node-fetch/README.md

node-fetch
==========

[![npm version][npm-image]][npm-url]
[![build status][travis-image]][travis-url]
[![coverage status][codecov-image]][codecov-url]
[![install size][install-size-image]][install-size-url]

A light-weight module that brings `window.fetch` to Node.js

(We are looking for [v2 maintainers and collaborators](https://github.com/bitinn/node-fetch/issues/567))

<!-- TOC -->

- [Motivation](#motivation)
- [Features](#features)
- [Difference from client-side fetch](#difference-from-client-side-fetch)
- [Installation](#installation)
- [Loading and configuring the module](#loading-and-configuring-the-module)
- [Common Usage](#common-usage)
    - [Plain text or HTML](#plain-text-or-html)
    - [JSON](#json)
    - [Simple Post](#simple-post)
    - [Post with JSON](#post-with-json)
    - [Post with form parameters](#post-with-form-parameters)
    - [Handling exceptions](#handling-exceptions)
    - [Handling client and server errors](#handling-client-and-server-errors)
- [Advanced Usage](#advanced-usage)
    - [Streams](#streams)
    - [Buffer](#buffer)
    - [Accessing Headers and other Meta data](#accessing-headers-and-other-meta-data)
    - [Extract Set-Cookie Header](#extract-set-cookie-header)
    - [Post data using a file stream](#post-data-using-a-file-stream)
    - [Post with form-data (detect multipart)](#post-with-form-data-detect-multipart)
    - [Request cancellation with AbortSignal](#request-cancellation-with-abortsignal)
- [API](#api)
    - [fetch(url[, options])](#fetchurl-options)
    - [Options](#options)
    - [Class: Request](#class-request)
    - [Class: Response](#class-response)
    - [Class: Headers](#class-headers)
    - [Interface: Body](#interface-body)
    - [Class: FetchError](#class-fetcherror)
- [License](#license)
- [Acknowledgement](#acknowledgement)

<!-- /TOC -->

## Motivation

Instead of implementing `XMLHttpRequest` in Node.js to run browser-specific [Fetch polyfill](https://github.com/github/fetch), why not go from native `http` to `fetch` API directly? Hence `node-fetch`, minimal code for a `window.fetch` compatible API on Node.js runtime.

See Matt Andrews' [isomorphic-fetch](https://github.com/matthew-andrews/isomorphic-fetch) or Leonardo Quixada's [cross-fetch](https://github.com/lquixada/cross-fetch) for isomorphic usage (exports `node-fetch` for server-side, `whatwg-fetch` for client-side).

## Features

- Stay consistent with `window.fetch` API.
- Make conscious trade-off when following [WHATWG fetch spec][whatwg-fetch] and [stream spec](https://streams.spec.whatwg.org/) implementation details, document known differences.
- Use native promise, but allow substituting it with [insert your favorite promise library].
- Use native Node streams for body, on both request and response.
- Decode content encoding (gzip/deflate) properly, and convert string output (such as `res.text()` and `res.json()`) to UTF-8 automatically.
- Useful extensions such as timeout, redirect limit, response size limit, [explicit errors](ERROR-HANDLING.md) for troubleshooting.

## Difference from client-side fetch

- See [Known Differences](LIMITS.md) for details.
- If you happen to use a missing feature that `window.fetch` offers, feel free to open an issue.
- Pull requests are welcomed too!

## Installation

Current stable release (`2.x`)

```sh
$ npm install node-fetch --save
```

## Loading and configuring the module
We suggest you load the module via `require`, pending the stabalizing of es modules in node:
```js
const fetch = require('node-fetch');
```

If you are using a Promise library other than native, set it through fetch.Promise:
```js
const Bluebird = require('bluebird');

fetch.Promise = Bluebird;
```

## Common Usage

NOTE: The documentation below is up-to-date with `2.x` releases, [see `1.x` readme](https://github.com/bitinn/node-fetch/blob/1.x/README.md), [changelog](https://github.com/bitinn/node-fetch/blob/1.x/CHANGELOG.md) and [2.x upgrade guide](UPGRADE-GUIDE.md) for the differences.

#### Plain text or HTML
```js
fetch('https://github.com/')
    .then(res => res.text())
    .then(body => console.log(body));
```

#### JSON

```js

fetch('https://api.github.com/users/github')
    .then(res => res.json())
    .then(json => console.log(json));
```

#### Simple Post
```js
fetch('https://httpbin.org/post', { method: 'POST', body: 'a=1' })
    .then(res => res.json()) // expecting a json response
    .then(json => console.log(json));
```

#### Post with JSON

```js
const body = { a: 1 };

fetch('https://httpbin.org/post', {
        method: 'post',
        body:    JSON.stringify(body),
        headers: { 'Content-Type': 'application/json' },
    })
    .then(res => res.json())
    .then(json => console.log(json));
```

#### Post with form parameters
`URLSearchParams` is available in Node.js as of v7.5.0. See [official documentation](https://nodejs.org/api/url.html#url_class_urlsearchparams) for more usage methods.

