WSO2 ESB supports standard XPath functions and variables through its underlying XPath engine. The ESB also provides custom XPath functions and variables for accessing message properties.
XPath extension functions
There are two custom functions supported by the ESB as follows:
- synapse:get-property() function
- base64Encode() function
synapse:get-property()
The get-property() function allows any XPath expression used in a configuration to look up information from the current message context. Using property mediator, you can retrieve properties previously set, and/or information from the Synapse, Axis2 message contexts or transport header.
The syntax of the function takes the following format.
- get-property(String propertyName)
- get-property(String scope, String propertyName)
The function accepts scope as an optional parameter. It retrieves a message property at the given scope, which can be synapse, axis2 or transport. If you provide only the property name without the scope, the default Synapse scope will be used.
synapse:get-property( [(axis2 | axis2-client | transport),] <property_name> [,<dateformat>] )
You can use the get-property() function to retrieve Axis2 message context properties or transport headers. For example, synapse:get-property('transport', 'USER_AGENT'). Given below are special properties supported by the get-property() function.
| Name | Return Value |
| To | Incoming URL as a String or empty string («») if a To address is not defined. |
| From | From address as a String or empty string («») if a From address is not defined |
| Action | SOAP Addressing Action header value as a String or empty string («») if a Action is not defined |
| FaultTo | SOAP FautTo header value as a String or empty string («») if a FaultTo address is not defined |
| ReplyTo | ReplyTo header value as a String or empty string («») if a ReplyTo address is not defined |
| MessageID | A unique identifier (UUID) for the message as a String or empty string («») if MessageID is not defined. This id is guaranteed to be unique. |
| FAULT | TRUE if the message has a fault or empty string if message doesn't have a fault |
| MESSAGE_FORMAT | Returns pox, get, soap11, soap12 depending on the message. If a message type is unknown this returns soap12 |
| OperationName | Operation name corresponding to the message. A proxy service with a WSDL can have different operations. If the WSDL is not defined ESB defines fixed operations |
base64Encode() function
The syntax of the function takes the following format.
- base64Encode(string)
It returns the base64 encoded value of the string argument.
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, expression="$body/getQuote" refers to the first getQuote element in the SOAP body regardless of whether the message is SOAP-11 or SOAP-12.
Header
The SOAP 1.1 or 1.2 header element. For example, expression="$header/wsa:To refers to the addressing To header regardless of whether this message is SOAP-11 or SOAP-12.
$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 $axis2 usage:
1. Deploy the following proxy service.
Note the property, <property name="stockprop" expression="$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="$axis2:REST_URL_POSTFIX"/>
</log>
<send>
<endpoint>
<address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
</endpoint>
</send>
</inSequence>
<outSequence>
<send/>
</outSequence>
</target>
<description></description>
</proxy>
2. Send the StockQuoteRequest using sample stockquote client as follows.
ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy/test/prefix
3. Note the following message in the ESB log.
INFO - LogMediator To: http://localhost:8280/services/StockQuoteProxy/test/prefix, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:ecd228c5-106a-4448-9c83-3b1e957e2fe5, Direction: request, stockprop = /test/prefix
In this example, the property definition, <property name="stockprop" expression="$axis2:REST_URL_POSTFIX"/> is equivalent to <property name="stockprop" expression="get-property('axis2','REST_URL_POSTFIX')"/>
Similarly, you can use $axis2 prefix with HTTP Transport Properties.
ctx
Prefix for Synapse MessageContext properties. For example, expression="$ctx:RESPONSE" gives the value of the Synapse message context property with name "RESPONSE."
$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 $trp usage:
1. Deploy the following proxy service. Note the property, <property name="stockprop" expression="$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="$trp:Content-Type"/>
</log>
<send>
<endpoint>
<address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
</endpoint>
</send>
</inSequence>
<outSequence>
<send/>
</outSequence>
</target>
<description></description>
</proxy>
2. Send the StockQuoteRequest using sample stockquote client as follows.
ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy
3. You will notice the following message in ESB log.
[2013-03-18 12:23:14,101] INFO - LogMediator To: http://localhost:8280/services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:25a3143a-5b18-4cbb-b8e4-27d4dd1895d2, Direction: request, stockprop = text/xml; charset=UTF-8
In this example, the property definition, <property name="stockprop" expression="$trp:Content-Type"/> is equivalent to <property name="stockprop" expression="get-property('transport','Content-Type')"/>
Similarly, we can use $trp prefix with the following properties.
<List down all properties in transport scope> - http://docs.wso2.org/wiki/display/ESB460/HTTP+Transport+Specific+Properties
$ctx
Gets a property at the default scope.
For example, to get the property named 'foo' at the default scope use the following XPath expression:
$ctx:foo
$url
Gets a URL parameter.
For example, to get the URL parameter named 'bar' use the following XPath expression:
$url:foo
Syntax
<property name="string" [action=set|remove] (value="literal" | expression="xpath") [scope=transport|axis2|axis2-client]/>