File manager

File manager - Edit - /usr/share/doc/varnish/html/users-guide/vcl-built-in-code.html

Back
<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>Built-in VCL — Varnish version 7.1.1 documentation</title> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="../_static/classic.css" type="text/css" /> <script id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script src="../_static/jquery.js"></script> <script src="../_static/underscore.js"></script> <script src="../_static/doctools.js"></script> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="next" title="Request and response VCL objects" href="vcl-variables.html" /> <link rel="prev" title="Built-in subroutines" href="vcl-built-in-subs.html" /> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="vcl-variables.html" title="Request and response VCL objects" accesskey="N">next</a> \|</li> <li class="right" > <a href="vcl-built-in-subs.html" title="Built-in subroutines" accesskey="P">previous</a> \|</li> <li class="nav-item nav-item-0"><a href="../index.html">Varnish version 7.1.1 documentation</a> »</li> <li class="nav-item nav-item-1"><a href="index.html" >The Varnish Users Guide</a> »</li> <li class="nav-item nav-item-2"><a href="vcl.html" accesskey="U">VCL - Varnish Configuration Language</a> »</li> <li class="nav-item nav-item-this"><a href="">Built-in VCL</a></li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="built-in-vcl"> <span id="vcl-built-in-code"></span><h1>Built-in VCL<a class="headerlink" href="#built-in-vcl" title="Permalink to this headline">¶</a></h1> <p>Whenever a VCL program is loaded, the built-in VCL is appended to it. The <a class="reference internal" href="vcl-built-in-subs.html#vcl-built-in-subs"><span class="std std-ref">Built-in subroutines</span></a> have a special property, they can appear multiple times and the result is concatenation of all built-in subroutines.</p> <p>For example, let’s take the following snippet:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">sub</span> <span class="n">vcl_recv</span> <span class="p">{</span> <span class="c1"># loaded code for vcl_recv</span> <span class="p">}</span> </pre></div> </div> <p>The effective VCL that is supplied to the compiler looks like:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">sub</span> <span class="n">vcl_recv</span> <span class="p">{</span> <span class="c1"># loaded code for vcl_recv</span> <span class="c1"># built-in code for vcl_recv</span> <span class="p">}</span> </pre></div> </div> <p>This is how it is guaranteed that all <a class="reference internal" href="../reference/states.html#reference-states"><span class="std std-ref">Varnish Processing States</span></a> have at least one <code class="docutils literal notranslate"><span class="pre">return</span> <span class="pre">(<action>)</span></code>.</p> <p>It is generally recommended not to invariably return from loaded code to let Varnish execute the built-in code, because the built-in code provides essentially a sensible default behavior for an HTTP cache.</p> <div class="section" id="built-in-subroutines-split"> <h2>Built-in subroutines split<a class="headerlink" href="#built-in-subroutines-split" title="Permalink to this headline">¶</a></h2> <p>It might however not always be practical that the built-in VCL rules take effect at the very end of a state, so some subroutines like <code class="docutils literal notranslate"><span class="pre">vcl_recv</span></code> are split into multiple calls to other subroutines.</p> <p>By convention, those assistant subroutines are named after the variable they operate on, like <code class="docutils literal notranslate"><span class="pre">req</span></code> or <code class="docutils literal notranslate"><span class="pre">beresp</span></code>. This allows for instance to circumvent default behavior.</p> <p>For example, <code class="docutils literal notranslate"><span class="pre">vcl_recv</span></code> in the built-in VCL prevents caching when clients have a cookie. If you can trust your backend to always specify whether a response is cacheable or not regardless of whether the request contained a cookie you can do this:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">sub</span> <span class="n">vcl_req_cookie</span> <span class="p">{</span> <span class="k">return</span><span class="p">;</span> <span class="p">}</span> </pre></div> </div> <p>With this, all other default behaviors from the built-in <code class="docutils literal notranslate"><span class="pre">vcl_recv</span></code> are executed and only cookie handling is affected.</p> <p>Another example is how the built-in <code class="docutils literal notranslate"><span class="pre">vcl_backend_response</span></code> treats a negative TTL as a signal not to cache. It’s a historical mechanism to mark a response as uncacheable, but only if the built-in <code class="docutils literal notranslate"><span class="pre">vcl_backend_response</span></code> is not circumvented by a <code class="docutils literal notranslate"><span class="pre">return</span> <span class="pre">(<action>)</span></code>.</p> <p>However, in a multi-tier architecture where a backend might be another Varnish server, you might want to cache stale responses to allow the delivery of graced objects and enable revalidation on the next fetch. This can be done with the following snippet:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">sub</span> <span class="n">vcl_beresp_stale</span> <span class="p">{</span> <span class="k">if</span> <span class="p">(</span><span class="n">beresp</span><span class="o">.</span><span class="n">ttl</span> <span class="o">+</span> <span class="n">beresp</span><span class="o">.</span><span class="n">grace</span> <span class="o">></span> <span class="mi">0</span><span class="n">s</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> </pre></div> </div> <p>This granularity, and the general goal of the built-in subroutines split is to allow to circumvent a specific aspect of the default rules without giving the entire logic up.</p> </div> <div class="section" id="built-in-vcl-reference"> <h2>Built-in VCL reference<a class="headerlink" href="#built-in-vcl-reference" title="Permalink to this headline">¶</a></h2> <p>A copy of the <code class="docutils literal notranslate"><span class="pre">builtin.vcl</span></code> file might be provided with your Varnish installation but <a class="reference internal" href="../reference/varnishd.html#varnishd-1"><span class="std std-ref">varnishd</span></a> is the reference to determine the code that is appended to any loaded VCL.</p> <p>The VCL compilation happens in two passes:</p> <ul class="simple"> <li><p>the first one compiles the built-in VCL only,</p></li> <li><p>and the second pass compiles the concatenation of the loaded and built-in VCLs.</p></li> </ul> <p>Any VCL subroutine present in the built-in VCL can be extended, in which case the loaded VCL code will be executed before the built-in code.</p> </div> </div> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../index.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">Built-in VCL</a><ul> <li><a class="reference internal" href="#built-in-subroutines-split">Built-in subroutines split</a></li> <li><a class="reference internal" href="#built-in-vcl-reference">Built-in VCL reference</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="vcl-built-in-subs.html" title="previous chapter">Built-in subroutines</a></p> <h4>Next topic</h4> <p class="topless"><a href="vcl-variables.html" title="next chapter">Request and response VCL objects</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/users-guide/vcl-built-in-code.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3 id="searchlabel">Quick search</h3> <div class="searchformwrapper"> <form class="search" action="../search.html" method="get"> <input type="text" name="q" aria-labelledby="searchlabel" /> <input type="submit" value="Go" /> </form> </div> </div> <script>$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="vcl-variables.html" title="Request and response VCL objects" >next</a> \|</li> <li class="right" > <a href="vcl-built-in-subs.html" title="Built-in subroutines" >previous</a> \|</li> <li class="nav-item nav-item-0"><a href="../index.html">Varnish version 7.1.1 documentation</a> »</li> <li class="nav-item nav-item-1"><a href="index.html" >The Varnish Users Guide</a> »</li> <li class="nav-item nav-item-2"><a href="vcl.html" >VCL - Varnish Configuration Language</a> »</li> <li class="nav-item nav-item-this"><a href="">Built-in VCL</a></li> </ul> </div> <div class="footer" role="contentinfo"> © Copyright 2010-2014, Varnish Software AS. Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 3.4.3. </div> </body> </html>

| ver. 1.4 | Github | . | PHP 8.2.9 | Generation time: 0.22 | proxy | phpinfo | Settings