NOTE: The `Content-Type` header is only set automatically to `x-www-form-urlencoded` when an instance of `URLSearchParams` is given as such:

```js
const { URLSearchParams } = require('url');

const params = new URLSearchParams();
params.append('a', 1);

fetch('https://httpbin.org/post', { method: 'POST', body: params })
    .then(res => res.json())
    .then(json => console.log(json));
```

#### Handling exceptions
NOTE: 3xx-5xx responses are *NOT* exceptions, and should be handled in `then()`, see the next section.

Adding a catch to the fetch promise chain will catch *all* exceptions, such as errors originating from node core libraries, like network errors, and operational errors which are instances of FetchError. See the [error handling document](ERROR-HANDLING.md)  for more details.

```js
fetch('https://domain.invalid/')
    .catch(err => console.error(err));
```

#### Handling client and server errors
It is common to create a helper function to check that the response contains no client (4xx) or server (5xx) error responses:

```js
function checkStatus(res) {
    if (res.ok) { // res.status >= 200 && res.status < 300
        return res;
    } else {
        throw MyCustomError(res.statusText);
    }
}

fetch('https://httpbin.org/status/400')
    .then(checkStatus)
    .then(res => console.log('will not get here...'))
```

## Advanced Usage

#### Streams
The "Node.js way" is to use streams when possible:

```js
fetch('https://assets-cdn.github.com/images/modules/logos_page/Octocat.png')
    .then(res => {
        const dest = fs.createWriteStream('./octocat.png');
        res.body.pipe(dest);
    });
```

#### Buffer
If you prefer to cache binary data in full, use buffer(). (NOTE: buffer() is a `node-fetch` only API)

```js
const fileType = require('file-type');

fetch('https://assets-cdn.github.com/images/modules/logos_page/Octocat.png')
    .then(res => res.buffer())
    .then(buffer => fileType(buffer))
    .then(type => { /* ... */ });
```

#### Accessing Headers and other Meta data
```js
fetch('https://github.com/')
    .then(res => {
        console.log(res.ok);
        console.log(res.status);
        console.log(res.statusText);
        console.log(res.headers.raw());
        console.log(res.headers.get('content-type'));
    });
```

#### Extract Set-Cookie Header

Unlike browsers, you can access raw `Set-Cookie` headers manually using `Headers.raw()`, this is a `node-fetch` only API.

```js
fetch(url).then(res => {
    // returns an array of values, instead of a string of comma-separated values
    console.log(res.headers.raw()['set-cookie']);
});
```

#### Post data using a file stream

```js
const { createReadStream } = require('fs');

const stream = createReadStream('input.txt');

fetch('https://httpbin.org/post', { method: 'POST', body: stream })
    .then(res => res.json())
    .then(json => console.log(json));
```

#### Post with form-data (detect multipart)

```js
const FormData = require('form-data');

const form = new FormData();
form.append('a', 1);

fetch('https://httpbin.org/post', { method: 'POST', body: form })
    .then(res => res.json())
    .then(json => console.log(json));

// OR, using custom headers
// NOTE: getHeaders() is non-standard API

const form = new FormData();
form.append('a', 1);

const options = {
    method: 'POST',
    body: form,
    headers: form.getHeaders()
}

fetch('https://httpbin.org/post', options)
    .then(res => res.json())
    .then(json => console.log(json));
```

#### Request cancellation with AbortSignal

> NOTE: You may only cancel streamed requests on Node >= v8.0.0

You may cancel requests with `AbortController`. A suggested implementation is [`abort-controller`](https://www.npmjs.com/package/abort-controller).

An example of timing out a request after 150ms could be achieved as follows:

```js
import AbortController from 'abort-controller';

const controller = new AbortController();
const timeout = setTimeout(
  () => { controller.abort(); },
  150,
);

fetch(url, { signal: controller.signal })
  .then(res => res.json())
  .then(
    data => {
      useData(data)
    },
    err => {
      if (err.name === 'AbortError') {
        // request was aborted
      }
    },
  )
  .finally(() => {
    clearTimeout(timeout);
  });
```

See [test cases](https://github.com/bitinn/node-fetch/blob/master/test/test.js) for more examples.


## API

### fetch(url[, options])

- `url` A string representing the URL for fetching
- `options` [Options](#fetch-options) for the HTTP(S) request
- Returns: <code>Promise&lt;[Response](#class-response)&gt;</code>

Perform an HTTP(S) fetch.

