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sig.js
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sig.js
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const { URL } = require('url');
const querystring = require('querystring');
const Cache = require('./cache');
const utils = require('./utils');
// A shared cache to keep track of html5player.js tokens.
exports.cache = new Cache();
/**
* Extract signature deciphering tokens from html5player file.
*
* @param {string} html5playerfile
* @param {Object} options
* @returns {Promise<Array.<string>>}
*/
exports.getTokens = (html5playerfile, options) => exports.cache.getOrSet(html5playerfile, async() => {
const body = await utils.exposedMiniget(html5playerfile, options).text();
const tokens = exports.extractActions(body);
if (!tokens || !tokens.length) {
throw Error('Could not extract signature deciphering actions');
}
exports.cache.set(html5playerfile, tokens);
return tokens;
});
/**
* Decipher a signature based on action tokens.
*
* @param {Array.<string>} tokens
* @param {string} sig
* @returns {string}
*/
exports.decipher = (tokens, sig) => {
sig = sig.split('');
for (let i = 0, len = tokens.length; i < len; i++) {
let token = tokens[i], pos;
switch (token[0]) {
case 'r':
sig = sig.reverse();
break;
case 'w':
pos = ~~token.slice(1);
sig = swapHeadAndPosition(sig, pos);
break;
case 's':
pos = ~~token.slice(1);
sig = sig.slice(pos);
break;
case 'p':
pos = ~~token.slice(1);
sig.splice(0, pos);
break;
}
}
return sig.join('');
};
/**
* Swaps the first element of an array with one of given position.
*
* @param {Array.<Object>} arr
* @param {number} position
* @returns {Array.<Object>}
*/
const swapHeadAndPosition = (arr, position) => {
const first = arr[0];
arr[0] = arr[position % arr.length];
arr[position] = first;
return arr;
};
const jsVarStr = '[a-zA-Z_\\$][a-zA-Z_0-9]*';
const jsSingleQuoteStr = `'[^'\\\\]*(:?\\\\[\\s\\S][^'\\\\]*)*'`;
const jsDoubleQuoteStr = `"[^"\\\\]*(:?\\\\[\\s\\S][^"\\\\]*)*"`;
const jsQuoteStr = `(?:${jsSingleQuoteStr}|${jsDoubleQuoteStr})`;
const jsKeyStr = `(?:${jsVarStr}|${jsQuoteStr})`;
const jsPropStr = `(?:\\.${jsVarStr}|\\[${jsQuoteStr}\\])`;
const jsEmptyStr = `(?:''|"")`;
const reverseStr = ':function\\(a\\)\\{' +
'(?:return )?a\\.reverse\\(\\)' +
'\\}';
const sliceStr = ':function\\(a,b\\)\\{' +
'return a\\.slice\\(b\\)' +
'\\}';
const spliceStr = ':function\\(a,b\\)\\{' +
'a\\.splice\\(0,b\\)' +
'\\}';
const swapStr = ':function\\(a,b\\)\\{' +
'var c=a\\[0\\];a\\[0\\]=a\\[b(?:%a\\.length)?\\];a\\[b(?:%a\\.length)?\\]=c(?:;return a)?' +
'\\}';
const actionsObjRegexp = new RegExp(
`var (${jsVarStr})=\\{((?:(?:${
jsKeyStr}${reverseStr}|${
jsKeyStr}${sliceStr}|${
jsKeyStr}${spliceStr}|${
jsKeyStr}${swapStr
}),?\\r?\\n?)+)\\};`);
const actionsFuncRegexp = new RegExp(`${`function(?: ${jsVarStr})?\\(a\\)\\{` +
`a=a\\.split\\(${jsEmptyStr}\\);\\s*` +
`((?:(?:a=)?${jsVarStr}`}${
jsPropStr
}\\(a,\\d+\\);)+)` +
`return a\\.join\\(${jsEmptyStr}\\)` +
`\\}`);
const reverseRegexp = new RegExp(`(?:^|,)(${jsKeyStr})${reverseStr}`, 'm');
const sliceRegexp = new RegExp(`(?:^|,)(${jsKeyStr})${sliceStr}`, 'm');
const spliceRegexp = new RegExp(`(?:^|,)(${jsKeyStr})${spliceStr}`, 'm');
const swapRegexp = new RegExp(`(?:^|,)(${jsKeyStr})${swapStr}`, 'm');
/**
* Extracts the actions that should be taken to decipher a signature.
