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asyncIterator.spec.ts
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asyncIterator.spec.ts
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/**
* The following tests are copied from
* https://github.com/web-platform-tests/wpt/blob/309231a7f3e900d04914bc4963b016efd9989a00/streams/readable-streams/async-iterator.any.js
* and rewritten for Vitest
*/
import { assert, describe, test } from "vitest";
import { AsyncIterablePrototype } from "../src/core/asyncIterablePrototype.js";
import { flushAsyncEvents } from "./utils.js";
// remove possibly already implemented polyfills or apis
delete (ReadableStream.prototype as Partial<ReadableStream>).values;
delete (ReadableStream.prototype as Partial<ReadableStream>)[
Symbol.asyncIterator
];
// import this polyfill
await import("../src/polyfill/asyncIterator.js");
const error1 = new Error("error1");
test("Async iterator instances should have the correct list of properties", async () => {
const s = new ReadableStream();
const it = s.values();
const proto = Object.getPrototypeOf(it);
assert.strictEqual(
Object.getPrototypeOf(proto),
AsyncIterablePrototype,
"prototype should extend AsyncIterablePrototype",
);
const methods = ["next", "return"].sort();
assert.deepEqual(
Object.getOwnPropertyNames(proto).sort(),
methods,
"should have all the correct methods",
);
for (const m of methods) {
const propDesc = Object.getOwnPropertyDescriptor(
proto,
m,
) as PropertyDescriptor;
assert.isTrue(propDesc.enumerable, "method should be enumerable");
assert.isTrue(propDesc.configurable, "method should be configurable");
assert.isTrue(propDesc.writable, "method should be writable");
assert.strictEqual(typeof it[m], "function", "method should be a function");
assert.strictEqual(it[m].name, m, "method should have the correct name");
}
assert.strictEqual(it.next.length, 0, "next should have no parameters");
assert.strictEqual(it.return?.length, 1, "return should have 1 parameter");
assert.strictEqual(typeof it.throw, "undefined", "throw should not exist");
});
test("Async-iterating a push source", async () => {
const s = new ReadableStream({
start(c) {
c.enqueue(1);
c.enqueue(2);
c.enqueue(3);
c.close();
},
});
const chunks: unknown[] = [];
for await (const chunk of s) {
chunks.push(chunk);
}
assert.deepEqual(chunks, [1, 2, 3]);
});
test("Async-iterating a pull source", async () => {
let i = 1;
const s = new ReadableStream({
pull(c) {
c.enqueue(i);
if (i >= 3) {
c.close();
}
i += 1;
},
});
const chunks: unknown[] = [];
for await (const chunk of s) {
chunks.push(chunk);
}
assert.deepEqual(chunks, [1, 2, 3]);
});
test("Async-iterating a push source with undefined values", async () => {
const s = new ReadableStream({
start(c) {
c.enqueue(undefined);
c.enqueue(undefined);
c.enqueue(undefined);
c.close();
},
});
const chunks: unknown[] = [];
for await (const chunk of s) {
chunks.push(chunk);
}
assert.deepEqual(chunks, [undefined, undefined, undefined]);
});
test("Async-iterating a pull source with undefined values", async () => {
let i = 1;
const s = new ReadableStream({
pull(c) {
c.enqueue(undefined);
if (i >= 3) {
c.close();
}
i += 1;
},
});
const chunks: unknown[] = [];
for await (const chunk of s) {
chunks.push(chunk);
}
assert.deepEqual(chunks, [undefined, undefined, undefined]);
});
test("Async-iterating a pull source manually", async () => {
let i = 1;
const s = recordingReadableStream(
{
pull(c) {
c.enqueue(i);
if (i >= 3) {
c.close();
}
i += 1;
},
},
new CountQueuingStrategy({ highWaterMark: 0 }),
);
const it = s.values();
assert.deepEqual(s.events, []);
const read1 = await it.next();
assertIterResult(read1, 1, false);
assert.deepEqual(s.events, ["pull"]);
const read2 = await it.next();
assertIterResult(read2, 2, false);
assert.deepEqual(s.events, ["pull", "pull"]);
const read3 = await it.next();
assertIterResult(read3, 3, false);
assert.deepEqual(s.events, ["pull", "pull", "pull"]);
const read4 = await it.next();
assertIterResult(read4, undefined, true);
