Receive and send HL7 over MLLP in Python

MLLP — the Minimal Lower Layer Protocol — frames HL7 v2 messages over TCP so a receiver knows where each message starts and ends. MessageFoundry speaks it natively: declare a connection, and the engine runs the listener and hands every message to your code.

1. Install the engine

MessageFoundry installs from PyPI. Create a virtual environment and install it — no C compiler needed for the default install.

python -m venv .venv
# macOS / Linux:   . .venv/bin/activate
# Windows (PS):    .venv\Scripts\Activate.ps1

pip install messagefoundry

2. Define an MLLP inbound and outbound connection

Drop a Python module into a config directory. Declare an inbound MLLP listener (name it, give it a port, point it at a router) and an outbound MLLP sender (a downstream host and port).

from messagefoundry import MLLP, Send, inbound, outbound, router, handler

# receive HL7 v2 over MLLP on port 2575
inbound("IB_Lab_ORU", MLLP(port=2575), router="oru_router")

# send to a downstream system over MLLP
outbound("OB_EHR_ORU", MLLP(host="10.0.0.21", port=6661))

3. Route and transform each message

A router decides where a message goes by returning handler names. A handler transforms it and sends it on. Fields are addressed by HL7 path (MSH-9.1, OBR-25, …); returning an empty list leaves a message unrouted, and returning None filters it.

@router("oru_router")
def route(msg):
    if msg["MSH-9.1"] != "ORU":
        return []                    # UNROUTED — not a lab result
    return ["to_ehr"]

@handler("to_ehr")
def to_ehr(msg):
    if msg["OBR-25"] == "X":       # drop corrected-in-error
        return None                  # FILTERED
    return Send("OB_EHR_ORU", msg)

4. Run the engine

Point MessageFoundry at your config directory and a store database. It opens the MLLP listener, persists every message before it's acknowledged, and routes it through your code.

python -m messagefoundry serve --config config --db messagefoundry.db

# MLLP listening on 0.0.0.0:2575 — every message is stored, then routed

Validate the config before it ships with the commit gate: python -m messagefoundry check --config config.

5. Send a test HL7 message

Send any HL7 v2 message to port 2575 with your MLLP client of choice (the repository ships a small send_mllp.py helper). An ORU result routes to the downstream connection; anything else is logged unrouted.

python samples/send_mllp.py samples/messages/oru_r01.hl7
# → ORU routed to OB_EHR_ORU; non-ORU logged UNROUTED

MLLP over TLS

MessageFoundry supports MLLP-over-TLS, and TLS is enabled by default for connections whose peer supports it — so HL7 traffic is encrypted in transit without extra work. Many older ancillary systems still can't speak TLS; for those, MessageFoundry also supports plaintext MLLP, which remains HIPAA-compliant when it stays inside your organization's secure network perimeter. You choose per connection. The exact certificate and TLS settings live in the Configuration reference and the Deployment & network-exposure guide.