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Script Mediator

The Script Mediator is used to invoke the functions of a variety of scripting languages such as JavaScript, Groovy, or Ruby.

A Script mediator can be created using one of the following methods.

  • With the script program statements stored in a separate file, referenced via the Local or Remote Registry entry.
  • With the script program statements embedded inline within the Synapse configuration.

Synapse uses the Apache Bean Scripting Framework for scripting language support. Any script language supported by BSF may be used to implement the Synapse Mediator. With the Script Mediator, you can invoke a function in the corresponding script. With these functions, it is possible to access the Synapse predefined in a script variable named mc. The mc variable represents an implementation of the MessageContext, named ScriptMessageContext.java, which contains the following methods that can be accessed within the script as mc.methodName.

Return? Method Name Description
Yes getPayloadXML() This gets an XML representation of SOAP Body payload.
No setPayloadXML(payload) This sets the SOAP body payload from XML.
No addHeader(mustUnderstand, content) This adds a new SOAP header to the message.
Yes getEnvelopeXML() This gets the XML representation of the complete SOAP envelope.
No setTo(reference) This is used to set the value which specifies the receiver of the message.
Yes setFaultTo(reference) This is used to set the value which specifies the receiver of the faults relating to the message.
No setFrom(reference) This is used to set the value which specifies the sender of the message.
No setReplyTo(reference) This is used to set the value which specifies the receiver of the replies to the message.
Yes getPayloadJSON() This gets the JSON representation of a SOAP Body payload.
No setPayloadJSON( payload ) This sets the JSON representation of a payload obtained via the getPayloadJSON() method and sets it in the current message context.
Yes getProperty(name) This gets a property from the current message context.
No setProperty(key, value) This is used to set a property in the current message context. The previously set property values are replaced by this method.

Implementing a Mediator with a script language has advantages over using the built-in Synapse Mediator types or implementing a custom Java class Mediator. The Script Mediators have the flexibility of a class Mediator with access to the Synapse MessageContext and SynapseEnvironment APIs. Also, the ease of use and dynamic nature of scripting languages allow the rapid development and prototyping of custom mediators. An additional benefit of some scripting languages is that they have very simple and elegant XML manipulation capabilities, which make them very usable in a Synapse mediation environment. e.g., JavaScript E4X with RhinoJS or Ruby REXML.

For both types of script mediator definitions, the MessageContext passed into the script has additional methods over the standard Synapse MessageContext to enable working with XML natural to the scripting language. Example are when using JavaScript getPayloadXML and setPayloadXML , E4X XML objects and when using Ruby, REXML documents.

Limitations and Alternatives to Script Mediator

While the Script mediator offers enhanced extensibility in the Synapse configuration, it is important to consider its potential limitations. We highly recommend utilizing the Script mediator only when absolutely necessary. In cases where extension requirements can be fulfilled using alternatives such as the Class mediator, we advise opting for the latter due to several reasons. Notably, the use of a Script mediator in moderately complex to sophisticated mediation flows may introduce significant performance overhead compared to a Java-based Class mediator. Therefore, we suggest prioritizing Class mediators as extensions to the mediation flow over Script mediators. However, for simpler tasks, the Script mediator can still serve as a versatile option.

Note

The Micro Integrator uses GraalVM JS by default. If you have specified the language as rhinoJs, Rhino engine will be used to execute JavaScript. Rhino engine converts the script to a method inside a Java class. Therefore, when processing large JSON data volumes, the code length must be less than 65,536 characters, since the Script mediator converts the payload into a Java object. However, you can use the following alternative options to process large JSON data volumes.

  • Achieve the same functionality via a Class mediator.
  • If the original message consists of repetitive sections, you can use the Iterate mediator to generate a relatively small payload using those repetitive sections. This will then allow you to use the Script mediator.
  • The Script Mediator supports using the default GraalVM JS to execute JavaScript.

