src/utils/fetch-loader.ts

import {
  LoaderCallbacks,
  LoaderContext,
  Loader,
  LoaderStats,
  LoaderConfiguration,
  LoaderOnProgress,
} from '../types/loader';
import { LoadStats } from '../loader/load-stats';
import ChunkCache from '../demux/chunk-cache';

export function fetchSupported() {
  if (
    // @ts-ignore
    self.fetch &&
    self.AbortController &&
    self.ReadableStream &&
    self.Request
  ) {
    try {
      new self.ReadableStream({}); // eslint-disable-line no-new
      return true;
    } catch (e) {
      /* noop */
    }
  }
  return false;
}

class FetchLoader implements Loader<LoaderContext> {
  private fetchSetup: Function;
  private requestTimeout?: number;
  private request!: Request;
  private response!: Response;
  private controller: AbortController;
  public context!: LoaderContext;
  private config: LoaderConfiguration | null = null;
  private callbacks: LoaderCallbacks<LoaderContext> | null = null;
  public stats: LoaderStats;
  private loader: Response | null = null;

  constructor(config /* HlsConfig */) {
    this.fetchSetup = config.fetchSetup || getRequest;
    this.controller = new self.AbortController();
    this.stats = new LoadStats();
  }

  destroy(): void {
    this.loader = this.callbacks = null;
    this.abortInternal();
  }

  abortInternal(): void {
    const response = this.response;
    if (!response || !response.ok) {
      this.stats.aborted = true;
      this.controller.abort();
    }
  }

  abort(): void {
    this.abortInternal();
    if (this.callbacks?.onAbort) {
      this.callbacks.onAbort(this.stats, this.context, this.response);
    }
  }

  load(
    context: LoaderContext,
    config: LoaderConfiguration,
    callbacks: LoaderCallbacks<LoaderContext>
  ): void {
    const stats = this.stats;
    if (stats.loading.start) {
      throw new Error('Loader can only be used once.');
    }
    stats.loading.start = self.performance.now();

    const initParams = getRequestParameters(context, this.controller.signal);
    const onProgress: LoaderOnProgress<LoaderContext> | undefined =
      callbacks.onProgress;
    const isArrayBuffer = context.responseType === 'arraybuffer';
    const LENGTH = isArrayBuffer ? 'byteLength' : 'length';

    this.context = context;
    this.config = config;
    this.callbacks = callbacks;
    this.request = this.fetchSetup(context, initParams);
    self.clearTimeout(this.requestTimeout);
    this.requestTimeout = self.setTimeout(() => {
      this.abortInternal();
      callbacks.onTimeout(stats, context, this.response);
    }, config.timeout);

    self
      .fetch(this.request)
      .then((response: Response): Promise<string | ArrayBuffer> => {
        this.response = this.loader = response;

        if (!response.ok) {
          const { status, statusText } = response;
          throw new FetchError(
            statusText || 'fetch, bad network response',
            status,
            response
          );
        }
        stats.loading.first = Math.max(
          self.performance.now(),
          stats.loading.start
        );
        stats.total = parseInt(response.headers.get('Content-Length') || '0');

        if (onProgress && Number.isFinite(config.highWaterMark)) {
          return this.loadProgressively(
            response,
            stats,
            context,
            config.highWaterMark,
            onProgress
          );
        }

        if (isArrayBuffer) {
          return response.arrayBuffer();
        }
        return response.text();
      })
      .then((responseData: string | ArrayBuffer) => {
        const { response } = this;
        self.clearTimeout(this.requestTimeout);
        stats.loading.end = Math.max(
          self.performance.now(),
          stats.loading.first
        );
        const total = responseData[LENGTH];
        if (total) {
          stats.loaded = stats.total = total;
        }

        const loaderResponse = {
          url: response.url,
          data: responseData,
        };

        if (onProgress && !Number.isFinite(config.highWaterMark)) {
          onProgress(stats, context, responseData, response);
        }

        callbacks.onSuccess(loaderResponse, stats, context, response);
      })
      .catch((error) => {
        self.clearTimeout(this.requestTimeout);
        if (stats.aborted) {
          return;
        }
        // CORS errors result in an undefined code. Set it to 0 here to align with XHR's behavior
        // when destroying, 'error' itself can be undefined
        const code: number = !error ? 0 : error.code || 0;
        const text: string = !error ? null : error.message;
        callbacks.onError(
          { code, text },
          context,
          error ? error.details : null
        );
      });
  }

  getCacheAge(): number | null {
    let result: number | null = null;
    if (this.response) {
      const ageHeader = this.response.headers.get('age');
      result = ageHeader ? parseFloat(ageHeader) : null;
    }
    return result;
  }

  private loadProgressively(
    response: Response,
    stats: LoaderStats,
    context: LoaderContext,
    highWaterMark: number = 0,
    onProgress: LoaderOnProgress<LoaderContext>
  ): Promise<ArrayBuffer> {
    const chunkCache = new ChunkCache();
    const reader = (response.body as ReadableStream).getReader();

    const pump = (): Promise<ArrayBuffer> => {
      return reader
        .read()
        .then((data) => {
          if (data.done) {
            if (chunkCache.dataLength) {
              onProgress(stats, context, chunkCache.flush(), response);
            }

            return Promise.resolve(new ArrayBuffer(0));
          }
          const chunk: Uint8Array = data.value;
          const len = chunk.length;
          stats.loaded += len;
          if (len < highWaterMark || chunkCache.dataLength) {
            // The current chunk is too small to to be emitted or the cache already has data
            // Push it to the cache
            chunkCache.push(chunk);
            if (chunkCache.dataLength >= highWaterMark) {
              // flush in order to join the typed arrays
              onProgress(stats, context, chunkCache.flush(), response);
            }
          } else {
            // If there's nothing cached already, and the chache is large enough
            // just emit the progress event
            onProgress(stats, context, chunk, response);
          }
          return pump();
        })
        .catch(() => {
          /* aborted */
          return Promise.reject();
        });
    };

    return pump();
  }
}

function getRequestParameters(context: LoaderContext, signal): any {
  const initParams: any = {
    method: 'GET',
    mode: 'cors',
    credentials: 'same-origin',
    signal,
    headers: new self.Headers(Object.assign({}, context.headers)),
  };

  if (context.rangeEnd) {
    initParams.headers.set(
      'Range',
      'bytes=' + context.rangeStart + '-' + String(context.rangeEnd - 1)
    );
  }

  return initParams;
}

function getRequest(context: LoaderContext, initParams: any): Request {
  return new self.Request(context.url, initParams);
}

class FetchError extends Error {
  public code: number;
  public details: any;
  constructor(message: string, code: number, details: any) {
    super(message);
    this.code = code;
    this.details = details;
  }
}

export default FetchLoader;