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