74 lines
2.6 KiB
JavaScript
74 lines
2.6 KiB
JavaScript
// lib/id3v2/FrameHeader.ts
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import * as Token from 'token-types';
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import * as util from '../common/Util.js';
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import { UINT32SYNCSAFE } from './ID3v2Token.js';
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import { textDecode } from '@borewit/text-codec';
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import { Id3v2ContentError } from './FrameParser.js';
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/**
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* Frame header length (bytes) depending on ID3v2 major version.
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*/
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export function getFrameHeaderLength(majorVer) {
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switch (majorVer) {
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case 2: return 6;
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case 3:
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case 4: return 10;
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default: throw makeUnexpectedMajorVersionError(majorVer);
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}
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}
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function readFrameFlags(b) {
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return {
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status: {
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tag_alter_preservation: util.getBit(b, 0, 6),
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file_alter_preservation: util.getBit(b, 0, 5),
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read_only: util.getBit(b, 0, 4)
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},
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format: {
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grouping_identity: util.getBit(b, 1, 7),
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compression: util.getBit(b, 1, 3),
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encryption: util.getBit(b, 1, 2),
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unsynchronisation: util.getBit(b, 1, 1),
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data_length_indicator: util.getBit(b, 1, 0)
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}
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};
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}
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/**
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* Factory: parse a frame header from its header bytes (6 for v2.2, 10 for v2.3/v2.4).
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*
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* Note: It only *parses* and does light validation. It does not read payload bytes.
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*/
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export function readFrameHeader(uint8Array, majorVer, warningCollector) {
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switch (majorVer) {
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case 2:
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return parseFrameHeaderV22(uint8Array, majorVer, warningCollector);
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case 3:
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case 4:
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return parseFrameHeaderV23V24(uint8Array, majorVer, warningCollector);
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default:
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throw makeUnexpectedMajorVersionError(majorVer);
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}
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}
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function parseFrameHeaderV22(uint8Array, majorVer, warningCollector) {
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const header = {
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id: textDecode(uint8Array.subarray(0, 3), 'ascii'),
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length: Token.UINT24_BE.get(uint8Array, 3)
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};
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if (!header.id.match(/^[A-Z0-9]{3}$/)) {
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warningCollector.addWarning(`Invalid ID3v2.${majorVer} frame-header-ID: ${header.id}`);
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}
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return header;
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}
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function parseFrameHeaderV23V24(uint8Array, majorVer, warningCollector) {
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const header = {
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id: textDecode(uint8Array.subarray(0, 4), 'ascii'),
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length: (majorVer === 4 ? UINT32SYNCSAFE : Token.UINT32_BE).get(uint8Array, 4),
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flags: readFrameFlags(uint8Array.subarray(8, 10))
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};
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if (!header.id.match(/^[A-Z0-9]{4}$/)) {
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warningCollector.addWarning(`Invalid ID3v2.${majorVer} frame-header-ID: ${header.id}`);
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}
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return header;
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}
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function makeUnexpectedMajorVersionError(majorVer) {
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throw new Id3v2ContentError(`Unexpected majorVer: ${majorVer}`);
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}
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