`url` should be an absolute url, such as `https://example.com/`. A path-relative URL (`/file/under/root`) or protocol-relative URL (`//can-be-http-or-https.com/`) will result in a rejected promise.

<a id="fetch-options"></a>
### Options

The default values are shown after each option key.

```js
{
    // These properties are part of the Fetch Standard
    method: 'GET',
    headers: {},        // request headers. format is the identical to that accepted by the Headers constructor (see below)
    body: null,         // request body. can be null, a string, a Buffer, a Blob, or a Node.js Readable stream
    redirect: 'follow', // set to `manual` to extract redirect headers, `error` to reject redirect
    signal: null,       // pass an instance of AbortSignal to optionally abort requests

    // The following properties are node-fetch extensions
    follow: 20,         // maximum redirect count. 0 to not follow redirect
    timeout: 0,         // req/res timeout in ms, it resets on redirect. 0 to disable (OS limit applies). Signal is recommended instead.
    compress: true,     // support gzip/deflate content encoding. false to disable
    size: 0,            // maximum response body size in bytes. 0 to disable
    agent: null         // http(s).Agent instance or function that returns an instance (see below)
}
```

##### Default Headers

If no values are set, the following request headers will be sent automatically:

Header              | Value
------------------- | --------------------------------------------------------
`Accept-Encoding`   | `gzip,deflate` _(when `options.compress === true`)_
`Accept`            | `*/*`
`Connection`        | `close` _(when no `options.agent` is present)_
`Content-Length`    | _(automatically calculated, if possible)_
`Transfer-Encoding` | `chunked` _(when `req.body` is a stream)_
`User-Agent`        | `node-fetch/1.0 (+https://github.com/bitinn/node-fetch)`

Note: when `body` is a `Stream`, `Content-Length` is not set automatically.

##### Custom Agent

The `agent` option allows you to specify networking related options that's out of the scope of Fetch. Including and not limit to:

- Support self-signed certificate
- Use only IPv4 or IPv6
- Custom DNS Lookup

See [`http.Agent`](https://nodejs.org/api/http.html#http_new_agent_options) for more information.

In addition, `agent` option accepts a function that returns http(s).Agent instance given current [URL](https://nodejs.org/api/url.html), this is useful during a redirection chain across HTTP and HTTPS protocol.

```js
const httpAgent = new http.Agent({
    keepAlive: true
});
const httpsAgent = new https.Agent({
    keepAlive: true
});

const options = {
    agent: function (_parsedURL) {
        if (_parsedURL.protocol == 'http:') {
            return httpAgent;
        } else {
            return httpsAgent;
        }
    }
}
```

<a id="class-request"></a>
### Class: Request

An HTTP(S) request containing information about URL, method, headers, and the body. This class implements the [Body](#iface-body) interface.

Due to the nature of Node.js, the following properties are not implemented at this moment:

- `type`
- `destination`
- `referrer`
- `referrerPolicy`
- `mode`
- `credentials`
- `cache`
- `integrity`
- `keepalive`

The following node-fetch extension properties are provided:

- `follow`
- `compress`
- `counter`
- `agent`

See [options](#fetch-options) for exact meaning of these extensions.

#### new Request(input[, options])

<small>*(spec-compliant)*</small>

- `input` A string representing a URL, or another `Request` (which will be cloned)
- `options` [Options][#fetch-options] for the HTTP(S) request

Constructs a new `Request` object. The constructor is identical to that in the [browser](https://developer.mozilla.org/en-US/docs/Web/API/Request/Request).

In most cases, directly `fetch(url, options)` is simpler than creating a `Request` object.

<a id="class-response"></a>
### Class: Response

An HTTP(S) response. This class implements the [Body](#iface-body) interface.

The following properties are not implemented in node-fetch at this moment:

- `Response.error()`
- `Response.redirect()`
- `type`
- `trailer`

#### new Response([body[, options]])

<small>*(spec-compliant)*</small>

- `body` A string or [Readable stream][node-readable]
- `options` A [`ResponseInit`][response-init] options dictionary

Constructs a new `Response` object. The constructor is identical to that in the [browser](https://developer.mozilla.org/en-US/docs/Web/API/Response/Response).

Because Node.js does not implement service workers (for which this class was designed), one rarely has to construct a `Response` directly.

#### response.ok

<small>*(spec-compliant)*</small>

Convenience property representing if the request ended normally. Will evaluate to true if the response status was greater than or equal to 200 but smaller than 300.

#### response.redirected

<small>*(spec-compliant)*</small>

Convenience property representing if the request has been redirected at least once. Will evaluate to true if the internal redirect counter is greater than 0.

<a id="class-headers"></a>
### Class: Headers

This class allows manipulating and iterating over a set of HTTP headers. All methods specified in the [Fetch Standard][whatwg-fetch] are implemented.

