HL71 input → 0 outputs

HL7 Response

Sends an HL7 v2 ACK (acknowledgment) or NACK back to the hospital on the original MLLP socket. This is a terminal node — analogous to Node-RED's built-in http response node.

Details

When an inbound message arrives via HL7 In, the MLLP server attaches a socket ACK callback to msg._hl7SendAck. This node calls that callback with the configured (or overridden) ACK code, which sends an MLLP-framed MSH + MSA response back to the hospital.

The ACK is sent on the exact same TCP socket that received the original message — matching the HL7 v2 MLLP protocol requirement.

Inputs

ackCode string: Override the node's configured ACK code at runtime. Values: AA, AE, AR. Example: set msg.ackCode = 'AE' in a function node to conditionally reject a message.
errorMessage string: Override the MSA.3 error text at runtime. Used with AE and AR codes to send a meaningful reason to the hospital.
_hl7SendAck function: Internal. ACK callback injected by HL7 In. Do not modify.

ACK Codes

AA — Application Accept: message received and processed successfully
AE — Application Error: message received but processing failed
AR — Application Reject: message rejected (bad format, unknown type, etc.)
CA / CE / CR — Enhanced mode commit equivalents

Typical Flow

┌──────────┐   ┌────────────┐   ┌──────────────┐   ┌──────────────┐
│  HL7 In  │──▶│ HL7 Parser │──▶│  Your Logic  │──▶│ HL7 Response │
└──────────┘   └────────────┘   └──────────────┘   └──────────────┘
                                                         (terminal)

Dynamic ACK Code Example

// In a Function node before HL7 Response:
if (processingFailed) {
    msg.ackCode = 'AE';
    msg.errorMessage = 'Patient ID not found in EHR';
}
return msg;

Error Handling

If this node receives a message without msg._hl7SendAck, it means it was not wired after an HL7 In node. The node will log an error and do nothing.

A safety timeout in the MLLP server will auto-send AE after 30 seconds if this node is never reached (e.g. the flow throws an error).

Best Practices

Always wire HL7 Response at the end of every flow that starts with HL7 In
Add a catch node scoped to the flow, set msg.ackCode = 'AE', and wire to HL7 Response for error safety
Use AA only after you have successfully processed the message
Include a meaningful msg.errorMessage with AE/AR for hospital-side diagnostics

┌──────────┐ ┌────────────┐ ┌──────────────┐ ┌──────────────┐ │ HL7 In │──▶│ HL7 Parser │──▶│ Your Logic │──▶│ HL7 Response │ └──────────┘ └────────────┘ └──────────────┘ └──────────────┘ (terminal)