ESI Plugin

This plugin implements the ESI specification.


Supportted ESI tags:

<!--esi ... -->

extended ESI tags: esi:special-include

Supported variables:

$(HTTP_COOKIE{name}) or $(HTTP_COOKIE{name;subkey})

Note: the name is the key name such as “username”, “id” etc. For cookie support sub-name or sub-key, the format is: name;subkey, such as “l;u”, “l;t” etc. e.g. such cookie string: l=u=test&t=1350952328, the value of $(HTTP_COOKIE{“l;u”}) is test and the value of $(HTTP_COOKIE{“l;t”}) is 1350952328

Compile and Installation

This plugin is only built if the configure option


is given at build time. Note that this plugin is built and installed in combination with the combo handler module, since they share common code.

Enabling ESI

  1. First we need to set up /usr/local/etc/trafficserver/plugin.config and make sure the following line is present.
  1. There are four options you can add to the above.
  • “–private-response” will add private cache control and expires header to the processed ESI document.
  • “–packed-node-support” will enable the support for using packed node, which will improve the performance of parsing cached ESI document.
  • “–disable-gzip-output” will disable gzipped output, which will NOT gzip the output anyway.
  • “–first-byte-flush” will enable the first byte flush feature, which will flush content to users as soon as the entire ESI document is received and parsed without all ESI includes fetched (the flushing will stop at the ESI include markup till that include is fetched).
  1. HTTP_COOKIE variable supported is turned off by default. You can turn it on with ‘-f’ or ‘-handler option’ -f handler.conf

And inside handler.conf you can provide the list of cookie name that is allowed.

whitelistCookie A
whitelistCookie LOGIN

We can also allow all cookie for HTTP_COOKIE variable by using a wildcard character. e.g.

whitelistCookie *
  1. We need a mapping for origin server response that contains the ESI markup. Assume that the ATS server is And your origin server is and the response containing ESI markup is We will need the following line in /usr/local/etc/trafficserver/remap.config
  1. Your response should contain ESI markup and a response header of ‘X-Esi: 1’. e.g. using PHP,
<?php   header('X-Esi: 1'); ?>
Hello, <esi:include src=""/>
  1. You will need a mapping for the src of the ESI include in remap.config if it is not already present.

Or if both your ESI response and the ESI include comes from the same origin server, you can have the following line in remap.config instead to replace separate map rules for date.php and esi.php

  1. Here is a sample PHP for date.php
header ("Cache-control: no-cache");
echo date('l jS \of F Y h:i:s A');

Useful Note

  1. You can provide proper cache control header and the ESI response and ESI include response can be cached separately. It is extremely useful for rendering page with multiple modules. The page layout can be a ESI response with multiple ESI include include, each for different module. The page layour ESI response can be cached and each individual ESI include can also be cached with different duration.
  2. You should run the plugin without using “packed node support” because it is not fully tested.

Differences from Spec -

  1. <esi:include> does not support “alt” and “onerror” attributes
  2. <esi:inline> is not supported
  3. You cannot have <esi:try> inside another <esi:try>
  4. HTTP_USER_AGENT variable is not supported
  5. HTTP_COOKIE supports fetching for sub-key
  6. HTTP_HEADER supports accessing request headers as variables