Prerequisites

  • Listed below are the prerequisites for writing a Script mediator using JavaScript, Groovy, or Ruby.

    Scripting Language Prerequisite
    Groovy Download the groovy-all -2.4.4.jar file and copy it to the <MI_HOME>/ dropins directory. Note that when you define the script, you need to start by importing Groovy.
    Ruby

    Install the JRuby engine for mediation. This is available in the WSO2 P2 repository as a feature (WSO2 Carbon - JRuby Engine for Mediation).

    Alternatively, you can download and install the JRuby engine manually: Download the jruby-complete-1.3.0.wso2v1.jar file from the WSO2 P2 repository and copy it to the <MI_HOME>/ dropins directory.
    JavaScript The JavaScript based on GraalVM JS is enabled by default in the Micro Integrator and ready for use.

    Note

    The nashornJs language is deprecated in JDK 15 and above. If you are using JDK 15 or above, you need to manually copy the nashorn-core and asm-util JAR files to the <MI_HOME>/lib directory since Nashorn was removed from the JDK.

Syntax

Click on the relevant tab to view the syntax for a script mediator using an Inline script, or a script mediator using a script of a registry

  • Using an Inline script: The following syntax applies when you create a Script mediator with the script program statements embedded inline within the Synapse configuration. 
    <script language="js"><![CDATA[...script source code...]]></script>

  • Using a script of the registry: The following syntax applies when you create a Script mediator with the script program statements stored in a separate file, referenced via the Local or Remote Registry entry.

    Info

    If you are creating the Registry Resource via Tooling, you need not specify the content/media type, because it gets automatically applied when you select the JavaScript File Template.

    <script key="string" language="js" [function="script-function-name"]>
  <include key="string"/>
</script>

Configuration

  • Inline: If this script type is selected, the script is specified inline. The parameters available to configure a Script mediator using an inline script are as follows.

    Parameter Name Description
    Language

    The scripting language for the Script mediator. You can select from the following available languages.

    • JavaScript - This is represented as js in the source view.
    • Groovy - This is represented as groovy in the source view.
    • Ruby - This is represented as rb in the source view.
    Source

    Enter the source in this parameter.

    Note: If you are using Groovy as the scripting language, you need to first import Groovy in your script by adding the following:

    import groovy.json.*;

  • Registry: If this script type is selected, a script which is already saved in the registry will be referred using a key. The parameters available to configure a Script mediator using a script saved in the registry are as follows.

    Parameter Name Description
    Language

    The scripting language for the Script mediator. You can select from the following available languages.

    • JavaScript - This is represented as js in the source view.

    • Groovy - This is represented as groovy in the source view. Note: Be sure that your script starts with the following, which indicates that Groovy is imported:

      import groovy.json.*;
    • Ruby - This is represented as rb in the source view.
    Function The function of the selected script language to be invoked. This is an optional parameter. If no value is specified, a default function named mediate will be applied. This function considers the Synapse MessageContext as a single parameter. The function may return a boolean. If it does not, then the value true is assumed and the Script mediator returns this value.
    Key Type

    You can select one of the following options.

    • Static Key : If this is selected, an existing key can be selected from the registry for the Key parameter.
    • Dynamic Key : If this is selected, the key can be entered dynamically in the Key parameter.
    Key The Registry location of the source. You can click either Configuration Registry or the Governance Registry to select the source from the resource tree.
    Include keys

    This parameter allows you to include functions defined in two or more scripts your Script mediator configuration. After pointing to one script in the Key parameter, you can click Add Include Key to add the function in another script.

    When you click Add Include Key , the following parameters will be displayed. Enter the script to be included in the Key parameter by clicking either Configuration Registry or the Governance Registry and then selecting the relevant script from the resource tree.

Note

The Script mediator now utilizes the GraalVM JS engine for the js language. The GraalVM JS engine does not provide E4X support for XML. For E4X support, you can use the Rhino engine. To use the Rhino engine, you need to specify the language as rhinoJs in the Script mediator language configuration.

