Why do I get transport error in WSO2 ESB if I remove the filter? - wso2-esb

Question

I have the following proxy:
<proxy name="expedientes" transports="https http" startOnLoad="true" trace="enable" statistics="enable">
<target inSequence="main" outSequence="main" faultSequence="main">
<endpoint>
<address uri="https://someweb/somepath/"/>
<property name="Authorization" expression="fn:concat('Basic ', base64Encode('user:password'))" scope="transport"/>
</endpoint>
</target>
</proxy>
with the this default main sequence:
<sequence name="main">
<in>
<log level="full"/>
<filter source="get-property('To')" regex="http://localhost:9000.*">
<send/>
</filter>
</in>
<out>
<send/>
</out>
</sequence>
When I remove the filter and leave it as:
<sequence name="main">
<in>
<log level="full"/>
<send/>
</in>
<out>
<send/>
</out>
</sequence>
I get the following error "Unexpected error during sending message out: org.apache.axis2.AxisFault: The system cannot infer the transport information from the /services/expedientes/indice.xml":
TID: [] [WSO2 ESB] [2013-02-15 12:42:05,531] ERROR
{org.apache.synapse.core.axis2.Axis2Sender} - Unexpected error during sending message out
{org.apache.synapse.core.axis2.Axis2Sender}org.apache.axis2.AxisFault: The system cannot infer the transport information from the /services/expedientes/indice.xml URL. at
...
The out message should (obviously) use the same transport to answer the request (HTTP GET). But what has this to do with "filter"?

Answer 1

Basically in the segment of configuration above (the one with filter mediator) it checks the "TO" header property of your message weather it is equals to "http://localhost:9000.*" or not.
If that condition fired, it simply send your message to the destination. Else the message send inside the "out" mediator.
When you remove the expression what happened is, it trying to send the all messages which are coming inside "in" mediator without knowing weather there is a "To" property or not.
In your case the incoming messages aren't containing a valid "To" property.
The default mediator inside main sequence to send message out is the "out" mediator. The "in" mediator doesn't know the message is expected to send as a response otherwise you did not say it is a resonance message explicitly.You can do it by using configuration like this
<header action="remove" name="To"/>
<property action="set" name="RESPONSE" scope="default" type="STRING" value="true"/>
But It strongly depend on your usecase though
I suggest you to go through some references regarding message mediation with WSO2 ESB.
Following are good references which I found hope you can find more
Configuring the ESB to Perform Message Mediation
Message Mediation
Thanks,