Max message size

Lint rule that flags HL7v2 messages exceeding a maximum byte size or segment count.

What it does

Measures the UTF-8 byte length of the source message and, optionally, the number of segment nodes in the tree. Reports a warning when the message is larger than maxBytes (default 10,000,000) or when maxSegments is set and the tree contains more segments than allowed. Intended to protect downstream systems from oversized payloads that would cause resource or protocol limits to be hit.

Install

npm install @glion/lint-max-message-size

Use

import { hl7v2Parser } from "@glion/parser";
import hl7v2LintMaxMessageSize from "@glion/lint-max-message-size";
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(hl7v2LintMaxMessageSize, { maxBytes: 1_000_000, maxSegments: 100 })
  .process(message);

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

API

`unified().use(hl7v2LintMaxMessageSize[, options])`

A unified lint rule plugin.

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

export interface MaxMessageSizeOptions {
  /** Max allowed size of the source message in UTF-8 bytes. Default: 10_000_000 (10MB). */
  maxBytes?: number;
  /** Max allowed number of `segment` nodes. Default: undefined (disabled). */
  maxSegments?: number;
}

declare const hl7v2LintMaxMessageSize: Plugin<[MaxMessageSizeOptions?], Root>;
export default hl7v2LintMaxMessageSize;

What it checks

The message's UTF-8 byte length must not exceed maxBytes, and (when configured) the number of segment nodes must not exceed maxSegments.

Valid

A small message with maxBytes: 1_000_000 (well under the limit):

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

Invalid

A message whose UTF-8 size exceeds maxBytes:

Message size 2,000,000 bytes exceeds 1,000,000 bytes limit — trim payload or raise "maxBytes"

A tree with more segments than maxSegments:

Message contains 150 segments (limit 100 segments) — reduce segment count or raise "maxSegments"

Byte and segment counts are interpolated with pluralization. Both checks are independent — if the message violates both thresholds, two messages are reported.

Max message size

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