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306 lines
13 KiB
TypeScript
306 lines
13 KiB
TypeScript
/**
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* Classification labels on the wire (enterprise pack item 3). Pure
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* functions: the headers a label writes, reading a received label back,
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* the subject prefix, and the draft marker.
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*
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* Headers written:
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* - `SIO-Label` (RFC 7444) in the marking-only form with colours, as a raw
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* header: `marking="CONFIDENTIAL"; fgcolor=#ffffff; bgcolor=#d97706`.
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* A marking with non-ASCII characters uses RFC 2231
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* (`marking*=utf-8''VS-NUR%20F%C3%9CR...`): an RFC 2047 encoded word
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* inside a quoted parameter is invalid (RFC 2047 §5), which is what the
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* server's text form would produce.
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* - `Sensitivity` (RFC 2156 §5.3.4), what Outlook shows, when the label
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* sets one.
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* - The admin's extra header (X-Classification, msip_labels) when the label
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* has a value for it.
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* No SIO-Label-History: it needs who changed it and when, and RFC 7444
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* says it may leak.
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*
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* Drafts keep the user's choice in `X-Bulwark-Label` (the label id, or
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* `none` for a choice of no label), the way they keep the priority.
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*/
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import type { ClassificationLabel, OrganisationPolicy } from '@/lib/admin/organisation-policy';
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import { stripSubjectPrefixes } from '@/lib/subject-prefix';
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export type LabelsPolicy = OrganisationPolicy['labels'];
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export const SIO_LABEL_HEADER = 'SIO-Label';
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export const SENSITIVITY_HEADER = 'Sensitivity';
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export const DRAFT_LABEL_HEADER = 'X-Bulwark-Label';
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/** A draft whose sender picked "no label". */
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export const NO_LABEL = 'none';
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/** The marking a label writes: its own, else its name. */
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export function labelMarking(label: Pick<ClassificationLabel, 'marking' | 'name'>): string {
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return (label.marking || label.name).trim();
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}
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/** Black or white, whichever reads better on `bg` (#rrggbb). */
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export function textColorOn(bg: string): '#000000' | '#ffffff' {
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const m = /^#([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})$/i.exec(bg);
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if (!m) return '#ffffff';
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const [r, g, b] = [m[1], m[2], m[3]].map((h) => {
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const c = parseInt(h, 16) / 255;
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return c <= 0.03928 ? c / 12.92 : ((c + 0.055) / 1.055) ** 2.4;
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});
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const luminance = 0.2126 * r + 0.7152 * g + 0.0722 * b;
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return luminance > 0.179 ? '#000000' : '#ffffff';
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}
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// RFC 2231 attribute-char: anything but specials, space, controls, *, ' and %.
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const ATTRIBUTE_CHAR = /[A-Za-z0-9!#$&+\-.^_`|~]/;
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function percentEncode(value: string): string {
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let out = '';
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for (const byte of new TextEncoder().encode(value)) {
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const ch = String.fromCharCode(byte);
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out += byte < 0x80 && ATTRIBUTE_CHAR.test(ch) ? ch : `%${byte.toString(16).toUpperCase().padStart(2, '0')}`;
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}
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return out;
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}
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/** The marking parameter(s): quoted when ASCII, RFC 2231 (with continuations when long) otherwise. */
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function markingParameters(marking: string): string[] {
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const clean = marking.replace(/["\\\r\n]/g, '');
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if (/^[\x20-\x7e]*$/.test(clean)) return [`marking="${clean}"`];
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const encoded = percentEncode(clean);
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const MAX = 60;
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if (encoded.length + 15 <= MAX) return [`marking*=utf-8''${encoded}`];
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// Split between encoded characters, never inside a %XX.
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const units = encoded.match(/%[0-9A-F]{2}|[^%]/g) ?? [];
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const pieces: string[] = [];
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let piece = '';
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for (const unit of units) {
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if (piece.length + unit.length > MAX - 15) {
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pieces.push(piece);
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piece = '';
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}
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piece += unit;
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}
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if (piece) pieces.push(piece);
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return pieces.map((piece, i) => (i === 0 ? `marking*0*=utf-8''${piece}` : `marking*${i}*=${piece}`));
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}
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/** The SIO-Label value after "SIO-Label:", folded (leading space included). */
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export function sioLabelValue(label: Pick<ClassificationLabel, 'marking' | 'name' | 'color'>): string {
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const params = [...markingParameters(labelMarking(label)), `fgcolor=${textColorOn(label.color)}`, `bgcolor=${label.color}`];
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// "SIO-Label: " is 11 characters; fold between parameters past 78.
