The Synapse configuration language is designed to support a processing model where messages come into Synapse, are processed via some number of mediators and then delivered to an endpoint somewhere. It is currently direction agnostic, but directionality can easily be added as a selection mechanism for mediators (see below for details).
A Synapse configuration looks like the following at the top level:
<synapse>
registrydef
<definitions>
(sequencedef | endpointdef | literalpropertydef)+
<definitions>?
<proxies>
proxyservice+
</proxies>?
<rules [key="string"]>
mediator*
</rules>
</synapse>
A registrydef token represents a <registry> element which is used to define a Registry which is referenced within the configuration.
<registry [name="string"] provider="string"/> <property name="string" value="string"/>* </registry>
The registry definition without a name becomes the 'default' registry instance for the Synapse instance, and any reference to a registry which does not specify a registry name defaults to this instance. Optionally, a number of configuration properties may be specified to configure an instance of a registry.
The <definitions> section defines reusable elements that can be used from within the rules, and the <rules> section contains the sequence of mediators that every message passes through during mediation.
The token literalpropertydef refers to a <set-property> element as follows:
<set-property name="string" [value="string"] [src="url"] [key="string"]>
<inline-xml/>?
<set-property/>
These properties are top level properties which are set globally for the entire system. Values of these properties can be retrieved via the extension XPath function called "synapse:get-property(prop-name)".
A property can be static literal text (specified with the value attribute) or static XML specified as an inline XML fragment or specified as a URL (using the src attribute). A property can alternatively be a DynamicProperty which will reference a key on a Registry. If a property is a DynamicProperty, it will be fetched from the Registry and cached locally as per meta information provided by the Registry for caching. DynamicProperties are automatically refreshed when expired, and thus can be used to specify dynamic behaviour in Synapse.
Dynamic properties allows the creation of Dynamic Sequences, Endpoints and Proxies whose definition would change accordingly with any changes on the property.
A sequencedef token represents a <sequence> element which is used to define a named sequence of mediators that can be invoked later by name as a sequence of mediators.
<sequence name="string" [onError="string"] [key="string"]> mediator* </sequence>
If an optional error handler sequence name is specified through the attribute 'onError', an exception on this sequence will invoke the sequence specified by this name.
A Dynamic Sequence may be defined by specifying a Dynamic Property as its definition. As the dynamic property changes, the sequence will dynamically be updated accordingly.
An endpointdef token represents an <endpoint> element which is used to give a logical name to an endpoint address. If the address is not just a simple URL, then extensibility elements may be used to indicate the address (i.e. to compute the address at runtime).
<endpoint name="string" [address="url"] [key="string"]> <enableRM [policy="key"]/>? <enableSec/>? .. extensibility .. </endpoint>
An Axis2 Parameter element within an endpoint definition with the name " OutflowSecurity" describes the Apache Rampart security configuration to be used for messages flowing to this endpoint. Please see Rampart/Axis2 documentation for more details.
A Policy element within an endpoint definition with an Id of "RMPolicy" describes the Apache Sandesha2 RM configuration (or any overrides against the default) to be used for messages flowing to this endpoint. Please see Sandesha2/Axis2 documentation for more details.
The enableRM/enableSec options turns on WS-Security or WS-RM on outgoing messages to this endpoint.
A Dynamic Endpoint may be defined by specifying a Dynamic Property as its definition. As the dynamic property changes, the endpoint will dynamically be updated accordingly.
NOTE: The Rampart and/or Sandesha configuration options may change with Axis2 changes currently in progress
The <proxies> section defines Synapse Proxy services, which are real Axis2 services hosted on Synapse, which allows WSDL mediation as well as the ability to expose existing services on Synapse, with possibly different semantics, such as WS-Security, WS-RM and Transport switching etc.
A proxyservice token represents a <proxy> element which is used to define a Synapse Proxy service.
<proxy name="string" [description="string"] [transports="(http |https |jms )+|all"]>
<target sequence="name" | endpoint="name"/>? // defaults to the synapse main sequence
<wsdl key="string">?
<enableRM/>?
<enableSec/>?