assert.deepEqual(s.events, ["pull", "pull", "pull"]);
});
test("Async-iterating an errored stream throws", async () => {
const s = new ReadableStream({
start(c) {
c.error("e");
},
});
let reached = false;
try {
for await (const _ of s) {
/* empty */
}
reached = true;
} catch (e) {
assert.isFalse(reached);
assert.strictEqual(e, "e");
}
});
test("Async-iterating a closed stream never executes the loop body, but works fine", async () => {
const s = new ReadableStream({
start(c) {
c.close();
},
});
let reached = false;
for await (const _ of s) {
reached = true;
}
assert.isFalse(reached);
});
test("Async-iterating an empty but not closed/errored stream never executes the loop body and stalls the async function", async () => {
const s = new ReadableStream();
let reached1 = false;
let reached2 = false;
const loop = async () => {
for await (const _ of s) {
reached1 = true;
}
reached2 = true;
};
await Promise.race([loop(), flushAsyncEvents()]);
assert.isFalse(reached1);
assert.isFalse(reached2);
});
test("Async-iterating a partially consumed stream", async () => {
const s = new ReadableStream({
start(c) {
c.enqueue(1);
c.enqueue(2);
c.enqueue(3);
c.close();
},
});
const reader = s.getReader();
const readResult = (await reader.read()) as IteratorResult<unknown, unknown>;
assertIterResult(readResult, 1, false);
reader.releaseLock();
const chunks: unknown[] = [];
for await (const chunk of s) {
chunks.push(chunk);
}
assert.deepEqual(chunks, [2, 3]);
});
describe("Cancellation behavior", () => {
describe("Cancellation behavior inside loop body", () => {
for (const type of ["throw", "break", "return"]) {
for (const preventCancel of [false, true]) {
test(`Cancellation behavior when ${type}ing inside loop body; preventCancel = ${preventCancel}`, async () => {
const s = recordingReadableStream({
start(c) {
c.enqueue(0);
},
});
// use a separate function for the loop body so return does not stop the test
const loop = async () => {
for await (const _ of s.values({ preventCancel })) {
if (type === "throw") {
throw new Error();
}
if (type === "break") {
break;
}
if (type === "return") {
return;
}
}
};
try {
await loop();
} catch (e) {
/* empty */
}
if (preventCancel) {
assert.deepEqual(
s.events,
["pull"],
"cancel() should not be called",
);
} else {
assert.deepEqual(
s.events,
["pull", "cancel", undefined],
"cancel() should be called",
);
}
});
}
}
});
describe("Cancellation behavior when manually calling return()", () => {
for (const preventCancel of [false, true]) {
test(`Cancellation behavior when manually calling return(); preventCancel = ${preventCancel}`, async () => {
const s = recordingReadableStream({
start(c) {
c.enqueue(0);
},
});
const it = s.values({ preventCancel });
await it.return?.();
if (preventCancel) {
assert.deepEqual(s.events, [], "cancel() should not be called");
} else {
assert.deepEqual(
s.events,
["cancel", undefined],
"cancel() should be called",
);
}
});
}
});
});
test("next() rejects if the stream errors", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
if (timesPulled === 0) {
c.enqueue(0);
++timesPulled;
} else {
c.error(error1);
}
},
});
const it = s[Symbol.asyncIterator]();
const iterResult1 = await it.next();
assertIterResult(iterResult1, 0, false, "1st next()");
let reached = false;
try {
await it.next();
reached = true;
} catch (e) {
assert.strictEqual(error1, e, "2nd next()");
}
assert.isFalse(reached);
});
test("return() does not rejects if the stream has not errored yet", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
if (timesPulled === 0) {
c.enqueue(0);
++timesPulled;
} else {
c.error(error1);
}
},
});
const it = s[Symbol.asyncIterator]();
const iterResult = (await it.return?.("return value")) as IteratorResult<
unknown,
unknown
>;
assertIterResult(iterResult, "return value", true);
});
test("return() rejects if the stream has errored", async () => {
const s = new ReadableStream({
pull(c) {
// Do not error in start() because doing so would prevent acquiring a reader/async iterator.
