if you don't read anything from your transform stream, the internal buffer
is getting full and the pipe chains throttles down, no reads and writes
until you get something out of the buffer.
In my opinion your transform stream should be a Writable, that just emits
'messages' (since you do nothing really with the data gone out the pipe) OR
you should create a wirtable stream that consumes results from your
transform AND put your transform into objectMode, you you can this.push
full messages instead of chunks.
Am Montag, 17. Juni 2013 14:40:55 UTC+2 schrieb Jerry Liu:
>
> I may have incorrect use of stream.Transform.
>
> I piped one stream to my own transform object as source. And piped this
> transform obejct to another stream as destination, depending on conditions.
>
> Then I found that if I set no destination to this transform object, it
> works really slow. Unfortrunatly, I need emit events during transform no
> matter it pipes out or not.
>
> Code:
>
>
> StreamedSocketProtocol.prototype._transform = function(chunk, encoding,
> done) {
> this.buf.push(chunk);
> function tryParser() {
> // ...
> }
>
> // ...
> var result;
> while( result = tryParser(this.buf) ){ // buf may contain more than one
> message, or simply not even one
> this.emit('message', result); // good, found one
> this.push(result); // output
> }
> // ...
> this.buf.clear();
> done();
> }
>
> //...
>
> var transformStream = new StreamedSocketProtocol();
> transformStream.on('message', function() {
> // do something. But notice this may be very late
> });
>
> var sourceStream;
>
> sourceStream.pipe(transformStream, {end: false});
>
> // This is interesting, because if (somethingHappened == false) here,
> // transformStream may not work for a long time
> // That is, transform stream need a destnation or it may be very slow!
> if(somethingHappened) {
> var destinationStream;
> transformStream.pipe(destinationStream, {end: false});
> }
>
> // To make transform stream keep up, what I do is to use null device
>
> function createNullDevice () {
> if (os.type().match(/(windows)/i)) {
> return fs.createWriteStream('nul');
> }else{
> return fs.createWriteStream('/dev/null');
> }
> };
>
> var nullDevice = createNullDevice ();
>
> transformStream.pipe(nullDevice, {end: false});
>
> I may have used Transform incorrectly, but someone may encounter this
> problem again. And I do think Node.js needs a cross-platform null device.
>
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