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stream: make sure readable is called on empty chunk followed by eof #29762

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stream: make sure readable is called on empty chunk followed by eof #29762

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92bb697
stream: make sure readable is called on empty chunk followed by eof
ronag Sep 29, 2019
2c720a1
fixup: less significant changes
ronag Sep 29, 2019
2f13cdd
fixup: test
ronag Sep 29, 2019
9253f5e
fixup: test
ronag Sep 29, 2019
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7 changes: 6 additions & 1 deletion lib/_stream_readable.js
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Original file line number Diff line number Diff line change
Expand Up @@ -302,6 +302,8 @@ function readableAddChunk(stream, chunk, encoding, addToFront) {
}
} else if (!addToFront) {
state.reading = false;
if (state.needReadable)
emitReadable(stream);
maybeReadMore(stream, state);
}
}
Expand Down Expand Up @@ -593,9 +595,12 @@ function emitReadable_(stream) {
debug('emitReadable_', state.destroyed, state.length, state.ended);
if (!state.destroyed && (state.length || state.ended)) {
stream.emit('readable');
state.emittedReadable = false;
}

// Reset emittedReadable once it is safe to schedule another
// emitReadable.
state.emittedReadable = false;
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@mcollina: Please also observe this change. I'm pretty sure it's fine but just making sure I have a second opinion on that.


// The stream needs another readable event if
// 1. It is not flowing, as the flow mechanism will take
// care of it.
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19 changes: 19 additions & 0 deletions test/parallel/test-stream-duplex-empty-chunk.js
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@@ -0,0 +1,19 @@
'use strict';

const common = require('../common');
const makeDuplexPair = require('../common/duplexpair');

const { clientSide, serverSide } = makeDuplexPair();

serverSide.resume();
serverSide.on('end', function(buf) {
serverSide.write('out');
serverSide.write('');
serverSide.write('');
serverSide.end();
});

clientSide.end();

clientSide.on('data', common.mustCall());
clientSide.on('end', common.mustCall());
2 changes: 1 addition & 1 deletion test/parallel/test-stream2-compatibility.js
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Expand Up @@ -44,7 +44,7 @@ class TestReader extends R {
}

const reader = new TestReader();
setImmediate(function() {
process.nextTick(function() {
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@ronag ronag Sep 29, 2019 •
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This test kind of contradicts the added test, i.e. it expects the stream to stop reading after pushing an empty chunk.

Not sure if this is something that indicates whether this fix will cause other problems.

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Can you please articulate this a bit more? Is this change needed to make the test pass?

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@ronag ronag Sep 30, 2019 •
edited
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Yes, otherwise it live locks. Basically it gets into an infinite loop (with nextTick) between. Because it pushes an empty chunk, which invokes a read call which pushes an empty chunk etc...

By changing it to nextTick instead of setImmediate it's possible to get between that loop and end it. But as I wrote I'm unsure of the implications.

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I think we should avoid that live lock in code.

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I think we should avoid that live lock in code.

What does that mean in practice? Should we add a guard? Or is the current state of the PR ok in that regard?

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I think @mcollina would like to add a guard in the streams implementation that this can not cause an infinite loop / that this test does not need to change.

assert.strictEqual(ondataCalled, 1);
console.log('ok');
reader.push(null);
Expand Down