c.error(error1);
},
});
const it = s[Symbol.asyncIterator]();
await flushAsyncEvents();
let reached = false;
try {
await it.return?.("return value");
reached = true;
} catch (e) {
assert.strictEqual(e, error1);
}
assert.isFalse(reached);
});
test("next() that succeeds; next() that reports an error; next()", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
if (timesPulled === 0) {
c.enqueue(0);
++timesPulled;
} else {
c.error(error1);
}
},
});
const it = s[Symbol.asyncIterator]();
const iterResult1 = await it.next();
assertIterResult(iterResult1, 0, false, "1st next()");
let reached = false;
try {
await it.next();
reached = true;
} catch (e) {
assert.strictEqual(e, error1, "2nd next()");
}
assert.isFalse(reached);
const iterResult3 = await it.next();
assertIterResult(iterResult3, undefined, true, "3rd next()");
});
test("next() that succeeds; next() that reports an error; next() [no awaiting]", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
if (timesPulled === 0) {
c.enqueue(0);
++timesPulled;
} else {
c.error(error1);
}
},
});
const it = s[Symbol.asyncIterator]();
const iterResults = await Promise.allSettled([
it.next(),
it.next(),
it.next(),
]);
assert.strictEqual(
iterResults[0].status,
"fulfilled",
"1st next() promise status",
);
assertIterResult(
(iterResults[0] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
0,
false,
"1st next()",
);
assert.strictEqual(
iterResults[1].status,
"rejected",
"2nd next() promise status",
);
assert.strictEqual(
(iterResults[1] as PromiseRejectedResult).reason,
error1,
"2nd next() rejection reason",
);
assert.strictEqual(
iterResults[2].status,
"fulfilled",
"3rd next() promise status",
);
assertIterResult(
(iterResults[2] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
undefined,
true,
"3rd next()",
);
});
test("next() that succeeds; next() that reports an error; return()", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
if (timesPulled === 0) {
c.enqueue(0);
++timesPulled;
} else {
c.error(error1);
}
},
});
const it = s[Symbol.asyncIterator]();
const iterResult1 = await it.next();
assertIterResult(iterResult1, 0, false, "1st next()");
let reached = false;
try {
await it.next();
reached = true;
} catch (e) {
assert.strictEqual(e, error1, "2nd next()");
}
assert.isFalse(reached);
const iterResult3 = (await it.return?.("return value")) as IteratorResult<
unknown,
unknown
>;
assertIterResult(iterResult3, "return value", true, "return()");
});
test("next() that succeeds; next() that reports an error; return() [no awaiting]", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
if (timesPulled === 0) {
c.enqueue(0);
++timesPulled;
} else {
c.error(error1);
}
},
});
const it = s[Symbol.asyncIterator]();
const iterResults = await Promise.allSettled([
it.next(),
it.next(),
it.return?.("return value"),
]);
assert.strictEqual(
iterResults[0].status,
"fulfilled",
"1st next() promise status",
);
assertIterResult(
(iterResults[0] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
0,
false,
"1st next()",
);
assert.strictEqual(
iterResults[1].status,
"rejected",
"2nd next() promise status",
);
assert.strictEqual(
(iterResults[1] as PromiseRejectedResult).reason,
error1,
"2nd next() rejection reason",
);
assert.strictEqual(
iterResults[2].status,
"fulfilled",
"return() promise status",
);
assertIterResult(
(iterResults[2] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
"return value",
true,
"return()",
);
});
test("next() that succeeds; return()", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
c.enqueue(timesPulled);
++timesPulled;
},
});
const it = s[Symbol.asyncIterator]();
const iterResult1 = await it.next();
assertIterResult(iterResult1, 0, false, "next()");
const iterResult2 = (await it.return?.("return value")) as IteratorResult<
unknown,
unknown
>;
assertIterResult(iterResult2, "return value", true, "return()");
assert.strictEqual(timesPulled, 2);
});
test("next() that succeeds; return() [no awaiting]", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
c.enqueue(timesPulled);
++timesPulled;
