semantic-network/lib/representation/requestHeaders.js

A utility library for manipulating a list of links that form a semantic interface to a network of resources.

import { TrackedRepresentationUtil } from '../utils/trackedRepresentationUtil';
import { Status } from './status';
import { CheckHeaders } from './checkHeaders';
import { dateToGMTHeader } from '../utils/dateToGMTHeader';
/**
 * The goal is to leave all heavy lifting to the browser (ie implement caching rules). The key issue
 * here is whether to return the in-memory resource or push through to the browser request (ie xhr).
 */
export class RequestHeaders {
    /**
     * Add eTag detection for when feed items had the eTag included. Provides the request with a no-cache directive for http 1.0/1.1/2.
     *
     * Note: this directive used when a new resource based on eTag is detected the client requires the origin
     * server to provide a new resource. This is most likely to occur because of an out-of-band mechanism (ie another
     * process outside the direct context of the resource)
     *
     * In effect, this strategy mimics the "disable cache" mechanism if performing a manual intervention
     */
    static noCacheOnStaleEtagStatusHeaderStrategy(resource, options) {
        const { useStaleEtagStrategy = false } = Object.assign({}, options);
        if (useStaleEtagStrategy) {
            const trackedState = TrackedRepresentationUtil.getState(resource);
            if (trackedState.status === Status.staleFromETag) {
                return RequestHeaders.noCacheHeader;
            }
        }
        return RequestHeaders.emptyHeaders;
    }
    static ifNoneMatchesOnStaleEtagStatusHeaderStrategy(resource, options) {
        const { useStaleEtagStrategy = false } = Object.assign({}, options);
        if (useStaleEtagStrategy) {
            const trackedState = TrackedRepresentationUtil.getState(resource);
            if (trackedState.status === Status.staleFromETag && TrackedRepresentationUtil.hasFeedETag(resource)) {
                return RequestHeaders.conditionalGetHeaders(resource);
            }
        }
        return RequestHeaders.emptyHeaders;
    }
    /**
     *  Detect that the resource has a stale 'expires' header
     */
    static noCacheOnStaleExpiresHeaderStrategy(resource) {
        const { headers = undefined } = TrackedRepresentationUtil.getState(resource);
        if (headers && CheckHeaders.checkExpiresBeforeDateHeaderStrategy(headers)) {
            return RequestHeaders.noCacheHeader;
        }
        return RequestHeaders.emptyHeaders;
    }
}
/**
 * WARNING: if this is a CORS request that both pragma and cache-control must be registered as exposed
 *          Access-Control-Allow-Headers (otherwise failed CORS request in browser)
 *
 *          @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Request-Headers
 */
RequestHeaders.noCacheHeader = {
    // http 1.0 - @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching
    'pragma': 'no-cache',
    // http 1.1/2
    'cache-control': 'no-cache',
};
RequestHeaders.emptyHeaders = {};
RequestHeaders.defaultStrategies = [
    RequestHeaders.noCacheOnStaleEtagStatusHeaderStrategy,
    RequestHeaders.noCacheOnStaleExpiresHeaderStrategy,
];
RequestHeaders.conditionalGetHeaders = (documentResource) => ({
    'if-none-match': TrackedRepresentationUtil.getFeedETag(documentResource),
    'if-modified-since': TrackedRepresentationUtil.getFeedLastModified(documentResource) ||
        TrackedRepresentationUtil.getState(documentResource).headers['last-modified'] ||
        TrackedRepresentationUtil.getState(documentResource).headers['date'] ||
        dateToGMTHeader(new Date().toUTCString()),
});
//# sourceMappingURL=requestHeaders.js.map