<policy key="string">* // optional service level policies
// (e.g. WS-Security and/or WS-RM policies)
<property name="string" value="string"/>* // optional service parameters
// (e.g. transport.jms.ConnectionFactory)
</proxy>
A proxy service is created and exposed on the specified transports through the underlying Axis2 instance, exposing service EPR's as per the standard Axis2 conventions - based on the service name. (Note: that currently Axis2 does not allow custom URI's to be set for services on some transports.) The Proxy service could be exposed over all enabled Axis2 transports such as http, https, JMS etc. or on a subset of these. Each service could define the target for received messages as a named sequence or a direct endpoint. If a target is not supplied, the default Synapse rules will apply for incoming message mediation. Any supplied policies would apply as service level policies, and any properties could be passed into the proxy services' AxisService instance (e.g. the JMS destination etc). If the proxy service should enable WS-Reliable Messaging or Security, the appropriate modules could be engaged.
A Dynamic Proxy may be defined by specifying a Dynamic Property as its definition. As the dynamic property changes, the proxy will dynamically be updated accordingly.
A mediator token refers to any of the following tokens:
send | drop | log | makefault | transform | header | filter | switch | class | validate | setproperty | sequenceref | in | out | rm | try
In addition to the above, Synapse will be able to load mediators via the J2SE Service Provider model. Mediator extensions must implement the MediatorFactory interface, similarly to the configuration extensions mentioned previously.
The send token represents a <send> element. The <send> element is used to send messages out of Synapse to some endpoint, and stop further mediation of the message. The send mediator also copies any message context properties named "correlate/*" from the current message context to the reply message received on the execution of the send operation. This allows the reply messages to be correlated to the original messages in a flexible manner. Messages may be correlated by WS-A MessageID, or even simple custom text labels. See example 1 for more details.
In the simplest case, the place to send the message to is implicit in the message (via a property of the message itself)- that is indicated by the following:
<send/>
If the message is to be sent to one or more endpoints, then the following is used:
<send> (endpointref | endpoint)+ </send>
where the endpointref token refers to the following:
<endpoint ref="name"/>
and the endpoint token refers to an anonymous endpoint defined inline:
<endpoint address="url"/>
If the message is to be sent to an endpoint selected by load balancing across a set of endpoints, then it is indicated by the following:
<send>
<load-balance algorithm="uri">
(endpointref | endpoint)+
</load-balance>
</send>
Similarly, if the message is to be sent to an endpoint with failover semantics, then it is indicated by the following:
<send>
<failover>
(endpointref | endpoint)+
</failover>
</send>
Once the <send> mediator executes, further processing of the current message stops.
Note: Synapse does not yet support the load balancing or failover semantics, and supports only a single endpoint reference.
The drop token refers to a <drop> element which is used to drop a message:
<drop/>
Once the <drop> mediator executes, further processing of the current message stops.
The log token refers to a <log> element which may be used to log messages being mediated:
<log [level="string"] [separator="string"]> <property name="string" (value="literal" | expression="xpath")/>* </log>
The optional level attribute selects a pre-defined subset of properties to be logged.
e.g.
A separator if defined will be used to seperate the attributes being logged. The default separator is the ',' comma.
<makefault [version="soap11|soap12"]> <code (value="literal" | expression="xpath")/> <reason (value="literal" | expression="xpath")> <node>? <role>? <detail>? </makefault>
The <makefault> mediator transforms the current message into a fault message, but does NOT send it. The <send> mediator needs to be invoked to send a fault message created this way. The fault message "to" header is set to the "faultTo" of the original message if such a header existed on the original message, else it is set it to the "replyTo" of the original message.
<xslt key="string" [source="xpath"]> <property name="string" (value="literal" | expression="xpath")/>* </transform>
The <xslt> mediator applies the specified XSLT transformation to the given element. If the source element is not specified, it defaults to the first child of the soap body. Optionally parameters (XSLT) could be passed into the transformations through the <property> elements.
<header name="qname" (value="literal" | expression="xpath") [action="set"]/> <header name="qname" action="remove"/>
The <header> mediator sets or removes a specified header from the current soap message. Currently the set header only supports simple valued headers. In the future we may extend this to have XML structured headers by embedding the XML content within the element itself. The optional action attribute specifies whether the mediator should set or remove the header. If omitted, it defaults to a set-header.
<filter (source="xpath" regex="string") | xpath="xpath"> mediator+ </filter>
The <filter> mediator either test the given xpath expression as a boolean expression, or match the evaluation result of a source xpath expression against the given regular expression. If the test succeeds, the filter mediator will execute the enclosed mediators in sequence.
<switch source="xpath">
<case regex="string">
mediator+
</case>+
<default>
mediator+
</default>?
</switch>
The <switch> mediator will evaluate the given source xpath expression into its string value, and match it against the given regular expressions. If the specified cases does not match and a default case exists, it will be executed.
