Modifying Server Response Payload JSON

I'm modifying a response sent by a server. To do this I've set up a test API that is meant to just send back the IP, in a format like this:

{
  "origin": "202.37.75.130"
}

My unmodified code gives me back what I want.

What I wish to do as a test is to change the name of "origin" to "IP Address", hopefully getting a response like this:

{
  "IP Address": "202.37.75.130"
}

To do this I've modified my outSequence section of the code, to be this (all I've added is the PayloadFactoryMediator section, the filter was there before):

<outSequence>
  <payloadFactory media-type="json">
    <format>{
      "IP Address" : {
      "$1"
      }
      }
    </format>
    <args>
      <arg evaluator="json" expression="$.origin"/>
    </args>
  </payloadFactory>
  <filter source="get-property('CORS_ORIGIN')" regex=".+">
    <then>
      <property name="Access-Control-Allow-Origin" expression="get-property('CORS_ORIGIN')" scope="transport"/>
      <property name="Access-Control-Expose-Headers" value="Assertion,X-Jwt-Assertion,X-User-Name,X-User-Domain" scope="transport"/>
    </then>
  </filter>
  <send/>
</outSequence>

However, when I curl to the API as before I get a response:

curl: (52) Empty reply from server

Can anybody tell me what I may have done wrong?

Solution

I tried your scenario by creating a proxy service for the json service available at "http://ip.jsontest.com/" and I got the expected result. But I used the same "payloadFactory" configuration of yours. Check my full configuration below.

<?xml version="1.0" encoding="UTF-8"?>
<proxy xmlns="http://ws.apache.org/ns/synapse"
       name="ipservice"
       transports="https,http"
       statistics="disable"
       trace="disable"
       startOnLoad="true">
    <target>
        <outSequence>
            <payloadFactory media-type="json">
                <format>{
                    "IP Address" : {
                    "$1"
                    }
                    }
                </format>
                <args>
                    <arg evaluator="json" expression="$.ip"/>
                </args>
            </payloadFactory>
            <send/>
        </outSequence>
        <endpoint>
            <address uri="http://ip.jsontest.com/"/>
        </endpoint>
    </target>
    <description/>
</proxy>

I tried the above configuration with the filter tag also. It works fine. So there is no error in the above configuration. Please check your JSON service and other configurations.

I called the service using the following command.

curl -v -X GET "http://localhost:8280/services/ipservice"