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<!DOCTYPE document [
<!ENTITY project SYSTEM "project.xml">
]>
<document url="http2.html">
&project;
<properties>
<title>The HTTP2 Upgrade Protocol</title>
</properties>
<body>
<section name="Table of Contents">
<toc/>
</section>
<section name="Introduction">
<p>The <strong>HTTP Upgrade Protocol</strong> element represents an
<strong>Upgrade Protocol</strong> component that supports the HTTP/2 protocol.
An instance of this component must be associated with an existing
<a href="http.html">HTTP/1.1 Connector</a>.</p>
<p>HTTP/2 connectors use non-blocking I/O, only utilising a container thread
from the thread pool when there is data to read and write. However, because
the Servlet API is fundamentally blocking, each HTTP/2 stream requires a
dedicated container thread for the duration of that stream.</p>
<p>Requests processed using HTTP/2 will have the following additional request
attributes available:</p>
<ul>
<li><code>org.apache.coyote.connectionID</code> will return the HTTP/2
connection ID</li>
<li><code>org.apache.coyote.streamID</code> will return the HTTP/2 stream
ID</li>
</ul>
</section>
<section name="Attributes">
<subsection name="Common Attributes">
<p>All implementations of <strong>Upgrade Protocol</strong> support the
following attributes:</p>
<attributes>
<attribute name="className" required="true">
<p>This must be <code>org.apache.coyote.http2.Http2Protocol</code>.</p>
</attribute>
</attributes>
</subsection>
<subsection name="Standard Implementation">
<p>The HTTP/2 <strong>Upgrade Protocol</strong> implementation supports the
following attributes in addition to the common attributes listed above.</p>
<attributes>
<attribute name="discardRequestsAndResponses" required="false">
<p>A boolean value which can be used to enable or disable the recycling
of the container internal request and response processing objects. If set
to <code>true</code> the request and response objects will be set for
garbage collection after every request, otherwise they will be reused.
If not specified, this attribute is set to <code>false</code>.</p>
</attribute>
<attribute name="initialWindowSize" required="false">
<p>Controls the initial size of the flow control window for streams that
Tomcat advertises to clients. If not specified, the default value of
<code>65535</code> is used.</p>
</attribute>
<attribute name="keepAliveTimeout" required="false">
<p>The time, in milliseconds, that Tomcat will wait between HTTP/2 frames
when there is no active Stream before closing the connection. Negative
values will be treated as an infinite timeout. If not specified, a default
value of <code>20000</code> will be used.</p>
</attribute>
<attribute name="maxConcurrentStreamExecution" required="false">
<p>The controls the maximum number of streams for any one connection that
can be allocated threads from the container thread pool. If more streams
are active than threads are available, those streams will have to wait
for a stream to become available. If not specified, the default value of
<code>20</code> will be used.</p>
</attribute>
<attribute name="maxConcurrentStreams" required="false">
<p>The controls the maximum number of active streams permitted for any one
connection. If a client attempts to open more active streams than this
limit, the stream will be reset with a <code>STREAM_REFUSED</code> error.
If not specified, the default value of <code>100</code> will be used.</p>
</attribute>
<attribute name="maxHeaderCount" required="false">
<p>The maximum number of headers in a request that is allowed by the
container. A request that contains more headers than the specified limit
will be rejected. A value of less than 0 means no limit.
If not specified, a default of 100 is used.</p>
</attribute>
<attribute name="maxTrailerCount" required="false">
<p>The maximum number of trailer headers in a request that is allowed by
the container. A request that contains more trailer headers than the
specified limit will be rejected. A value of less than 0 means no limit.
