axios-cache-interceptor/src/interceptors/request.ts

import { deferred } from 'fast-defer';
import type { AxiosCacheInstance, CacheAxiosResponse } from '../cache/axios';
import type {
  CachedResponse,
  CachedStorageValue,
  LoadingStorageValue
} from '../storage/types';
import type { RequestInterceptor } from './build';
import {
  ConfigWithCache,
  createValidateStatus,
  isMethodIn,
  setRevalidationHeaders
} from './util';

export function defaultRequestInterceptor(axios: AxiosCacheInstance) {
  const onFulfilled: RequestInterceptor['onFulfilled'] = async (config) => {
    if (config.cache === false) {
      return config;
    }

    // merge defaults with per request configuration
    config.cache = { ...axios.defaults.cache, ...config.cache };

    if (!isMethodIn(config.method, config.cache.methods)) {
      return config;
    }

    const key = axios.generateKey(config);

    // Assumes that the storage handled staled responses
    let cache = await axios.storage.get(key);

    // Not cached, continue the request, and mark it as fetching
    emptyOrStale: if (cache.state === 'empty' || cache.state === 'stale') {
      /**
       * This checks for simultaneous access to a new key. The js event loop jumps on the
       * first await statement, so the second (asynchronous call) request may have already
       * started executing.
       */
      if (axios.waiting[key]) {
        cache = (await axios.storage.get(key)) as
          | CachedStorageValue
          | LoadingStorageValue;
        break emptyOrStale;
      }

      // Create a deferred to resolve other requests for the same key when it's completed
      axios.waiting[key] = deferred();

      /**
       * Add a default reject handler to catch when the request is aborted without others
       * waiting for it.
       */
      axios.waiting[key]?.catch(() => undefined);

      await axios.storage.set(key, {
        state: 'loading',
        data: cache.data
      });

      if (cache.state === 'stale') {
        setRevalidationHeaders(cache, config as ConfigWithCache<unknown>);
      }

      config.validateStatus = createValidateStatus(config.validateStatus);

      return config;
    }

    let cachedResponse: CachedResponse;

    if (cache.state === 'loading') {
      const deferred = axios.waiting[key];

      // Just in case, the deferred doesn't exists.
      /* istanbul ignore if 'really hard to test' */
      if (!deferred) {
        await axios.storage.remove(key);
        return config;
      }

      try {
        cachedResponse = await deferred;
      } catch {
        // The deferred is rejected when the request that we are waiting rejected cache.
        return config;
      }
    } else {
      cachedResponse = cache.data;
    }

    config.adapter = () =>
      /**
       * Even though the response interceptor receives this one from here, it has been
       * configured to ignore cached responses: true
       */
      Promise.resolve<CacheAxiosResponse<unknown, unknown>>({
        config,
        data: cachedResponse.data,
        headers: cachedResponse.headers,
        status: cachedResponse.status,
        statusText: cachedResponse.statusText,
        cached: true,
        id: key
      });

    return config;
  };

  return {
    onFulfilled,
    apply: () => axios.interceptors.request.use(onFulfilled)
  };
}