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';
const timeoutFetch = createTimeoutFetch(6e3)(fetch);
const request = timeoutFetch('https://example.com');
request.then((response) => response.json())
.then((data) => {
console.log(data);
});
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));
const request = retryFetch('https://example.com');
request.then((response) => response.json())
.then((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:
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,
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}/,
/^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,
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()(timeoutFetch);
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);
const request = enhancedFetch('https://example.com');
request.then((response) => response.json())
.then((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_,
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.