feat: 实现 DOCX 可编辑字体嵌入
This commit is contained in:
SkyJourney
@@ -0,0 +1,520 @@
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import { createHash } from "node:crypto";
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import {
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MAXIMUM_DOCX_FONT_FACE_COUNT,
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MAXIMUM_DOCX_FONT_SOURCE_BYTES,
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MAXIMUM_DOCX_FONT_TOTAL_SOURCE_BYTES
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} from "@md-to-pdf/core";
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import fontverter from "fontverter";
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export const MAXIMUM_DOCX_FONT_SFNT_BYTES = 16 * 1024 * 1024;
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export const MAXIMUM_DOCX_FONT_TOTAL_SFNT_BYTES =
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48 * 1024 * 1024;
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const MAXIMUM_FONT_CONVERSION_CACHE_ENTRIES = 8;
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const fontConversionCache = new Map<
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string,
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Promise<Uint8Array>
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>();
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let fontConversionQueue = Promise.resolve();
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const supportedSfntSignatures = new Set([
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"\u0000\u0001\u0000\u0000",
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"OTTO",
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"true"
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]);
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export type DocxFontStyle = "normal" | "italic";
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export type DocxFontEmbeddingPermission =
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| "installable"
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| "editable";
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export interface DocxFontSource {
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family: string;
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aliases: string[];
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source: string;
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weight: number;
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style: DocxFontStyle;
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license: string;
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content: Uint8Array;
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}
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export interface SfntFontMetadata {
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family: string;
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subfamily: string;
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postscriptName?: string;
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weightClass: number;
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fsType: number;
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permission: DocxFontEmbeddingPermission;
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noSubsetting: boolean;
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signature: "\u0000\u0001\u0000\u0000" | "OTTO" | "true";
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}
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export interface PreparedDocxFont {
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source: DocxFontSource;
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metadata: SfntFontMetadata;
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sfnt: Uint8Array;
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fingerprint: string;
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}
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export interface ObfuscatedDocxFont {
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content: Uint8Array;
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fontKey: string;
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partName: string;
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}
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interface SfntTable {
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offset: number;
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length: number;
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}
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function readTag(content: Uint8Array, offset: number) {
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return String.fromCharCode(
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content[offset] ?? 0,
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content[offset + 1] ?? 0,
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content[offset + 2] ?? 0,
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content[offset + 3] ?? 0
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);
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}
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function assertRange(
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content: Uint8Array,
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offset: number,
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length: number,
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label: string
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) {
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if (
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!Number.isSafeInteger(offset) ||
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!Number.isSafeInteger(length) ||
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offset < 0 ||
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length < 0 ||
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offset + length > content.byteLength
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) {
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throw new Error(`字体 ${label} 数据越界`);
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}
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}
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function readUint16(
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view: DataView,
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content: Uint8Array,
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offset: number,
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label: string
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) {
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assertRange(content, offset, 2, label);
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return view.getUint16(offset, false);
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}
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function readUint32(
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view: DataView,
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content: Uint8Array,
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offset: number,
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label: string
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) {
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assertRange(content, offset, 4, label);
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return view.getUint32(offset, false);
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}
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function readSfntTables(content: Uint8Array) {
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if (
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content.byteLength < 12 ||
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content.byteLength > MAXIMUM_DOCX_FONT_SFNT_BYTES
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) {
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throw new Error("SFNT 字体大小无效");
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}
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const signature = readTag(content, 0);
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if (!supportedSfntSignatures.has(signature)) {
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throw new Error("字体不是受支持的 TrueType 或 OpenType SFNT");
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}
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const view = new DataView(
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content.buffer,
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content.byteOffset,
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content.byteLength
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);
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const tableCount = readUint16(
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view,
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content,
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4,
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"表目录数量"
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);
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if (tableCount < 1 || tableCount > 256) {
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throw new Error("SFNT 字体表数量无效");
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}
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assertRange(content, 12, tableCount * 16, "表目录");
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const tables = new Map<string, SfntTable>();
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for (let index = 0; index < tableCount; index += 1) {
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const recordOffset = 12 + index * 16;
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const tag = readTag(content, recordOffset);
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const offset = readUint32(
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view,
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content,
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recordOffset + 8,
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`${tag} 表偏移`
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);
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const length = readUint32(
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view,
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content,
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recordOffset + 12,
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`${tag} 表长度`
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);
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assertRange(content, offset, length, `${tag} 表`);
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if (tables.has(tag)) {
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throw new Error(`SFNT 字体包含重复表：${tag}`);
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}
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tables.set(tag, { offset, length });
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}
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return {
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signature: signature as SfntFontMetadata["signature"],
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tables,
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view
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};
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}
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function decodeUtf16Be(content: Uint8Array) {
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if (content.byteLength % 2 !== 0) {
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throw new Error("字体名称 UTF-16BE 长度无效");
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}
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let value = "";
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for (let offset = 0; offset < content.byteLength; offset += 2) {