Examples

Use an inline script

The following configuration is an example of an inline mediator using JavaScript/E4X which returns false if the SOAP message body contains an element named symbol, which has a value of IBM.

<script language="js"><![CDATA[mc.getPayloadXML()..symbol != "IBM";]]></script>

Use a script saved in the registry

In the following example, script is loaded from the registry by using the key repository/conf/sample/resources/script/test.js.

<script language="js"
    key="repository/conf/sample/resources/script/test.js"
    function="testFunction"/>

script language="js" indicates that the function invoked should be in the JavaScript language. The function named testFunction which is invoked should be saved as a resource in the Registry. The script can be as shown in the example below.

function testFunction(mc) {
     var symbol = mc.getPayloadXML()..*::Code.toString();
     mc.setPayloadXML(
        <m:getQuote xmlns:m="http://services.samples/xsd">
           <m:request>
              <m:symbol>{symbol}</m:symbol>
           </m:request>
        </m:getQuote>);
}

Add an include key

The following configuration has an include key.

<script language="js" key="stockquoteScript" function="transformRequest">
    <include key="sampleScript"/>
</script>

The script is written in JavaScript. The function to be executed is transformRequest. This function may be as follows in a script saved in the Registry.

// stockquoteTransform.js
function transformRequest(mc) {
transformRequestFunction(mc);
}

function transformResponse(mc) {
transformResponseFunction(mc);
}

In addition, the function in the script named sampleScript which is included in the mediation configuration via the include key sub element is also executed in the mediation. Note that in order to do this, sampleScript script should also be saved as a resource in the Registry . This script can be as follows.

// sample.js
function transformRequestFunction(mc) {
var symbol = mc.getPayloadXML()..*::Code.toString();
mc.setPayloadXML(
    <m:getquote m="http://services.samples">
        <m:request>
            <m:symbol>{symbol}</m:symbol>
        </m:request>
    </m:getquote>);
}

function transformResponse(mc) {
var symbol = mc.getPayloadXML()..*::symbol.toString();
var price = mc.getPayloadXML()..*::last.toString();
mc.setPayloadXML(
    <m:checkpriceresponse m="http://services.samples/xsd">
        <m:code>{symbol}</m:code>
        <m:price>{price}</m:price>
    </m:checkpriceresponse>);
}

Add a custom SOAP header

You can add custom SOAP headers to a request by using the addHeader(mustUnderstand, content) of the Script mediator in a proxy service as shown in the example below.

<?xml version="1.0" encoding="UTF-8"?>
<proxy name="CustomSOAPHeaderProxy" startOnLoad="true" transports="http https" xmlns="http://ws.apache.org/ns/synapse">
    <target>
        <inSequence>
            <log category="INFO" level="full">
                <property name="Message" value="IncomingRequest"/>
            </log>
            <script description="javascript scripts" language="js"><![CDATA[mc.addHeader(false, <ns:sampleCustomHeader xmlns:ns="gsb:http://wso2.org/sample"><ns:customInfo>CustomHeader</ns:customInfo></ns:sampleCustomHeader>);]]></script>
            <log category="INFO" level="full">
                <property name="Message" value="UpdatedMessage"/>
            </log>
            <drop/>
        </inSequence>
        <faultSequence/>
    </target>
</proxy>

Example per method

The following table contains examples of how some of the commonly used methods can be included in the script invoked by the following sample Script mediator configuration.

<script language="js"
             key="conf:/repository/EI/transform.js"
             function="transform"/>
Return? Method Name Example
Yes getPayloadXML()

The script invoked can be as follows.

