music-metadata/lib/common/Util.js

Music metadata parser for Node.js, supporting virtual any audio and tag format.

import { StringType } from 'token-types';
import { FieldDecodingError } from '../ParseError.js';
export function getBit(buf, off, bit) {
    return (buf[off] & (1 << bit)) !== 0;
}
/**
 * Found delimiting zero in uint8Array
 * @param uint8Array Uint8Array to find the zero delimiter in
 * @param start Offset in uint8Array
 * @param end Last position to parse in uint8Array
 * @param encoding The string encoding used
 * @return Absolute position on uint8Array where zero found
 */
export function findZero(uint8Array, start, end, encoding) {
    let i = start;
    if (encoding === 'utf-16le') {
        while (uint8Array[i] !== 0 || uint8Array[i + 1] !== 0) {
            if (i >= end)
                return end;
            i += 2;
        }
        return i;
    }
    while (uint8Array[i] !== 0) {
        if (i >= end)
            return end;
        i++;
    }
    return i;
}
export function trimRightNull(x) {
    const pos0 = x.indexOf('\0');
    return pos0 === -1 ? x : x.substr(0, pos0);
}
function swapBytes(uint8Array) {
    const l = uint8Array.length;
    if ((l & 1) !== 0)
        throw new FieldDecodingError('Buffer length must be even');
    for (let i = 0; i < l; i += 2) {
        const a = uint8Array[i];
        uint8Array[i] = uint8Array[i + 1];
        uint8Array[i + 1] = a;
    }
    return uint8Array;
}
/**
 * Decode string
 */
export function decodeString(uint8Array, encoding) {
    // annoying workaround for a double BOM issue
    // https://github.com/leetreveil/musicmetadata/issues/84
    if (uint8Array[0] === 0xFF && uint8Array[1] === 0xFE) { // little endian
        return decodeString(uint8Array.subarray(2), encoding);
    }
    if (encoding === 'utf-16le' && uint8Array[0] === 0xFE && uint8Array[1] === 0xFF) {
        // BOM, indicating big endian decoding
        if ((uint8Array.length & 1) !== 0)
            throw new FieldDecodingError('Expected even number of octets for 16-bit unicode string');
        return decodeString(swapBytes(uint8Array), encoding);
    }
    return new StringType(uint8Array.length, encoding).get(uint8Array, 0);
}
export function stripNulls(str) {
    str = str.replace(/^\x00+/g, '');
    str = str.replace(/\x00+$/g, '');
    return str;
}
/**
 * Read bit-aligned number start from buffer
 * Total offset in bits = byteOffset * 8 + bitOffset
 * @param source Byte buffer
 * @param byteOffset Starting offset in bytes
 * @param bitOffset Starting offset in bits: 0 = lsb
 * @param len Length of number in bits
 * @return Decoded bit aligned number
 */
export function getBitAllignedNumber(source, byteOffset, bitOffset, len) {
    const byteOff = byteOffset + ~~(bitOffset / 8);
    const bitOff = bitOffset % 8;
    let value = source[byteOff];
    value &= 0xff >> bitOff;
    const bitsRead = 8 - bitOff;
    const bitsLeft = len - bitsRead;
    if (bitsLeft < 0) {
        value >>= (8 - bitOff - len);
    }
    else if (bitsLeft > 0) {
        value <<= bitsLeft;
        value |= getBitAllignedNumber(source, byteOffset, bitOffset + bitsRead, bitsLeft);
    }
    return value;
}
/**
 * Read bit-aligned number start from buffer
 * Total offset in bits = byteOffset * 8 + bitOffset
 * @param source Byte Uint8Array
 * @param byteOffset Starting offset in bytes
 * @param bitOffset Starting offset in bits: 0 = most significant bit, 7 is the least significant bit
 * @return True if bit is set
 */
export function isBitSet(source, byteOffset, bitOffset) {
    return getBitAllignedNumber(source, byteOffset, bitOffset, 1) === 1;
}
export function a2hex(str) {
    const arr = [];
    for (let i = 0, l = str.length; i < l; i++) {
        const hex = Number(str.charCodeAt(i)).toString(16);
        arr.push(hex.length === 1 ? `0${hex}` : hex);
    }
    return arr.join(' ');
}
/**
 * Convert power ratio to DB
 * ratio: [0..1]
 */
export function ratioToDb(ratio) {
    return 10 * Math.log10(ratio);
}
/**
 * Convert dB to ratio
 * db Decibels
 */
export function dbToRatio(dB) {
    return 10 ** (dB / 10);
}
/**
 * Convert replay gain to ratio and Decibel
 * @param value string holding a ratio like '0.034' or '-7.54 dB'
 */
export function toRatio(value) {
    const ps = value.split(' ').map(p => p.trim().toLowerCase());
    // @ts-ignore
    if (ps.length >= 1) {
        const v = Number.parseFloat(ps[0]);
        return ps.length === 2 && ps[1] === 'db' ? {
            dB: v,
            ratio: dbToRatio(v)
        } : {
            dB: ratioToDb(v),
            ratio: v
        };
    }
}
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