<validate key="string" [source="xpath"]>
<on-fail>
mediator+
</on-fail>
</validate>
The <validate> mediator validates the result of the evaluation of the source xpath expression, against the schema specified. If the source attribute is not specified, the validation is performed against the soap body content of the current message. If the validation fails, the on-fail sequence of mediators is executed.
Note: As the validation mediator is strongly dependent on the Xerces 2.8.0 parser, it is bundled with the Synapse extensions, so that the Synapse core will remain simple and lightweight.
<set-property name="string" (value="literal" | expression="xpath")/>
The setproperty token refers to a <set-property> element which is a mediator that has no direct impact on the message but rather on the message context flowing through Synapse. The properties thus set on the message context applies only to the current message and can be later retrieved through the synapse:get-property(prop-name) extension function.
<class name="class-name"> <property name="string" (value="literal" | expression="xpath")/>* </class>
The class mediator creates an instance of the specified class and sets it as a mediator. The class must implement the org.apache.synapse.api.Mediator interface. If any properties are specified, the corresponding setter methods are invoked on the class. However, Synapse will only support String properties.
<sequence ref="name"/>
A sequenceref token refers to a <sequence> element which is used to invoke a named sequence of mediators.
The Synapse configuration language could be easily extended, with configuration extensions as well as mediation extensions. The Spring mediator is such an example.
A Spring configuration could be created as a property or DynamicProperty providing a URL or a reference to a Registry. The configuration is then created on first use or as necessary (as per DynamicProperty semantics) by the mediators which reference this configuration.
<set-property name="string" key="string"/> <set-property name="string" src="url"/>
The name attribute specifies a unique name for the configuration, and the src, key or inlined XML references to the Spring configuration
<spring:spring bean="exampleBean1" key="string"/>
The <spring> element creates an instance of a mediator, which is managed by Spring. This Spring bean must implement the Mediator interface for it to act as a Mediator. The key will reference the Spring ApplicationContext/Configuration used for the bean
The following illustrates the hypothetical example used to illustrate the new Synapse configuration language syntax. However, features such as load balancing and failover etc are still not available with Synapse.
The sample configuration presented below applies in the following hypothetical scenario. Assume that two web service endpoints exists, where registration requests could be processed. Requests may fall into Gold and Silver categories, and a specialized endpoint exists to process the Gold requests. If the Gold endpoint cannot be reached for whatever reason, requests should be processed via the Silver endpoint (i.e. failover).
Once message arrive at Synapse, the 'to' address is looked up and different mediation rules applied depending on it. For registration messages, first we need to validate the incoming message against a schema, and if the validation fails, a log entry should be made and a fault reply should be sent back. For valid messages, we determine its category and attempt to use the Gold endpoint, failing which the Silver endpoint is tried. For requests that does not fall into the Gold category the default silver endpoint is used always.
<synapse>
<definitions>
<sequence name="registration_flow">
<validate schema="http://registry/xsd/registration.xsd" source="//regRequest">
<on-fail>
<set-property name="error-code" value="100"/>
<set-property name="error-reason" value="validation failed"/>
<sequence ref="fault_flow"/>
</on-fail>
</validate>
<filter xpath="/regRequest[@Category='GOLD']">
<send>
<failover>
<endpoint ref="gold_registration"/>
<endpoint ref="silver_registration"/>
</failover>
</send>
<filter>
<send>
<endpoint ref="silver_registration"/>
</send>
<sequence>
<sequence name="fault_flow">
<log level="simple">
<property name="application" value="synapse:get-property('reg-app')"/>
</log>
<makefault version="soap11">
<code value="synapse:get-property('error-code')"/>
<reason expression="synapse:get-property('error-reason')">
<makefault>
<send/>
<sequence>
<endpoint name="gold_registration" address="http://gold/registration"/>
<endpoint name="silver_registration" address="http://silver/registration"/>
<set-property name="reg_app" value="Registration Application"/>
</definitions>
<rules>
<switch source="synapse:get-property('to')">
<case regex="/registration">
<sequence ref="registration_flow"/>
</case>
<case regex="someother">
...
