@glion/lint-required-message-header

Lint rule that requires the message header segment (MSH) to be the first segment of an HL7v2 message.

What it does

Walks the parsed tree and checks that the first segment node is named MSH. If a different segment appears first, the rule reports one fail message naming the offending segment and stops. HL7v2 messages must begin with MSH because it carries the metadata required for routing and interpretation.

Install

npm install @glion/lint-required-message-header

Use

import { hl7v2Parser } from "@glion/parser";
import hl7v2LintRequiredMessageHeader from "@glion/lint-required-message-header";
import { unified } from "unified";
import { reporter } from "vfile-reporter";

const message =
  "MSH|^~\\&|SENDER|FAC|RECV|RFAC|20250601120000||ADT^A01^ADT_A01|MSG00001|P|2.5";

const file = await unified()
  .use(hl7v2Parser)
  .use(hl7v2LintRequiredMessageHeader)
  .process(message);

console.error(reporter([file]));

API

unified().use(hl7v2LintRequiredMessageHeader)

A unified lint rule plugin. Takes no options.

The plugin visits the tree and finds the first segment node (descending through any nested groups). If it is not named MSH, the plugin calls file.fail(...) — this is a hard failure, not a warning.

import type { Plugin } from "unified";
import type { Root } from "@glion/ast";

declare const hl7v2LintRequiredMessageHeader: Plugin<[], Root>;
export default hl7v2LintRequiredMessageHeader;

What it checks

The first segment of the message must be MSH.

Valid

MSH comes first, followed by any other segments:

MSH|^~\&|SENDER|FAC|RECV|RFAC|20250601120000||ADT^A01^ADT_A01|MSG00001|P|2.5
PID|1||PATID1234^^^HOSP^MR||DOE^JANE||19800101|F
OBX|1|TX|...

Invalid

A non-MSH segment appears first:

PID|1||PATID1234^^^HOSP^MR||DOE^JANE||19800101|F

Reported message:

Message header (MSH) segment is required as the first segment — received 'PID' instead

The name of the first segment found is interpolated into the message. The rule reports at most one failure per tree.

Part of Glion

@glion/lint-required-message-header is part of Glion, the application framework for HL7v2. See the Glion README for the full package catalog and architecture.