# etag
  
  [![NPM Version][npm-image]][npm-url]
  [![NPM Downloads][downloads-image]][downloads-url]
  [![Node.js Version][node-version-image]][node-version-url]
  [![Build Status][travis-image]][travis-url]
  [![Test Coverage][coveralls-image]][coveralls-url]
  
  Create simple HTTP ETags
  
  This module generates HTTP ETags (as defined in RFC 7232) for use in
  HTTP responses.
  
  ## Installation
  
  This is a [Node.js](https://nodejs.org/en/) module available through the
  [npm registry](https://www.npmjs.com/). Installation is done using the
  [`npm install` command](https://docs.npmjs.com/getting-started/installing-npm-packages-locally):
  
  ```sh
  $ npm install etag
  ```
  
  ## API
  
  <!-- eslint-disable no-unused-vars --> 
  
  ```js
  var etag = require('etag')
  ```
  
  ### etag(entity, [options])
  
  Generate a strong ETag for the given entity. This should be the complete
  body of the entity. Strings, `Buffer`s, and `fs.Stats` are accepted. By
  default, a strong ETag is generated except for `fs.Stats`, which will
  generate a weak ETag (this can be overwritten by `options.weak`).
  
  <!-- eslint-disable no-undef --> 
  
  ```js
  res.setHeader('ETag', etag(body))
  ```
  
  #### Options
  
  `etag` accepts these properties in the options object.
  
  ##### weak
  
  Specifies if the generated ETag will include the weak validator mark (that
  is, the leading `W/`). The actual entity tag is the same. The default value
  is `false`, unless the `entity` is `fs.Stats`, in which case it is `true`.
  
  ## Testing
  
  ```sh
  $ npm test
  ```
  
  ## Benchmark
  
  ```bash
  $ npm run-script bench
  
  > etag@1.8.0 bench nodejs-etag
  > node benchmark/index.js
  
    http_parser@2.7.0
    node@6.9.1
    v8@5.1.281.84
    uv@1.9.1
    zlib@1.2.8
    ares@1.10.1-DEV
    icu@57.1
    modules@48
    openssl@1.0.2j
  
  > node benchmark/body0-100b.js
  
    100B body
  
    4 tests completed.
  
  * buffer - strong x 498,600 ops/sec ±0.82% (191 runs sampled)
  * buffer - weak   x 496,249 ops/sec ±0.59% (179 runs sampled)
    string - strong x 466,298 ops/sec ±0.88% (186 runs sampled)
    string - weak   x 464,298 ops/sec ±0.84% (184 runs sampled)
  
  > node benchmark/body1-1kb.js
  
    1KB body
  
    4 tests completed.
  
  * buffer - strong x 346,535 ops/sec ±0.32% (189 runs sampled)
  * buffer - weak   x 344,958 ops/sec ±0.52% (185 runs sampled)
    string - strong x 259,672 ops/sec ±0.82% (191 runs sampled)
    string - weak   x 260,931 ops/sec ±0.76% (190 runs sampled)
  
  > node benchmark/body2-5kb.js
  
    5KB body
  
    4 tests completed.
  
  * buffer - strong x 136,510 ops/sec ±0.62% (189 runs sampled)
  * buffer - weak   x 136,604 ops/sec ±0.51% (191 runs sampled)
    string - strong x  80,903 ops/sec ±0.84% (192 runs sampled)
    string - weak   x  82,785 ops/sec ±0.50% (193 runs sampled)
  
  > node benchmark/body3-10kb.js
  
    10KB body
  
    4 tests completed.
  
  * buffer - strong x 78,650 ops/sec ±0.31% (193 runs sampled)
  * buffer - weak   x 78,685 ops/sec ±0.41% (193 runs sampled)
    string - strong x 43,999 ops/sec ±0.43% (193 runs sampled)
    string - weak   x 44,081 ops/sec ±0.45% (192 runs sampled)
  
  > node benchmark/body4-100kb.js
  
    100KB body
  
    4 tests completed.
  
    buffer - strong x 8,860 ops/sec ±0.66% (191 runs sampled)
  * buffer - weak   x 9,030 ops/sec ±0.26% (193 runs sampled)
    string - strong x 4,838 ops/sec ±0.16% (194 runs sampled)
    string - weak   x 4,800 ops/sec ±0.52% (192 runs sampled)
  
  > node benchmark/stats.js
  
    stat
  
    4 tests completed.
  
  * real - strong x 1,468,073 ops/sec ±0.32% (191 runs sampled)
  * real - weak   x 1,446,852 ops/sec ±0.64% (190 runs sampled)
    fake - strong x   635,707 ops/sec ±0.33% (194 runs sampled)
    fake - weak   x   627,708 ops/sec ±0.36% (192 runs sampled)
  ```
  
  ## License
  
  [MIT](LICENSE)
  
  [npm-image]: https://img.shields.io/npm/v/etag.svg
  [npm-url]: https://npmjs.org/package/etag
  [node-version-image]: https://img.shields.io/node/v/etag.svg
  [node-version-url]: https://nodejs.org/en/download/
  [travis-image]: https://img.shields.io/travis/jshttp/etag/master.svg
  [travis-url]: https://travis-ci.org/jshttp/etag
  [coveralls-image]: https://img.shields.io/coveralls/jshttp/etag/master.svg
  [coveralls-url]: https://coveralls.io/r/jshttp/etag?branch=master
  [downloads-image]: https://img.shields.io/npm/dm/etag.svg
  [downloads-url]: https://npmjs.org/package/etag