5 files changed, 275 insertions, 0 deletions
diff --git a/std/util/async.ts b/std/util/async.ts
new file mode 100644
index 000000000..6e2db69dc
--- /dev/null
+++ b/std/util/async.ts
@@ -0,0 +1,117 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+// TODO(ry) It'd be better to make Deferred a class that inherits from
+// Promise, rather than an interface. This is possible in ES2016, however
+// typescript produces broken code when targeting ES5 code.
+// See https://github.com/Microsoft/TypeScript/issues/15202
+// At the time of writing, the github issue is closed but the problem remains.
+export interface Deferred<T> extends Promise<T> {
+  resolve: (value?: T | PromiseLike<T>) => void;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  reject: (reason?: any) => void;
+}
+
+/** Creates a Promise with the `reject` and `resolve` functions
+ * placed as methods on the promise object itself. It allows you to do:
+ *
+ *     const p = deferred<number>();
+ *     // ...
+ *     p.resolve(42);
+ */
+export function deferred<T>(): Deferred<T> {
+  let methods;
+  const promise = new Promise<T>((resolve, reject): void => {
+    methods = { resolve, reject };
+  });
+  return Object.assign(promise, methods)! as Deferred<T>;
+}
+
+interface TaggedYieldedValue<T> {
+  iterator: AsyncIterableIterator<T>;
+  value: T;
+}
+
+/** The MuxAsyncIterator class multiplexes multiple async iterators into a
+ * single stream. It currently makes a few assumptions:
+ * - The iterators do not throw.
+ * - The final result (the value returned and not yielded from the iterator)
+ *   does not matter; if there is any, it is discarded.
+ */
+export class MuxAsyncIterator<T> implements AsyncIterable<T> {
+  private iteratorCount = 0;
+  private yields: Array<TaggedYieldedValue<T>> = [];
+  private signal: Deferred<void> = deferred();
+
+  add(iterator: AsyncIterableIterator<T>): void {
+    ++this.iteratorCount;
+    this.callIteratorNext(iterator);
+  }
+
+  private async callIteratorNext(
+    iterator: AsyncIterableIterator<T>
+  ): Promise<void> {
+    const { value, done } = await iterator.next();
+    if (done) {
+      --this.iteratorCount;
+    } else {
+      this.yields.push({ iterator, value });
+    }
+    this.signal.resolve();
+  }
+
+  async *iterate(): AsyncIterableIterator<T> {
+    while (this.iteratorCount > 0) {
+      // Sleep until any of the wrapped iterators yields.
+      await this.signal;
+
+      // Note that while we're looping over `yields`, new items may be added.
+      for (let i = 0; i < this.yields.length; i++) {
+        const { iterator, value } = this.yields[i];
+        yield value;
+        this.callIteratorNext(iterator);
+      }
+
+      // Clear the `yields` list and reset the `signal` promise.
+      this.yields.length = 0;
+      this.signal = deferred();
+    }
+  }
+
+  [Symbol.asyncIterator](): AsyncIterableIterator<T> {
+    return this.iterate();
+  }
+}
+
+/** Collects all Uint8Arrays from an AsyncIterable and retuns a single
+ * Uint8Array with the concatenated contents of all the collected arrays.
+ */
+export async function collectUint8Arrays(
+  it: AsyncIterable<Uint8Array>
+): Promise<Uint8Array> {
+  const chunks = [];
+  let length = 0;
+  for await (const chunk of it) {
+    chunks.push(chunk);
+    length += chunk.length;
+  }
+  if (chunks.length === 1) {
+    // No need to copy.
+    return chunks[0];
+  }
+  const collected = new Uint8Array(length);
+  let offset = 0;
+  for (const chunk of chunks) {
+    collected.set(chunk, offset);
+    offset += chunk.length;
+  }
+  return collected;
+}
+
+// Delays the given milliseconds and resolves.
