This Kong plugin is developed in Python and uses the Python library lxml.etree binding for the GNOME C libraries libxml2 and libxslt.

The plugin handles the XML Request (in the HTTP body) in this order:

1. Transform the XML with XSLT (XSLTransformation)
2. Replace the values of XPath entries
3. Validate XML against its XSD schema

Each handling is optional.

In case of misconfiguration the Plugin sends to the consumer an HTTP 500 Internal Server Error <soap:Fault> (with the error detailed message)

1. Build a new Docker 'Kong Gateway' image with Python dependencies and the plugin code

docker build -t kong-gateway-xml-request-handling .

2. Create and prepare a PostgreDB called kong-database-xml-request-handling. See documentation.

3. Start the Kong Gateway

./start-kong.sh

1. Create a Kong Service named calcWebService with this URL: https://ecs.syr.edu/faculty/fawcett/Handouts/cse775/code/calcWebService/Calc.asmx. This simple backend Web Service adds 2 numbers.

2. Create a Route on the Service calcWebService with the path value /calcWebService

3. Install the xml-hanlding plugin on the Service calcWebService and use the default parameters. The XsdSoapSchema property checks the entire SOAP XML content against its schema. The default value is defined by W3C, it can be found here: https://schemas.xmlsoap.org/soap/envelope/

4. Call the calcWebService through the Kong Gateway Route by using httpie tool

http POST http://localhost:8000/calcWebService \
Content-Type:"text/xml; charset=utf-8" \
SOAPAction: "http://tempuri.org/Add" \
--raw "<?xml version=\"1.0\" encoding=\"utf-8\"?>
<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\"
xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">
  <soap:Body>
    <Add xmlns=\"http://tempuri.org/\">
      <a>5</a>
      <b>7</b>
    </Add>
  </soap:Body>
</soap:Envelope>"

The expected result is 12:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" ...>
  <soap:Body>
    <AddResponse xmlns="http://tempuri.org/">
      <AddResult>12</AddResult>
    </AddResponse>
  </soap:Body>
</soap:Envelope>

The plugin applies a XSLT Transformation on XML request. In this example the XSLT adds the value <b>8</b> that will be not present in the request. Configure the plugin with:

• XsltTransform property with this XSLT definition:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output omit-xml-declaration="yes" indent="yes"/>
    <xsl:strip-space elements="*"/>
    <xsl:template match="node()|@*">
        <xsl:copy>
            <xsl:apply-templates select="node()|@*"/>
        </xsl:copy>
    </xsl:template>   
    <xsl:template match="//*[local-name()='a']">
       <xsl:copy-of select="."/>
       <b>8</b>
   </xsl:template>
</xsl:stylesheet>

Use request defined at step #4, remove <b>7</b>, the expected result is no longer 12 but 13:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" ...>
  <soap:Body>
    <AddResponse xmlns="http://tempuri.org/">
      <AddResult>13</AddResult>
    </AddResponse>
  </soap:Body>
</soap:Envelope>

The plugin applies a XSLT Transformation on XML request. In this example we change the Tag name from <Subtract>...</Subtract> (present in the request) to <Add>...</Add>.

Configure the plugin with:

• XsltTransform property with no value

Without XSLT: Use request defined at step #4, rename the Tag <Add>...</Add>, to <Subtract>...</Subtract> the expected result is -2

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" ...>
  <soap:Body>
    <SubtractResponse xmlns="http://tempuri.org/">
      <SubtractResult>-2</SubtractResult>
    </SubtractResponse>
  </soap:Body>
</soap:Envelope>

Configure the plugin with:

• XsltTransform property with this XSLT definition:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="@*|node()">
        <xsl:copy>
            <xsl:apply-templates select="@*|node()" />
        </xsl:copy>
    </xsl:template>
    <xsl:template match="//*[local-name()='Subtract']">
       <Add xmlns="http://tempuri.org/"><xsl:apply-templates select="@*|node()" /></Add>
   </xsl:template>
</xsl:stylesheet>

With XSLT: Use request defined at step #4, rename the Tag <Add>...</Add>, to <Subtract>...</Subtract> the expected result is 12:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" ...>
  <soap:Body>
    <AddResponse xmlns="http://tempuri.org/">
      <AddResult>13</AddResult>
    </AddResponse>
  </soap:Body>
</soap:Envelope>

The plugin searches the 1st XPath entry and replaces the value with new one. In case of we want to change all XPath entries, just enable the XPathReplaceAll checkbox of the plugin property.