},
});
const it = s[Symbol.asyncIterator]();
const iterResults = await Promise.allSettled([
it.next(),
it.return?.("return value"),
]);
assert.strictEqual(
iterResults[0].status,
"fulfilled",
"next() promise status",
);
assertIterResult(
(iterResults[0] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
0,
false,
"next()",
);
assert.strictEqual(
iterResults[1].status,
"fulfilled",
"return() promise status",
);
assertIterResult(
(iterResults[1] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
"return value",
true,
"return()",
);
assert.strictEqual(timesPulled, 2);
});
test("return(); next()", async () => {
const rs = new ReadableStream();
const it = rs.values();
const iterResult1 = (await it.return?.("return value")) as IteratorResult<
unknown,
unknown
>;
assertIterResult(iterResult1, "return value", true, "return()");
const iterResult2 = await it.next();
assertIterResult(iterResult2, undefined, true, "next()");
});
test("return(); next() [no awaiting]", async () => {
const rs = new ReadableStream();
const it = rs.values();
const iterResults = await Promise.allSettled([
it.return?.("return value"),
it.next(),
]);
assert.strictEqual(
iterResults[0].status,
"fulfilled",
"return() promise status",
);
assertIterResult(
(iterResults[0] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
"return value",
true,
"return()",
);
assert.strictEqual(
iterResults[1].status,
"fulfilled",
"next() promise status",
);
assertIterResult(
(iterResults[1] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
undefined,
true,
"next()",
);
});
test("return(); return()", async () => {
const rs = new ReadableStream();
const it = rs.values();
const iterResult1 = (await it.return?.("return value 1")) as IteratorResult<
unknown,
unknown
>;
assertIterResult(iterResult1, "return value 1", true, "1st return()");
const iterResult2 = (await it.return?.("return value 2")) as IteratorResult<
unknown,
unknown
>;
assertIterResult(iterResult2, "return value 2", true, "1st return()");
});
test("return(); return() [no awaiting]", async () => {
const rs = new ReadableStream();
const it = rs.values();
const iterResults = await Promise.allSettled([
it.return?.("return value 1"),
it.return?.("return value 2"),
]);
assert.strictEqual(
iterResults[0].status,
"fulfilled",
"1st return() promise status",
);
assertIterResult(
(iterResults[0] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
"return value 1",
true,
"1st return()",
);
assert.strictEqual(
iterResults[1].status,
"fulfilled",
"2nd return() promise status",
);
assertIterResult(
(iterResults[1] as PromiseFulfilledResult<IteratorResult<unknown, unknown>>)
.value,
"return value 2",
true,
"1st return()",
);
});
test("values() throws if there's already a lock", () => {
const s = new ReadableStream({
start(c) {
c.enqueue(0);
c.close();
},
});
s.values();
assert.throw(() => s.values(), TypeError, undefined, "values() should throw");
});
test("Acquiring a reader after exhaustively async-iterating a stream", async () => {
const s = new ReadableStream({
start(c) {
c.enqueue(1);
c.enqueue(2);
c.enqueue(3);
c.close();
},
});
const chunks: unknown[] = [];
for await (const chunk of s) {
chunks.push(chunk);
}
assert.deepEqual(chunks, [1, 2, 3]);
const reader = s.getReader();
await reader.closed;
});
test("Acquiring a reader after returning from a stream that errors", async () => {
let timesPulled = 0;
const s = new ReadableStream({
pull(c) {
if (timesPulled === 0) {
c.enqueue(0);
++timesPulled;
} else {
c.error(error1);
}
},
});
const it = s.values({ preventCancel: true });
const iterResult1 = await it.next();
assertIterResult(iterResult1, 0, false, "1st next()");
let reached1 = false;
try {
await it.next();
reached1 = true;
} catch (e) {
assert.strictEqual(e, error1, "2nd next()");
}
assert.isFalse(reached1);
const iterResult2 = (await it.return?.("return value")) as IteratorResult<
unknown,
unknown
>;
assertIterResult(iterResult2, "return value", true, "return()");
// i.e. it should not reject with a generic "this stream is locked" TypeError.
