72 lines
2.4 KiB
TypeScript
72 lines
2.4 KiB
TypeScript
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export interface BinaryPlistObjectTableLayout {
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readonly offsetWidth: number;
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readonly objectCount: number;
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readonly tableOffset: number;
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}
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/** Read the trailer fields that locate a binary plist's object offset table. */
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export const readBinaryPlistObjectTableLayout = (
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bytes: Buffer,
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): BinaryPlistObjectTableLayout => {
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const trailer = bytes.length - 32;
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return {
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offsetWidth: bytes[trailer + 6] ?? 0,
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objectCount: Number(bytes.readBigUInt64BE(trailer + 8)),
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tableOffset: Number(bytes.readBigUInt64BE(trailer + 24)),
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};
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};
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/** Decode one object's offset-table entry using the table's declared width. */
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export const readBinaryPlistObjectOffset = (
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bytes: Buffer,
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table: BinaryPlistObjectTableLayout,
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objectId: number,
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): number => {
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const entry = table.tableOffset + objectId * table.offsetWidth;
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let offset = 0;
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for (let byte = 0; byte < table.offsetWidth; byte += 1)
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offset = offset * 256 + (bytes[entry + byte] ?? 0);
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return offset;
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};
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/** Repoint one object while preserving the table's declared offset width. */
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export const writeBinaryPlistObjectOffset = (
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bytes: Buffer,
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table: BinaryPlistObjectTableLayout,
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objectId: number,
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offset: number,
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): void => {
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const entry = table.tableOffset + objectId * table.offsetWidth;
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let remaining = offset;
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for (let byte = table.offsetWidth - 1; byte >= 0; byte -= 1) {
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bytes[entry + byte] = remaining & 0xff;
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remaining = Math.floor(remaining / 256);
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}
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if (remaining !== 0) throw new Error("fixture offset width is insufficient");
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};
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/** Finish a small hand-authored binary plist with one-byte object offsets. */
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export const binaryPlistObjectTable = (
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bytes: Buffer,
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objectOffsets: readonly number[],
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tableOffset: number,
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): Buffer => {
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Buffer.from("bplist00", "ascii").copy(bytes);
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bytes.set(objectOffsets, tableOffset);
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const trailer = bytes.length - 32;
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bytes[trailer + 6] = 1;
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bytes[trailer + 7] = 1;
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bytes.writeBigUInt64BE(BigInt(objectOffsets.length), trailer + 8);
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bytes.writeBigUInt64BE(0n, trailer + 16);
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bytes.writeBigUInt64BE(BigInt(tableOffset), trailer + 24);
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return bytes;
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};
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/** Date and empty-data objects deliberately share bytes in a valid offset table. */
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export const binaryPlistWithOverlappingDateAndData = (): Buffer => {
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const bytes = Buffer.alloc(55);
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bytes.set([0xa2, 1, 2, 0x33], 8);
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bytes.writeDoubleBE(0.0005, 12);
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bytes[13] = 0x40;
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return binaryPlistObjectTable(bytes, [8, 11, 13], 20);
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};
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