In this example we replace the value of:

• <a>: former: 5 to new: 10
• <b>: former: 7 to new: 9

Configure the plugin with:

• XsltTransform property with no value
• XPathReplace property with the value .//{http://tempuri.org/}a, .//{http://tempuri.org/}b
• XPathReplaceValue property with the value 10,9

Use request defined at step #4, the expected result is no longer 12 but 19:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" ...>
  <soap:Body>
    <AddResponse xmlns="http://tempuri.org/">
      <AddResult>19</AddResult>
    </AddResponse>
  </soap:Body>
</soap:Envelope>

We call incorrectly the Service by injecting a SOAP error; the plugin detects it, sends an error message to the Consumer and Kong doesn't call the SOAP backend API.

Configure the plugin with:

• XsltTransform property with no value
• XPathReplace property with no value
• XPathReplaceValue property with no value
• XsdSoapSchema property with the default value (defined by W3C) which checks the entire SOAP XML content against its schema

Use request defined at step #4, change </soap:Envelope> by </soap:EnvelopeKong> => Kong says:

<faultstring>XSD validation failed: line 10: b'Opening and ending tag mismatch: Envelope line 2 and EnvelopeKong' (line 10)</faultstring>

Configure the plugin with:

• XsdApiSchema property with this value:

<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://tempuri.org/" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="Add" type="tem:AddType" xmlns:tem="http://tempuri.org/"/>
  <xs:complexType name="AddType">
    <xs:sequence>
      <xs:element type="xs:integer" name="a" minOccurs="1"/>
      <xs:element type="xs:integer" name="b" minOccurs="1"/>
    </xs:sequence>
  </xs:complexType>
</xs:schema>

Use request defined at step #4, remove <a>5</a> => there is an error because the <a> tag has the minOccurs="1" XSD property and Kong says:

<faultstring>XSD validation failed: Element '{http://tempuri.org/}b': This element is not expected. Expected is ( {http://tempuri.org/}a ). (<string>, line 0)</faultstring>

Use request defined at step #4, replace <b>7</b> by <b>ABCD</b> => there is an error because the <b> tag has the type="xs:integer" XSD property and Kong says:

<faultstring>XSD validation failed: "Element '{http://tempuri.org/}b': 'ABCD' is not a valid value of the atomic type 'xs:integer'. (<string>, line 0)<faultstring>

Configure the plugin with:

• XsltTransform property with no value
• XPathReplace property with no value
• XPathReplaceValue property with no value
• XsdApiSchema property with the value defined at example #4
• XsdSoapSchema property with the default value

1. XSD schema Validation

Use request defined at step #4, remove <b>7</b> => there is an error because <b> is not present

2. XSLTransformation + XSD schema Validation

Configure the plugin with:

• XsltTransform property with this XSLT definition which adds the value <b>ABCD</b> that will be not present in the request but injected with a String value (instead of Integer)

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output omit-xml-declaration="yes" indent="yes"/>
    <xsl:strip-space elements="*"/>
    <xsl:template match="node()|@*">
        <xsl:copy>
            <xsl:apply-templates select="node()|@*"/>
        </xsl:copy>
    </xsl:template>   
    <xsl:template match="//*[local-name()='a']">
       <xsl:copy-of select="."/>
       <b>ABCD</b>
   </xsl:template>
</xsl:stylesheet>

Use request defined at step #4, remove <b>7</b> => there is an error because <b> is present but with a String value instead of Integer

3. XSLTransformation + XPath replacement + XSD schema Validation

• XPathReplace property with the value .//{http://tempuri.org/}b
• XPathReplaceValue property with the value 7

Use request defined at step #4, remove <b>7</b> => there is no more error because:

• XSLTransformation adds the <b>ABCD</b>
• Plugin replaces the value of <b> XPath entry: ABCD replaced by 7
• The SOAP request is validated successfully against its XSD schema

So, the backend Web Service is successfully called and the result is 12