Synapse XPath Variables

There is a set of predefined XPath variables that you can directly use to write XPaths in the Synapse configuration, instead of using the synapse:get-property() function. These XPath variables get properties of various scopes as follows:

$body

The SOAP 1.1 or 1.2 body element. For example, the expression $body/getQuote refers to the first getQuote element in a SOAP body, regardless of whether the message is SOAP-11 or SOAP-12. We have discussed an example below.

Example of $body usage:

1. Deploy the following proxy service using instructions in Adding a Proxy Service.
   
   Note the property, <property xmlns:m0=" http://services.samples " name="stockprop" expression="$body/m0:getQuote"/> in the configuration. It is used to log the first <m0:getQuote> element of the request SOAP body.

   <proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true">
      <target>
         <inSequence>
            <log>
               <property xmlns:m0="http://services.samples" name="stockprop" expression="$body/m0:getQuote"/>
            </log>
            <send>
               <endpoint>
                  <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
               </endpoint>
            </send>
         </inSequence>
         <outSequence>
            <send/>
         </outSequence>
      </target>
      <description></description>
   </proxy> 

2. Send the following StockQuote request using the sample StockQuote client. For information on the sample client, refer to the Sample Clients sub heading in Setting Up the ESB Samples.

   ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy

3. Note the following message in the ESB log.

   [2013-03-18 14:04:41,019] INFO - LogMediator To: /services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:930f68f5-199a-4eff-90d2-ea679c2362ab, Direction: request, stockprop = <m0:getQuotexmlns:m0="http://services.samples"><m0:request><m0:symbol>IBM</m0:symbol></m0:request></m0:getQuote>

$Header

The SOAP 1.1 or 1.2 header element. For example, the expression $header/wsa:To refers to the addressing To header regardless of whether this message is SOAP-11 or SOAP-12. We have discussed an example below.

Example of $Header usage:

1. Deploy the following proxy service using instructions in   Adding a Proxy Service .
   
   Note the property, <property xmlns:wsa=" http://www.w3.org/2005/08/addressing " name="stockprop" expression="$header/wsa:To"/> in the configuration. It is used to log the value of wsa:To header of the SOAP request. 

   <proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true">
      <target>
         <inSequence>
            <log>
               <property xmlns:wsa="http://www.w3.org/2005/08/addressing" name="stockprop" expression="$header/wsa:To"/>
            </log>
            <send>
               <endpoint>
                  <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
               </endpoint>
            </send>
         </inSequence>
         <outSequence>
            <send/>
         </outSequence>
      </target>
      <description></description>
   </proxy> 

2. Send the following StockQuote request using the sample StockQuote client. For information on the sample client, refer to the Sample Clients sub heading in Setting Up the ESB Samples.

   ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy

3. Note the following message in the ESB log.

   [2013-03-18 14:14:16,356] INFO - LogMediator To: http://localhost:9000/services/SimpleStockQuoteService, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:8a64c9cb-b82f-4d6f-a45d-bef37f8b664a, Direction: request,
   stockprop = http://localhost:9000/services/SimpleStockQuoteService

$axis2

Prefix for Axis2 MessageContext properties. This is used to get the property value at the axis2 scope. For example, to get the value of Axis2 message context property with name REST_URL_POSTFIX, use the XPath expression $axis2:REST_URL_POSTFIX. We have discussed an example below.

Example of $axis2 usage:

1. Deploy the following proxy service using instructions in Adding a Proxy Service.
   
   Note the property, <property name="stockprop" expression="$axis2:REST_URL_POSTFIX"/> in the configuration which is used to log the REST_URL_POSTFIX value of the request message. 

   <proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true">
      <target>
         <inSequence>
            <log>
               <property name="stockprop" expression="$axis2:REST_URL_POSTFIX"/>
            </log>
            <send>
               <endpoint>
                 <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
               </endpoint>
            </send>
         </inSequence>
         <outSequence>
            <send/>
         </outSequence>
      </target>
      <description></description>
   </proxy>

2. Send the following StockQuote request using the sample StockQuote client. For information on the sample client, refer to the Sample Clients sub heading in Setting Up the ESB Samples.

   ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy/test/prefix

3. Note the following message in the ESB log.

   INFO - LogMediator To: http://localhost:8280/services/StockQuoteProxy/test/prefix, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:ecd228c5-106a-4448-9c83-3b1e957e2fe5, Direction: request, stockprop = /test/prefix

In this example, the property definition, <property name="stockprop" expression="$axis2:REST_URL_POSTFIX"/> is equivalent to <property name="stockprop" expression="get-property('axis2','REST_URL_POSTFIX')"/>

Similarly, you can use $axis2 prefix with HTTP Transport Properties.

$ctx

Prefix for Synapse MessageContext properties and gets a property at the default scope. For example, to get the value of Synapse message context property with name ERROR_MESSAGE, use the XPath expression $ctx:ERROR_MESSAGE. We have discussed an example below.

Example of $ctx usage:

This example sends a request to a sample proxy service, and sets the target endpoint to a non-existent endpoint reference key. It causes a mediation fault, which triggers the fault sequence.

1. Deploy the following proxy service using instructions in Adding a Proxy Service.
   
   Note the property, <property name="stockerrorprop" expression="$ctx:ERROR_MESSAGE"/> in the fault sequence configuration. It is used to log the error message that occurs due to a  mediation fault. 

   <proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true">
      <target>
         <inSequence>
           <send>
               <endpoint key="ep2"/>
            </send>
         </inSequence>
         <outSequence>
            <send/>
         </outSequence>
         <faultSequence>
            <log>
               <property name="stockerrorprop" expression="$ctx:ERROR_MESSAGE"/>
               <property name="Cause" expression="get-property('ERROR_MESSAGE')"/>
            </log>
         </faultSequence>
      </target>
      <description></description>
   </proxy> 

2. Send the following StockQuote request using the sample StockQuote client. For information on the sample client, refer to the Sample Clients sub heading in Setting Up the ESB Samples.

   ant stockquote -Dtrpurl=http://localhost:8280/services/StockQuoteProxy

3. Note the following message in the ESB log.

   INFO - LogMediator To: /services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:54205f7d-359b-4e82-9099-0f8e3bf9d014, Direction: request, stockerrorprop = Couldn't find the endpoint with the key : ep2 

In this example, the property definition, <property name="stockerrorprop" expression="$ctx:ERROR_MESSAGE"/> is equivalent to <property name="stockerrorprop" expression="get-property('ERROR_MESSAGE')"/>.

Similarly, you can use $ctx prefix with Generic Properties.

$trp

Prefix used to get the transport headers. For example, to get the transport header named Content-Type of the current message, use the XPath expression $trp:Content-Type. HTTP transport headers are not case sensitive. Therefore, $trp:Content-Type and $trp:CONTENT-TYPE are regarded as the same. We have discussed an example below.

Example of $trp usage:

1. Deploy the following proxy service using instructions given in section Adding a Proxy Service.
   
   Note the property, <property name="stockprop" expression="$trp:Content-Type"/> in the configuration, which is used to log the Content-Type HTTP header of the request message.
   

   <proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true">
      <target>
         <inSequence>
            <log>
                <property name="stockprop" expression="$trp:Content-Type"/>
            </log>
            <send>
               <endpoint>
                  <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
               </endpoint>
            </send>
         </inSequence>
         <outSequence>
            <send/>
         </outSequence>
      </target>
      <description></description>
   </proxy> 

    

2. Send the following StockQuote request using the sample StockQuote client. For information on the sample client, refer to the Sample Clients sub heading in Setting Up the ESB Samples.
   

   ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy

    

3. Note the following message in the ESB log.
   

   [2013-03-18 12:23:14,101] INFO - LogMediator To: http://localhost:8280/services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:25a3143a-5b18-4cbb-b8e4-27d4dd1895d2, Direction: request, stockprop = text/xml; charset=UTF-8 

In this example, the property definition, <property name="stockprop" expression="$trp:Content-Type"/> is equivalent to <property name="stockprop" expression="get-property('transport','Content-Type')"/>. Similarly, you can use $trp prefix with HTTP Transport Properties.

