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This is a simple VMOD for Varnish Cache which provides query string filtering. It accepts a whitelist of parameter names and returns the request URL with only the provided parameters and their values.

Sort and Filter Functionality

The order of query string parameters is typically not considered, so an effective caching strategy involves sorting the querystring parameters so that identical name/value pairs that are in a different order for a given URL do not create multiple cache records.

Libvmod-queryfilter does not require separate sort and filter calls because it works by traversing the provided parameters and filtering as it goes. The output contains parameter names in the same order that they were provided to the VMOD, so by passing in parameter names in a consistent manner (e.g., alphabetical order), a resulting filtered request URL will be unique for its combination of parameter names and values.


Copyright © 2014-2020 The New York Times Company. Licensed under the Apache 2.0 License. See LICENSE for more information.

See the NOTICE file for a list of contributors.

(To list individual developers, try git shortlog -s or this page).


Rewrite the request URL so that the query string only contains parameter name/value pairs for the "id" and "q" parameters:

Query Arrays Disabled
import queryfilter;
set req.url = queryfilter.filterparams(req.url, "id,q", false);
Query Arrays Enabled
import queryfilter;
set req.url = queryfilter.filterparams(req.url, "id,q,vals[]", true);

Query Arrays

When query arrays are disabled, libvmod-queryfilter assumes query parameters are individual name/value pairs (e.g. a=1&b=2...). Support for arrays in query parameters - e.g. a[]=1&a[]=2... (see this Stackoverflow Question or Issue #2 for more examples) can be enabled by passing true for the arrays_enabled argument. When this option is enabled, array parameters will be preserved - in order - in the output URI.


Libvmod-queryfilter attempts to be 100% C99 conformant. You should, therefore, be able to build it without issue on most major compilers. The vmod can be built against a compiled varnish source, or against an installed varnish-dev/-devel package which includes the appropriate .pc files.


Before anything else is done, your source directory has to be initialized:



To build against a standard varnish development package, you should be able to simply invoke:

./configure && make && make check

(See ./configure --help for configure-time options)

This vmod can also be compiled against a pre-built Varnish Cache 3.x/4.x/5.x/6.x source by indicating the path to the (pre-compiled!) varnish source using the VARNISHSRC configuration variable, like so:

./configure VARNISHSRC=path/to/varnish-M.m.p && make && make check

Additional configuration variables and options can be found by invoking configure --help.

Check Targets

Libvmod-queryfilter provides a set of simple unit tests driven by varnishtest. They can be executed as part of the build process by invoking make check.