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<title>Synapse Configuration Language</title>
<h1>Synapse Configuration Language</h1>
<p>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).</p>
<h2>Overall Structure</h2>
<p>A Synapse configuration looks like the following at the top level:</p>
<pre> &lt;synapse&gt;
(sequencedef | endpointdef | literalpropertydef)+
&lt;rules [key="string"]&gt;
<p>A registrydef token represents a &lt;registry&gt; element which is used to
define a Registry which is referenced within the configuration.</p>
<pre> &lt;registry [name="string"] provider="string"/&gt;
&lt;property name="string" value="string"/&gt;*
<p>The registry definition without a name becomes the 'default' registry 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
<p>The &lt;definitions&gt; section defines reusable elements that can be used
from within the rules, and the &lt;rules&gt; section contains the sequence of
mediators that every message passes through during mediation.</p>
<p>The token literalpropertydef refers to a &lt;set-property&gt; element as
<pre> &lt;set-property name="string" [value="string"] [src="url"] [key="string"]&gt;
<p>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)".</p>
<p>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.</p>
<p>Dynamic properties allows the creation of Dynamic Sequences, Endpoints and
Proxies whose definition would change accordingly with any changes on the
<p>A sequencedef token represents a &lt;sequence&gt; element which is used to
define a named sequence of mediators that can be invoked later by name as a
sequence of mediators.</p>
<pre> &lt;sequence name="string" [onError="string"] [key="string"]&gt;
<p>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.</p>
<p>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.</p>
<p>An endpointdef token represents an &lt;endpoint&gt; 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).</p>
<pre> &lt;endpoint name="string" [address="url"] [key="string"] [force="soap|pox"] [optimize="mtom|swa"]&gt;
&lt;enableSec [policy="key"]/&gt;?
&lt;enableAddressing separateListener="true|false"/&gt;?
.. extensibility ..
<p>The enableRM/enableSec options turns on WS-Security or WS-RM on outgoing
messages to this endpoint and specific policies may be specified for
<p>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.</p>
<p>NOTE: The Rampart and/or Sandesha configuration options may change with
Axis2 changes currently in progress</p>
<h3>Proxy services</h3>
<p>The &lt;proxies&gt; 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.</p>
<p>A proxyservice token represents a &lt;proxy&gt; element which is used to
define a Synapse Proxy service.</p>
<pre> &lt;proxy name="string" [description="string"] [transports="(http |https |jms )+|all"]&gt;
&lt;target (inSequence="name" outSequence="name") | endpoint="name"/&gt;? // defaults to the synapse main sequence
&lt;wsdl key="string"&gt;?
&lt;policy key="string"&gt;* // optional service level policies
// (e.g. WS-Security and/or WS-RM policies)
&lt;property name="string" value="string"/&gt;* // optional service parameters
// (e.g. transport.jms.ConnectionFactory)
<p>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.</p>
<p>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.</p>
<p>A mediator token refers to any of the following tokens:</p>
<pre> send | drop | log | makefault | transform | header | filter |
switch | class | validate | setproperty | sequenceref | in | out | rm | try</pre>
<p>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.</p>
<p>The send token represents a &lt;send&gt; element. The &lt;send&gt; 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 correlation
message context properties 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. Also see the set-property mediator.</p>
<p>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
<pre> &lt;send/&gt;</pre>
<p>If the message is to be sent to one or more endpoints, then the following
is used:</p>
<pre> &lt;send&gt;
(endpointref | endpoint)+
<p>where the endpointref token refers to the following:</p>
<pre> &lt;endpoint ref="name"/&gt;</pre>
<p>and the endpoint token refers to an anonymous endpoint defined inline:</p>
<pre> &lt;endpoint address="url"/&gt;</pre>
<p>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:</p>
<pre> &lt;send&gt;
&lt;load-balance algorithm="uri"&gt;
(endpointref | endpoint)+
<p>Similarly, if the message is to be sent to an endpoint with failover
semantics, then it is indicated by the following:</p>
<pre> &lt;send&gt;
(endpointref | endpoint)+
<p>Once the &lt;send&gt; mediator executes, further processing of the current
message stops.</p>
<p>Note: Synapse does not yet support the load balancing or failover
semantics, and supports only a single endpoint reference.</p>
<p>The drop token refers to a &lt;drop&gt; element which is used to drop a
<pre> &lt;drop/&gt;</pre>
<p>Once the &lt;drop&gt; mediator executes, further processing of the current
message stops.</p>
<p>The log token refers to a &lt;log&gt; element which may be used to log
messages being mediated:</p>
<pre> &lt;log [level="string"] [separator="string"]&gt;
&lt;property name="string" (value="literal" | expression="xpath")/&gt;*
<p>The optional level attribute selects a pre-defined subset of properties to
be logged.</p>
<li>simple = To, From, WSAction, SOAPAction, ReplyTo, MessageID and any
<li>headers = All SOAP header blocks and any properties</li>
<li>full = all attributes included in log level 'simple' and the SOAP
envelope and any properties</li>
<li>custom = Only properties specified to the Log mediator</li>
<p>A separator if defined will be used to seperate the attributes being
logged. The default separator is the ',' comma.</p>
<pre> &lt;makefault [version="soap11|soap12"]&gt;
&lt;code (value="literal" | expression="xpath")/&gt;
&lt;reason (value="literal" | expression="xpath")&gt;
<p>The &lt;makefault&gt; mediator transforms the current message into a fault
message, but does NOT send it. The &lt;send&gt; 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
