Handling multiple response types

[elavy-harris]

I have an HTTP Sender destination for HL7v2 messages. Under normal circumstances, I get an HL7v2 response, but under certain error conditions, I get back HTML.

I've been using the "HL7 v2.x" datatype, but when I receive an HTML response, that throws an error without recording the response content.

In an attempt to handle both, I've changed the outbound datatype for the destination to be Raw and added the logic below to my response script.

Questions:

1. Is there a way for me to examine the Content-Type of the response to make the distinction, instead of looking for "MSH"? Is there anything else that would be better?
2. Have I replicated the built-in HL7v2 response handling correctly? Anything missing? What about the "no response" case?

function isHL7Response() {
	let result = false;
	if (msg.startsWith('MSH')) {
		let originalMessage = msg;
		let serializationProperties = SerializerFactory.getDefaultSerializationProperties('HL7V2');
		let serializer = SerializerFactory.getSerializer('HL7V2', serializationProperties, null);
		let xml = serializer.toXML(msg);
		msg = new XML(xml);
		result = true;

		let msa1 = msg['MSA']['MSA.1']['MSA.1.1'].toString();
		if (msa1 != 'AA' && msa1 != 'CA') {
			responseStatus = ERROR;
			responseErrorMessage = 'NACK sent from receiver.';
			if (msg['ERR']) {
				for (let i = 0 ; i < msg['ERR'].length() ; i++) {
					responseErrorMessage += '\n' + msg['ERR'][i]['ERR.1']['ERR.1.1'].toString();
				}
			}
			responseErrorMessage += '\n\n' + originalMessage;
		}
	} else if (msg.length !== 0) {
		responseStatus = ERROR;
		responseErrorMessage = msg;
	}
	return result;	
}

if (isHL7Response()) {
	// Normal response handling here
}

[pacmano1]

There are few things you need to do in a use case like this (ignoring your code for now):

1. check the response code from the http call itself (for example the server can be down)
2. if a 200, just serialize the message in try...catch
3. Analyze the message (for example it could in fact be entirely blank)
4. If all steps passed collect your ACK.
5. Obviously set the response status like you are.

[pacmano1]

var responseStatusLine = $('responseStatusLine');
var responseCode = parseInt(responseStatusLine.split(' ')[1], 10);

I can't answer your question on a blank response. That is your call. I pester the vendor when that happens.

[elavy-harris]

In case anyone's interested, here's the function I settled on:

/**
 * Evaluates the response message content and indicates whether or not the content is an HL7 message.
 * If so, updates the "msg" variable to be XML content and checks for NAKs.
 * If not, and if there is a non-empty response, sets the responseStatus to ERROR and records the response as responseErrorMessage
 *
 * @returns {boolean} True if the response is an HL7 response
 */
function isHL7Response() {
	let responseStatusLine = $('responseStatusLine');
	let responseCode = parseInt(responseStatusLine.split(' ')[1], 10);

	let result = false;
	if (Math.floor(responseCode / 100) === 2) {
		let originalMessage = msg;
		let serializationProperties = SerializerFactory.getDefaultSerializationProperties('HL7V2');
		let serializer = SerializerFactory.getSerializer('HL7V2', serializationProperties, null);
		let xml = serializer.toXML(msg);
		msg = new XML(xml);
		result = true;

		let msa1 = msg['MSA']['MSA.1']['MSA.1.1'].toString();
		if (msa1 != 'AA' && msa1 != 'CA') {
			responseStatus = ERROR;
			responseErrorMessage = 'NACK sent from receiver.';
			if (msg['ERR']) {
				for (let i = 0 ; i < msg['ERR'].length() ; i++) {
					responseErrorMessage += '\n' + msg['ERR'][i]['ERR.1']['ERR.1.1'].toString();
				}
			}
			responseErrorMessage += '\n\n' + originalMessage;
		}
	} else if (responseStatusLine.length !== 0) {
		responseStatus = ERROR;
		responseErrorMessage = responseStatusLine + '\n' + msg;
	} else if (msg.length !== 0) {
		responseStatus = ERROR;
		responseErrorMessage = msg;
	} else {
		// Probably a timeout of some kind. No action required.
	}
	return result;	
}

[pacmano1]

Reminder that the response transformer should be set to RAW (for others).

[pacmano1]

@elavy-harris , can't the serialize fail here? I think you want to wrap that in a try..catch.

[elavy-harris]

@elavy-harris , can't the serialize fail here? I think you want to wrap that in a try..catch.

It's actually new XML() that fails with non-HL7 input. I figured I was safe because I had checked the HTTP status already, but safer is better. Here's an improved version:

/**
 * Evaluates the response message content and indicates whether or not the content is an HL7 message.
 * If so, updates the "msg" variable to be XML content and checks for NAKs.
 * If not, and if there is a non-empty response, sets the responseStatus to ERROR and records the response as responseErrorMessage
 *
 * @returns {boolean} True if the response is an HL7 response
 */
function isHL7Response() {
	let responseStatusLine = connectorMap.get('responseStatusLine') || '';
	let responseCode = parseInt(responseStatusLine.split(' ')[1], 10);

	let isHL7 = false;
	if (Math.floor(responseCode / 100) === 2) {
		let originalMessage = msg;
		let serializationProperties = SerializerFactory.getDefaultSerializationProperties('HL7V2');
		let serializer = SerializerFactory.getSerializer('HL7V2', serializationProperties, null);
		try {
			let xml = serializer.toXML(msg);
			msg = new XML(xml);
			isHL7 = true;
		} catch (e) {
			responseStatus = ERROR;
			responseErrorMessage = 'Couldn\'t parse response: ' +  e.message + '\n\n' + originalMessage;
		}

		if (isHL7) {
			let msa1 = msg['MSA']['MSA.1']['MSA.1.1'].toString();
			if (msa1 != 'AA' && msa1 != 'CA') {
				responseStatus = ERROR;
				responseErrorMessage = 'NACK sent from receiver.';
				if (msg['ERR']) {
					for (let i = 0 ; i < msg['ERR'].length() ; i++) {
						responseErrorMessage += '\n' + msg['ERR'][i]['ERR.1']['ERR.1.1'].toString();
					}
				}
				responseErrorMessage += '\n\n' + originalMessage;
			}
		}
	} else if (responseStatusLine.length !== 0) {
		responseStatus = ERROR;
		responseErrorMessage = responseStatusLine + '\n' + msg;
	} else if (msg.length !== 0) {
		responseStatus = ERROR;
		responseErrorMessage = msg;
	} else {
		// Probably a timeout of some kind. No action required.
	}
	return isHL7;	
}