Add buffer size argument to copy (#4907)

cli/js/tests/io_test.ts

@@ -0,0 +1,57 @@
+// 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 | Deno.EOF> => {
+    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);
+});