test-utils/mock-response.ts

/**
 * @license
 * Copyright 2024 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import * as fs from "fs";
import { join } from "path";

const mockResponseDir = join(__dirname, "mock-responses");

/**
 * Mock native Response.body
 * Streams contents of json file in 20 character chunks
 */
export function getChunkedStream(
  input: string,
  chunkLength = 20,
): ReadableStream<Uint8Array> {
  const encoder = new TextEncoder();
  let currentChunkStart = 0;

  const stream = new ReadableStream<Uint8Array>({
    start(controller) {
      while (currentChunkStart < input.length) {
        const substring = input.slice(
          currentChunkStart,
          currentChunkStart + chunkLength,
        );
        currentChunkStart += chunkLength;
        const chunk = encoder.encode(substring);
        controller.enqueue(chunk);
      }
      controller.close();
    },
  });

  return stream;
}

/**
 * Returns a stream which would throw the given error.
 */
export function getErrorStream(err: Error): ReadableStream<Uint8Array> {
  const stream = new ReadableStream<Uint8Array>({
    start(controller) {
      controller.error(err);
    },
  });
  return stream;
}

export function getMockResponseStreaming(
  filename: string,
  chunkLength: number = 20,
): Partial<Response> {
  const fullText = fs.readFileSync(join(mockResponseDir, filename), "utf-8");

  return {
    body: getChunkedStream(fullText, chunkLength),
  };
}

export function getMockResponse(filename: string): Partial<Response> {
  const fullText = fs.readFileSync(join(mockResponseDir, filename), "utf-8");
  return {
    ok: true,
    json: () => Promise.resolve(JSON.parse(fullText)),
  };
}