#### new Headers([init])

<small>*(spec-compliant)*</small>

- `init` Optional argument to pre-fill the `Headers` object

Construct a new `Headers` object. `init` can be either `null`, a `Headers` object, an key-value map object, or any iterable object.

```js
// Example adapted from https://fetch.spec.whatwg.org/#example-headers-class

const meta = {
  'Content-Type': 'text/xml',
  'Breaking-Bad': '<3'
};
const headers = new Headers(meta);

// The above is equivalent to
const meta = [
  [ 'Content-Type', 'text/xml' ],
  [ 'Breaking-Bad', '<3' ]
];
const headers = new Headers(meta);

// You can in fact use any iterable objects, like a Map or even another Headers
const meta = new Map();
meta.set('Content-Type', 'text/xml');
meta.set('Breaking-Bad', '<3');
const headers = new Headers(meta);
const copyOfHeaders = new Headers(headers);
```

<a id="iface-body"></a>
### Interface: Body

`Body` is an abstract interface with methods that are applicable to both `Request` and `Response` classes.

The following methods are not yet implemented in node-fetch at this moment:

- `formData()`

#### body.body

<small>*(deviation from spec)*</small>

* Node.js [`Readable` stream][node-readable]

The data encapsulated in the `Body` object. Note that while the [Fetch Standard][whatwg-fetch] requires the property to always be a WHATWG `ReadableStream`, in node-fetch it is a Node.js [`Readable` stream][node-readable].

#### body.bodyUsed

<small>*(spec-compliant)*</small>

* `Boolean`

A boolean property for if this body has been consumed. Per spec, a consumed body cannot be used again.

#### body.arrayBuffer()
#### body.blob()
#### body.json()
#### body.text()

<small>*(spec-compliant)*</small>

* Returns: <code>Promise</code>

Consume the body and return a promise that will resolve to one of these formats.

#### body.buffer()

<small>*(node-fetch extension)*</small>

* Returns: <code>Promise&lt;Buffer&gt;</code>

Consume the body and return a promise that will resolve to a Buffer.

#### body.textConverted()

<small>*(node-fetch extension)*</small>

* Returns: <code>Promise&lt;String&gt;</code>

Identical to `body.text()`, except instead of always converting to UTF-8, encoding sniffing will be performed and text converted to UTF-8, if possible.

(This API requires an optional dependency on npm package [encoding](https://www.npmjs.com/package/encoding), which you need to install manually. `webpack` users may see [a warning message](https://github.com/bitinn/node-fetch/issues/412#issuecomment-379007792) due to this optional dependency.)

<a id="class-fetcherror"></a>
### Class: FetchError

<small>*(node-fetch extension)*</small>

An operational error in the fetching process. See [ERROR-HANDLING.md][] for more info.

<a id="class-aborterror"></a>
### Class: AbortError

<small>*(node-fetch extension)*</small>

An Error thrown when the request is aborted in response to an `AbortSignal`'s `abort` event. It has a `name` property of `AbortError`. See [ERROR-HANDLING.MD][] for more info.

## Acknowledgement

Thanks to [github/fetch](https://github.com/github/fetch) for providing a solid implementation reference.

`node-fetch` v1 was maintained by [@bitinn](https://github.com/bitinn); v2 was maintained by [@TimothyGu](https://github.com/timothygu), [@bitinn](https://github.com/bitinn) and [@jimmywarting](https://github.com/jimmywarting); v2 readme is written by [@jkantr](https://github.com/jkantr).

## License

MIT

[npm-image]: https://flat.badgen.net/npm/v/node-fetch
[npm-url]: https://www.npmjs.com/package/node-fetch
[travis-image]: https://flat.badgen.net/travis/bitinn/node-fetch
[travis-url]: https://travis-ci.org/bitinn/node-fetch
[codecov-image]: https://flat.badgen.net/codecov/c/github/bitinn/node-fetch/master
[codecov-url]: https://codecov.io/gh/bitinn/node-fetch
[install-size-image]: https://flat.badgen.net/packagephobia/install/node-fetch
[install-size-url]: https://packagephobia.now.sh/result?p=node-fetch
[whatwg-fetch]: https://fetch.spec.whatwg.org/
[response-init]: https://fetch.spec.whatwg.org/#responseinit
[node-readable]: https://nodejs.org/api/stream.html#stream_readable_streams
[mdn-headers]: https://developer.mozilla.org/en-US/docs/Web/API/Headers
[LIMITS.md]: https://github.com/bitinn/node-fetch/blob/master/LIMITS.md
[ERROR-HANDLING.md]: https://github.com/bitinn/node-fetch/blob/master/ERROR-HANDLING.md
[UPGRADE-GUIDE.md]: https://github.com/bitinn/node-fetch/blob/master/UPGRADE-GUIDE.md