text: // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
  import { unitTest, assertEquals } from "./test_util.ts";
  
  const DEFAULT_BUF_SIZE = 32 * 1024;
  
  type Spy = { calls: number };
  
  function repeat(c: string, bytes: number): Uint8Array {
    assertEquals(c.length, 1);
    const ui8 = new Uint8Array(bytes);
    ui8.fill(c.charCodeAt(0));
    return ui8;
  }
  
  function spyRead(obj: Deno.Buffer): Spy {
    const spy: Spy = {
      calls: 0,
    };
  
    const orig = obj.read.bind(obj);
  
    obj.read = (p: Uint8Array): Promise<number | null> => {
      spy.calls++;
      return orig(p);
    };
  
    return spy;
  }
  
  unitTest(async function copyWithDefaultBufferSize() {
    const xBytes = repeat("b", DEFAULT_BUF_SIZE);
    const reader = new Deno.Buffer(xBytes.buffer as ArrayBuffer);
    const write = new Deno.Buffer();
  
    const readSpy = spyRead(reader);
  
    const n = await Deno.copy(reader, write);
  
    assertEquals(n, xBytes.length);
    assertEquals(write.length, xBytes.length);
    assertEquals(readSpy.calls, 2); // read with DEFAULT_BUF_SIZE bytes + read with 0 bytes
  });
  
  unitTest(async function copyWithCustomBufferSize() {
    const bufSize = 1024;
    const xBytes = repeat("b", DEFAULT_BUF_SIZE);
    const reader = new Deno.Buffer(xBytes.buffer as ArrayBuffer);
    const write = new Deno.Buffer();
  
    const readSpy = spyRead(reader);
  
    const n = await Deno.copy(reader, write, { bufSize });
  
    assertEquals(n, xBytes.length);
    assertEquals(write.length, xBytes.length);
    assertEquals(readSpy.calls, DEFAULT_BUF_SIZE / bufSize + 1);
  });
  
  unitTest({ perms: { write: true } }, async function copyBufferToFile() {
    const filePath = "test-file.txt";
    // bigger than max File possible buffer 16kb
    const bufSize = 32 * 1024;
    const xBytes = repeat("b", bufSize);
    const reader = new Deno.Buffer(xBytes.buffer as ArrayBuffer);
    const write = await Deno.open(filePath, { write: true, create: true });
  
    const n = await Deno.copy(reader, write, { bufSize });
  
    assertEquals(n, xBytes.length);
  
    write.close();
    await Deno.remove(filePath);
  });
  