Stefan HildebrandtandLinus Rath
8af6694152
The prefix-stripping regex only matched an ASCII ":", so a localized prefix from a CJK mail client (e.g. "回复：foo", using the full-width colon U+FF1A) was left in place. On reply this caused the user's own prefix to be stacked on top, growing the subject chain. Accept both ":" and "：" after the prefix token. Adds tests.
122 lines
4.8 KiB
TypeScript
122 lines
4.8 KiB
TypeScript
// Reply / forward subject prefix handling.
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//
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// Real-world email subjects accumulate prefixes across clients and languages:
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// "Re: AW: WG: Fwd: Re: foo". The deduplication regex needs to know ALL
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// commonly-used reply/forward markers - not just the current locale's, since
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// inbound messages may come from any locale. Failing to strip a foreign-locale
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// prefix means the user's locale prefix gets *added on top* and the subject
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// chain keeps growing.
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//
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// Sources: de-facto conventions in Outlook / Thunderbird / Apple Mail per
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// language. Includes a handful of legacy short-forms (R:, Fw:) that some
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// mobile clients still emit.
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const REPLY_TOKENS = [
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"Re", // English, Italian, French (also generic ISO)
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"RE", // Outlook variant
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"AW", // German (Antwort)
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"Antw", // German verbose
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"Sv", // Danish / Swedish / Norwegian (Svar)
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"Yn", // Turkish (Yanit)
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"Yanit", // Turkish verbose
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"Odp", // Polish (Odpowiedz)
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"Ответ", // Russian
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"Resp", // Spanish/Portuguese variant
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"Vá", // Hungarian
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"回复", // Chinese
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"回覆", // Chinese traditional
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"답장", // Korean
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// NB: deliberately no bare "R" token — a single letter would strip the first
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// word of legitimate subjects like "R: budget 2024". The full "Re" covers
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// the common Italian/English case anyway.
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];
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const FORWARD_TOKENS = [
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"Fwd", // English standard
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"Fw", // English short / Polish / German short
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"WG", // German (Weitergeleitet)
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"Tr", // French (Transfert)
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"Vs", // Danish (Videresend)
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"Enc", // Portuguese (Encaminhar)
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"ENC", // Portuguese caps
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"Rv", // Spanish (Reenviar)
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"RV", // Spanish caps
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"Rvf", // Spanish variant
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"Inol", // Italian (Inoltro)
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// NB: deliberately no bare "I" token — see the REPLY_TOKENS note above.
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"PD", // Polish (Przekazane Dalej)
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"PR", // Czech (Preposlat)
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"İlt", // Turkish (Ilet)
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"Ilt", // Turkish ASCII
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"Пересл", // Russian (Peresylka)
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"Пер", // Russian short
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"转发", // Chinese
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"轉寄", // Chinese traditional
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"전달", // Korean
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];
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// Match a single prefix token + optional [N] counter (Outlook) or *N (Eudora)
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// + colon + whitespace. Case-insensitive. The non-capturing groups keep the
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// regex composable for stripping multiple prefixes in a row.
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function buildPrefixRegex(tokens: string[]): RegExp {
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// Escape regex specials in tokens (none currently, but be defensive)
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const escaped = tokens.map((t) => t.replace(/[.*+?^${}()|[\]\\]/g, "\\$&"));
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// Sort by length DESC so longer tokens (e.g. "Пересл") win over their
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// shorter prefixes (e.g. "Пер") during alternation matching.
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escaped.sort((a, b) => b.length - a.length);
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// Accept both the ASCII colon and the full-width colon "：" (U+FF1A) that CJK
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// mail clients emit after a localized prefix (e.g. "回复：foo").
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return new RegExp(
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`^\\s*(?:${escaped.join("|")})(?:\\[\\d+\\]|\\*\\d*)?\\s*[:\\uFF1A]\\s*`,
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"i",
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);
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}
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const ANY_PREFIX_RE = buildPrefixRegex([...REPLY_TOKENS, ...FORWARD_TOKENS]);
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/**
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* Strip any leading sequence of reply/forward prefixes (across languages) from
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* a subject line. Idempotent and safe for empty input.
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*
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* Examples:
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* stripSubjectPrefixes("Re: AW: WG: foo") === "foo"
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* stripSubjectPrefixes("Re[2]: foo") === "foo"
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* stripSubjectPrefixes("RE: Re: foo") === "foo"
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* stripSubjectPrefixes("foo") === "foo"
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* stripSubjectPrefixes("") === ""
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*/
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export function stripSubjectPrefixes(subject: string | undefined | null): string {
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if (!subject) return "";
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let s = subject;
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// Bounded loop: in practice you never see more than ~10 prefixes; the bound
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// protects against pathological input. Each iteration must consume input.
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for (let i = 0; i < 20; i++) {
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const next = s.replace(ANY_PREFIX_RE, "");
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if (next === s) break;
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s = next;
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}
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return s;
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}
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/**
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* Build a reply subject with the given locale-aware prefix. Strips any
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* pre-existing prefixes (in any language) first so chains don't accumulate.
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*
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* buildReplySubject("AW: WG: foo", "Re:") === "Re: foo"
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* buildReplySubject("foo", "AW:") === "AW: foo"
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* buildReplySubject("", "AW:") === "AW:"
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*/
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export function buildReplySubject(subject: string | undefined | null, prefix: string): string {
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const stripped = stripSubjectPrefixes(subject);
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return stripped ? `${prefix} ${stripped}` : prefix;
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}
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/**
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* Build a forward subject. Same logic as buildReplySubject but conceptually
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* separate for clarity at the call site.
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*/
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export function buildForwardSubject(subject: string | undefined | null, prefix: string): string {
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const stripped = stripSubjectPrefixes(subject);
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return stripped ? `${prefix} ${stripped}` : prefix;
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}
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