@burglekitt/gmt/dist/zoned/parse/parseRfc2822.js

Temporal-based date and time utilities with timezone support and polyfill integration

import { Temporal } from "@js-temporal/polyfill";
import { ENGLISH_MONTH_NAMES } from "../../internal/index.js";
import { rfc2822DateTime } from "../../regex/index.js";
// RFC 5322 §4.3 "obsolete date and time" — named zones an email parser must
// still accept even though `formatRfc2822` never emits them. Any obs-zone
// single-letter military zone outside this table is unrecognized ("" per
// the spec's own admission that those are ambiguous) and rejected.
const NAMED_ZONE_OFFSETS = {
    UT: "+0000",
    GMT: "+0000",
    EST: "-0500",
    EDT: "-0400",
    CST: "-0600",
    CDT: "-0500",
    MST: "-0700",
    MDT: "-0600",
    PST: "-0800",
    PDT: "-0700",
};
/**
 * Parse an RFC 5322 (RFC 2822) date-time string — the fixed grammar email
 * `Date:` headers use — into a zoned ISO 8601 datetime string.
 *
 * - **Decoding, not display.** Accepts English weekday/month abbreviations
 *   only, per the fixed grammar (see `formatRfc2822`'s JSDoc and roadmap
 *   Decision 1).
 * - Accepts a leading day-of-week (not cross-validated against the computed
 *   date, the same deliberate scope limit `parseDateTimeWithPattern`/J11
 *   uses for its `EEEE`/`EEE` tokens) and an optional `:ss` seconds field.
 * - Accepts a 1- or 2-digit day (the formal grammar's `1*2DIGIT`), unlike
 *   `parseHttp`/`parseSql`, which both require exactly 2 digits.
 * - Accepts a numeric `+HHMM`/`-HHMM` offset or one of RFC 5322's obsolete
 *   named zones (`GMT`, `UT`, and the eight North American zones); any other
 *   obs-zone letter is unrecognized and rejected.
 * - The resulting offset becomes the zoned string's time zone identifier
 *   (e.g. `-05:00`), since RFC 2822 carries no IANA zone name to recover.
 *
 * @param value RFC 5322 date-time string (e.g. "Fri, 15 Mar 2024 14:30:00 -0400")
 * @returns zoned ISO 8601 datetime string, or "" on invalid input
 *
 * @example parseRfc2822("Fri, 15 Mar 2024 14:30:00 -0400") // "2024-03-15T14:30:00-04:00[-04:00]"
 * @example parseRfc2822("5 Jan 2024 09:00:00 GMT") // "2024-01-05T09:00:00+00:00[+00:00]"
 * @example parseRfc2822("not a date") // ""
 */
export function parseRfc2822(value) {
    if (typeof value !== "string")
        return "";
    const match = rfc2822DateTime.exec(value);
    if (match === null)
        return "";
    const [, , dayStr, monthName, yearStr, hourStr, minuteStr, secondStr, zone] = match;
    const monthIndex = ENGLISH_MONTH_NAMES.indexOf(monthName);
    if (monthIndex === -1)
        return "";
    const numericOffset = NAMED_ZONE_OFFSETS[zone] ?? zone;
    const offset = `${numericOffset.slice(0, 3)}:${numericOffset.slice(3)}`;
    try {
        const plainDateTime = Temporal.PlainDateTime.from({
            year: Number(yearStr),
            month: monthIndex + 1,
            day: Number(dayStr),
            hour: Number(hourStr),
            minute: Number(minuteStr),
            second: secondStr === undefined ? 0 : Number(secondStr),
        }, { overflow: "reject" });
        return plainDateTime.toZonedDateTime(offset).toString();
    }
    catch {
        return "";
    }
}