$url

The prefix used to get the URI element of a request URL

Example of $url usage:

1. Create a REST API with the following configuration using instructions given in page Creating APIs.

   <api xmlns="http://ws.apache.org/ns/synapse" name="Editing" context="/editing">
      <resource methods="GET" uri-template="/edit?a={symbol}&b={value}">
         <inSequence>
            <log level="full">
               <property name="SYMBOL" expression="$url:a"></property>
               <property name="VALUE" expression="$url:b"></property>
            </log>
            <respond></respond>
         </inSequence>
      </resource>
   </api>

2. Send a request to the REST API you created using a browser as follows:

    http://10.100.5.73:8280/editing/edit?a=wso2&b=2.4

   You would see the following in the ESB log:
    

   LogMediator To: /editing/edit?a=wso2&b=2.4, MessageID: urn:uuid:36cb5ad7-f150-490d-897a-ee7b86a9307d, Direction: request, SYMBOL = wso2, VALUE = 2.4, Envelope: <?xml version="1.0" encoding="utf-8"?><soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"><soapenv:Body></soapenv:Body></soapenv:Envelope>

$func

The prefix used to refer to a particular parameter value passed externally by an invoker such as the Call Template Mediator.

Example of $func usage:

1. Add a sequence template with the following configuration. See Adding a New Sequence Template for detailed instructions.

   <template xmlns="http://ws.apache.org/ns/synapse" name="HelloWordLogger">
      <sequence>
         <log level="full">
            <property xmlns:ns2="http://org.apache.synapse/xsd" xmlns:ns="http://org.apache.synapse/xsd" name="message" expression="$func:message"></property>
         </log>
      </sequence>
   </template>

2. Deploy the following proxy service using instructions given in section  Adding a Proxy Service .

   <proxy xmlns="http://ws.apache.org/ns/synapse"
          name="StockQuoteProxy"
          transports="https,http"
          statistics="disable"
          trace="disable"
          startOnLoad="true">
      <target>
         <inSequence>
            <call-template target="HelloWorldLogger">
               <with-param name="message" value="HelloWorld"/>
            </call-template>
            <log/>
         </inSequence>
         <outSequence>
            <send/>
         </outSequence>
         <endpoint>
            <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
         </endpoint>
      </target>
      <description/>
   </proxy>

3. Send the following StockQuote request using the sample StockQuote client. For information on the sample client, refer to the Sample Clients sub heading in Setting Up the ESB Samples.
    

   ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy

4. Note the following message in the ESB log.

   LogMediator To: http://localhost:8280/services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:8d90e21b-b5cc-4a02-98e2-24b324fa704c, Direction: request, message = HelloWorld

$env

Prefix used to get a SOAP 1.1 or 1.2 envelope level element. For example, to get the body element from the SOAP envelope, use the expression $env/*[local-name()='Body'].

Example of $env usage:

1. Create an API with the following configuration. For information on how to create an API, see Creating APIs.

   <api context="/soapEnvelopeTest" name="SoapEnvelopeTest">
           <resource url-mapping="/*">
               <inSequence>
                   <loopback/>
               </inSequence>
               <outSequence>
                   <property name="messageType" scope="axis2" value="application/xml"/>
                   <payloadFactory media-type="xml">
                       <format>
                           <theData xmlns="http://some.namespace">
                               <item>$1</item>
                           </theData>
                       </format>
                       <args>
                           <arg evaluator="xml" expression="$env/*[local-name()='Body']/*[local-name()='jsonObject']/*"/>
                   </payloadFactory>
                   <property name="messageType" scope="axis2" value="application/json"/>
                   <send/>
               </outSequence>
           </resource>
   </api>

2. Send a post request to the API you created (i.e.,http://localhost:8280/soapEnvelopeTest) with the following json payload.

    {"content":{ "paramA": "ValueA", "paramB": "valueB" }}

   You will see the following on the ESB log:

   {"theData":{"item":{"content":{"paramA":"ValueA","paramB":"valueB"}}}}