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    @americanexpress/fetch-enhancers

    1.1.3 • Public • Published

    Fetch Enhancers - One Amex

    A library of middleware for enhancing Fetch.

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    📖 Table of Contents

    🤹‍ Usage

    Installation

    npm install --save @americanexpress/fetch-enhancers

    Fetch Enhancers

    Each fetch enhancer follows the same pattern:

    • Called with any arguments required for configuration fetchEnhancer(configuration)
    • Return a function which takes a fetch client as the sole argument fetchEnhancer(configuration)(fetch)

    createTimeoutFetch [Server & Browser]

    import { createTimeoutFetch } from '@americanexpress/fetch-enhancers';

    createTimeoutFetch makes use of the AbortController to abort requests which exceed the given time limit.

    Configuring

    createTimeoutFetch takes a single argument which sets the default timeout.

    const enhancedTimeoutFetch = createTimeoutFetch(6e3)(fetch);

    When called, the enhanced fetch will accept an additional option, timeout, allowing for the default timeout value to be overridden for a single request.

    const slowRequest = timeoutFetch('https://example.com/some-slow-api', { timeout: 10e3 });

    Example

    import { createTimeoutFetch } from '@americanexpress/fetch-enhancers';
    
    // set your default timeout
    const timeoutFetch = createTimeoutFetch(6e3)(fetch);
    
    // Then use timeoutFetch as you would normally
    const request = timeoutFetch('https://example.com');
    request.then((response) => response.json())
      .then((data) => {
        console.log(data);
      });
    
    // each request can override the default timeout
    const fastRequest = timeoutFetch('https://example.com/fast', { timeout: 1e3 });

    createRetryFetch [Server & Browser]

    import { createRetryFetch } from '@americanexpress/fetch-enhancers';

    Configuring

    createRetryFetch accepts the an object with the following configuration: an optional maxRetry (default 3), and an optional back off strategy function:

    const enhancedRetryFetch = createRetryFetch()(fetch);

    Optional retry count and back off strategy function that accepts the current retry count:

    const enhancedRetryFetch = createRetryFetch({
      maxRetry: 5,
      backoffStrategy: (n) => new Promise((res) => { setTimeout(res, n * 1000); }),
    })(fetch);

    Example

    import { createRetryFetch } from '@americanexpress/fetch-enhancers';
    
    const retryFetch = createRetryFetch()(createTimeoutFetch(5e3)(fetch));
    
    // Then use retryFetch as you would normally
    const request = retryFetch('https://example.com');
    request.then((response) => response.json())
      .then((data) => {
        // do something with data
      });

    createBrowserLikeFetch [Server only]

    import { createBrowserLikeFetch } from '@americanexpress/fetch-enhancers';

    createBrowserLikeFetch is for use on the server only. It enables the forwarding of cookies and headers from the request made to the host server to trusted outbound requests made during a server side render. Cookies which are returned are stored for the life of the host servers requests allowing those cookies to be included, when valid, on subsequent requests.

    Configuring

    createBrowserLikeFetch accepts the following named arguments:

    headers

    Object containing any headers to be included on fetch requests.

    An example of how you could build the headers

    const parseHeaders = (req) => ({
      Referer: url.format({
        protocol: req.protocol,
        hostname: req.hostname,
        pathname: req.path,
      }),
      cookie: req.headers.cookie,
    });
    
    const headers = parseHeaders(req);
    const fetchWithRequestHeaders = createBrowserLikeFetch({
      headers,
      hostname: req.hostname,
      res, // Express response
      trustedURLs: [/^https:\/\/(www\.){0,1}(.*\.)example\.com[#/:?]{0,1}/],
    })(mockFetch);
    hostname

    Hostname which should be derived from the Host HTTP header. Used to determine if set setCookie will be called. If using Express this can be retrieved from the req object.

    res

    Typically this would be an Express response object. createBrowserLikeFetch makes use of the cookie function to set cookies on the response.

    If you wish to provide your own function to set cookies, use setCookie.

    res.cookie() function provided by express requires this to be set to the context of the express middleware.

    setCookie

    This takes precedence over res.cookie provided in the res argument.

    setCookie(name, value [, options])

    A callback function invoked when a fetch response contains cookies with a domain which matches to the given hostname. This can be used to set the cookie on a response object.

    setCookie is called with the same options as though it's the Express response cookie function. If you are passing in your own setCookie function it is important to note that the maxAge option will be in milliseconds.

