ESI includes in JSON response

I'm struggling getting ESI includes to be replaced in a JSON context.

The following working correctly. Resulting in the ESI tag replaced by the actual contents.

<esi:include src="http://domain.com/esipath/" />

And this is not working. The ESI tag isn't replaced.

{
    "test": "<esi:include src="http://domain.com/esipath/" />"
}

I have found some resources on google and a possible solution seems to set esi_syntax to 0x3 for varnish to skip checking for valid XML. This doesn't seem to work on Varnish 4. When I start the deamon with the runtime param I get the following error.

 Error: Unknown parameter "esi_syntax".

Is this setting deprecated in Varnish 4?

Any ideas to get this working?

Solution

indeed that parameter is depricated in varnish4. What you have to do is to activate the feature ESI_DISABLE_XML_CHECK.

For me I edit /etc/default/varnish (debian based system) and add

-p feature=+esi_disable_xml_check

to the DEAMON_OPTS parameters, for example:

DAEMON_OPTS="-a :6081 \
             -T localhost:6082 \
             -f /etc/varnish/default.vcl \
             -S /etc/varnish/secret \
             -s malloc,4GB \
             -p feature=+esi_disable_xml_check"