[streams] _flush not being called

[missinglink]

In the following testcase the _flush callback is not being called after stream.end().

Simply removing the stream.write(null); line works fine.

Is it possible to end a stream with stream.write(null) and stream.end() or only the latter.

If so, why does stream.write(null) prevent stream.end() from triggering _flush?

var Transform = require('readable-stream/transform'),
    inherits  = require('util').inherits;

function MyTransform(opts){
  Transform.call(this, opts);
}

inherits(MyTransform, Transform);

MyTransform.prototype._transform = function( chunk, enc, next ){
  console.log('.');
  next();
};

MyTransform.prototype._flush = function(){
  console.log('END');
};

// ---

var stream = new MyTransform({ objectMode: true });

stream.write({ a: 'b' });
stream.write(null);
stream.end();

same behaviour on v0.11.14 and v0.10.33

ref: #89

[missinglink]

@rvagg, @isaacs I'm happy to look in to this and submit a PR.

Can you please confirm that sending stream.write(undefined), stream.write(null) and calling stream.end() should all end a Transform stream in the same way?

Is this the same behaviour for objectMode:true and objectMode:false?

ref: https://github.com/isaacs/readable-stream/blob/master/test/simple/test-stream2-transform.js#L453

[chrisdickinson]

Can you please confirm that sending stream.write(undefined), stream.write(null) and calling stream.end() should all end a Transform stream in the same way?

stream.write(null | undefined) should not end a stream -- the null EOF is only triggered through the readable's internal_-ish_ .push method.

It's down to this line -- specifically the isNull check. This sits at a weird place on the "bug or normal behavior" spectrum: without the check, all of the tests still pass, and in objectMode one would expect any value written to the stream to be transformed, but as it stands, in most cases null is an "out of alphabet" value for streams and represents the end of a stream.

(Tangentially, I'd love to move away from null-as-EOF in the future for this (and other) reasons.)

[sonewman]

I agree since it always feels weird to me calling .push(null) when ending a readable stream.