Required message header
Lint rule that requires the message header segment (MSH) to be the first segment of an HL7v2 message.
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-headerUse
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|FReported message:
Message header (MSH) segment is required as the first segment — received 'PID' insteadThe name of the first segment found is interpolated into the message. The rule reports at most one failure per tree.