# 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

> [email protected] bench nodejs-etag
> node benchmark/index.js

  [email protected]
  [email protected]
  [email protected]
  [email protected]
  [email protected]
  [email protected]
  [email protected]
  modules@48
  [email protected]

> node benchmark/body0-100b.js

  100B body

  4 tests completed.

  buffer - strong x 258,647 ops/sec ±1.07% (180 runs sampled)
  buffer - weak   x 263,812 ops/sec ±0.61% (184 runs sampled)
  string - strong x 259,955 ops/sec ±1.19% (185 runs sampled)
  string - weak   x 264,356 ops/sec ±1.09% (184 runs sampled)

> node benchmark/body1-1kb.js

  1KB body

  4 tests completed.

  buffer - strong x 189,018 ops/sec ±1.12% (182 runs sampled)
  buffer - weak   x 190,586 ops/sec ±0.81% (186 runs sampled)
  string - strong x 144,272 ops/sec ±0.96% (188 runs sampled)
  string - weak   x 145,380 ops/sec ±1.43% (187 runs sampled)

> node benchmark/body2-5kb.js

  5KB body

  4 tests completed.

  buffer - strong x 92,435 ops/sec ±0.42% (188 runs sampled)
  buffer - weak   x 92,373 ops/sec ±0.58% (189 runs sampled)
  string - strong x 48,850 ops/sec ±0.56% (186 runs sampled)
  string - weak   x 49,380 ops/sec ±0.56% (190 runs sampled)

> node benchmark/body3-10kb.js

  10KB body

  4 tests completed.

  buffer - strong x 55,989 ops/sec ±0.93% (188 runs sampled)
  buffer - weak   x 56,148 ops/sec ±0.55% (190 runs sampled)
  string - strong x 27,345 ops/sec ±0.43% (188 runs sampled)
  string - weak   x 27,496 ops/sec ±0.45% (190 runs sampled)

> node benchmark/body4-100kb.js

  100KB body

  4 tests completed.

  buffer - strong x 7,083 ops/sec ±0.22% (190 runs sampled)
  buffer - weak   x 7,115 ops/sec ±0.26% (191 runs sampled)
  string - strong x 3,068 ops/sec ±0.34% (190 runs sampled)
  string - weak   x 3,096 ops/sec ±0.35% (190 runs sampled)

> node benchmark/stats.js

  stat

  4 tests completed.

  real - strong x 871,642 ops/sec ±0.34% (189 runs sampled)
  real - weak   x 867,613 ops/sec ±0.39% (190 runs sampled)
  fake - strong x 401,051 ops/sec ±0.40% (189 runs sampled)
  fake - weak   x 400,100 ops/sec ±0.47% (188 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