How to return error response to calling channel when TCP destination gives 'Connection refused' - mirth

Question

I have this pattern:
channel ESANTE_MPI_CREATE_PATIENT_LISTENER (with a MLLP listener) calls channel ESANTE_MPI_CREATE_PATIENT that calls a TCP destination.
If connection cannot be done in the TCP destination inside ESANTE_MPI_CREATE_PATIENT then this channel reports an error for this destination:(ERROR: ConnectException: Connection refused (Connection refused))
The response transformer does not seem to be called (which is normal as there is no response).
I wonder how I can report the error back to the calling channel ESANTE_MPI_CREATE_PATIENT_LISTENER ?
PS: When tcp destination responds, then I use the response transformer to parse the received frame and create a response message (json error/ok) for the calling channel. Everything works fine here.
My question ends up with: How to trap a Connection refused in a TCP destination to create a response message.

Answer 1

I finally managed this by using the postprocessor script in ESANTE_MPI_CREATE_PATIENT to get the response of the connector and then force a message.
// fake error message prepared for connection refused.
// we put this as the response of the channel destination in order to force a understandable error message.
const sErrorMsg = {
status: "error",
error: "connection refused to eSanté MPI"
};
const TCP_CONNECTOR_ESANTE_MPI_RANK = 2; // WARNING: be sure to take the correct connector ID as displayed into destination.
const TCP_CONNECTOR_ESANTE_MPI_DNAME = 'd' + TCP_CONNECTOR_ESANTE_MPI_RANK; // WARNING: be sure to take the correct connector ID as displayed into destination.
/*
var cms = message.getConnectorMessages(); // returns message but as Immutable
responses. not what we want: we use responseMap instead.
var key = TCP_CONNECTOR_ESANTE_MPI_RANK;
logger.debug(" Response Data=" + cms.get(key).getResponseData());
logger.debug(" Response Data0=" + cms.get(key).getResponseError());
logger.debug(" Response Data1=" + cms.get(key).getResponseData().getError());
logger.debug(" Response Data2=" + cms.get(key).getResponseData().getMessage());
logger.debug(" Response Data3=" + cms.get(key).getResponseData().getStatusMessage());
logger.debug(" Response Data4=" + cms.get(key).getResponseData().getStatus());
*/
var responseMPI = responseMap.get(TCP_CONNECTOR_ESANTE_MPI_DNAME); // return a mutable reponse :-)
if (responseMPI.getStatus()=='ERROR' &&
responseMPI.getStatusMessage().startsWith('ConnectException: Connection refused')) {
// build a error message for this dedicated case
logger.error("connection refused detected");
responseMPI.setMessage(JSON.stringify(sErrorMsg)); // force the message to be responsed.
}
return;