*
* This searches for a function that performs string manipulations on
* the signature. We already know what the 3 possible changes to a signature
* are in order to decipher it. There is
*
* * Reversing the string.
* * Removing a number of characters from the beginning.
* * Swapping the first character with another position.
*
* Note, `Array#slice()` used to be used instead of `Array#splice()`,
* it's kept in case we encounter any older html5player files.
*
* After retrieving the function that does this, we can see what actions
* it takes on a signature.
*
* @param {string} body
* @returns {Array.<string>}
*/
exports.extractActions = body => {
const objResult = actionsObjRegexp.exec(body);
const funcResult = actionsFuncRegexp.exec(body);
if (!objResult || !funcResult) { return null; }
const obj = objResult[1].replace(/\$/g, '\\$');
const objBody = objResult[2].replace(/\$/g, '\\$');
const funcBody = funcResult[1].replace(/\$/g, '\\$');
let result = reverseRegexp.exec(objBody);
const reverseKey = result && result[1]
.replace(/\$/g, '\\$')
.replace(/\$|^'|^"|'$|"$/g, '');
result = sliceRegexp.exec(objBody);
const sliceKey = result && result[1]
.replace(/\$/g, '\\$')
.replace(/\$|^'|^"|'$|"$/g, '');
result = spliceRegexp.exec(objBody);
const spliceKey = result && result[1]
.replace(/\$/g, '\\$')
.replace(/\$|^'|^"|'$|"$/g, '');
result = swapRegexp.exec(objBody);
const swapKey = result && result[1]
.replace(/\$/g, '\\$')
.replace(/\$|^'|^"|'$|"$/g, '');
const keys = `(${[reverseKey, sliceKey, spliceKey, swapKey].join('|')})`;
const myreg = `(?:a=)?${obj
}(?:\\.${keys}|\\['${keys}'\\]|\\["${keys}"\\])` +
`\\(a,(\\d+)\\)`;
const tokenizeRegexp = new RegExp(myreg, 'g');
const tokens = [];
while ((result = tokenizeRegexp.exec(funcBody)) !== null) {
let key = result[1] || result[2] || result[3];
switch (key) {
case swapKey:
tokens.push(`w${result[4]}`);
break;
case reverseKey:
tokens.push('r');
break;
case sliceKey:
tokens.push(`s${result[4]}`);
break;
case spliceKey:
tokens.push(`p${result[4]}`);
break;
}
}
return tokens;
};
/**
* @param {Object} format
* @param {string} sig
*/
exports.setDownloadURL = (format, sig) => {
let decodedUrl;
if (format.url) {
decodedUrl = format.url;
} else {
return;
}
try {
decodedUrl = decodeURIComponent(decodedUrl);
} catch (err) {
return;
}
// Make some adjustments to the final url.
const parsedUrl = new URL(decodedUrl);
// This is needed for a speedier download.
// See https://github.com/fent/node-ytdl-core/issues/127
parsedUrl.searchParams.set('ratebypass', 'yes');
if (sig) {
// When YouTube provides a `sp` parameter the signature `sig` must go
// into the parameter it specifies.
// See https://github.com/fent/node-ytdl-core/issues/417
parsedUrl.searchParams.set(format.sp || 'signature', sig);
}
format.url = parsedUrl.toString();
};
/**
* Applies `sig.decipher()` to all format URL's.
*
* @param {Array.<Object>} formats
* @param {string} html5player
* @param {Object} options
*/
exports.decipherFormats = async(formats, html5player, options) => {
let decipheredFormats = {};
let tokens = await exports.getTokens(html5player, options);
formats.forEach(format => {
let cipher = format.signatureCipher || format.cipher;
if (cipher) {
Object.assign(format, querystring.parse(cipher));
delete format.signatureCipher;
delete format.cipher;
}
const sig = tokens && format.s ? exports.decipher(tokens, format.s) : null;
exports.setDownloadURL(format, sig);
decipheredFormats[format.url] = format;
});
return decipheredFormats;
};