309 lines
14 KiB
XML
309 lines
14 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<!DOCTYPE document [
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<!ENTITY project SYSTEM "project.xml">
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]>
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<document url="http2.html">
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&project;
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<properties>
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<title>The HTTP2 Upgrade Protocol</title>
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</properties>
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<body>
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<section name="Table of Contents">
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<toc/>
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</section>
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<section name="Introduction">
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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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</section>
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<section name="Attributes">
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<subsection name="Common Attributes">
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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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<attributes>
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<attribute name="className" required="true">
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<p>This must be <code>org.apache.coyote.http2.Http2Protocol</code>.</p>
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</attribute>
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</attributes>
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</subsection>
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<subsection name="Standard Implementation">
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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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<attributes>
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<attribute name="allowedTrailerHeaders" required="false">
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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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</attribute>
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<attribute name="compressibleMimeType" required="false">
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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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</attribute>
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<attribute name="compression" required="false">
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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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</attribute>
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<attribute name="compressionMinSize" required="false">
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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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</attribute>
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<attribute name="initialWindowSize" required="false">
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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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</attribute>
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<attribute name="keepAliveTimeout" required="false">
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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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</attribute>
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<attribute name="maxConcurrentStreamExecution" required="false">
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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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</attribute>
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<attribute name="maxConcurrentStreams" required="false">
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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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</attribute>
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<attribute name="maxHeaderCount" required="false">
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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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</attribute>
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<attribute name="maxHeaderSize" required="false">
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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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</attribute>
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<attribute name="maxTrailerCount" required="false">
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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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</attribute>
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<attribute name="maxTrailerSize" required="false">
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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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</attribute>
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<attribute name="noCompressionStrongETag" required="false">
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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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</attribute>
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<attribute name="noCompressionUserAgents" required="false">
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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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</attribute>
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<attribute name="overheadContinuationThreshold" required="false">
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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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</attribute>
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<attribute name="overheadCountFactor" required="false">
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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</code>. The count is decreased for each
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data frame sent or received and each headers frame received. The count is
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increased by the <code>overheadCountFactor</code>for each setting
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received, priority frame received and ping received. If the overhead count
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exceeds zero, the connection is closed. A value of less than
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<code>1</code> disables this protection. In normal usage a value of
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<code>3</code> or more will close the connection before any streams can
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complete. If not specified, a default value of <code>1</code> will be
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used.</p>
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</attribute>
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<attribute name="overheadDataThreshold" required="false">
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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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</attribute>
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<attribute name="overheadWindowUpdateThreshold" required="false">
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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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</attribute>
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<attribute name="readTimeout" required="false">
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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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</attribute>
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<attribute name="streamReadTimeout" required="false">
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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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</attribute>
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<attribute name="streamWriteTimeout" required="false">
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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 conenction 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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</attribute>
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<attribute name="writeTimeout" required="false">
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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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</attribute>
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</attributes>
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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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</subsection>
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</section>
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<section name="Nested Components">
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<p>This component does not support any nested components.</p>
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</section>
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<section name="Special Features">
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<p>This component does not support any special features.</p>
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</section>
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</body>
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</document>
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