How to trigger browser download from Node.JS socket stream?

Question

my node.js app connects through var socket = net.createConnection(port, ip); to download a file from another server. As soon as connection is made the server sends the file as data.

I catch it then by doing

socket.on('data', function(data) {

}).on('connect', function() {

}).on('end', function() {
console.log('DONE');
});

My initial goal is, to download the file using the method above and at the same time give the bytes to the client's browser as a downloadable file. For example: user clicks a button on the site which triggers the server-side download function and the user gets the file-save prompt. Node.JS then downloads the file from the remote server and at the same time gives each new byte to the user at the browser client. Is this possible? I imagine it would need to send headers of octet-stream to trigger file transfer between browser Node.JS. But how?

Update

Now I tried the code below with the help of the answer below:

app.get('/download', function (req, res) {

res.setHeader('Content-disposition', 'attachment; filename=' + "afile.txt");
res.setHeader('Content-Length', "12468")

var socket = net.createConnection(1024, "localhost");
console.log('Socket created.');
socket.on('data', function(data) {

    socket.pipe(res)

}).on('connect', function() {
// // Manually write an HTTP request.
// socket.write("GET / HTTP/1.0\r\n\r\n");
}).on('end', function() {
    console.log('DONE');
    socket.end();
});

 });

The data is being sent to the user's browser as a download, but the end result is a broken file. I checked the contents within and it seeems that something along the process causes the file to corrupt. I think now I have to write byte per byte? rather than doing socket.pipe?

You can't do that, but you can receive the whole file in memory using sockets and then make the user download the file using a data URI. Like so: http://stackoverflow.com/questions/3665115/create-a-file-in-memory-for-user-to-download-not-through-server. Streaming the file directly for the user to download however isn't possible using websockets. — Kerstomaat, Jan 07 '14 at 01:28
File download is only avaialable over http. That interface is not there for websocket as sending file over it is yet to be standardised. See another similar question http://stackoverflow.com/questions/9871357/receive-file-via-websocket-and-initiate-download-dialog. — user568109, Jan 07 '14 at 06:19
You are mixing on('data') and pipe. Your first chunk of data is lost when you attach `.pipe` — Andrey Sidorov, Jan 07 '14 at 13:20

score 2 · Accepted Answer · answered Jan 07 '14 at 01:10

2

You need to set content-disposition header in your http response:

  response.writeHead(200, {
    'Content-Disposition': 'attachment; filename=genome.jpeg; modification-date="Wed, 12 Feb 1997 16:29:51 -0500"'
  });
  yourDataStream.pipe(response);

see RFC2183

answered Jan 07 '14 at 01:10

Andrey Sidorov

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The file is being sent over websocket. – user568109 Jan 07 '14 at 05:38
why can't you serve it over http? – Andrey Sidorov Jan 07 '14 at 05:58
You can but that is not what OP is asking for. – user568109 Jan 07 '14 at 06:10
I don't see reference to websockets in the question. Everything in question is possible via plain old http/ajax – Andrey Sidorov Jan 07 '14 at 07:32
Sorry, may be you're right. I assumed the code in question that catches file runs on browser. Otherwise you answer it correctly. – user568109 Jan 07 '14 at 08:47

score 2 · Answer 2 · answered Jan 07 '14 at 14:00

It looks like you may want this:

app.get('/download', function (req, res) {
  res.attachment('afile.txt');
  require('http').get('http://localhost:1234/', function(response) {
    response.pipe(res);
  }).on('error', function(err) {
    res.send(500, err.message);
  });
});

score 0 · Answer 3 · edited Oct 11 '20 at 13:58

I found the solution! by doing res.write(d) i was able to direct the bytes from the other connection to the user browser download.

app.get('/download', function (req, res) {

res.setHeader('Content-disposition', 'attachment; filename=' + "afile.jpg");
res.setHeader('Content-Length', "383790");
res.setHeader('Content-Type','image/jpeg');

var socket = net.createConnection(1024, "localhost");
console.log('Socket created.');
//socket.setEncoding("utf8");
socket.on('data', function(d) {
    console.log(d);
    res.write(d);
}).on('connect', function() {
// // Manually write an HTTP request.
// socket.write("GET / HTTP/1.0\r\n\r\n");
}).on('end', function() {
    console.log('DONE');
    socket.end();
});


});

How to trigger browser download from Node.JS socket stream?

3 Answers3