https://oncodesign.io/2021/12/05/smooks-dfdl-filter-in-a-cross-domain-solution/

bad-data.xml

<nitf:NITF xmlns:nitf="urn:nitf:2.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <InvalidData>
        4E49544630322E3130303342463031695F33303031612020203139393731323137313032363330436865636B7320616E20756E636F6D7072657373
        656420313032347831303234203820626974206D6F6E6F20696D61676520776974682047454F63656E7472696320646174612E204169726669656C
        6455202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020
        2020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020
        2020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020303030303030303030
        3030EF...
    </InvalidData>
</nitf:NITF>

good-data.xml

<nitf:NITF xmlns:nitf="urn:nitf:2.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <nitf:ValidData>
        <Header>
            <FileProfileName>NITF</FileProfileName>
            <FileVersion>02.10</FileVersion>
            <ComplexityLevel>3</ComplexityLevel>
            <StandardType>BF01</StandardType>
            <OriginatingStationID>i_3001a</OriginatingStationID>
            <FileDateAndTime>1997-12-17T10:26:30+00:00</FileDateAndTime>
            <FileTitle>Checks an uncompressed 1024x1024 8 bit mono image with GEOcentric data. Airfield</FileTitle>
            <SecurityClassification>U</SecurityClassification>
            <SecurityClassificationSystem xsi:nil="true"/>
            <Codewords xsi:nil="true"/>
            <ControlAndHandling xsi:nil="true"/>
            <ReleasingInstructions xsi:nil="true"/>
            <DeclassificationType xsi:nil="true"/>
            <DeclassificationDate xsi:nil="true"/>
            <DeclassificationExemption xsi:nil="true"/>
            <Downgrade xsi:nil="true"/>
            <DowngradeDate xsi:nil="true"/>
            <ClassificationText xsi:nil="true"/>
            <ClassificationAuthorityType xsi:nil="true"/>
            <ClassificationAuthority xsi:nil="true"/>
            <ClassificationReason xsi:nil="true"/>
            <SecuritySourceDate xsi:nil="true"/>
            <SecurityControlNumber xsi:nil="true"/>
        ...
    </nitf:ValidData>
</nitf:NITF>

smooks-config.xml

<?xml version="1.0"?>
<smooks-resource-list xmlns="https://www.smooks.org/xsd/smooks-2.0.xsd"
                      xmlns:core="https://www.smooks.org/xsd/smooks/smooks-core-1.6.xsd"
                      xmlns:dfdl="https://www.smooks.org/xsd/smooks/dfdl-1.0.xsd">

    <!-- ingest the stream from the input source (i.e., untrusted system) -->
    <dfdl:parser schemaURI="/nitf.dfdl.xsd"/>

    <core:smooks filterSourceOn="/NITF">
        <core:action>
            <core:inline>
                <!-- consume the root event (i.e., 'NITF') and its descendants -->
                <core:replace/>
            </core:inline>
        </core:action>
        <core:config>
            <smooks-resource-list>
                <!-- happy path: serialize the valid event stream to NITF before writing it out to the execution result stream (i.e., trusted system) -->
                <dfdl:unparser schemaURI="/nitf.dfdl.xsd" unparseOnNode="//*[not(self::InvalidData)]"
                               distinguishedRootNode="{urn:nitf:2.1}ValidData"/>
            </smooks-resource-list>
        </core:config>
    </core:smooks>

    <!-- unhappy path: write the invalid event stream to a side output resource -->
    <core:smooks filterSourceOn="/NITF/InvalidData">
        <core:action>
            <core:outputTo outputStreamResource="deadLetterStream"/>
        </core:action>
    </core:smooks>

</smooks-resource-list>