    If desired you can use setCookie to add additional checks or modify options passed to req.cookie.

    const buildStringURIEncodingSetCookie = (res) => (name, value, options) => {
      res.cookie(name, value, { ...options, encode: String });
    };
    
    const fetchWithRequestHeaders = createBrowserLikeFetch({
      headers,
      hostname: req.hostname,
      setCookie: (name, value, options) => res.cookie(name, value, {
        ...options, encode: String,
      }),
      trustedURLs: [/^https:\/\/(www\.){0,1}(.*\.)example\.com[#/:?]{0,1}/],
    })(mockFetch);
    trustedURLs

    A list of regular expressions used to test the first argument given to fetch when making a request. If the test is successful the enhanced fetch will include provided cookies.

    const trustedURLs = [
      /^https:\/\/api\.example\.com[#/:?]{0,1}/,
      /^https:\/\/another\.example\.com[#/:?]{0,1}/,
      // or, more permissively all subdomains, including none
      /^https:\/\/(www\.){0,1}(.*\.)example\.com[#/:?]{0,1}/,
    ];

    As these are regular expressions, be careful to consider values that you also do not want matched (ex: https://example.com.evil.tld/pwned).

    trustedDomains

    Renamed to trustedURLs. Usage of trustedDomains is deprecated, but values are added to those of trustedURLs until the next breaking version.

    Example

    const parseHeaders = (req) => ({
      Referer: url.format({
        protocol: req.protocol,
        hostname: req.hostname,
        pathname: req.path,
      }),
      cookie: req.headers.cookie,
      'some-header': req.headers['some-header'] || '1234',
    });
    
    const fetchWithRequestHeaders = createBrowserLikeFetch({
      headers: parseHeaders(req),
      hostname: req.hostname,
      res, // Express response
      trustedURLs: [/^https:\/\/(www\.){0,1}(.*\.)example\.com[#/:?]{0,1}/],
    })(mockFetch);
    
    fetchWithRequestHeaders('https://example.com', {
      credentials: 'include',
    });

    Composing fetch enhancers

    You can chain together multiple enhancers to build a specific enhanced fetch client

    import { createTimeoutFetch } from '@americanexpress/fetch-enhancers';
    import { yourFetch } from './safeFetch';
    
    const timeoutFetch = createTimeoutFetch(6e3)(fetch);
    const myTimeoutFetch = yourFetch(/* options for configuring yourFetch */)(timeoutFetch);
    
    // use the enhanced fetch as you would normally
    const response = myTimeoutFetch('https://example.com');

    You can also use Redux's compose function

    import { compose } from 'redux';
    import { createTimeoutFetch } from '@americanexpress/fetch-enhancers';
    import { yourFetch } from './safeFetch';
    
    const enhancedFetch = compose(
      yourFetch(),
      createTimeoutFetch(6e3)
    )(fetch);
    
    // Then use the enhanced fetch as you would normally
    const request = enhancedFetch('https://example.com');
    request.then((response) => response.json())
      .then((data) => {
        // do something with data
      });

    Creating your own fetch enhancer

    Each enhancer must return a function which accepts fetch as a single argument.

    const strictCookieFetch = ({ allowSameOrigin }) => (nextFetch) => {
      (url, arguments_) => nextFetch(url, {
        ...arguments_,
        // use config arg allowSameOrigin
        credentials: allowSameOrigin ? 'same-origin' : 'omit',
      });
    };
    
    const safeFetch = strictCookieFetch()(fetch);

    🏆 Contributing

    We welcome Your interest in the American Express Open Source Community on Github. Any Contributor to any Open Source Project managed by the American Express Open Source Community must accept and sign an Agreement indicating agreement to the terms below. Except for the rights granted in this Agreement to American Express and to recipients of software distributed by American Express, You reserve all right, title, and interest, if any, in and to Your Contributions. Please fill out the Agreement.

    Please feel free to open pull requests and see CONTRIBUTING.md to learn how to get started contributing.

    🗝️ License

    Any contributions made under this project will be governed by the Apache License 2.0.

    🗣️ Code of Conduct

    This project adheres to the American Express Community Guidelines. By participating, you are expected to honor these guidelines.

    Keywords

    Install

    npm i @americanexpress/fetch-enhancers

    DownloadsWeekly Downloads

    116

    Version

    1.1.3

    License

    Apache 2.0

    Unpacked Size

    44.8 kB

    Total Files

    16

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    Collaborators

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    • jsmartfo
    • amexopensource