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ant/examples/spec/streams-transform.js
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streams-transform.js
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import { test, testDeep, testThrows, summary } from './helpers.js';
console.log('TransformStream / TransformStreamDefaultController Tests\n');
const READABLE_NO_BACKPRESSURE = { highWaterMark: 1 };
test('TS typeof', typeof TransformStream, 'function');
test('TS toStringTag', Object.prototype.toString.call(new TransformStream()), '[object TransformStream]');
testThrows('TS requires new', () => TransformStream());
testThrows('TS rejects readableType', () => new TransformStream({ readableType: 'bytes' }));
testThrows('TS rejects writableType', () => new TransformStream({ writableType: 'bytes' }));
const ts0 = new TransformStream();
test('TS readable is ReadableStream', ts0.readable instanceof ReadableStream, true);
test('TS writable is WritableStream', ts0.writable instanceof WritableStream, true);
testThrows('TSController cannot be constructed', () => new TransformStreamDefaultController());
test('TSController toStringTag', typeof TransformStreamDefaultController, 'function');
test('TS can be constructed with no transform', true, (() => { new TransformStream({}); return true; })());
let startCtrl = null;
const ts1 = new TransformStream({ start(c) { startCtrl = c; } });
test('start called with controller', startCtrl !== null, true);
test('controller toStringTag', Object.prototype.toString.call(startCtrl), '[object TransformStreamDefaultController]');
async function testIdentity() {
const ts = new TransformStream();
const writer = ts.writable.getWriter();
writer.write('a');
const reader = ts.readable.getReader();
const result = await reader.read();
test('identity value', result.value, 'a');
test('identity done', result.done, false);
}
async function testTransformUppercase() {
let c;
const ts = new TransformStream({
start(controller) { c = controller; },
transform(chunk) { c.enqueue(chunk.toUpperCase()); }
});
const writer = ts.writable.getWriter();
writer.write('hello');
const reader = ts.readable.getReader();
const result = await reader.read();
test('uppercase transform', result.value, 'HELLO');
}
async function testTransformDoubler() {
let c;
const ts = new TransformStream({
start(controller) { c = controller; },
transform(chunk) {
c.enqueue(chunk.toUpperCase());
c.enqueue(chunk.toUpperCase());
}
});
const writer = ts.writable.getWriter();
writer.write('x');
const reader = ts.readable.getReader();
const r1 = await reader.read();
const r2 = await reader.read();
test('doubler chunk 1', r1.value, 'X');
test('doubler chunk 2', r2.value, 'X');
}
async function testFlush() {
let flushed = false;
const ts = new TransformStream({
transform() {},
flush() { flushed = true; }
});
await ts.writable.getWriter().close();
test('flush called on close', flushed, true);
}
async function testFlushEnqueue() {
let c;
const ts = new TransformStream({
start(controller) { c = controller; },
transform() {},
flush() { c.enqueue('flushed'); }
});
const writer = ts.writable.getWriter();
writer.write('a');
writer.close();
const reader = ts.readable.getReader();
const r1 = await reader.read();
test('flush enqueue value', r1.value, 'flushed');
}
async function testCloseClosesReadable() {
const ts = new TransformStream({ transform() {} });
const writer = ts.writable.getWriter();
writer.close();
await Promise.all([writer.closed, ts.readable.getReader().closed]);
test('close propagates to readable', true, true);
}
async function testTransformError() {
const err = new Error('transform boom');
const ts = new TransformStream({
transform() { throw err; }
}, undefined, READABLE_NO_BACKPRESSURE);
const writer = ts.writable.getWriter();
const reader = ts.readable.getReader();
try {
await writer.write('a');
test('write should reject on transform error', false, true);
} catch (e) {
test('write rejects with transform error', e, err);
}
try {
await reader.read();
test('read should reject on transform error', false, true);
} catch (e) {
test('read rejects with transform error', e, err);
}
}
async function testFlushError() {
const err = new Error('flush boom');
const ts = new TransformStream({
transform() {},
flush() { throw err; }
}, undefined, READABLE_NO_BACKPRESSURE);
const writer = ts.writable.getWriter();
await writer.write('a');
try {
await writer.close();
test('close should reject on flush error', false, true);
} catch (e) {
test('close rejects with flush error', e, err);
}
}
async function testControllerError() {
let ctrl;
const ts = new TransformStream({
start(c) { ctrl = c; }
});
ctrl.error(new Error('controller error'));
const reader = ts.readable.getReader();
try {
await reader.read();
test('read should reject after controller.error', false, true);
} catch (e) {
test('controller.error errors readable', e.message, 'controller error');
}
}
async function testControllerTerminate() {
let ctrl;
const ts = new TransformStream({
start(c) { ctrl = c; }
});
ctrl.terminate();
const reader = ts.readable.getReader();
const result = await reader.read();
test('terminate closes readable', result.done, true);
}
async function testDesiredSize() {
let ctrl;
const ts = new TransformStream({
start(c) { ctrl = c; }
});
test('desiredSize initially 0', ctrl.desiredSize, 0);
}
async function testDefaultHWM() {
const ts = new TransformStream();
const writer = ts.writable.getWriter();
test('writable default HWM is 1', writer.desiredSize, 1);
}
async function testCustomWritableHWM() {
const ts = new TransformStream({}, { highWaterMark: 17 });
const writer = ts.writable.getWriter();