+export function delay(ms: number): Promise<void> {
+  return new Promise((res): number =>
+    setTimeout((): void => {
+      res();
+    }, ms)
+  );
+}
diff --git a/std/util/async_test.ts b/std/util/async_test.ts
new file mode 100644
index 000000000..adaac1e22
--- /dev/null
+++ b/std/util/async_test.ts
@@ -0,0 +1,73 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { test, runIfMain } from "../testing/mod.ts";
+import { assert, assertEquals, assertStrictEq } from "../testing/asserts.ts";
+import { collectUint8Arrays, deferred, MuxAsyncIterator } from "./async.ts";
+
+test(async function asyncDeferred(): Promise<void> {
+  const d = deferred<number>();
+  d.resolve(12);
+});
+
+async function* gen123(): AsyncIterableIterator<number> {
+  yield 1;
+  yield 2;
+  yield 3;
+}
+
+async function* gen456(): AsyncIterableIterator<number> {
+  yield 4;
+  yield 5;
+  yield 6;
+}
+
+test(async function asyncMuxAsyncIterator(): Promise<void> {
+  const mux = new MuxAsyncIterator<number>();
+  mux.add(gen123());
+  mux.add(gen456());
+  const results = new Set();
+  for await (const value of mux) {
+    results.add(value);
+  }
+  assertEquals(results.size, 6);
+});
+
+test(async function collectUint8Arrays0(): Promise<void> {
+  async function* gen(): AsyncIterableIterator<Uint8Array> {}
+  const result = await collectUint8Arrays(gen());
+  assert(result instanceof Uint8Array);
+  assertEquals(result.length, 0);
+});
+
+test(async function collectUint8Arrays0(): Promise<void> {
+  async function* gen(): AsyncIterableIterator<Uint8Array> {}
+  const result = await collectUint8Arrays(gen());
+  assert(result instanceof Uint8Array);
+  assertStrictEq(result.length, 0);
+});
+
+test(async function collectUint8Arrays1(): Promise<void> {
+  const buf = new Uint8Array([1, 2, 3]);
+  async function* gen(): AsyncIterableIterator<Uint8Array> {
+    yield buf;
+  }
+  const result = await collectUint8Arrays(gen());
+  assertStrictEq(result, buf);
+  assertStrictEq(result.length, 3);
+});
+
+test(async function collectUint8Arrays4(): Promise<void> {
+  async function* gen(): AsyncIterableIterator<Uint8Array> {
+    yield new Uint8Array([1, 2, 3]);
+    yield new Uint8Array([]);
+    yield new Uint8Array([4, 5]);
+    yield new Uint8Array([6]);
+  }
+  const result = await collectUint8Arrays(gen());
+  assert(result instanceof Uint8Array);
+  assertStrictEq(result.length, 6);
+  for (let i = 0; i < 6; i++) {
+    assertStrictEq(result[i], i + 1);
+  }
+});
+
+runIfMain(import.meta);
diff --git a/std/util/deep_assign.ts b/std/util/deep_assign.ts
new file mode 100644
index 000000000..b1c9f9ac9
--- /dev/null
+++ b/std/util/deep_assign.ts
@@ -0,0 +1,31 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+export function deepAssign(
+  target: Record<string, unknown>,
+  ...sources: object[]
+): object | undefined {
+  for (let i = 0; i < sources.length; i++) {
+    const source = sources[i];
+    if (!source || typeof source !== `object`) {
+      return;
+    }
+    Object.entries(source).forEach(([key, value]: [string, unknown]): void => {
+      if (value instanceof Date) {
+        target[key] = new Date(value);
+        return;
+      }
+      if (!value || typeof value !== `object`) {
+        target[key] = value;
+        return;
+      }
+      if (Array.isArray(value)) {
+        target[key] = [];
+      }
+      // value is an Object
+      if (typeof target[key] !== `object` || !target[key]) {
+        target[key] = {};
+      }
+      deepAssign(target[key] as Record<string, unknown>, value!);
+    });
+  }
+  return target;
+}
diff --git a/std/util/deep_assign_test.ts b/std/util/deep_assign_test.ts
new file mode 100644
index 000000000..c197344f7
--- /dev/null
+++ b/std/util/deep_assign_test.ts
@@ -0,0 +1,24 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { test } from "../testing/mod.ts";
+import { assertEquals, assert } from "../testing/asserts.ts";
+import { deepAssign } from "./deep_assign.ts";
+
+test(function deepAssignTest(): void {
+  const date = new Date("1979-05-27T07:32:00Z");
+  const reg = RegExp(/DENOWOWO/);
+  const obj1 = { deno: { bar: { deno: ["is", "not", "node"] } } };
+  const obj2 = { foo: { deno: date } };
+  const obj3 = { foo: { bar: "deno" }, reg: reg };
+  const actual = deepAssign(obj1, obj2, obj3);
+  const expected = {
+    foo: {
+      deno: new Date("1979-05-27T07:32:00Z"),
+      bar: "deno"
+    },
+    deno: { bar: { deno: ["is", "not", "node"] } },
+    reg: RegExp(/DENOWOWO/)
+  };
+  assert(date !== expected.foo.deno);
+  assert(reg !== expected.reg);
+  assertEquals(actual, expected);
+});
diff --git a/std/util/has_own_property.ts b/std/util/has_own_property.ts
new file mode 100644
index 000000000..707d951d3
--- /dev/null
+++ b/std/util/has_own_property.ts
@@ -0,0 +1,30 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+/**
+ * Determines whether an object has a property with the specified name.
+ * Avoid calling prototype builtin `hasOwnProperty` for two reasons:
+ *
+ * 1. `hasOwnProperty` is defined on the object as something else:
+ *
+ *      const options = {
+ *        ending: 'utf8',
+ *        hasOwnProperty: 'foo'
+ *      };
+ *      options.hasOwnProperty('ending') // throws a TypeError
+ *
+ * 2. The object doesn't inherit from `Object.prototype`:
+ *
+ *       const options = Object.create(null);
+ *       options.ending = 'utf8';
+ *       options.hasOwnProperty('ending'); // throws a TypeError
+ *
+ * @param obj A Object.
+ * @param v A property name.
+ * @see https://eslint.org/docs/rules/no-prototype-builtins
+ */
+export function hasOwnProperty<T>(obj: T, v: PropertyKey): boolean {
+  if (obj == null) {
+    return false;
+  }
+  return Object.prototype.hasOwnProperty.call(obj, v);
+}