xref: /expo/packages/@expo/cli/src/api/rest/cache/wrapFetchWithCache.ts (revision 8a424beb)

/**
 * Copyright (c) 2021 Expo, Inc.
 * Copyright (c) 2020 mistval.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * Based on https://github.com/mistval/node-fetch-cache/blob/9c40ddf786b0de22ce521d8bdaa6347bc44dd629/src/index.js#L1
 * But with TypeScript support to fix Jest tests, and removed unused code.
 */
import crypto from 'crypto';
import FormData from 'form-data';
import fs from 'fs';
import { Request, RequestInfo, RequestInit, Response } from 'node-fetch';
import { URLSearchParams } from 'url';

import { FileSystemCache } from './FileSystemCache';
import { NFCResponse } from './response';
import { FetchLike } from '../client.types';

const CACHE_VERSION = 3;

const lockPromiseForKey: Record<string, Promise<any>> = {};
const unlockFunctionForKey: Record<string, any> = {};

/**
 * Take out a lock. When this function returns (asynchronously),
 * you have the lock.
 * @param {string} key - The key to lock on. Anyone else who
 *   tries to lock on the same key will need to wait for it to
 *   be unlocked.
 */
async function lock(key: string) {
  if (!lockPromiseForKey[key]) {
    lockPromiseForKey[key] = Promise.resolve();
  }

  const takeLockPromise = lockPromiseForKey[key];
  lockPromiseForKey[key] = takeLockPromise.then(
    () =>
      new Promise((fulfill) => {
        unlockFunctionForKey[key] = fulfill;
      })
  );

  return takeLockPromise;
}

/**
 * Release a lock.
 * @param {string} key - The key to release the lock for.
 *   The next person in line will now be able to take out
 *   the lock for that key.
 */
function unlock(key: string) {
  if (unlockFunctionForKey[key]) {
    unlockFunctionForKey[key]();
    delete unlockFunctionForKey[key];
  }
}

function md5(str: string) {
  return crypto.createHash('md5').update(str).digest('hex');
}

// Since the boundary in FormData is random,
// we ignore it for purposes of calculating
// the cache key.
function getFormDataCacheKey(formData: FormData) {
  const cacheKey = { ...formData };
  const boundary = formData.getBoundary();

  // @ts-expect-error
  delete cacheKey._boundary;

  const boundaryReplaceRegex = new RegExp(boundary, 'g');

  // @ts-expect-error
  cacheKey._streams = cacheKey._streams.map((s) => {
    if (typeof s === 'string') {
      return s.replace(boundaryReplaceRegex, '');
    }

    return s;
  });

  return cacheKey;
}

function getBodyCacheKeyJson(body: any) {
  if (!body) {
    return body;
  }
  if (typeof body === 'string') {
    return body;
  }
  if (body instanceof URLSearchParams) {
    return body.toString();
  }
  if (body instanceof fs.ReadStream) {
    return body.path;
  }
  if (body.toString && body.toString() === '[object FormData]') {
    return getFormDataCacheKey(body);
  }
  if (body instanceof Buffer) {
    return body.toString();
  }

  throw new Error(
    'Unsupported body type. Supported body types are: string, number, undefined, null, url.URLSearchParams, fs.ReadStream, FormData'
  );
}

function getRequestCacheKey(req: any) {
  return {
    cache: req.cache,
    credentials: req.credentials,
    destination: req.destination,
    headers: req.headers,
    integrity: req.integrity,
    method: req.method,
    redirect: req.redirect,
    referrer: req.referrer,
    referrerPolicy: req.referrerPolicy,
    url: req.url,
    body: getBodyCacheKeyJson(req.body),
  };
}

function getCacheKey(requestArguments: any[]) {
  const resource = requestArguments[0];
  const init = requestArguments[1] || {};

  const resourceCacheKeyJson =
    resource instanceof Request ? getRequestCacheKey(resource) : { url: resource };

  const initCacheKeyJson = { ...init };

  // @ts-ignore
  resourceCacheKeyJson.body = getBodyCacheKeyJson(resourceCacheKeyJson.body);
  initCacheKeyJson.body = getBodyCacheKeyJson(initCacheKeyJson.body);

  delete initCacheKeyJson.agent;

  return md5(JSON.stringify([resourceCacheKeyJson, initCacheKeyJson, CACHE_VERSION]));
}

export function wrapFetchWithCache(
  fetch: FetchLike,
  cache: FileSystemCache
): (url: RequestInfo, init?: RequestInit | undefined) => Promise<Response> {
  async function getResponse(
    cache: FileSystemCache,
    url: RequestInfo,
    init?: RequestInit | undefined
  ) {
    const cacheKey = getCacheKey([url, init]);
    let cachedValue = await cache.get(cacheKey);

    const ejectSelfFromCache = () => cache.remove(cacheKey);

    if (cachedValue) {
      return new NFCResponse(
        cachedValue.bodyStream,
        cachedValue.metaData,
        ejectSelfFromCache,
        true
      );
    }

    await lock(cacheKey);
    try {
      cachedValue = await cache.get(cacheKey);
      if (cachedValue) {
        return new NFCResponse(
          cachedValue.bodyStream,
          cachedValue.metaData,
          ejectSelfFromCache,
          true
        );
      }

      const fetchResponse = await fetch(url, init);
      const serializedMeta = NFCResponse.serializeMetaFromNodeFetchResponse(fetchResponse);

      const newlyCachedData = await cache.set(
        cacheKey,
        // @ts-expect-error
        fetchResponse.body,
        serializedMeta
      );

      return new NFCResponse(
        newlyCachedData!.bodyStream,
        newlyCachedData!.metaData,
        ejectSelfFromCache,
        false
      );
    } finally {
      unlock(cacheKey);
    }
  }
  return (url: RequestInfo, init?: RequestInit | undefined) => getResponse(cache, url, init);
}