I agree with both suggestions.
Another hole is the non-objectMode special behavior of
readable.push('');
http://nodejs.org/docs/latest/api/stream.html#stream_stream_push
When called by a Readable implementation, it is supposed to signal that the
stream is done getting data from its upstream source, but there was no data
to fetch. The Readable internals then ensure that another _read() loop is
called (including checking first if the stream has been paused).
When in objectMode, though, this is ambiguous. .push('') Could mean that
the implementation would like to push out the empty string, since that's a
valid object.
I actually need to change this this week (break the spec?) in my
browser-based implementation of objectMode streams3.
https://github.com/Livefyre/stream
Currently, .push(), ie pushing undefined, is treated like .push(null),
which signals EOF and ends the Readable. Instead, I'm going to make .push()
be the equivalent of .push('') in non-objectMde streams.
This would actually be bad for your case. Just like you sometimes expect
.read() to return null, theoretically some user may want to .push() the
value 'undefined'. I'm kind of fine making that sacrifice, but curious if
you or anyone has a better idea. It could be .push(readable.NULL) or
something ( :/ ). Similarly, if you needed to be able to .read() out the
value 'null', .read() could return something like readable.NULL. But these
seem gross..
On Saturday, October 19, 2013 8:18:28 PM UTC-7, Chaoran Yang wrote:
>
> Hi all,
>
> I'm trying to implement a stream in object mode. It's a very complex
> stream that allows user read and write database records. But for this
> discussion, you can just imagine it as a duplex stream that reads and
> writes database records in a table.
>
> [Question] I've read the API doc on streams. It's a bit unclear about the
> usage of highWaterMark in object mode. Does it limit the number of objects
> that it internally buffered? If not, how do I control the memory usage of
> the internal buffer?
>
> [Suggestion] The API doc said "a readable stream in object mode will
> always return a single item from a call to readable.read(size), regardless
> of what the size argument is", which feels very unintuitive for me. I think
> it should be more intuitive if readable.read(size) returns "size" items.
>
> [Suggestion] Currently, The special value null still retains its special
> value for object mode streams. That is, for object mode readable streams,
> null as a return value from stream.read() indicates that there is no more
> data, and stream.push(null) will signal the end of stream data (EOF).
> However, in the stream I want to implement, a null object is exactly what I
> want to return to the consumer, and it should not indicate that there is no
> more data. Wouldn't it be more appropriate to use "undefined" as the
> special value to indicate the end of stream data?
>
> Thanks,
> Chaoran Yang
>
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