serwist/src/lib/rangeRequests/createPartialResponse.ts

A Swiss Army knife for service workers.

/*
  Copyright 2018 Google LLC

  Use of this source code is governed by an MIT-style
  license that can be found in the LICENSE file or at
  https://opensource.org/licenses/MIT.
*/

import { assert } from "../../utils/assert.js";
import { logger } from "../../utils/logger.js";
import { SerwistError } from "../../utils/SerwistError.js";
import { calculateEffectiveBoundaries } from "./utils/calculateEffectiveBoundaries.js";
import { parseRangeHeader } from "./utils/parseRangeHeader.js";

/**
 * Given a request and a response, this will return a
 * promise that resolves to a partial response.
 *
 * If the original response already contains partial content (i.e. it has
 * a status of 206), then this assumes it already fulfills the `Range`
 * requirements, and will return it as-is.
 *
 * @param request A request, which should contain a `Range`
 * header.
 * @param originalResponse A response.
 * @returns Either a `206 Partial Content` response, with
 * the response body set to the slice of content specified by the request's
 * `Range` header, or a `416 Range Not Satisfiable` response if the
 * conditions of the `Range` header can't be met.
 */
export const createPartialResponse = async (request: Request, originalResponse: Response): Promise<Response> => {
  try {
    if (process.env.NODE_ENV !== "production") {
      assert!.isInstance(request, Request, {
        moduleName: "@serwist/range-requests",
        funcName: "createPartialResponse",
        paramName: "request",
      });

      assert!.isInstance(originalResponse, Response, {
        moduleName: "@serwist/range-requests",
        funcName: "createPartialResponse",
        paramName: "originalResponse",
      });
    }

    if (originalResponse.status === 206) {
      // If we already have a 206, then just pass it through as-is;
      // see https://github.com/GoogleChrome/workbox/issues/1720
      return originalResponse;
    }

    const rangeHeader = request.headers.get("range");
    if (!rangeHeader) {
      throw new SerwistError("no-range-header");
    }

    const boundaries = parseRangeHeader(rangeHeader);
    const originalBlob = await originalResponse.blob();

    const effectiveBoundaries = calculateEffectiveBoundaries(originalBlob, boundaries.start, boundaries.end);

    const slicedBlob = originalBlob.slice(effectiveBoundaries.start, effectiveBoundaries.end);
    const slicedBlobSize = slicedBlob.size;

    const slicedResponse = new Response(slicedBlob, {
      // Status code 206 is for a Partial Content response.
      // See https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/206
      status: 206,
      statusText: "Partial Content",
      headers: originalResponse.headers,
    });

    slicedResponse.headers.set("Content-Length", String(slicedBlobSize));
    slicedResponse.headers.set("Content-Range", `bytes ${effectiveBoundaries.start}-${effectiveBoundaries.end - 1}/` + `${originalBlob.size}`);

    return slicedResponse;
  } catch (error) {
    if (process.env.NODE_ENV !== "production") {
      logger.warn("Unable to construct a partial response; returning a " + "416 Range Not Satisfiable response instead.");
      logger.groupCollapsed("View details here.");
      logger.log(error);
      logger.log(request);
      logger.log(originalResponse);
      logger.groupEnd();
    }

    return new Response("", {
      status: 416,
      statusText: "Range Not Satisfiable",
    });
  }
};