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let line = 11;
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let out = '';
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params.forEach((param, i) => {
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const piece = i === params.length - 1 ? param : `${param};`;
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if (i > 0 && line + 1 + piece.length > 78) {
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out += `\r\n ${piece}`;
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line = 1 + piece.length;
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} else {
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out += ` ${piece}`;
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line += 1 + piece.length;
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}
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});
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return out;
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}
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/** The label's headers as [name, value] pairs, the extra header's value as plain text. */
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function labelHeaderPairs(label: ClassificationLabel, extraHeader: string): Array<[string, string, 'raw' | 'text']> {
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const pairs: Array<[string, string, 'raw' | 'text']> = [[SIO_LABEL_HEADER, sioLabelValue(label), 'raw']];
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if (label.sensitivity) pairs.push([SENSITIVITY_HEADER, label.sensitivity, 'text']);
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const extraValue = label.extraHeaderValue.trim();
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if (extraHeader && extraValue) pairs.push([extraHeader, extraValue, 'text']);
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return pairs;
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}
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/** The label's headers as JMAP Email/set create properties (RFC 8621 §4.1.3). */
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export function labelHeaderProperties(label: ClassificationLabel, extraHeader: string): Record<string, string> {
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const out: Record<string, string> = {};
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for (const [name, value, form] of labelHeaderPairs(label, extraHeader)) {
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// The server writes "Name: " itself; a raw value keeps only its own folds.
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out[form === 'raw' ? `header:${name}:asRaw` : `header:${name}:asText`] = form === 'raw' ? value.trimStart() : value;
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}
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return out;
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}
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function encodedWord(value: string): string {
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if (/^[\x20-\x7e]*$/.test(value)) return value;
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let binary = '';
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for (const byte of new TextEncoder().encode(value)) binary += String.fromCharCode(byte);
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return `=?UTF-8?B?${btoa(binary)}?=`;
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}
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/** The label's headers as raw header lines (CRLF-free each), for raw MIME. */
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export function labelHeaderLines(label: ClassificationLabel, extraHeader: string): string[] {
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return labelHeaderPairs(label, extraHeader).map(([name, value, form]) =>
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form === 'raw' ? `${name}:${value}` : `${name}: ${encodedWord(value)}`);
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}
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/** The draft marker property: the label id, or `none` for no label. */
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export function draftLabelProperty(choice: string | null | undefined): Record<string, string> {
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if (choice === undefined) return {};
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return { [`header:${DRAFT_LABEL_HEADER}:asText`]: choice ?? NO_LABEL };
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}
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type HeaderRecord = Record<string, string | string[]> | null | undefined;
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function header(headers: HeaderRecord, name: string): string | undefined {
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if (!headers || typeof headers !== 'object' || Array.isArray(headers)) return undefined;
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const lower = name.toLowerCase();
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for (const [key, value] of Object.entries(headers)) {
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if (key.toLowerCase() !== lower) continue;
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const first = Array.isArray(value) ? value[0] : value;
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if (typeof first === 'string') return first;
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}
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return undefined;
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}
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/**
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* The choice a re-opened draft carries: a label id, null for "no label",
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* undefined when the draft says nothing (a draft of another client, or one
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* saved before labels).
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*/
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export function draftLabelChoice(headers: HeaderRecord): string | null | undefined {
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const value = header(headers, DRAFT_LABEL_HEADER)?.trim();
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if (!value) return undefined;
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return value === NO_LABEL ? null : value;
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}
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function decodePercent(value: string, charset: string): string {
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const bytes: number[] = [];
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for (let i = 0; i < value.length; i++) {
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if (value[i] === '%' && /^[0-9a-f]{2}$/i.test(value.slice(i + 1, i + 3))) {
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bytes.push(parseInt(value.slice(i + 1, i + 3), 16));
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i += 2;
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} else {
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bytes.push(value.charCodeAt(i) & 0xff);
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}
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}
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try {
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return new TextDecoder(charset || 'utf-8').decode(Uint8Array.from(bytes));
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} catch {
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return new TextDecoder('utf-8').decode(Uint8Array.from(bytes));
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}
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}
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/** Decodes RFC 2047 encoded words a server may have put into a value. */
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function decodeEncodedWords(value: string): string {
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return value.replace(/=\?([^?]+)\?([bBqQ])\?([^?]*)\?=/g, (whole, charset: string, enc: string, text: string) => {
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try {
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let bytes: Uint8Array;
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if (enc.toLowerCase() === 'b') bytes = Uint8Array.from(atob(text), (c) => c.charCodeAt(0));
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else bytes = Uint8Array.from(text.replace(/_/g, ' ').replace(/=([0-9a-f]{2})/gi, (_, h: string) => String.fromCharCode(parseInt(h, 16))), (c) => c.charCodeAt(0));
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return new TextDecoder(charset).decode(bytes);
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} catch {
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return whole;
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}
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});
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}
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/**
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* The `marking` of a raw SIO-Label value (RFC 7444 §2): a quoted or token
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* value, or the RFC 2231 forms (encoded and continued). Null without one.
