How to pipe one readable stream into two writable streams at once in Node.js?

Question

The goal is to:

1. Create a file read stream.
2. Pipe it to gzip (zlib.createGzip())

3. Then pipe the read stream of zlib output to:

   1) HTTP response object

   2) and writable file stream to save the gzipped output.

Now I can do down to 3.1:

var gzip = zlib.createGzip(),
    sourceFileStream = fs.createReadStream(sourceFilePath),
    targetFileStream = fs.createWriteStream(targetFilePath);

response.setHeader('Content-Encoding', 'gzip');

sourceFileStream.pipe(gzip).pipe(response);

... which works fine, but I need to also save the gzipped data to a file so that I don't need to regzip every time and be able to directly stream the gzipped data as a response.

So how do I pipe one readable stream into two writable streams at once in Node?

Would sourceFileStream.pipe(gzip).pipe(response).pipe(targetFileStream); work in Node 0.8.x?

Answer 1

Pipe chaining/splitting doesn't work like you're trying to do here, sending the first to two different subsequent steps:

sourceFileStream.pipe(gzip).pipe(response);

However, you can pipe the same readable stream into two writeable streams, eg:

var fs = require('fs');

var source = fs.createReadStream('source.txt');
var dest1 = fs.createWriteStream('dest1.txt');
var dest2 = fs.createWriteStream('dest2.txt');

source.pipe(dest1);
source.pipe(dest2);