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value += String.fromCharCode(
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((content[offset] ?? 0) << 8) |
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(content[offset + 1] ?? 0)
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);
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}
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return value.replaceAll("\0", "").trim();
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}
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function decodeName(
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content: Uint8Array,
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platformId: number
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) {
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if (platformId === 0 || platformId === 3) {
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return decodeUtf16Be(content);
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}
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return new TextDecoder("windows-1252")
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.decode(content)
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.replaceAll("\0", "")
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.trim();
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}
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function readFontName(
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content: Uint8Array,
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table: SfntTable,
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nameIds: readonly number[]
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) {
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if (table.length < 6) {
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throw new Error("字体 name 表不完整");
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}
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const view = new DataView(
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content.buffer,
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content.byteOffset,
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content.byteLength
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);
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const count = readUint16(
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view,
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content,
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table.offset + 2,
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"name 记录数量"
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);
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const stringsOffset = readUint16(
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view,
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content,
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table.offset + 4,
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"name 字符串偏移"
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);
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assertRange(content, table.offset + 6, count * 12, "name 记录");
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const candidates: Array<{
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value: string;
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priority: number;
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}> = [];
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for (let index = 0; index < count; index += 1) {
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const offset = table.offset + 6 + index * 12;
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const platformId = readUint16(
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view,
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content,
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offset,
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"name platformID"
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);
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const languageId = readUint16(
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view,
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content,
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offset + 4,
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"name languageID"
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);
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const nameId = readUint16(
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view,
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content,
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offset + 6,
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"name nameID"
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);
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const requestedIndex = nameIds.indexOf(nameId);
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if (requestedIndex < 0) {
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continue;
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}
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const length = readUint16(
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view,
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content,
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offset + 8,
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"name 字符串长度"
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);
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const relativeOffset = readUint16(
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view,
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content,
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offset + 10,
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"name 字符串位置"
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);
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const valueOffset =
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table.offset + stringsOffset + relativeOffset;
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assertRange(content, valueOffset, length, "name 字符串");
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const value = decodeName(
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content.subarray(valueOffset, valueOffset + length),
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platformId
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);
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if (!value) {
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continue;
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}
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const platformPriority =
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platformId === 3 ? 30 : platformId === 0 ? 20 : 10;
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const languagePriority =
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languageId === 0x0409 ? 2 : languageId === 0 ? 1 : 0;
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candidates.push({
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value,
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priority:
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(nameIds.length - requestedIndex) * 100 +
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platformPriority +
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languagePriority
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});
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}
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return candidates.sort(
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(left, right) => right.priority - left.priority
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)[0]?.value;
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}
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export function resolveFontEmbeddingPermission(fsType: number) {
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if (
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!Number.isInteger(fsType) ||
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fsType < 0 ||
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fsType > 0xffff
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) {
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throw new Error("字体 fsType 无效");
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}
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if ((fsType & 0xfef0) !== 0) {
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throw new Error(
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`字体 fsType 包含不支持的保留或位图嵌入标志：0x${fsType
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.toString(16)
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.padStart(4, "0")}`
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);
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}
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const usage = fsType & 0x000f;
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if (usage === 0) {
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return "installable" satisfies DocxFontEmbeddingPermission;
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}
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if (usage === 0x0008) {
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return "editable" satisfies DocxFontEmbeddingPermission;
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}
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if (usage === 0x0002) {
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throw new Error("字体许可证禁止嵌入");
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}
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if (usage === 0x0004) {
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throw new Error("字体仅允许预览和打印嵌入，不能用于可编辑 DOCX");
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}
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throw new Error(
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`字体 fsType 使用权限组合无效：0x${usage
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.toString(16)
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.padStart(4, "0")}`
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);
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}
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export function readSfntFontMetadata(
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content: Uint8Array
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): SfntFontMetadata {
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const { signature, tables, view } = readSfntTables(content);
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const os2 = tables.get("OS/2");
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const name = tables.get("name");
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if (!os2 || os2.length < 10) {
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throw new Error("SFNT 字体缺少完整 OS/2 表");
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}
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if (!name) {
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throw new Error("SFNT 字体缺少 name 表");
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}
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const family = readFontName(content, name, [16, 1]);
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const subfamily = readFontName(content, name, [17, 2]);
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if (!family || !subfamily) {
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throw new Error("SFNT 字体缺少家族或字形面名称");
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}
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const fsType = readUint16(
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view,
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content,
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os2.offset + 8,
