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git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1830489 13f79535-47bb-0310-9956-ffa450edef68
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Luca Toscano
2018-04-29 05:58:52 +00:00
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docs/manual/howto/http2.html.en
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<li><img alt="" src="../images/down.gif" /> <a href="#clients">Clients</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#tools">Useful tools to debug HTTP/2</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#push">Server Push</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#earlyhints">Early Hints</a></li>
</ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_http2.html">mod_http2</a></li><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
@ -261,6 +262,48 @@
is the <a href="https://tools.ietf.org/html/draft-ruellan-http-accept-push-policy-00">
Accept-Push-Policy Header Field</a> where a client can, for each request, define
what kind of PUSHes it accepts.</p>
<p>
PUSH might not always trigger the request/response/performance that one expects or
hopes for. There are various studies on this topic to be found on the web that explain
benefits and weaknesses and how different features of client and network influence
the outcome. For example: just because the server PUSHes a resource does not mean
a browser will actually use the data.</p>
<p>The major thing that influences the response being PUSHed is the request that was
simulated. The request URL for a PUSH is given by the application, but where do the
request headers come from? For example, will the PUSH request a <code>accept-language</code>
header and if yes with what value?</p>
<p>Apache will look at the original request (the one that triggered the PUSH) and copy the
following headers over to PUSH requests: <code>user-agent</code>, <code>accept</code>,
<code>accept-encoding</code>, <code>accept-language</code>, <code>cache-control</code>.</p>
<p>All other headers are ignored. Cookies will also not be copied over. PUSHing resources
that require a cookie to be present will not work. This can be a matter of debate. But
unless this is more clearly discussed with browser, let's err on the side of caution and
not expose cookie where they might oridinarily not be visible.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="earlyhints" id="earlyhints">Early Hints</a><a title="Permanent link" href="#earlyhints" class="permalink">&para;</a></h2>
<p>An alternative to PUSHing resources is to send <code>Link</code> headers to the
client before the response is even ready. This uses the HTTP feature called "Early Hints" and
is described in <a href="https://tools.ietf.org/html/rfc8297">RFC 8297</a>.</p>
<p>In order to use this, you need to explicitly enable it on the server via</p>
<pre class="prettyprint lang-config">H2EarlyHints on</pre>
<p>(It is not enabled by default since some older browser tripped on such responses.)</p>
<p>If this feature is on, you can the directive <code>H2PushResource</code> to
trigger early hints and resource PUSHes:</p>
<pre class="prettyprint lang-config">&lt;Location /xxx.html&gt;
H2PushResource /xxx.css
H2PushResource /xxx.js
&lt;/Location&gt;</pre>
<p>This will send out a <code>"103 Early Hints"</code> response to a client as soon
as the server <em>starts</em> processing the request. This may be much early than
the time the first response headers have been determined, depending on your web
application.</p>
<p>If <code>H2Push</code> is enabled, this will also start the PUSH right after the
103 response. If <code>H2Push</code> is disabled however, the 103 response will be send
nevertheless to the client.</p>
</div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/howto/http2.html" title="English">&nbsp;en&nbsp;</a> |

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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.es.xsl"?>
<!-- English Revision: 1779744 -->
<!-- English Revision: 1779744:1830439 (outdated) -->
<!-- Spanish translation : Daniel Ferradal -->
<!-- Reviewed & updated by Luis Gil de Bernabé Pfeiffer lgilbernabe[AT]apache.org -->

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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.fr.xsl"?>
<!-- English Revision: 1779744 -->
<!-- English Revision: 1779744:1830439 (outdated) -->
<!-- French translation : Lucien GENTIS -->
<!-- Reviewed by : Vincent Deffontaines -->

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<variants>
<variant>en</variant>
<variant>es</variant>
<variant>fr</variant>
<variant outdated="yes">es</variant>
<variant outdated="yes">fr</variant>
</variants>
</metafile>