flow-control.js
'use strict';
if (self.importScripts) {
self.importScripts('/resources/testharness.js');
self.importScripts('../resources/test-utils.js');
self.importScripts('../resources/rs-utils.js');
self.importScripts('../resources/recording-streams.js');
}
const error1 = new Error('error1!');
error1.name = 'error1';
promise_test(t => {
const rs = recordingReadableStream({
start(controller) {
controller.enqueue('a');
controller.enqueue('b');
controller.close();
}
});
const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
const pipePromise = rs.pipeTo(ws, { preventCancel: true });
// Wait and make sure it doesn't do any reading.
return flushAsyncEvents().then(() => {
ws.controller.error(error1);
})
.then(() => promise_rejects(t, error1, pipePromise, 'pipeTo must reject with the same error'))
.then(() => {
assert_array_equals(rs.eventsWithoutPulls, []);
assert_array_equals(ws.events, []);
})
.then(() => readableStreamToArray(rs))
.then(chunksNotPreviouslyRead => {
assert_array_equals(chunksNotPreviouslyRead, ['a', 'b']);
});
}, 'Piping from a non-empty ReadableStream into a WritableStream that does not desire chunks');
promise_test(() => {
const rs = recordingReadableStream({
start(controller) {
controller.enqueue('b');
controller.close();
}
});
let resolveWritePromise;
const ws = recordingWritableStream({
write() {
if (!resolveWritePromise) {
// first write
return new Promise(resolve => {
resolveWritePromise = resolve;
});
}
return undefined;
}
});
const writer = ws.getWriter();
const firstWritePromise = writer.write('a');
assert_equals(writer.desiredSize, 0, 'after writing the writer\'s desiredSize must be 0');
writer.releaseLock();
// firstWritePromise won't settle until we call resolveWritePromise.
const pipePromise = rs.pipeTo(ws);
return flushAsyncEvents().then(() => resolveWritePromise())
.then(() => Promise.all([firstWritePromise, pipePromise]))
.then(() => {
assert_array_equals(rs.eventsWithoutPulls, []);
assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'close']);
});
}, 'Piping from a non-empty ReadableStream into a WritableStream that does not desire chunks, but then does');
promise_test(() => {
const rs = recordingReadableStream();
const startPromise = Promise.resolve();
let resolveWritePromise;
const ws = recordingWritableStream({
start() {
return startPromise;
},
write() {
if (!resolveWritePromise) {
// first write
return new Promise(resolve => {
resolveWritePromise = resolve;
});
}
return undefined;
}
});
const writer = ws.getWriter();
writer.write('a');
return startPromise.then(() => {
assert_array_equals(ws.events, ['write', 'a']);
assert_equals(writer.desiredSize, 0, 'after writing the writer\'s desiredSize must be 0');
writer.releaseLock();
const pipePromise = rs.pipeTo(ws);
rs.controller.enqueue('b');
resolveWritePromise();
rs.controller.close();
return pipePromise.then(() => {
assert_array_equals(rs.eventsWithoutPulls, []);
assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'close']);
});
});
}, 'Piping from an empty ReadableStream into a WritableStream that does not desire chunks, but then the readable ' +
'stream becomes non-empty and the writable stream starts desiring chunks');
promise_test(() => {
const unreadChunks = ['b', 'c', 'd'];
const rs = recordingReadableStream({
pull(controller) {
controller.enqueue(unreadChunks.shift());
if (unreadChunks.length === 0) {
controller.close();
}
}
}, new CountQueuingStrategy({ highWaterMark: 0 }));
let resolveWritePromise;
const ws = recordingWritableStream({
write() {
if (!resolveWritePromise) {
// first write
return new Promise(resolve => {
resolveWritePromise = resolve;
});
}
return undefined;
}
}, new CountQueuingStrategy({ highWaterMark: 3 }));
const writer = ws.getWriter();
const firstWritePromise = writer.write('a');
assert_equals(writer.desiredSize, 2, 'after writing the writer\'s desiredSize must be 2');
writer.releaseLock();
// firstWritePromise won't settle until we call resolveWritePromise.
const pipePromise = rs.pipeTo(ws);
return flushAsyncEvents().then(() => {
assert_array_equals(ws.events, ['write', 'a']);
assert_equals(unreadChunks.length, 1, 'chunks should continue to be enqueued until the HWM is reached');
}).then(() => resolveWritePromise())
.then(() => Promise.all([firstWritePromise, pipePromise]))
.then(() => {
assert_array_equals(rs.events, ['pull', 'pull', 'pull']);
assert_array_equals(ws.events, ['write', 'a', 'write', 'b','write', 'c','write', 'd', 'close']);
});
}, 'Piping from a ReadableStream to a WritableStream that desires more chunks before finishing with previous ones');
class StepTracker {
constructor() {
this.waiters = [];
this.wakers = [];
}
// Returns promise which resolves when step `n` is reached. Also schedules step n + 1 to happen shortly after the
// promise is resolved.