</case>
<default>
<drop/>
</default>
<switch>
</rules>
</synapse>
<synapse xmlns="http://ws.apache.org/ns/synapse">
<definitions>
<sequence name="stockquote">
<!-- set the To address to the real endpoint -->
<header name="To" value="http://ws.invesbot.com/stockquotes.asmx"/>
<!-- check if the symbol is MSFT -->
<filter xpath="//*[wsx:symbol='MSFT']" xmlns:wsx="http://ws.invesbot.com/">
<!-- if it is throw a fault -->
<makefault>
<code value="tns:Receiver"
xmlns:tns="http://www.w3.org/2003/05/soap-envelope"/>
<reason value="Isn't there a Windows API for that?"/>
</makefault>
</filter>
</sequence>
</definitions>
<rules>
<!-- now log the message using log4j -->
<log level="full"/>
<!-- Check if the URL matches the stockquote gateway/dumb case -->
<filter source="get-property('To')" regex=".*/StockQuote.*">
<sequence ref="stockquote"/>
</filter>
<!-- check if the URL matches the virtual url - either the proxy or ws-add case -->
<filter source="get-property('To')" regex="http://.*stockquotes.*">
<sequence ref="stockquote"/>
</filter>
<!-- send the message on -->
<send/>
</rules>
</synapse>
The above configuration is available with the Synapse distribution and illustrates the usual Stock quote examples. The client code for these are available with the Synapse samples, and the README.txt of the samples defines these in detail.
<synapse xmlns="http://ws.apache.org/ns/synapse">
<definitions>
<sequence name="customrequest">
<!-- set the To address to the real endpoint -->
<header name="To" value="http://ws.invesbot.com/stockquotes.asmx"/>
<!-- set correlation field to custom label -->
<set-property name="correlate/label" value="customquote"/>
<!-- transform the custom quote into a standard quote requst -->
<transform xslt="file:synapse_repository/conf/sample/transform.xslt"/>
<!-- send message to real endpoint and stop -->
<send/>
</sequence>
<sequence name="customresponse">
<!-- transform the custom quote into a standard quote requst -->
<transform xslt="file:synapse_repository/conf/sample/transform_back.xslt"/>
<!-- now send the custom response back to the client and stop -->
<send/>
</sequence>
<sequence name="stockquote">
<!-- set the To address to the real endpoint -->
<header name="To" value="http://ws.invesbot.com/stockquotes.asmx"/>
<!-- check if the symbol is MSFT -->
<filter xpath="//*[wsx:symbol='MSFT']" xmlns:wsx="http://www.webserviceX.NET/">
<!-- if it is throw a fault -->
<makefault>
<code value="tns:Receiver" xmlns:tns="http://www.w3.org/2003/05/soap-envelope"/>
<reason value="Isn't there a Windows API for that?"/>
</makefault>
</filter>
<send/>
</sequence>
<sequence name="standardrequest">
<!-- now log the message using log4j -->
<log level="full"/>
<!-- Check if the URL matches the stockquote gateway/dumb case -->
<filter source="get-property('To')" regex=".*/StockQuote.*">
<sequence ref="stockquote"/>
</filter>
<!-- check if the URL matches the virtual url -
either the proxy or ws-add case -->
<filter source="get-property('To')" regex="http://stockquote.*">
<sequence ref="stockquote"/>
</filter>
<!-- send the message on -->
<send/>
</sequence>
</definitions>
<rules>
<in>
<!-- is this a custom stock quote message? -->
<filter xpath="//m0:CheckPriceRequest"
xmlns:m0="http://www.apache-synapse.org/test">
<sequence ref="customrequest"/>
</filter>
<!-- else, proceed as usual with the standard processing rules -->
<sequence ref="standardrequest"/>
</in>
<out>
<!-- is this a custom stock quote reply? -->
<filter source="get-property('correlate/label')" regex="customquote">
<sequence ref="customresponse"/>
</filter>
<!-- just let the message flow through -->
<send/>
</out>
</rules>
</synapse>
This example illustrates the correlation of incoming and outgoing messages and the use of the <in> and <out> mediators that simplify the mediation configuration. This example also shows how an XSLT transformation of a message may be performed on receipt or reply, and also how a SOAP fault message may be created when required.
