// dd if=/dev/urandom of=file count=10 bs=1m var through2 = require('through2'); var fs = require('fs'); fs.createReadStream('file').pipe(slowTransform()).pipe(process.stdout); function slowTransform() { return through2(function(buffer, encoding, callback) { var self = this; setTimeout(function(buffer) { self.push(buffer.length + '\n'); }, 100, buffer); callback(); }); }