<code>65535</code> is used.</p>
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</td></tr><tr><td><code class="attributeName">keepAliveTimeout</code></td><td>
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<p>The time, in milliseconds, that Tomcat will wait between HTTP/2 frames
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when there is no active Stream before closing the connection. Negative
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values will be treated as an infinite timeout. If not specified, a default
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value of <code>20000</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">maxConcurrentStreamExecution</code></td><td>
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<p>The controls the maximum number of streams for any one connection that
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can be allocated threads from the container thread pool. If more streams
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are active than threads are available, those streams will have to wait
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for a stream to become available. If not specified, the default value of
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<code>20</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">maxConcurrentStreams</code></td><td>
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<p>The controls the maximum number of active streams permitted for any one
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connection. If a client attempts to open more active streams than this
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limit, the stream will be reset with a <code>STREAM_REFUSED</code> error.
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If not specified, the default value of <code>100</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">maxHeaderCount</code></td><td>
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<p>The maximum number of headers in a request that is allowed by the
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container. A request that contains more headers than the specified limit
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will be rejected. A value of less than 0 means no limit.
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If not specified, a default of 100 is used.</p>
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</td></tr><tr><td><code class="attributeName">maxHeaderSize</code></td><td>
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<p>The maximum total size for all headers in a request that is allowed by
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the container. Total size for a header is calculated as the uncompressed
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size of the header name in bytes, plus the uncompressed size of the header
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value in bytes plus an HTTP/2 overhead of 3 bytes per header. A request
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that contains a set of headers that requires more than the specified limit
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will be rejected. A value of less than 0 means no limit. If not specified,
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a default of 8192 is used.</p>
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</td></tr><tr><td><code class="attributeName">maxTrailerCount</code></td><td>
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<p>The maximum number of trailer headers in a request that is allowed by
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the container. A request that contains more trailer headers than the
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specified limit will be rejected. A value of less than 0 means no limit.
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If not specified, a default of 100 is used.</p>
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</td></tr><tr><td><code class="attributeName">maxTrailerSize</code></td><td>
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<p>The maximum total size for all trailer headers in a request that is
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allowed by the container. Total size for a header is calculated as the
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uncompressed size of the header name in bytes, plus the uncompressed size
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of the header value in bytes plus an HTTP/2 overhead of 3 bytes per
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header. A request that contains a set of trailer headers that requires
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more than the specified limit will be rejected. A value of less than 0
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means no limit. If not specified, a default of 8192 is used.</p>
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</td></tr><tr><td><code class="attributeName">noCompressionStrongETag</code></td><td>
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<p>This flag configures whether resources with a stong ETag will be
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considered for compression. If <code>true</code>, resources with a strong
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ETag will not be compressed. The default value is <code>true</code>.</p>
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<p>This attribute is deprecated. It will be removed in Tomcat 10 onwards
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where it will be hard-coded to <code>true</code>.</p>
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</td></tr><tr><td><code class="attributeName">noCompressionUserAgents</code></td><td>
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<p>The value is a regular expression (using <code>java.util.regex</code>)
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matching the <code>user-agent</code> header of HTTP clients for which
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compression should not be used,
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because these clients, although they do advertise support for the
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feature, have a broken implementation.