test('writable custom HWM', writer.desiredSize, 17);
}
async function testBackpressure() {
const ts = new TransformStream(undefined, undefined, { highWaterMark: 0 });
const writer = ts.writable.getWriter();
const reader = ts.readable.getReader();
const readPromise = reader.read();
writer.write('a');
const result = await readPromise;
test('backpressure read value', result.value, 'a');
test('backpressure read done', result.done, false);
}
async function testAsyncTransform() {
let c;
const ts = new TransformStream({
start(controller) { c = controller; },
transform(chunk) {
return new Promise(resolve => {
setTimeout(() => {
c.enqueue(chunk.toUpperCase());
resolve();
}, 10);
});
}
});
const writer = ts.writable.getWriter();
writer.write('a');
const reader = ts.readable.getReader();
const result = await reader.read();
test('async transform value', result.value, 'A');
}
async function testStartThrows() {
try {
new TransformStream({
start() { throw new URIError('start thrown'); }
});
test('TS ctor should throw on start error', false, true);
} catch (e) {
test('TS ctor throws start error', e instanceof URIError, true);
}
}
async function testCancelCallable() {
let cancelled = null;
const reason = new Error('cancel reason');
const ts = new TransformStream({
cancel(r) { cancelled = r; }
});
await ts.readable.cancel(reason);
test('cancel called with reason', cancelled, reason);
}
async function testAbortCallsCancel() {
let aborted = null;
const reason = new Error('abort reason');
const ts = new TransformStream({
cancel(r) { aborted = r; }
});
await ts.writable.abort(reason);
test('abort calls cancel with reason', aborted, reason);
}
async function testTransformThisBinding() {
let c;
const ts = new TransformStream({
suffix: '-suffix',
start(controller) { c = controller; },
transform(chunk) { c.enqueue(chunk + this.suffix); },
flush() { c.enqueue('flushed' + this.suffix); }
});
const writer = ts.writable.getWriter();
writer.write('a');
writer.close();
const reader = ts.readable.getReader();
const r1 = await reader.read();
test('this binding transform', r1.value, 'a-suffix');
const r2 = await reader.read();
test('this binding flush', r2.value, 'flushed-suffix');
}
async function testSubclass() {
class MyTS extends TransformStream {
myMethod() { return 42; }
}
const ts = new MyTS();
test('subclass instanceof', ts instanceof TransformStream, true);
test('subclass method', ts.myMethod(), 42);
test('subclass readable', ts.readable instanceof ReadableStream, true);
}
async function testReadableHWM() {
let ctrl;
new TransformStream({
start(c) { ctrl = c; }
}, undefined, { highWaterMark: 9 });
test('readable custom HWM desiredSize', ctrl.desiredSize, 9);
}
async function testNegativeHWMThrows() {
testThrows('negative writable HWM', () => new TransformStream(undefined, { highWaterMark: -1 }));
testThrows('negative readable HWM', () => new TransformStream(undefined, undefined, { highWaterMark: -1 }));
testThrows('NaN writable HWM', () => new TransformStream(undefined, { highWaterMark: NaN }));
testThrows('NaN readable HWM', () => new TransformStream(undefined, undefined, { highWaterMark: NaN }));
}
async function testCancelReadableErrorsWritable() {
const err = new Error('cancel reason');
const ts = new TransformStream();
const writer = ts.writable.getWriter();
ts.readable.cancel(err);
try {
await writer.closed;
test('writer.closed should reject after cancel', false, true);
} catch (e) {
test('writer.closed rejects with cancel reason', e, err);
}
}
async function testWritableStrategySize() {
let writableSizeCalled = false;
let readableSizeCalled = false;
const ts = new TransformStream(
{
transform(chunk, controller) {
controller.enqueue(chunk);
}
},
{
size() { writableSizeCalled = true; return 1; }
},
{
size() { readableSizeCalled = true; return 1; },
highWaterMark: Infinity
}
);
await ts.writable.getWriter().write('x');
test('writable size called', writableSizeCalled, true);
test('readable size called', readableSizeCalled, true);
}
async function testPipeThrough() {
const rs = new ReadableStream({
start(c) { c.enqueue(1); c.enqueue(2); c.enqueue(3); c.close(); }
});
const ts = new TransformStream({
transform(chunk, controller) {
controller.enqueue(chunk * 10);
}
});
const result = rs.pipeThrough(ts);
test('pipeThrough returns readable', result instanceof ReadableStream, true);
const reader = result.getReader();
const chunks = [];
while (true) {
const { value, done } = await reader.read();
if (done) break;
chunks.push(value);
}
testDeep('pipeThrough transforms data', chunks, [10, 20, 30]);
}
async function testEnqueueAfterTerminateThrows() {
let threw = false;
new TransformStream({
start(controller) {
controller.terminate();
try {
controller.enqueue('x');
} catch (e) {
threw = true;
}
}
});
test('enqueue after terminate throws', threw, true);
}
await testIdentity();
await testTransformUppercase();
await testTransformDoubler();
await testFlush();
await testFlushEnqueue();
await testCloseClosesReadable();
await testTransformError();
await testFlushError();
await testControllerError();
await testControllerTerminate();
await testDesiredSize();
await testDefaultHWM();
await testCustomWritableHWM();
await testBackpressure();
await testAsyncTransform();
await testStartThrows();
await testCancelCallable();
await testAbortCallsCancel();
await testTransformThisBinding();
await testSubclass();
await testReadableHWM();
testNegativeHWMThrows();
await testCancelReadableErrorsWritable();
await testWritableStrategySize();
await testPipeThrough();
await testEnqueueAfterTerminateThrows();
summary();

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