How to transform (simple) streaming XML in Node.js?

Question

I'm proxying an S3 call through my Node.js server and want to tweak just a couple of the returned XML values before proxying them. Except for those tweaks, I'd like to maintain the rest of each response, e.g. the response headers.

I can of course gather the whole response first, parse the XML, transform it, and return it back, but for large responses that'll be both slow and memory-intensive. Is there a way I can achieve basically a stream.pipe() but with maybe a transformation function?

I've looked at sax-js, which can pipe but doesn't have any transform ability. Do I have to resort to listening to low-level parse events and generating and outputting the resulting XML myself?

I've also looked at libxmljs which has a "push parser" and a higher-level DOM API, but it looks like I'd again have to listen to low-level parse events myself, plus I'm not sure I can stream the resulting XML out as it's generated.

Is there any easier way than either of these two approaches? Thanks!

P.S. The XML tweaks are simple: just removing a substring from some text elements.

Answer 1

In this case you can collect all chunks together, like this:

var data='', tstream = new stream.Transform();
tstream._transform = function (chunk, encoding, done) {
    data += chunk.toString();
    done();
};

And do what you need at last call in _flush function:

tstream._flush = function(done){
    data += 'hola muheres';
    this.push(data);
    done();
};

so all together it can look like:

req.pipe(anotherstream).pipe(tstream).pipe(response);