parseRfc2822

Signature

parseRfc2822(value: string): string

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. Weekday and month names are English, per the fixed grammar (see formatRfc2822’s JSDoc); like every ABNF literal they match in any case (RFC 5234 §2.3).
• Reads what a conformant receiver must. RFC 5322 §3.3 syntax: folding white space (spaces, tabs, folded lines), nested comments such as a trailing (EDT), a 1- or 2-digit day, a 4-or-more-digit year and optional seconds. §4 obsolete syntax, which “MUST be accepted and parsed”: comments and white space between any tokens, and 2- or 3-digit years (00–49 → 20xx, 50–99 → 19xx, 3 digits → +1900).
• Zones. A numeric +hhmm/-hhmm (minutes 00–59), or an obsolete alphabetic zone: UT/GMT are +0000, and EST/EDT/CST/CDT/ MST/MDT/PST/PDT have the offsets §4.3 gives them. Military one-letter zones and any other alphabetic zone are read as -0000, as §4.3 says they SHOULD be; J is not a zone and returns "".
• -0000 and +0000 both become +00:00. RFC 5322 §3.3 gives -0000 the meaning “no information about the local time zone”; a Temporal offset cannot carry that distinction, so it is lost.
• The day-of-week must match the date. RFC 5322 §3.3: “the day-of-week (if included) MUST be the day implied by the date”. A mismatch returns "".
• The resulting offset becomes the zoned string’s time zone identifier (e.g. -05:00), since RFC 5322 carries no IANA zone name to recover. An offset of 24 hours or more cannot be represented and returns "".
• An impossible calendar date (31 Feb, 29 Feb 2023) returns "": a parser never invents a date, so fields are validated with overflow: "reject", not clamped.
• For the strict current-syntax shape alone, test the exported rfc2822DateTime pattern.
• Compatibility: before 1.16.0 a day-of-week that did not match the date was ignored. Remove the day-of-week to parse such a string: the date alone decides the result.

Parameters

Parameter	Type	Description
value	string	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

Examples

import { parseRfc2822 } from "@northguild/gmt/zoned/parse";

parseRfc2822("Fri, 15 Mar 2024 14:30:00 -0400") // "2024-03-15T14:30:00-04:00[-04:00]"

value

output

 

Source

zoned/parse/parseRfc2822.ts