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docs.push({path: [ "release-roadmap.md", ], url: "/docs/reference/release-roadmap.html", title: "Roadmap", order: 60, overview: "What Istio will become in the coming months."}); docs.push({path: [ "writing-config.md", ], url: "/docs/reference/writing-config.html", title: "Writing Configuration", order: 70, overview: "How to write Istio config YAML content."}); genNavBarTree(docs) </script></ul></div><div id="tab-container" class="col-xs-1 tab-neg-margin pull-left"> <a id="sidebar-tab" class="glyphicon glyphicon-chevron-left" href="javascript:void 0;"></a></div><div id="content-container" class="thin-left-border col-sm-9 markdown"><div id="toc" class="toc"></div><div id="doc-content"><h1>Expression Language</h1><p>This page describes how to use the Mixer config expression language (CEXL).</p><h2 id="background">Background</h2><p>Mixer configuration uses an expression language (CEXL) to specify <a href="/v0.1/docs/concepts/policy-and-control/mixer-config.html#selectors">selectors</a> and <a href="/v0.1/docs/concepts/policy-and-control/mixer-config.html#attribute-expressions">mapping expressions</a>. CEXL expressions map a set of typed <a href="/v0.1/docs/concepts/policy-and-control/attributes.html">attributes</a> and constants to a typed <a href="https://github.com/istio/api/blob/master/mixer/v1/config/descriptor/value_type.proto#L23">value</a>.</p><h2 id="syntax">Syntax</h2><p>CEXL accepts a subset of <strong><a href="https://golang.org/ref/spec#Expressions">Go expressions</a></strong>, which defines the syntax. CEXL implements a subset of the Go operators that constrains the set of accepted Go expressions. CEXL also supports arbitrary parenthesization.</p><h2 id="functions">Functions</h2><p>CEXL supports the following functions.</p><table><thead><tr><th>Operator</th><th>Description</th><th>Example</th></tr></thead><tbody><tr><td><code>==</code></td><td>Equals</td><td><code>request.size == 200</code></td></tr><tr><td><code>==</code></td><td>Equals Prefix</td><td><code>service.name == "svc1.*"</code></td></tr><tr><td><code>==</code></td><td>Equals Suffix</td><td><code>service.name == "*.ns1.svc.cluster.local"</code></td></tr><tr><td><code>!=</code></td><td>Not Equals</td><td><code>request.user != "admin"</code></td></tr><tr><td><code>||</code></td><td>Logical OR</td><td><code>(request.size == 200) || (request.user == "admin")</code></td></tr><tr><td><code>&&</code></td><td>Logical AND</td><td><code>(request.size == 200) && (request.user == "admin")</code></td></tr><tr><td><code>[ ]</code></td><td>Map Access</td><td><code>request.headers["x-id"]</code></td></tr><tr><td><code>|</code></td><td>First non empty</td><td><code>source.labels["app"] | source.labels["svc"] | "unknown"</code></td></tr></tbody></table><h2 id="type-checking">Type checking</h2><p>CEXL variables are attributes from the typed <a href="/v0.1/docs/reference/config/mixer/attribute-vocabulary.html">attribute vocabulary</a>, constants are implicitly typed and, functions are explicitly typed.</p><p>Mixer validates a CEXL expression and resolves it to a type during config validation. Selectors must resolve to a boolean value and mapping expressions must resolve to the type they are mapping into. Config validation fails if a selector fails to resolve to a boolean or if a mapping expression resolves to an incorrect type.</p><p>For example, if an operator specifies a <em>string</em> label as <code>request.size | 200</code>, validation fails because the expression resolves to an integer.</p><h2 id="missing-attributes">Missing attributes</h2><p>If an expression uses an attribute that is not available during request processing, the expression evaluation fails. Use the <code>|</code> operator to provide a default value if an attribute may be missing.</p><p>For example, the expression <code>request.user == "user1"</code> fails evaluation if the request.user attribute is missing. The <code>|</code> (OR) operator addresses the problem: <code>(request.user | "nobody" ) == "user1"</code>.</p><h2 id="examples">Examples</h2><table><thead><tr><th>Expression</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td><code>request.size| 200</code></td><td><strong>int</strong></td><td>request.size if available, otherwise 200.</td></tr><tr><td><code>request.header["X-FORWARDED-HOST"] == "myhost"</code></td><td><strong>boolean</strong></td><td> </td></tr><tr><td><code>(request.header["x-user-group"] == "admin") || (request.user == "admin")</code></td><td><strong>boolean</strong></td><td>True if the user is admin or in the admin group.</td></tr><tr><td><code>(request.user | "nobody" ) == "user1"</code></td><td><strong>boolean</strong></td><td>True if request.user is “user1”, The expression will not error out if request.user is missing.</td></tr><tr><td><code>source.labels["app"]=="reviews" && source.labels["version"]=="v3"</code></td><td><strong>boolean</strong></td><td>True if app label is reviews and version label is v3, false otherwise.</td></tr></tbody></table></div></div></div></div></div></div><script src="/v0.1/js/sidemenu.js"></script><footer><div class="container"><div class="row"><div class="col-md-2"></div><div class="col-md-3 col-sm-4 col-xs-12 center-block"><ul class="toggle"><p class="header">Docs</p><li><a href="/v0.1/docs/">Welcome</a></li><li><a href="/v0.1/docs/concepts">Concepts</a></li><li><a href="/v0.1/docs/tasks">Tasks</a></li><li><a href="/v0.1/docs/samples">Samples</a></li><li><a href="/v0.1/docs/reference">Reference</a></li></ul></div><hr class="footer-sections" /><div class="col-md-3 col-sm-4 col-xs-12 center-block"><ul class="toggle"><p class="header">Resources</p><li><a href="/v0.1/faq">Frequently Asked Questions</a></li><li><a href="/v0.1/troubleshooting">Troubleshooting Guide</a></li><li><a href="/v0.1/bugs">Report a Bug</a></li><li><a href="https://github.com/istio/istio.github.io/issues/new?title=Issue with _docs/reference/config/mixer/expression-language.md">Report a Doc Issue</a></li><li><a href="https://github.com/istio/istio.github.io/edit/master/_docs/reference/config/mixer/expression-language.md">Edit This Page on GitHub</a></li></ul></div><hr class="footer-sections" /><div class="col-md-3 col-sm-4 col-xs-12 center-block"><ul class="toggle"><p class="header">Community</p><li><a href="https://groups.google.com/forum/#!forum/istio-users" target="_blank"><span class="group">User</span></a> | <a href="https://groups.google.com/forum/#!forum/istio-dev" target="_blank">Dev Mailing Lists</a></li><li><a href="https://twitter.com/IstioMesh" target="_blank"><span class="twitter">Twitter</span></a></li><li><a href="https://github.com/istio/istio" target="_blank"><span class="github">GitHub</span></a></li></ul></div><div class="col-md-1"></div></div><div class="row"><p class="description small text-center"> Copyright © 2017 Istio Authors<br> Istio 0.1<br> Archived on 20-Jul-2017</p></div></div></footer><script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.15.0/jquery.validate.min.js"></script> <script src="/v0.1/js/jquery.form.min.js"></script> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.1/js/bootstrap.min.js"></script> <script src="/v0.1/js/slick.min.js"></script> <script src="/v0.1/js/jquery.visible.min.js"></script> <script src="/v0.1/js/common.js" type="text/javascript" charset="utf-8"></script> <script src="/v0.1/js/buttons.js"></script> <script src="/v0.1/js/search.js"></script> <script src="/v0.1/js/prism.js"></script></body></html>
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