// sample.js02.function transformRequestFunction(mc) {
var symbol = mc.getPayloadXML()..*::Code.toString();
mc.setPayloadXML(
    <m:getquote m="http://services.samples">
        <m:request>
            <m:symbol>{symbol}</m:symbol>
        </m:request>
    </m:getquote>);
}

mc.getPayloadXML() returns the response received in XML form.
No setPayloadXML(payload) See the example above for the getPayloadXML() method. mc.setPayloadXML( <m:getquote m="http://services.samples"> <m:request> <m:symbol>{symbol}</m:symbol </m:request> </m:getquote> ) is used in that script to set the XML representation of the SOAP body (obtained using the getPayloadXML() method) to the current message context.
No addHeader(mustUnderstand, Object content)

The script invoked can be as follows.

<script language="js"> 
<![CDATA[
var wsse = new Namespace('http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd'); 
var envelope = mc.getEnvelopeXML(); 
var username = envelope..wsse::Username.toString(); 
var password = envelope..wsse::Password.toString();   
mc.addHeader(false, <urn:AuthenticationInfo><urn:userName>{username}</urn:userName><urn:password>{password}</urn:password></urn:AuthenticationInfo>); 
]]>
</script>

The addHeader method configured as

mc.addHeader(false, <urn:AuthenticationInfo><urn:userName>{username}</urn:userName><urn:password>{password}</urn:password></urn:AuthenticationInfo>) in the above script is used to extract user name and password values included in the request and add them to the header structure required for the backend service.
No getEnvelopeXML()

The script invoked can be as follows.

<script language="js"> 
<![CDATA[
var wsse = new Namespace('http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd'); 
var envelope = mc.getEnvelopeXML(); 
var username = envelope..wsse::Username.toString(); 
var password = envelope..wsse::Password.toString();   
mc.addHeader(false, <urn:AuthenticationInfo><urn:userName>{username}</urn:userName><urn:password>{password}</urn:password></urn:AuthenticationInfo>); ]]> </script> 
See more at: http://sajithblogs.blogspot.com/2013/08/wso2-EI-adding-complex-soap-headers-to.html#sthash.jqpiEmf0.dpuf
Yes getPayloadJSON()

The script invoked can be as follows.

function transform(mc) {
    payload = mc.getPayloadJSON();
    results = payload.results;
    var response = new Array();
    for (i = 0; i < results.length; ++i) {
        location_object = results[i];
        l = new Object();
        l.name = location_object.name;
        l.tags = location_object.types;
        l.id = "ID:" + (location_object.id);
        response[i] = l;
    }
    mc.setPayloadJSON(response);
}

mc.getPayloadJSON() returns the JSON payload (received as the response) as a JavaScript object. This object can be manipulated as a normal JavaScript variable within a script as shown in the above JavaScript code. See JSON Support for further information about how this script is used.
No setPayloadJSON(payload)

See the example script for the getPayloadJSON() method.

The mc.setPayloadJSON() method can be used to replace the existing payload with a new payload. In the above script, we build a new array object by using the fields of the incoming JSON payload and set that array object as the new payload. See JSON Support for further information about how this script is used
Yes getProperty (name)

The script invoked can be as follows.

<script language="js">
<![CDATA[
 var time1 = mc.getProperty("TIME_1");
 var time2 = mc.getProperty("TIME_2");
 var timeTaken = time2 - time1;
 print("Time Duration :  " + timeTaken + " ms ");
 mc.setProperty("RESPONSE_TIME", timeTaken);
]]>
</script>

In this example, the getProperty method is used to get two time durations. The difference between the two time durations is calculated and the setProperty method is used to set this difference in the message context.
No setProperty(property)

See the example for the getProperty method. The setProperty method is used to set the response time calculated from the time durations obtained (using the getProperty method) in the message context.

In the following example, var result = "a" and then result = result + "b" . When concatenating these strings, the script invoked needs to be as follows:

<script language="js">
<![CDATA[
{var result = "a";
 result = result + "b";
 mc.setProperty('result_str', result.toString()); 
}]]>
</script>