If not specified, a default of 100 is used.</p>
</attribute>
<attribute name="overheadContinuationThreshold" required="false">
<p>The threshold below which the payload size of a non-final
<code>CONTINUATION</code> frame will trigger an increase in the overhead
count (see <strong>overheadCountFactor</strong>). The overhead count will
be increased by <code>overheadContinuationThreshold/payloadSize</code> so
that the smaller the <code>CONTINUATION</code> frame, the greater the
increase in the overhead count. A value of zero or less disables the
checking of non-final <code>CONTINUATION</code> frames. If not specified,
a default value of <code>1024</code> will be used.</p>
</attribute>
<attribute name="overheadCountFactor" required="false">
<p>The factor to apply when counting overhead frames to determine if a
connection has too high an overhead and should be closed. The overhead
count starts at <code>-10 * overheadCountFactor</code>. The count is
decreased by 20 for each data frame sent or received and each headers frame
received. The count is increased by the <code>overheadCountFactor</code>
for each setting, priority, priority update and ping frame received. If
the overhead count exceeds zero, the connection is closed. A value of less
than <code>1</code> disables this protection. In normal usage a value of
approximately <code>20</code> or higher will close the connection before
any streams can complete. If not specified, a default value of
<code>10</code> will be used.</p>
</attribute>
<attribute name="overheadResetFactor" required="false">
<p>The amount by which the overhead count (see
<strong>overheadCountFactor</strong>) will be increased for each reset
frame received or sent. If not specified, a default value of
<code>50</code> will be used. A value of less than zero will be treated as
zero.</p>
</attribute>
<attribute name="overheadDataThreshold" required="false">
<p>The threshold below which the average payload size of the current and
previous non-final <code>DATA</code> frames will trigger an increase in
the overhead count (see <strong>overheadCountFactor</strong>). The
overhead count will be increased by
<code>overheadDataThreshold/average</code> so that the smaller the
average, the greater the increase in the overhead count. A value of zero
or less disables the checking of non-final <code>DATA</code> frames. If
not specified, a default value of <code>1024</code> will be used.</p>
</attribute>
<attribute name="overheadWindowUpdateThreshold" required="false">
<p>The threshold below which the average size of current and previous
<code>WINDOW_UPDATE</code> frame will trigger an increase in the overhead
count (see <strong>overheadCountFactor</strong>). The overhead count will
be increased by <code>overheadWindowUpdateThreshold/average</code> so
that the smaller the average, the greater the increase in the overhead
count. A value of zero or less disables the checking of
<code>WINDOW_UPDATE</code> frames. If not specified, a default value of
<code>1024</code> will be used.</p>
</attribute>
<attribute name="readTimeout" required="false">
<p>The time, in milliseconds, that Tomcat will wait for additional data
when a partial HTTP/2 frame has been received. Negative values will be
treated as an infinite timeout. If not specified, a default value of
<code>5000</code> will be used.</p>
</attribute>
<attribute name="streamReadTimeout" required="false">
<p>The time, in milliseconds, that Tomcat will wait for additional data
frames to arrive for the stream when an application is performing a
blocking I/O read and additional data is required. Negative values will be
treated as an infinite timeout. If not specified, a default value of
<code>20000</code> will be used.</p>
</attribute>
<attribute name="streamWriteTimeout" required="false">
<p>The time, in milliseconds, that Tomcat will wait for additional window
update frames to arrive for the stream and/or connection when an
application is performing a blocking I/O write and the stream and/or
connection flow control window is too small for the write to complete.
Negative values will be treated as an infinite timeout. If not specified,
a default value of <code>20000</code> will be used.</p>
</attribute>
<attribute name="useSendfile" required="false">
<p>Use this boolean attribute to enable or disable sendfile capability.
The default value is <code>true</code>.</p>
<p>This setting is ignored, and the sendfile capability disabled, if the
<strong>useAsyncIO</strong> attribute of the associated
<strong>Connector</strong> is set to <code>false</code>.</p>
<p>The HTTP/2 sendfile capability uses <a
href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/nio/MappedByteBuffer.html"
>MappedByteBuffer</a> which is known to cause file locking on Windows.</p>
</attribute>
<attribute name="writeTimeout" required="false">
<p>The time, in milliseconds, that Tomcat will wait to write additional
data when an HTTP/2 frame has been partially written. Negative values will
be treated as an infinite timeout. If not specified, a default value of
<code>5000</code> will be used.</p>
</attribute>
</attributes>
<p>The HTTP/2 upgrade protocol will also inherit the following attributes from
the <a href="http.html">HTTP Connector</a> within which it is nested:</p>
<ul>
<li>allowedTrailerHeaders</li>
<li>compressibleMimeType</li>
<li>compression</li>
<li>compressionMinSize</li>
<li>maxCookieCount</li>
<li>maxHttpHeaderSize</li>
<li>maxHttpRequestHeaderSize</li>
<li>maxParameterCount</li>
<li>maxPartCount</li>
<li>maxPartHeaderSize</li>
<li>maxPostSize</li>
<li>maxSavePostSize</li>
<li>maxTrailerSize</li>
<li>noCompressionUserAgents</li>
<li>server</li>
<li>serverRemoveAppProvidedValues</li>
</ul>
</subsection>
</section>
<section name="Nested Components">
<p>This component does not support any nested components.</p>
</section>
<section name="Special Features">
<p>This component does not support any special features.</p>
</section>
</body>
</document>