Several times in the past, on some client installations of our Healthcare application (> 1000 hospitals across Europe), we had to correct some behaviors using undertow filters.
Fortunately, some filters are already included out of the box inside wildfly including rewrite, response-header, request-limit, gzip…
But what happens if you need more like:

  • modifying request headers for example to change/adapt/fix a media-type
  • correcting incoming request or updating response to fix an issue in a JSON message

Wouldn’t it be great if you could dynamically add a powerfull filter written in plain javascript?

That’s the main purpose of the undertow-jsfilters project I have created: to write filters in javascript.
The javascript filters are interpreted via Nashorn and just need to be declared as wildfly/undertow custom-filter using CLI commands or by updating the standalone.xml.

<subsystem xmlns="urn:jboss:domain:undertow:3.1">
    <buffer-cache name="default"/>
    <server name="default-server">
        <http-listener name="default" socket-binding="http"/>
        <host name="default-host" alias="localhost">
            <location name="/" handler="welcome-content"/>
            <filter-ref name="server-header"/>
...
            <filter-ref name="jsfilter-version"/>
            
        </host>
    </server>
    <filters>
        <response-header name="server-header" header-name="Server" header-value="WildFly/10"/>
...
        <filter name="jsfilter-version" class-name="fr.brouillard.oss.undertow.JSFilter" module="fr.brouillard.oss.undertow.jsfilters">
            <param name="fileName" value="D:/dev/projects/personnal/oss/undertow/js-filters/src/test/js/jsfilters-version-header.js"/>
            <param name="refresh" value="true"/>
        </filter>
    </filters>
</subsystem>

Do not hesitate to visit the project page & open issues on purpose.