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/*!
* etag
* Copyright(c) 2014-2016 Douglas Christopher Wilson
* MIT Licensed
*/
'use strict'
/**
* Module exports.
* @public
*/
module.exports = etag
/**
* Module dependencies.
* @private
*/
var crypto = require('crypto')
var Stats = require('fs').Stats
/**
* Module variables.
* @private
*/
var toString = Object.prototype.toString
/**
* Generate an entity tag.
*
* @param {Buffer|string} entity
* @return {string}
* @private
*/
function entitytag (entity) {
if (entity.length === 0) {
// fast-path empty
return '"0-2jmj7l5rSw0yVb/vlWAYkK/YBwk"'
}
// compute hash of entity
var hash = crypto
.createHash('sha1')
.update(entity, 'utf8')
.digest('base64')
.substring(0, 27)
// compute length of entity
var len = typeof entity === 'string'
? Buffer.byteLength(entity, 'utf8')
: entity.length
return '"' + len.toString(16) + '-' + hash + '"'
}
/**
* Create a simple ETag.
*
* @param {string|Buffer|Stats} entity
* @param {object} [options]
* @param {boolean} [options.weak]
* @return {String}
* @public
*/
function etag (entity, options) {
if (entity == null) {
throw new TypeError('argument entity is required')
}
// support fs.Stats object
var isStats = isstats(entity)
var weak = options && typeof options.weak === 'boolean'
? options.weak
: isStats
// validate argument
if (!isStats && typeof entity !== 'string' && !Buffer.isBuffer(entity)) {
throw new TypeError('argument entity must be string, Buffer, or fs.Stats')
}
// generate entity tag
var tag = isStats
? stattag(entity)
: entitytag(entity)
return weak
? 'W/' + tag
: tag
}
/**
* Determine if object is a Stats object.
*
* @param {object} obj
* @return {boolean}
* @api private
*/
function isstats (obj) {
// genuine fs.Stats
if (typeof Stats === 'function' && obj instanceof Stats) {
return true
}
// quack quack
return obj && typeof obj === 'object' &&
'ctime' in obj && toString.call(obj.ctime) === '[object Date]' &&
'mtime' in obj && toString.call(obj.mtime) === '[object Date]' &&
'ino' in obj && typeof obj.ino === 'number' &&
'size' in obj && typeof obj.size === 'number'
}
/**
* Generate a tag for a stat.
*
* @param {object} stat
* @return {string}
* @private
*/
function stattag (stat) {
var mtime = stat.mtime.getTime().toString(16)
var size = stat.size.toString(16)
return '"' + size + '-' + mtime + '"'
}
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