The pipeline
<p:declare-step xmlns:c="http://www.w3.org/ns/xproc-step" xmlns:p="http://www.w3.org/ns/xproc" name="main" version="3.0">
<p:output port="result" sequence="true"/>
<p:identity name="inline">
<p:with-input port="source">
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YII=
</p:inline>
</p:with-input>
</p:identity>
<p:cast-content-type content-type="application/xml" name="properties">
<p:with-input port="source" select="p:document-properties(.)"/>
</p:cast-content-type>
<p:cast-content-type name="cast" content-type="application/xml">
<p:with-input port="source" pipe="@inline"/>
</p:cast-content-type>
<p:wrap-sequence wrapper="c:result">
<p:with-input port="source" pipe="@properties @cast"/>
</p:wrap-sequence>
</p:declare-step>
Schematron validation
<s:schema xmlns="http://www.w3.org/1999/xhtml" xmlns:s="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt2">
<s:ns prefix="j" uri="http://www.w3.org/2005/xpath-functions"/>
<s:ns prefix="c" uri="http://www.w3.org/ns/xproc-step"/>
<s:pattern>
<s:rule context="/*">
<s:assert test="self::c:result">The pipeline root is not c:result</s:assert>
<s:assert test="j:map">The result does not include j:map</s:assert>
<s:assert test="c:data">
The result does not include c:data
</s:assert>
</s:rule>
<s:rule context="/c:result/j:map">
<s:assert test="empty(*[@key='content-length']) or (*[@key='content-length'] = 3764)">
The wrong content-length is reported
</s:assert>
<s:assert test="j:string[@key ='content-type']/text() = 'image/png'">
The content type of the result is not image/png
</s:assert>
</s:rule>
<s:rule context="/c:result/c:data">
<s:assert test="@encoding='base64'">
The encoding is not base64
</s:assert>
<s:assert test="starts-with(string(.), 'iVBORw0KGgoAAAA') and ends-with(string(.), 'YII=')">
The encoded content appears to be wrong
</s:assert>
</s:rule>
</s:pattern>
</s:schema>