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"OS/2 fsType"
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);
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const permission = resolveFontEmbeddingPermission(fsType);
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const postscriptName = readFontName(content, name, [6]);
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return {
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family,
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subfamily,
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...(postscriptName ? { postscriptName } : {}),
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weightClass: readUint16(
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view,
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content,
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os2.offset + 4,
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"OS/2 usWeightClass"
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),
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fsType,
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permission,
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noSubsetting: (fsType & 0x0100) !== 0,
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signature
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};
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}
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export async function prepareDocxFont(
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source: DocxFontSource
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): Promise<PreparedDocxFont> {
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if (
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source.content.byteLength < 32 ||
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source.content.byteLength > MAXIMUM_DOCX_FONT_SOURCE_BYTES
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) {
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throw new Error(`字体资源大小无效：${source.source}`);
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}
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const sourceFingerprint = createHash("sha256")
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.update(source.content)
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.digest("hex");
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let conversion = fontConversionCache.get(sourceFingerprint);
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if (!conversion) {
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if (
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fontConversionCache.size >=
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MAXIMUM_FONT_CONVERSION_CACHE_ENTRIES
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) {
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const oldest = fontConversionCache.keys().next().value;
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if (oldest !== undefined) {
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fontConversionCache.delete(oldest);
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}
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}
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const sourceContent = Buffer.from(source.content);
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conversion = fontConversionQueue
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.then(() => fontverter.convert(sourceContent, "sfnt"))
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.then((converted) => {
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if (
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converted.byteLength < 32 ||
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converted.byteLength > MAXIMUM_DOCX_FONT_SFNT_BYTES
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) {
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throw new Error(
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`字体解码后大小超过限制：${source.source}`
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);
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}
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return new Uint8Array(converted);
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});
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fontConversionQueue = conversion.then(
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() => undefined,
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() => undefined
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);
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fontConversionCache.set(sourceFingerprint, conversion);
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void conversion.catch(() => {
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if (
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fontConversionCache.get(sourceFingerprint) === conversion
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) {
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fontConversionCache.delete(sourceFingerprint);
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}
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});
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}
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const sfnt = (await conversion).slice();
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const metadata = readSfntFontMetadata(sfnt);
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const fingerprint = createHash("sha256")
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.update(sfnt)
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.digest("hex");
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return {
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source,
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metadata,
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sfnt,
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fingerprint
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};
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}
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export async function prepareDocxFonts(
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sources: readonly DocxFontSource[]
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) {
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if (sources.length > MAXIMUM_DOCX_FONT_FACE_COUNT) {
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throw new Error("DOCX 字体字形面数量超过限制");
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}
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const totalSourceBytes = sources.reduce(
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(total, source) => total + source.content.byteLength,
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0
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);
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if (totalSourceBytes > MAXIMUM_DOCX_FONT_TOTAL_SOURCE_BYTES) {
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throw new Error("DOCX 字体资源总大小超过限制");
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}
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const fonts = await Promise.all(sources.map(prepareDocxFont));
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const totalSfntBytes = fonts.reduce(
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(total, font) => total + font.sfnt.byteLength,
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0
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);
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if (totalSfntBytes > MAXIMUM_DOCX_FONT_TOTAL_SFNT_BYTES) {
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throw new Error("DOCX 字体解码后总大小超过限制");
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}
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return fonts;
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}
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function formatGuid(bytes: Uint8Array) {
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const hex = Buffer.from(bytes).toString("hex").toUpperCase();
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return `{${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(
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12,
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16
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)}-${hex.slice(16, 20)}-${hex.slice(20)}}`;
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}
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function fontKeyBytes(fontKey: string) {
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const hex = fontKey.replace(/[{}-]/gu, "");
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if (!/^[0-9a-f]{32}$/iu.test(hex)) {
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throw new Error("DOCX 字体混淆键无效");
|
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}
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return Uint8Array.from(
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Array.from({ length: 16 }, (_, index) =>
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Number.parseInt(hex.slice(index * 2, index * 2 + 2), 16)
|
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)
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).reverse();
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}
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export function xorDocxFont(
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content: Uint8Array,
|
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fontKey: string
|
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) {
|
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if (content.byteLength < 32) {
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throw new Error("待混淆字体内容不足 32 字节");
|
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}
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const result = content.slice();
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const key = fontKeyBytes(fontKey);
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for (let index = 0; index < 32; index += 1) {
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result[index] =
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(result[index] ?? 0) ^ (key[index % key.length] ?? 0);
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}
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return result;
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}
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export function obfuscateDocxFont(
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font: PreparedDocxFont
|
||||
): ObfuscatedDocxFont {
|
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const keyBytes = createHash("sha256")
|
||||
.update(font.sfnt)
|
||||
.update("\0", "utf8")
|
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.update(font.source.family, "utf8")
|
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.update("\0", "utf8")
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.update(String(font.source.weight), "utf8")
|
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.update("\0", "utf8")
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.update(font.source.style, "utf8")
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.digest()
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.subarray(0, 16);
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keyBytes[6] = ((keyBytes[6] ?? 0) & 0x0f) | 0x40;
|
||||
keyBytes[8] = ((keyBytes[8] ?? 0) & 0x3f) | 0x80;
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||||
const fontKey = formatGuid(keyBytes);
|
||||
const partStem = fontKey.slice(1, -1).toLowerCase();
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return {
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||||
content: xorDocxFont(font.sfnt, fontKey),
|
||||
fontKey,
|
||||
partName: `word/fonts/${partStem}.odttf`
|
||||
};
|
||||
}
|
||||
Reference in New Issue
Block a user