/*!
|
|
* etag
|
|
* Copyright(c) 2014 Douglas Christopher Wilson
|
|
* MIT Licensed
|
|
*/
|
|
|
|
/**
|
|
* Module exports.
|
|
*/
|
|
|
|
module.exports = etag
|
|
|
|
/**
|
|
* Module dependencies.
|
|
*/
|
|
|
|
var crc = require('crc').crc32
|
|
var crypto = require('crypto')
|
|
var Stats = require('fs').Stats
|
|
|
|
/**
|
|
* Module variables.
|
|
*/
|
|
|
|
var crc32threshold = 1000 // 1KB
|
|
var NULL = new Buffer([0])
|
|
var toString = Object.prototype.toString
|
|
|
|
/**
|
|
* Create a simple ETag.
|
|
*
|
|
* @param {string|Buffer|Stats} entity
|
|
* @param {object} [options]
|
|
* @param {boolean} [options.weak]
|
|
* @return {String}
|
|
* @api public
|
|
*/
|
|
|
|
function etag(entity, options) {
|
|
if (entity == null) {
|
|
throw new TypeError('argument entity is required')
|
|
}
|
|
|
|
var isStats = isstats(entity)
|
|
var weak = options && typeof options.weak === 'boolean'
|
|
? options.weak
|
|
: isStats
|
|
|
|
// support fs.Stats object
|
|
if (isStats) {
|
|
return stattag(entity, weak)
|
|
}
|
|
|
|
if (typeof entity !== 'string' && !Buffer.isBuffer(entity)) {
|
|
throw new TypeError('argument entity must be string, Buffer, or fs.Stats')
|
|
}
|
|
|
|
var hash = weak
|
|
? weakhash(entity)
|
|
: stronghash(entity)
|
|
|
|
return weak
|
|
? 'W/"' + hash + '"'
|
|
: '"' + hash + '"'
|
|
}
|
|
|
|
/**
|
|
* Determine if object is a Stats object.
|
|
*
|
|
* @param {object} obj
|
|
* @return {boolean}
|
|
* @api private
|
|
*/
|
|
|
|
function isstats(obj) {
|
|
// not even an object
|
|
if (obj === null || typeof obj !== 'object') {
|
|
return false
|
|
}
|
|
|
|
// genuine fs.Stats
|
|
if (obj instanceof Stats) {
|
|
return true
|
|
}
|
|
|
|
// quack quack
|
|
return 'atime' in obj && toString.call(obj.atime) === '[object Date]'
|
|
&& '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 {Buffer} entity
|
|
* @return {String}
|
|
* @api private
|
|
*/
|
|
|
|
function stattag(stat, weak) {
|
|
var mtime = stat.mtime.toISOString()
|
|
var size = stat.size.toString(16)
|
|
|
|
if (weak) {
|
|
return 'W/"' + size + '-' + crc(mtime) + '"'
|
|
}
|
|
|
|
var hash = crypto
|
|
.createHash('md5')
|
|
.update('file', 'utf8')
|
|
.update(NULL)
|
|
.update(size, 'utf8')
|
|
.update(NULL)
|
|
.update(mtime, 'utf8')
|
|
.digest('base64')
|
|
|
|
return '"' + hash + '"'
|
|
}
|
|
|
|
/**
|
|
* Generate a strong hash.
|
|
*
|
|
* @param {Buffer} entity
|
|
* @return {String}
|
|
* @api private
|
|
*/
|
|
|
|
function stronghash(entity) {
|
|
if (entity.length === 0) {
|
|
// fast-path empty
|
|
return '1B2M2Y8AsgTpgAmY7PhCfg=='
|
|
}
|
|
|
|
return crypto
|
|
.createHash('md5')
|
|
.update(entity, 'utf8')
|
|
.digest('base64')
|
|
}
|
|
|
|
/**
|
|
* Generate a weak hash.
|
|
*
|
|
* @param {Buffer} entity
|
|
* @return {String}
|
|
* @api private
|
|
*/
|
|
|
|
function weakhash(entity) {
|
|
if (entity.length === 0) {
|
|
// fast-path empty
|
|
return '0-0'
|
|
}
|
|
|
|
var len = typeof entity === 'string'
|
|
? Buffer.byteLength(entity, 'utf8')
|
|
: entity.length
|
|
|
|
if (len <= crc32threshold) {
|
|
// crc32 plus length when it's fast
|
|
// crc(str) only accepts utf-8 encoding
|
|
return len.toString(16) + '-' + crc(entity).toString(16)
|
|
}
|
|
|
|
// use md4 for long strings
|
|
return crypto
|
|
.createHash('md4')
|
|
.update(entity, 'utf8')
|
|
.digest('base64')
|
|
}
|