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

import type { AxiosRequestConfig, Method } from 'axios';
import { deferred } from 'fast-defer';
import type { CacheProperties } from '..';
import type {
  AxiosCacheInstance,
  CacheAxiosResponse,
  CacheRequestConfig
} from '../cache/axios';
import type {
  CachedResponse,
  CachedStorageValue,
  LoadingStorageValue,
  StaleStorageValue
} from '../storage/types';
import { Header } from '../util/headers';
import type { AxiosInterceptor } from './types';

export class CacheRequestInterceptor<D>
  implements AxiosInterceptor<CacheRequestConfig<D>>
{
  constructor(readonly axios: AxiosCacheInstance) {}

  readonly use = (): void => {
    this.axios.interceptors.request.use(this.onFulfilled);
  };

  readonly onFulfilled = async (
    config: CacheRequestConfig<D>
  ): Promise<CacheRequestConfig<D>> => {
    if (config.cache === false) {
      return config;
    }

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

    if (
      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
      !CacheRequestInterceptor.isMethodAllowed(config.method!, config.cache)
    ) {
      return config;
    }

    const key = this.axios.generateKey(config);

    // Assumes that the storage handled staled responses
    let cache = await this.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 (this.axios.waiting[key]) {
        cache = (await this.axios.storage.get(key)) as
          | CachedStorageValue
          | LoadingStorageValue;
        break emptyOrStale;
      }

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

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

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

      if (cache.state === 'stale') {
        //@ts-expect-error type infer couldn't resolve this
        CacheRequestInterceptor.setRevalidationHeaders(cache, config);
      }

      config.validateStatus = CacheRequestInterceptor.createValidateStatus(
        config.validateStatus
      );

      return config;
    }

    let cachedResponse: CachedResponse;

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

      // Just in case, the deferred doesn't exists.
      /* istanbul ignore if 'really hard to test' */
      if (!deferred) {
        await this.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<any, D>>({
        config: config,
        data: cachedResponse.data,
        headers: cachedResponse.headers,
        status: cachedResponse.status,
        statusText: cachedResponse.statusText,
        cached: true,
        id: key
      });

    return config;
  };

  static readonly isMethodAllowed = (
    method: Method,
    properties: Partial<CacheProperties>
  ): boolean => {
    const requestMethod = method.toLowerCase();

    for (const method of properties.methods || []) {
      if (method.toLowerCase() === requestMethod) {
        return true;
      }
    }

    return false;
  };

  static readonly setRevalidationHeaders = <D>(
    cache: StaleStorageValue,
    config: CacheRequestConfig<D> & { cache: Partial<CacheProperties> }
  ): void => {
    config.headers ||= {};

    const { etag, modifiedSince } = config.cache;

    if (etag) {
      const etagValue = etag === true ? cache.data?.headers[Header.ETag] : etag;
      if (etagValue) {
        config.headers[Header.IfNoneMatch] = etagValue;
      }
    }

    if (modifiedSince) {
      config.headers[Header.IfModifiedSince] =
        modifiedSince === true
          ? // If last-modified is not present, use the createdAt timestamp
            cache.data.headers[Header.LastModified] ||
            new Date(cache.createdAt).toUTCString()
          : modifiedSince.toUTCString();
    }
  };

  /**
   * Creates a new validateStatus function that will use the one already used and also
   * accept status code 304.
   */
  static readonly createValidateStatus = (
    oldValidate?: AxiosRequestConfig['validateStatus']
  ) => {
    return (status: number): boolean => {
      return oldValidate
        ? oldValidate(status) || status === 304
        : (status >= 200 && status < 300) || status === 304;
    };
  };
}