@wordpress/api-fetch/build-module/middlewares/fetch-all-middleware.js

Utility to make WordPress REST API requests.

/**
 * WordPress dependencies
 */
import { addQueryArgs } from '@wordpress/url';

/**
 * Internal dependencies
 */
import apiFetch from '..';

/**
 * Apply query arguments to both URL and Path, whichever is present.
 *
 * @param {import('../types').APIFetchOptions} props
 * @param {Record<string, string | number>}    queryArgs
 * @return {import('../types').APIFetchOptions} The request with the modified query args
 */
const modifyQuery = ({
  path,
  url,
  ...options
}, queryArgs) => ({
  ...options,
  url: url && addQueryArgs(url, queryArgs),
  path: path && addQueryArgs(path, queryArgs)
});

/**
 * Duplicates parsing functionality from apiFetch.
 *
 * @param {Response} response
 * @return {Promise<any>} Parsed response json.
 */
const parseResponse = response => response.json ? response.json() : Promise.reject(response);

/**
 * @param {string | null} linkHeader
 * @return {{ next?: string }} The parsed link header.
 */
const parseLinkHeader = linkHeader => {
  if (!linkHeader) {
    return {};
  }
  const match = linkHeader.match(/<([^>]+)>; rel="next"/);
  return match ? {
    next: match[1]
  } : {};
};

/**
 * @param {Response} response
 * @return {string | undefined} The next page URL.
 */
const getNextPageUrl = response => {
  const {
    next
  } = parseLinkHeader(response.headers.get('link'));
  return next;
};

/**
 * @param {import('../types').APIFetchOptions} options
 * @return {boolean} True if the request contains an unbounded query.
 */
const requestContainsUnboundedQuery = options => {
  const pathIsUnbounded = !!options.path && options.path.indexOf('per_page=-1') !== -1;
  const urlIsUnbounded = !!options.url && options.url.indexOf('per_page=-1') !== -1;
  return pathIsUnbounded || urlIsUnbounded;
};

/**
 * The REST API enforces an upper limit on the per_page option. To handle large
 * collections, apiFetch consumers can pass `per_page=-1`; this middleware will
 * then recursively assemble a full response array from all available pages.
 *
 * @type {import('../types').APIFetchMiddleware}
 */
const fetchAllMiddleware = async (options, next) => {
  if (options.parse === false) {
    // If a consumer has opted out of parsing, do not apply middleware.
    return next(options);
  }
  if (!requestContainsUnboundedQuery(options)) {
    // If neither url nor path is requesting all items, do not apply middleware.
    return next(options);
  }

  // Retrieve requested page of results.
  const response = await apiFetch({
    ...modifyQuery(options, {
      per_page: 100
    }),
    // Ensure headers are returned for page 1.
    parse: false
  });
  const results = await parseResponse(response);
  if (!Array.isArray(results)) {
    // We have no reliable way of merging non-array results.
    return results;
  }
  let nextPage = getNextPageUrl(response);
  if (!nextPage) {
    // There are no further pages to request.
    return results;
  }

  // Iteratively fetch all remaining pages until no "next" header is found.
  let mergedResults = /** @type {any[]} */[].concat(results);
  while (nextPage) {
    const nextResponse = await apiFetch({
      ...options,
      // Ensure the URL for the next page is used instead of any provided path.
      path: undefined,
      url: nextPage,
      // Ensure we still get headers so we can identify the next page.
      parse: false
    });
    const nextResults = await parseResponse(nextResponse);
    mergedResults = mergedResults.concat(nextResults);
    nextPage = getNextPageUrl(nextResponse);
  }
  return mergedResults;
};
export default fetchAllMiddleware;
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