const reader = s.getReader();
let reached2 = false;
try {
await reader.closed;
reached2 = true;
} catch (e) {
assert.strictEqual(
e,
error1,
"closed on the new reader should reject with the error",
);
}
assert.isFalse(reached2);
});
test("Acquiring a reader after partially async-iterating a stream", async () => {
const s = new ReadableStream({
start(c) {
c.enqueue(1);
c.enqueue(2);
c.enqueue(3);
c.close();
},
});
// read the first two chunks, then cancel
const chunks: unknown[] = [];
for await (const chunk of s) {
chunks.push(chunk);
if (chunk >= 2) {
break;
}
}
assert.deepEqual(chunks, [1, 2]);
const reader = s.getReader();
await reader.closed;
});
test("Acquiring a reader and reading the remaining chunks after partially async-iterating a stream with preventCancel = true", async () => {
const s = new ReadableStream({
start(c) {
c.enqueue(1);
c.enqueue(2);
c.enqueue(3);
c.close();
},
});
// read the first two chunks, then release lock
const chunks: unknown[] = [];
for await (const chunk of s.values({ preventCancel: true })) {
chunks.push(chunk);
if (chunk >= 2) {
break;
}
}
assert.deepEqual(chunks, [1, 2]);
const reader = s.getReader();
const readResult = (await reader.read()) as IteratorResult<unknown, unknown>;
assertIterResult(readResult, 3, false);
await reader.closed;
});
for (const preventCancel of [false, true]) {
test(`return() should unlock the stream synchronously when preventCancel = ${preventCancel}`, () => {
const rs = new ReadableStream();
rs.values({ preventCancel }).return?.();
// The test passes if this line doesn't throw.
rs.getReader();
});
}
test("close() while next() is pending", async () => {
const rs = new ReadableStream({
async start(c) {
c.enqueue("a");
c.enqueue("b");
c.enqueue("c");
await flushAsyncEvents();
// At this point, the async iterator has a read request in the stream's queue for its pending next() promise.
// Closing the stream now causes two things to happen *synchronously*:
// 1. ReadableStreamClose resolves reader.[[closedPromise]] with undefined.
// 2. ReadableStreamClose calls the read request's close steps, which calls ReadableStreamReaderGenericRelease,
// which replaces reader.[[closedPromise]] with a rejected promise.
c.close();
},
});
const chunks: unknown[] = [];
for await (const chunk of rs) {
chunks.push(chunk);
}
assert.deepEqual(chunks, ["a", "b", "c"]);
});
function recordingReadableStream<R>(
extras: UnderlyingDefaultSource<R> = {},
strategy?: CountQueuingStrategy,
) {
interface ExposedRecords {
events: unknown[];
eventsWithoutPulls: unknown[];
controller: ReadableStreamDefaultController<R>;
}
let controllerToCopyOver: ReadableStreamDefaultController<R> | undefined;
const stream: ReadableStream<R> & ExposedRecords = new ReadableStream(
{
type: extras.type,
start(controller) {
controllerToCopyOver = controller;
if (extras.start) {
return extras.start(controller);
}
return undefined;
},
pull(controller) {
stream.events.push("pull");
if (extras.pull) {
return extras.pull(controller);
}
return undefined;
},
cancel(reason) {
stream.events.push("cancel", reason);
stream.eventsWithoutPulls.push("cancel", reason);
if (extras.cancel) {
return extras.cancel(reason);
}
return undefined;
},
},
strategy,
) as ReadableStream<R> & ExposedRecords;
stream.controller =
controllerToCopyOver as ReadableStreamDefaultController<R>;
stream.events = [];
stream.eventsWithoutPulls = [];
return stream;
}
function assertIterResult<R>(
iterResult: IteratorResult<R, unknown>,
value: R,
done: boolean,
message?: string,
) {
const prefix = message === undefined ? "" : `${message} `;
assert.strictEqual(typeof iterResult, "object", `${prefix}type is object`);
assert.strictEqual(
Object.getPrototypeOf(iterResult),
Object.prototype,
`${prefix}[[Prototype]]`,
);
assert.deepEqual(
Object.getOwnPropertyNames(iterResult).sort(),
["done", "value"],
`${prefix}property names`,
);
assert.strictEqual(iterResult.value, value, `${prefix}value`);
assert.strictEqual(iterResult.done, done, `${prefix}done`);
}