<pre> &lt;xslt key="string" [source="xpath"]&gt;
&lt;property name="string" (value="literal" | expression="xpath")/&gt;*
<p>The &lt;xslt&gt; 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 &lt;property&gt; elements.</p>
<pre> &lt;header name="qname" (value="literal" | expression="xpath") [action="set"]/&gt;
&lt;header name="qname" action="remove"/&gt;</pre>
<p>The &lt;header&gt; 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.</p>
<pre> &lt;filter (source="xpath" regex="string") | xpath="xpath"&gt;
<p>The &lt;filter&gt; 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.</p>
<pre> &lt;switch source="xpath"&gt;
&lt;case regex="string"&gt;
<p>The &lt;switch&gt; 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.</p>
<pre> &lt;validate [source="xpath"]&gt;
&lt;schema key="string"/&gt;+
<p>The &lt;validate&gt; 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 first
child of the SOAP body of the current message. If the validation fails, the
on-fail sequence of mediators is executed.</p>
<p>Note: As the validation mediator is strongly dependent on the Xerces2-J
2.8.0 parser, it is bundled with the Synapse extensions, so that the Synapse
core will remain simple and lightweight.</p>
<pre> &lt;set-property name="string" (value="literal" | expression="xpath") [scope=correlate|axis2]/&gt;</pre>
<p>The setproperty token refers to a &lt;set-property&gt; 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. If a scope is
specified for a property, the property could be set as a correlation property
or an (underlying) Axis2 message context property.</p>
<pre> &lt;try&gt;
<p>The try token refers to a &lt;try&gt; element which is a mediator that has
a set of child mediators. If an exception is encountered during the execution
of these child mediators, the list of mediators specified as the 'onError'
sequence is executed. The 'finally' list of mediators is then executed
irrespective of whether an exception was encountered or not.</p>
<h4>Class Mediators</h4>
<pre> &lt;class name="class-name"&gt;
&lt;property name="string" (value="literal" | expression="xpath")/&gt;*
&lt;/class&gt; </pre>
<p>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
<h4>Reusing Sequences</h4>
<pre> &lt;sequence ref="name"/&gt;</pre>
<p>A sequenceref token refers to a &lt;sequence&gt; element which is used to
invoke a named sequence of mediators.</p>
<h3>Extensibility of Synapse</h3>
<p>The Synapse configuration language could be easily extended, with
configuration extensions as well as mediation extensions. The Spring mediator
is such an example.</p>
<h4>Spring Configuration</h4>
<p>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.</p>
<pre> &lt;set-property name="string" key="string"/&gt;
&lt;set-property name="string" src="url"/&gt;</pre>
<p>The name attribute specifies a unique name for the configuration, and the
src, key or inlined XML references to the Spring configuration</p>
<h4>Spring mediator</h4>
<pre> &lt;spring:spring bean="exampleBean1" key="string"/&gt;</pre>
<p>The &lt;spring&gt; 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</p>
<h4>Script Language Mediators</h4>
<p>Synapse supports Mediators implemented in a variety of scripting languages
such as JavaScript, Python or Ruby.</p>
<p>There are two ways of defining script mediators, either with the script
program statements stored in a separate file which is referenced via a
Synapse property, or with the script program statements embedded in-line
within the Synapse configuration.</p>
<p>A script mediator using a registry property is defined as follows:</p>
<pre> &lt;script key="property-key" [function="script-function-name"]/&gt;</pre>
<p>The property-key is a Synapse registry property containing a URL to the
script source. The function is an optional attribute defining the name of the
script function to call, if not specified it defaults to a function named
'mediate'. The function is passed a single parameter which is the Synapse
MessageContext. The function may return a boolean, if it does not then true
is assumed. The language the script is written in is determined from the file
name suffix of the property key value.</p>
<p>An inline script mediator has the script source embedded in the config
<pre> &lt;script.LL&gt;...script source code...&lt;script.LL/&gt;</pre>
<p>where LL is the script language name extension. For example, script.js
indicates a JavaScript program, script.rb a Ruby program, or a
Python program. The environment of the script has the Synapse MessageContext
predefined in a script variable named 'mc'.</p>
<p>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' would be:</p>
<pre> &lt;script.js&gt;mc.getPayloadXML()..symbol != "IBM";&lt;script.js/&gt;</pre>
<p>The boolean response from the inlined mediator is either the response from
the evaluation of the script statements or if that result is not a boolean
then a response of true is assumed.</p>
<p>Synapse uses the Apache <a href="">Bean
Scripting Framework</a> for the script language support, any script language
supported by BSF may be used to implement a Synapse Mediator.</p>
<p>Implementing a Mediator with a script language can have advantages over
using the built in Synapse Mediator types or implementing a custom Java class
Mediator. Script Mediators have all the flexibility of a class Mediator with
access to the Synapse MessageContext and SynapseEnvironment APIs, and the
ease of use and dynamic nature of scripting languages allows 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, for example JavaScript E4X or Ruby REXML, so this
makes them well suited for use in the Synapse mediation environment.</p>
<p>For both types of script mediator definition the MessageContext passed in
to the script has additional methods over the standard Synapse MessageContext
to enable working with the XML in a way natural to the scripting language.
For example when using JavaScript get/setPayloadXML use E4X XML objects, when
using Ruby they use REXML documents.</p>