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utils.js
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utils.js
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'use strict';
const { promisify } = require('util');
const { access } = require('fs');
const { normalize } = require('path');
const BUFFER_LENGTH = 262;
const accessAsync = promisify(access);
/**
* Returns true if value is a String
* @param {*} val
* @returns {Boolean}
*/
function isString(val) {
return typeof val === 'string';
}
/**
* Returns true if value is an Object
* @param {*} val
* @returns {Boolean}
*/
function isObject(val) {
return Object.prototype.toString.call(val) === '[object Object]';
}
/**
* Returns true if value is a Buffer, UInt8Array or ArrayBuffer
* @param {*} val
* @returns {Boolean}
*/
function isBuffer(val) {
return Buffer.isBuffer(val) || val instanceof Uint8Array || val instanceof ArrayBuffer;
}
/**
* Returns true if value is a Readable Stream
* @param {*} val
* @returns {Boolean}
*/
function isStream(val) {
return typeof val === 'object' && typeof val.pipe === 'function'
&& val.readable !== false && typeof val._read === 'function' && !val.closed && !val.destroyed;
}
/**
* Tests whether or not the given path exists
* @param {String} path
* @returns {Promise<Boolean>}
* @async
*/
async function isExists(path) {
try {
await accessAsync(normalize(path));
return true;
} catch (e) {
return false;
}
}
/**
* Read a chunk from a stream
* @param {ReadableStream} stream
* @returns {Promise<Buffer>}
* @async
*/
async function streamChunk(stream) {
return new Promise((resolve, reject) => {
stream.once('error', reject);
stream.once('readable', () => {
const chunk = stream.read(BUFFER_LENGTH) || stream.read();
if (chunk) {
stream.unshift(chunk);
}
return resolve(chunk);
});
});
}
module.exports = {
isString,
isObject,
isBuffer,
isStream,
isExists,
streamChunk,
BUFFER_LENGTH
};