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*/
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export function parseSioLabelMarking(raw: string | undefined | null): string | null {
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if (!raw) return null;
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const value = raw.replace(/\r?\n[ \t]+/g, ' ');
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const params = new Map<string, string>();
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const re = /([A-Za-z0-9*-]+)\s*=\s*("(?:[^"\\]|\\.)*"|[^;\s]*)/g;
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let m: RegExpExecArray | null;
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while ((m = re.exec(value))) {
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let v = m[2];
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if (v.startsWith('"')) v = v.slice(1, -1).replace(/\\(.)/g, '$1');
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params.set(m[1].toLowerCase(), v);
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}
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if (params.has('marking')) return decodeEncodedWords(params.get('marking')!).trim() || null;
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if (params.has('marking*')) {
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const [charset, , text] = splitExtended(params.get('marking*')!);
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return decodePercent(text, charset).trim() || null;
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}
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// Continuations: marking*0*, marking*1, ... joined before decoding (a
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// character's bytes may be split across two of them, RFC 2231 §4.1).
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let joinedEncoded = '';
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let charset = 'utf-8';
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for (let i = 0; i < 100; i++) {
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const encoded = params.get(`marking*${i}*`);
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const plain = params.get(`marking*${i}`);
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if (encoded === undefined && plain === undefined) break;
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if (encoded !== undefined) {
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let text = encoded;
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if (i === 0) [charset, , text] = splitExtended(encoded);
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joinedEncoded += text;
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} else {
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joinedEncoded += percentEncode(plain!);
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}
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}
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const joined = decodePercent(joinedEncoded, charset).trim();
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return joined || null;
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}
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function splitExtended(value: string): [string, string, string] {
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const first = value.indexOf("'");
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const second = first >= 0 ? value.indexOf("'", first + 1) : -1;
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if (first < 0 || second < 0) return ['utf-8', '', value];
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return [value.slice(0, first), value.slice(first + 1, second), value.slice(second + 1)];
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}
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const normalise = (s: string) => s.normalize('NFC').replace(/\s+/g, ' ').trim().toLowerCase();
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/**
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* The known label a received message carries: by its SIO-Label marking
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* first, then by the admin's extra header value. Unknown values show
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* nothing. Shown as information only: anyone can write these headers.
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*/
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export function receivedLabel(headers: HeaderRecord, policy: LabelsPolicy | null | undefined): ClassificationLabel | null {
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if (!policy || policy.list.length === 0) return null;
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const marking = parseSioLabelMarking(header(headers, SIO_LABEL_HEADER));
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if (marking) {
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const wanted = normalise(marking);
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const byMarking = policy.list.find((label) => normalise(labelMarking(label)) === wanted);
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if (byMarking) return byMarking;
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}
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if (policy.extraHeader) {
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const raw = header(headers, policy.extraHeader);
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if (raw) {
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const wanted = normalise(decodeEncodedWords(raw.replace(/\r?\n[ \t]+/g, ' ')));
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const byExtra = policy.list.find((label) => label.extraHeaderValue && normalise(label.extraHeaderValue) === wanted);
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if (byExtra) return byExtra;
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}
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}
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return null;
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}
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function escapeRegExp(value: string): string {
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return value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
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}
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/**
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* The subject with `label`'s prefix in front, once: every known label
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* prefix in the leading chain of reply and forward prefixes is taken out
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* first ("Re: [Confidential] x" → "[Strictly confidential] Re: x"), so a
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* reply doesn't double it and a changed label replaces the old one.
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*/
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export function applyLabelPrefix(subject: string, label: ClassificationLabel | null, labels: ClassificationLabel[]): string {
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const prefixes = [...new Set(labels.map((l) => l.subjectPrefix.trim()).filter(Boolean))].sort((a, b) => b.length - a.length);
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let rest = subject.trimStart();
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const kept: string[] = [];
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const labelRes = prefixes.map((p) => new RegExp(`^${escapeRegExp(p)}(?:\\s*:)?(?:\\s+|$)`, 'i'));
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for (let i = 0; i < 40; i++) {
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const labelMatch = labelRes.map((re) => re.exec(rest)).find(Boolean);
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if (labelMatch) {
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rest = rest.slice(labelMatch[0].length).trimStart();
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continue;
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}
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const stripped = stripSubjectPrefixes(rest);
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if (stripped === rest) break;
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// Keep the reply/forward prefix as written, one token at a time.
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const token = rest.slice(0, rest.length - stripped.length);
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const one = /^\s*[^:：]+[:：]\s*/.exec(token)?.[0] ?? token;
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kept.push(one.trim());
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rest = rest.slice(one.length).trimStart();
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}
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const chain = [...kept, rest].filter(Boolean).join(' ');
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const prefix = label?.subjectPrefix.trim();
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return prefix ? (chain ? `${prefix} ${chain}` : prefix) : chain;
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}
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