you can count bytes with by putting a passthrough stream in between
var counter = new stream.Transform
var count = 0
counter._transform = function(chunk, encoding, callback){
count += (chunk && chunk.length) || 0
this.push(chunk)
callback()
}
slowSourceStream.pipe(counter).pipe(destinationStream)
Am Samstag, 8. Februar 2014 01:12:37 UTC+1 schrieb Denys Khanzhiyev:
>
> Hello,
>
> I have a task where one slow stream is piped to fs.writeStream and after
> some event I need to read from that writen file, i.e. read from growing
> file from some position. A have seen `node-growing-file`, and
> `tailing-stream` nothing seems to solve my problem.
>
> It looks like I do not understand how streams work
> Here is my helper object (though it is called PxyStream it is not stream
> in fact),
>
> var
> fs = require('fs');
>
> function PxyStream(path,readStream,writeStream,start,end){
> this.path = path;
> this.readStream = readStream;
> this.writeStream = writeStream;
> this._offset = start;
> this.endPos = end;
> this.writeStream.on('finish',function(){
> this._writeStreamFinished = true;
> this.nextStream();
> }.bind(this))
> }
>
>
> PxyStream.prototype.pipe = function(destination){
> this.destination = destination;
> this.nextStream();
> }
>
> PxyStream.prototype.nextStream = function(){
> if(!this._stream){
> var options = {
> start: this._offset
> };
> var last = this._writeStreamFinished;
> console.log('new read stream',this._offset, last);
> this._stream = fs.createReadStream(this.path,options);
> this._stream.pipe(this.destination,{end: false});
> this._stream.on('data',function(data){
> this._offset += data.length;
> }.bind(this));
>
> this._stream.on('end',function(){
> console.log('read stream end',this._offset, last);
> this._stream.unpipe();
> this._stream = null;
> if(last) {
> this.destination.emit('end');
> }
> this._watch();
> }.bind(this));
> }
> }
>
> PxyStream.prototype._watch = function(){
> this.readStream.once('data',function(){
> this.nextStream();
> }.bind(this))
> }
>
> exports.PxyStream = PxyStream;
>
>
> I am using it as
>
> pxyStream = new PxyStream(filePath,<slowReadStream>,
> <fsWriteStream>,start,null);
> // i need end position too but lets skip it for now
> pxyStream.pipe(<otherSlowStream>);
>
> my problem is I see 'read stream end' message far before otherSlowStream
> ends.
> In fact it never ends, but i can see its progress.
> Actually destination is http.response stream.
> I thought stream.pipe should slow down reading in order to keep buffers
> short.
> Maybe attached 'data' event makes it read fast, but how can I count bytes
> then?
> The other problem is I can not end destination properly.
>
>
>
>
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