mattermost-redux/src/client/fetch_etag.ts

Common code (API client, Redux stores, logic, utility functions) for building a Mattermost client

// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

import {Options} from 'types/client4';

const data: {[x: string]: any} = {};
const etags: {[x: string]: string} = {};

export default ((url: string, options: Options = {headers: {}}): Promise<Response> => {
    url = url || options.url || ''; // eslint-disable-line no-param-reassign

    if (options.method === 'GET' || !options.method) {
        const etag = etags[url!];
        const cachedResponse = data[`${url}${etag}`]; // ensure etag is for url
        if (etag) {
            options.headers!['If-None-Match'] = etag;
        }

        return fetch(url!, options).
            then((response) => {
                if (response.status === 304) {
                    return cachedResponse.clone();
                }

                if (response.status === 200) {
                    const responseEtag = response.headers.get('Etag');

                    if (responseEtag) {
                        data[`${url}${responseEtag}`] = response.clone();
                        etags[url!] = responseEtag;
                    }
                }

                return response;
            });
    }

    // all other requests go straight to fetch
    return Reflect.apply(fetch, undefined, [url, options]);
});