xfetch

xfetch

A light-weight HTTP client for Node.js.

• API
• Configuration
• Behaviour
  • HTTP proxy
  • Throws an error if response code is non-2xx
  • Timeout
• Cookbook
  • Retry request
  • Validate response
  • Make cookies persist between requests

Motivation

It started as a light-wrapper of node-fetch due to the lack of HTTP_PROXY support.

The surface grew to incorporate new requirements. In comparison to the WHATWG Fetch, xfetch API is designed to keep the code minimal by providing short-cuts to common operations.

On top of the node-fetch, xfetch implements:

• HTTP proxy support.
• Response validation.
• Retry request strategy.
• In-built CookieJar.
• Strictly typed API.

API

type HeadersConfigurationType = {
  [key: string]: string | number
};

type RawHeadersType = {|
  [key: string]: $ReadOnlyArray<string>
|};

type HeadersType = {|
  +raw: () => RawHeadersType,
  +get: (name: string) => string
|};

type IsResponseRedirectType = (Response: ResponseType) => boolean;
type IsResponseValidType = (response: ResponseType) => boolean | Promise<boolean>;

type HttpMethodType = 'get' | 'post' | 'delete' | 'post' | 'trace';

/**
 * @see https://github.com/tim-kos/node-retry#retrytimeoutsoptions
 */
type RetryConfigurationType = {
  factor?: number,
  maxTimeout?: number,
  minTimeout?: number,
  randomize?: boolean,
  retries?: number
};

type ResponseType = {|
  +headers: HeadersType,
  +json: () => Promise<Object>,
  +status: number,
  +text: () => Promise<string>,
  +url: string
|} | string;

/**
 * @property isResponseValid Used to validate response. Refer to [Validate response](#validate-response).
 * @property retry Used to retry requests that produce response that does not pass validation. Refer to [Retry request](#retry-request) and [Validating response](#validating-response).
 * @property jar An instance of `tough-cookie` [`CookieJar`](https://github.com/salesforce/tough-cookie#cookiejar). Used to collect & set cookies.
 * @property timeout Timeout in milliseconds.
 */
type UserConfigurationType = {
  +body?: string | URLSearchParams | FormData,
  +compress?: boolean,
  +headers?: HeadersConfigurationType,
  +isResponseRedirect?: IsResponseRedirectType,
  +isResponseValid?: IsResponseValidType,
  +jar?: CookieJar,
  +method?: HttpMethodType,
  +query?: Object,
  +responseType?: 'full' | 'text' | 'json',
  +retry?: RetryConfigurationType,
  +timeout?: number
};

type fetch = (url: string, configuration?: UserConfigurationType) => Promise<ResponseType>;

Behaviour

HTTP proxy

Uses HTTP_PROXY (http://host:port) environment variable value to configure HTTP proxy.

Note: You must also configure NODE_TLS_REJECT_UNAUTHORIZED=0. This is a lazy workaround to enable the proxy to work with TLS.

Throws an error if response code is non-2xx or 3xx

Throws UnexpectedResponseCodeError error if response code is non-2xx or 3xx.

This behaviour can be overridden using isResponseValid configuration.

Timeout

xfetch defaults to a 30 seconds timeout after which ResponseTimeoutError error is thrown.

A timeout error does not trigger the request retry strategy.

import xfetch, {
  ResponseTimeoutError
} from 'xfetch';

try {
  await fetch('http://gajus.com/', {
    timeout: 30 * 1000
  });
} catch (error) {
  if (error instanceof ResponseTimeoutError) {
    // Request has not received a response within 30 seconds.
  }

  throw error;
}

Cookbook

Retry request

Requests that result in non-2xx response will be retried.

retry option is used to configure request retry strategy.

The retry configuration shape matches configuration of the retry module.

Validate response

Define a custom validator function to force use the request retry strategy.

A custom validator is configured using isResponseValid configuration, e.g.

import xfetch, {
  UnexpectedResponseError
};

const isResponseValid = async (response) => {
  const body = await response.text();

  if (body.includes('rate error')) {
    throw new UnexpectedResponseError(response);
  }

  return true;
}

await xfetch('http://gajus.com', {
  isResponseValid
});

A custom validator must return a boolean flag indicating whether the response is valid. A custom validator can throw an error that extends UnexpectedResponseError error.

xfetch default validator can be imported and used to extend a custom validator, e.g.

import xfetch, {
  UnexpectedResponseError,
  isResponseValid as defaultIsResponseValid
};

const isResponseValid = async (response) => {
  const responseIsValid = await defaultIsResponseValid(response);

  if (!responseIsValid) {
    return responseIsValid;
  }

  const body = await response.text();

  if (body.includes('rate error')) {
    throw new UnexpectedResponseError(response);
  }

  return true;
}

await xfetch('http://gajus.com', {
  isResponseValid
});

Make cookies persist between requests

jar parameter can be passed an instance of tough-cookie CookieJar to collect cookies and use them for the following requests.

import xfetch, {
  CookieJar
};

const jar = new CookieJar();

await xfetch('http://gajus.com/this-url-sets-cookies', {
  jar
});

await xfetch('http://gajus.com/this-url-requires-cookies-to-be-present', {
  jar
});

Note:

xfetch exports CookieJar class that can be used to construct an instance of tough-cookie CookieJar.