waitThenAdvance(n) {
if (this.waiters[n] === undefined) {
this.waiters[n] = new Promise(resolve => {
this.wakers[n] = resolve;
});
this.waiters[n]
.then(() => flushAsyncEvents())
.then(() => {
if (this.wakers[n + 1] !== undefined) {
this.wakers[n + 1]();
}
});
}
if (n == 0) {
this.wakers[0]();
}
return this.waiters[n];
}
}
promise_test(() => {
const steps = new StepTracker();
const desiredSizes = [];
const rs = recordingReadableStream({
start(controller) {
steps.waitThenAdvance(1).then(() => enqueue('a'));
steps.waitThenAdvance(3).then(() => enqueue('b'));
steps.waitThenAdvance(5).then(() => enqueue('c'));
steps.waitThenAdvance(7).then(() => enqueue('d'));
steps.waitThenAdvance(11).then(() => controller.close());
function enqueue(chunk) {
controller.enqueue(chunk);
desiredSizes.push(controller.desiredSize);
}
}
});
const chunksFinishedWriting = [];
const writableStartPromise = Promise.resolve();
let writeCalled = false;
const ws = recordingWritableStream({
start() {
return writableStartPromise;
},
write(chunk) {
const waitForStep = writeCalled ? 12 : 9;
writeCalled = true;
return steps.waitThenAdvance(waitForStep).then(() => {
chunksFinishedWriting.push(chunk);
});
}
});
return writableStartPromise.then(() => {
const pipePromise = rs.pipeTo(ws);
steps.waitThenAdvance(0);
return Promise.all([
steps.waitThenAdvance(2).then(() => {
assert_array_equals(chunksFinishedWriting, [], 'at step 2, zero chunks must have finished writing');
assert_array_equals(ws.events, ['write', 'a'], 'at step 2, one chunk must have been written');
// When 'a' (the very first chunk) was enqueued, it was immediately used to fulfill the outstanding read request
// promise, leaving the queue empty.
assert_array_equals(desiredSizes, [1],
'at step 2, the desiredSize at the last enqueue (step 1) must have been 1');
assert_equals(rs.controller.desiredSize, 1, 'at step 2, the current desiredSize must be 1');
}),
steps.waitThenAdvance(4).then(() => {
assert_array_equals(chunksFinishedWriting, [], 'at step 4, zero chunks must have finished writing');
assert_array_equals(ws.events, ['write', 'a'], 'at step 4, one chunk must have been written');
// When 'b' was enqueued at step 3, the queue was also empty, since immediately after enqueuing 'a' at
// step 1, it was dequeued in order to fulfill the read() call that was made at step 0. Thus the queue
// had size 1 (thus desiredSize of 0).
assert_array_equals(desiredSizes, [1, 0],
'at step 4, the desiredSize at the last enqueue (step 3) must have been 0');
assert_equals(rs.controller.desiredSize, 0, 'at step 4, the current desiredSize must be 0');
}),
steps.waitThenAdvance(6).then(() => {
assert_array_equals(chunksFinishedWriting, [], 'at step 6, zero chunks must have finished writing');
assert_array_equals(ws.events, ['write', 'a'], 'at step 6, one chunk must have been written');
// When 'c' was enqueued at step 5, the queue was not empty; it had 'b' in it, since 'b' will not be read until
// the first write completes at step 9. Thus, the queue size is 2 after enqueuing 'c', giving a desiredSize of
// -1.
assert_array_equals(desiredSizes, [1, 0, -1],
'at step 6, the desiredSize at the last enqueue (step 5) must have been -1');
assert_equals(rs.controller.desiredSize, -1, 'at step 6, the current desiredSize must be -1');
}),
steps.waitThenAdvance(8).then(() => {
assert_array_equals(chunksFinishedWriting, [], 'at step 8, zero chunks must have finished writing');
assert_array_equals(ws.events, ['write', 'a'], 'at step 8, one chunk must have been written');
// When 'd' was enqueued at step 7, the situation is the same as before, leading to a queue containing 'b', 'c',
// and 'd'.
assert_array_equals(desiredSizes, [1, 0, -1, -2],
'at step 8, the desiredSize at the last enqueue (step 7) must have been -2');
assert_equals(rs.controller.desiredSize, -2, 'at step 8, the current desiredSize must be -2');
}),
steps.waitThenAdvance(10).then(() => {
assert_array_equals(chunksFinishedWriting, ['a'], 'at step 10, one chunk must have finished writing');
assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
'at step 10, two chunks must have been written');
assert_equals(rs.controller.desiredSize, -1, 'at step 10, the current desiredSize must be -1');
}),
pipePromise.then(() => {
assert_array_equals(desiredSizes, [1, 0, -1, -2], 'backpressure must have been exerted at the source');
assert_array_equals(chunksFinishedWriting, ['a', 'b', 'c', 'd'], 'all chunks finished writing');
assert_array_equals(rs.eventsWithoutPulls, [], 'nothing unexpected should happen to the ReadableStream');
assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'write', 'c', 'write', 'd', 'close'],
'all chunks were written (and the WritableStream closed)');
})
]);
});
}, 'Piping to a WritableStream that does not consume the writes fast enough exerts backpressure on the ReadableStream');
done();