<synapse xmlns="http://ws.apache.org/ns/synapse">
<definitions>
<!-- define global properties -->
<set-property name="version" value="0.1"/>
<!-- define a reuseable endpoint definition and use it within config -->
<endpoint name="invesbot" address="http://ws.invesbot.com/stockquotes.asmx"/>
<sequence name="customrequest">
<!-- is this a valid custom request ? -->
<validate schema="file:synapse_repository/conf/sample/validate.xsd">
<on-fail>
<!-- if the request does not validate againt schema throw a fault -->
<makefault>
<code value="tns:Receiver"
xmlns:tns="http://www.w3.org/2003/05/soap-envelope"/>
<reason value="Invalid custom quote request"/>
</makefault>
<!-- send the fault and stop processing -->
<send/>
</on-fail>
</validate>
<switch source="//m0:CheckPriceRequest/m0:Code"
xmlns:m0="http://www.apache-synapse.org/test">
<case regex="IBM">
<set-property name="symbol" value="Great stock - IBM"/>
</case>
<case regex="MSFT">
<set-property name="symbol" value="Are you sure? - MSFT"/>
</case>
<default>
<set-property name="symbol"
expression="fn:concat('Normal Stock - ', //m0:CheckPriceRequest/m0:Code)"
xmlns:m0="http://www.apache-synapse.org/test"/>
</default>
</switch>
<!-- set a dynamic (local) message property -->
<!-- set correlation field to custom label -->
<set-property name="correlate/label" value="customquote"/>
<!-- transform the custom quote into a standard quote requst -->
<transform xslt="file:synapse_repository/conf/sample/transform.xslt"/>
<log level="custom">
<property name="Text" value="Sending quote request"/>
<property name="version" expression="get-property('version')"/>
<property name="symbol" expression="get-property('symbol')"/>
</log>
<!-- send message to real endpoint referenced by name "invesbot" and stop -->
<send>
<endpoint ref="invesbot"/>
</send>
</sequence>
<sequence name="customresponse">
<!-- transform the custom quote into a standard quote requst -->
<transform xslt="file:synapse_repository/conf/sample/transform_back.xslt"/>
<!-- now send the custom response back to the client and stop -->
<send/>
</sequence>
<sequence name="stockquote">
<!-- set the To address to the real endpoint -->
<header name="To" value="http://ws.invesbot.com/stockquotes.asmx"/>
<!-- check if the symbol is MSFT -->
<filter xpath="//*[wsx:symbol='MSFT']" xmlns:wsx="http://www.webserviceX.NET/">
<!-- if it is throw a fault -->
<makefault>
<code value="tns:Receiver"
xmlns:tns="http://www.w3.org/2003/05/soap-envelope"/>
<reason value="Isn't there a Windows API for that?"/>
</makefault>
</filter>
<send/>
</sequence>
<sequence name="standardrequest">
<!-- now log the message using log4j -->
<log level="full"/>
<!-- Check if the URL matches the stockquote gateway/dumb case -->
<filter source="get-property('To')" regex=".*/StockQuote.*">
<sequence ref="stockquote"/>
</filter>
<!-- check if the URL matches the virtual url - either the proxy or ws-add case -->
<filter source="get-property('To')" regex="http://stockquote.*">
<sequence ref="stockquote"/>
</filter>
<!-- send the message on -->
<send/>
</sequence>
</definitions>
<rules>
<in>
<!-- is this a custom stock quote message? -->
<filter xpath="//m0:CheckPriceRequest" xmlns:m0="http://www.apache-synapse.org/test">
<sequence ref="customrequest"/>
</filter>
<!-- else, proceed as usual with the standard processing rules -->
<sequence ref="standardrequest"/>
</in>
<out>
<!-- is this a custom stock quote reply? -->
<filter source="get-property('correlate/label')" regex="customquote">
<sequence ref="customresponse"/>
</filter>
<!-- just let the message flow through -->
<send/>
</out>
</rules>
</synapse>
This example adds onto the example 2 shown above and shows how the validate mediator could be used to perform message validation. This also illustrates the use of custom properties with the log mediator, global properties and message context properties and how they may be queried via the synapse:get-property(name) XPath extension function. See the Synapse samples for more information on this example and to try it out for real with the given test client. You will need to place the Xerces 2.8.0 jars into your <JAVA_HOME>/lib/endorsed directory, and the synapse-extensions.jar into the <SYNAPSE>/lib folder for this excersice as the validation mediator extension is dependent on the Xerces parser.
<synapse xmlns="http://ws.apache.org/ns/synapse" xmlns:spring="http://ws.apache.org/ns/synapse/spring">
<registry provider="org.apache.synapse.registry.url.SimpleURLRegistry">
<property name="root" value="file:./../../repository/"/>
<property name="cachableDuration" value="15000"/>
</registry>
<definitions>
<set-property name="springconfig1" key="conf/sample/springsample.xml"/>
<set-property name="springconfig2" src="conf/sample/springsample.xml"/>
</definitions>
<rules>
<spring:spring bean="springtest" key="springconfig1"/>
<spring:spring bean="springtest" key="springconfig2"/>
</rules>
</synapse>