Build an MLLP server to receive inbound HL7v2 messages

Verified steps

1. Open a TCP server socket bound to your designated MLLP port; for each accepted client connection, handle it in a dedicated thread or async task to support concurrent senders
2. Read bytes from the socket in a loop, buffering until you detect the MLLP start-block byte (0x0B); once found, continue reading until you detect the end-block byte (0x1C) followed by carriage return (0x0D) — the content between these delimiters is one complete HL7v2 message
3. Parse the raw message bytes (typically ISO-8859-1 or UTF-8 encoding) to extract the MSH segment and determine message type from MSH-9 for routing to the appropriate handler
4. Process the message through your business logic (persist, transform, forward) and capture any processing errors with enough detail to construct a meaningful ACK
5. Construct an ACK message: copy the MSH from the original message, swap MSH-3/MSH-5 and MSH-4/MSH-6 to reverse sender/receiver, set MSH-9 to ACK, set MSA-1 to AA on success or AE on processing error, and populate MSA-2 with the original message control ID from MSH-10
6. Wrap the ACK in MLLP framing and write it back to the same TCP socket before reading the next message; do not close the connection between messages unless the sender disconnects