vmod_querystring - Man Page

new xfilter = querystring.filter(
   BOOL sort=0,
   BOOL uniq=0,
   ENUM {name, param} match=name
)

A filter is first set up in vcl_init and then used during transactions. The setup includes the creation of the filter to which you add criteria. During transactions, you may apply the filter to URLs (like req.url or a Location header) or extract the filtered query-string.

A filter may sort its parameters, but by default it will maintain order. The filter constructor takes an optional sort argument, you may use its name to improve readability.

Example

import querystring;

sub vcl_init {
    new qf = querystring.filter(sort = true);
    qf.add_string("_"); # a timestamp used to bypass caches
    qf.add_glob("utm_*"); # google analytics parameters
    qf.add_regex("sess[0-9]+"); # anti-CSRF token
}

sub vcl_hash {
    hash_data(qf.apply()); # implicitly on req.url
    hash_data(req.http.host);
    return (lookup);
}

It is also possible for a filter to either match parameters by name, or by themselves. By default the criteria are tested against the name only, leaving alone the contents starting at the equal sign when there's one. For that the constructor takes another optional match argument that can take either name (default) or param.

Example

sub vcl_init {
    new fr = querystring.filter(match = param);
    fr.add_regex("^lang=fr(-..)?$");
}

sub vcl_recv {
    if (fr.extract()) {
        set req.backend_hint = www_fr;
    }
}

Finally, a filter can drop consecutive duplicate parameters if the optional uniq argument. Combined with a sort, this effectively removes all the duplicates from the URL. The match argument determines how parameters are considered duplicates.

Since most of the time it is either req.url or bereq.url that is filtered, omitting the url argument for functions that take one will default to one of them depending on whether the function was called during a client or backend transaction.

Description

Use the string argument as an exact-match criterion.

Description

Use the string argument as a GLOB pattern matching criterion. The underlying fnmatch function may fail, in which case the query-param is kept to avoid spurious filtering and the error is logged.

Description

The string argument is compiled to a regular expression that will be used as the matching criterion. If the regular expression is invalid, it will fail the vcl.load command and report the error in the varnish-cli output.

STRING xfilter.apply([STRING url], ENUM {keep, drop} mode=drop)

Description

The url argument is filtered against the filter's criteria, previously added using the add_*() methods in vcl_init. The result is a new URL with a clean (possibly sorted and de-duplicated) query-string.

Depending on the optional mode argument the matching criteria act as a black list for drop (default) or a white list for keep. In the resulting URL the query-string will either contain only the matching parameters or everything but them.

Example

set req.url = myfilter.apply(mode = drop);

STRING xfilter.extract(
      [STRING url],
      ENUM {keep, drop} mode=drop
)

Description

This method works exactly like .apply and discards all URL parts but the query-string.

Description

This is a shorthand function that works like applying a filter with no criteria. It will keep all parameters and shave off the empty ones.

Example

set req.url = querystring.clean();

Description

This is a shorthand function that works like applying a sorting-enabled filter with no criteria matching full parameters, not just their names. It will keep all parameters and shave off the empty ones. If the uniq argument is true duplicate parameters are also removed.

Example

set req.url = querystring.sort();

Description

This is a shorthand function that works like applying a filter with a catch-all criteria. It will return the given URL with its query-string removed. For better efficiency, it is not backed by an actual filter.

Example

set req.url = querystring.remove();