Node.js & Express: Serving text files in parts

Question

I have a webserver with node.js and express. When I serve a text file that is big, it takes a lot of time to load into the browser. Imagine a 34 MB text file being served to the client, he would have to download the 34 MB only to check for something in the log file.

Is there something I could do about it? Serve it in parts perhaps? Like: Part 1/10 - Part 10/10

Answer 1

To serve a file partial, you could take a byte range, and read that range with the filesystem function fs.createReadStream() . For example, if you wanted one tenth of a file, you could measure its size, and calculate the byte range.

app.get('/log', function(req, res) {
  fs.stat('log.txt', function(err, stats) {
    var end = Math.ceil(stats.size / 10);
    var stream = fs.createReadStream('log.txt', {start: 0, end: end});

    var log = new String();
    readable.on('data', function(chunk) {
      log += chunk;
    });

    readable.on('end', function() {
      res.send(log);
    });
  });
});

You could always modify the code to send from 10-20%, or to send the last 10% of the file, etc.

Answer 2

Have you looked into Node streams ? You can use them to send your data in small chunks, and offer feedback to show how much of it has been downloaded.