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The default value is an empty String (regexp matching disabled).</p>
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</td></tr><tr><td><code class="attributeName">overheadContinuationThreshold</code></td><td>
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<p>The threshold below which the payload size of a non-final
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<code>CONTINUATION</code> frame will trigger an increase in the overhead
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count (see <strong>overheadCountFactor</strong>). The overhead count will
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be increased by <code>overheadContinuationThreshold/payloadSize</code> so
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that the smaller the <code>CONTINUATION</code> frame, the greater the
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increase in the overhead count. A value of zero or less disables the
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checking of non-final <code>CONTINUATION</code> frames. If not specified,
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a default value of <code>1024</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">overheadCountFactor</code></td><td>
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<p>The factor to apply when counting overhead frames to determine if a
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connection has too high an overhead and should be closed. The overhead
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count starts at <code>-10 * overheadCountFactor</code>. The count is
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decreased by 20 for each data frame sent or received and each headers frame
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received. The count is increased by the <code>overheadCountFactor</code>
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for each setting received, priority frame received and ping received. If
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the overhead count exceeds zero, the connection is closed. A value of less
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than <code>1</code> disables this protection. In normal usage a value of
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approximately <code>20</code> or higher will close the connection before
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any streams can complete. If not specified, a default value of
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<code>10</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">overheadDataThreshold</code></td><td>
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<p>The threshold below which the average payload size of the current and
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previous non-final <code>DATA</code> frames will trigger an increase in
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the overhead count (see <strong>overheadCountFactor</strong>). The
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overhead count will be increased by
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<code>overheadDataThreshold/average</code> so that the smaller the
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average, the greater the increase in the overhead count. A value of zero
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or less disables the checking of non-final <code>DATA</code> frames. If
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not specified, a default value of <code>1024</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">overheadWindowUpdateThreshold</code></td><td>
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<p>The threshold below which the average size of current and previous
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<code>WINDOW_UPDATE</code> frame will trigger an increase in the overhead
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count (see <strong>overheadCountFactor</strong>). The overhead count will
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be increased by <code>overheadWindowUpdateThreshold/average</code> so
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that the smaller the average, the greater the increase in the overhead
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count. A value of zero or less disables the checking of
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<code>WINDOW_UPDATE</code> frames. If not specified, a default value of
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<code>1024</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">readTimeout</code></td><td>
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<p>The time, in milliseconds, that Tomcat will wait for additional data
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when a partial HTTP/2 frame has been received. Negative values will be
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treated as an infinite timeout. If not specified, a default value of
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<code>5000</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">streamReadTimeout</code></td><td>
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<p>The time, in milliseconds, that Tomcat will wait for additional data
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frames to arrive for the stream when an application is performing a
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blocking I/O read and additional data is required. Negative values will be
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treated as an infinite timeout. If not specified, a default value of
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<code>20000</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">streamWriteTimeout</code></td><td>
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<p>The time, in milliseconds, that Tomcat will wait for additional window
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update frames to arrive for the stream and/or connection when an
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application is performing a blocking I/O write and the stream and/or
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connection flow control window is too small for the write to complete.
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Negative values will be treated as an infinite timeout. If not specified,
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a default value of <code>20000</code> will be used.</p>
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</td></tr><tr><td><code class="attributeName">useSendfile</code></td><td>
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<p>Use this boolean attribute to enable or disable sendfile capability.
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The default value is <code>true</code>.</p>
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<p>This setting is ignored, and the sendfile capability disabled, if the
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<strong>useAsyncIO</strong> attribute of the associated
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<strong>Connector</strong> is set to <code>false</code>.</p>
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<p>The HTTP/2 sendfile capability uses <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/MappedByteBuffer.html">MappedByteBuffer</a> which is known to cause file locking on Windows.</p>
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</td></tr><tr><td><code class="attributeName">writeTimeout</code></td><td>
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<p>The time, in milliseconds, that Tomcat will wait to write additional
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data when an HTTP/2 frame has been partially written. Negative values will
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be treated as an infinite timeout. If not specified, a default value of
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<code>5000</code> will be used.</p>
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</td></tr></table>
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<p>The HTTP/2 upgrade protocol will also inherit the following limits from the
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<a href="http.html">HTTP Connector</a> it is nested with:</p>
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<ul>
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<li>maxCookieCount</li>
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<li>maxParameterCount</li>
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<li>maxPostSize</li>
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<li>maxSavePostSize</li>
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</ul>
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</div></div>
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</div><h3 id="Nested_Components">Nested Components</h3><div class="text">
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<p>This component does not support any nested components.</p>
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</div><h3 id="Special_Features">Special Features</h3><div class="text">
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<p>This component does not support any special features.</p>
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</div></div></div></div></div><footer><div id="footer">
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Copyright © 1999-2023, The Apache Software Foundation
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</div></footer></div></body></html>
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