Concatenating Buffer chunks received from Gridfs - node.js

Question

Only 255kb of data is being sent back, which is the default chunk size in gridfs. In mongolab, however I see that multiple chunks are being stored. So the problem is only with the read code. Here it is-
Retrive from gridfs and send response code-
app.get('/download/:fileid', function(req, res) {
var buffer = [];
var id = req.params.fileid;
var base64string;
var readStream = gfs.createReadStream({_id: id});
readStream.on('data', function(chunk) {
buffer.push(chunk);
});
readStream.on('end', function() {
base64string = Buffer(buffer.concat()[0]).toString('base64');
fs.writeFile("base64.txt", base64string);
res.statusCode = 200;
res.setHeader('Content-Type', 'application/json');
res.write(JSON.stringify({body : base64string}));
res.end();
});
});
[Edit]- Further analysis suggests that I am getting all the chunks. So the problem is in concatenation-
base64string = Buffer(buffer.concat()[0]).toString('base64');
[Edit]- Buffer.concat() does not work. How do I create a single buffer out of these three buffers?
[ <Buffer ff d8 ff e0 00 10 4a 46 49 46 00 01 02 01 00 60 00 60 00 00 ff e1 0f 07 45 78 69 66 00 00 4d 4d 00 2a 00 00 00
08 00 06 01 32 00 02 00 00 00 14 00 00 ... >,
<Buffer a1 b1 42 92 56 81 43 43 5e b8 46 61 0f 96 09 c1 c4 e8 96 2b 75 52 54 21 2a 7d 46 ba c6 66 80 01 95 3c 3d a7 16
31 ed d9 56 b5 2b 91 5e 07 14 cb 2f ee ... >,
<Buffer a6 b6 92 5a 4f 1a da c9 e8 55 97 8e d1 da 4a b3 88 26 2f e5 2c 23 2a 54 10 59 1b 9e eb 35 e8 92 cc 2e da 8b 16
91 d3 e2 91 93 99 62 e0 8e a3 80 56 aa ... >,
<Buffer 71 e6 83 65 5e b0 f1 5f 61 a6 21 a3 68 83 be 72 0b 7a 7d 47 d6 d3 69 ee 59 37 92 1a de 06 8a 22 2a 3a a0 a3 1f
1a 0e 7e ec 67 3b 8f e9 c5 87 6b 41 5b ... > ]
[EDIT] Piping the readstream into response as per neils recommendation. However I get a syntax error on client side. [Unexpected Token]
RESPONSE CODE-
app.get('/download/:fileid', function(req, res) {
var id = req.params.fileid;
res.set('Content-Type', 'image/jpeg');
gfs.createReadStream({_id: id}).pipe(res); });
CLIENT CODE-
download() {
this._http.get('http://localhost:9000/download/' + this._fileid)
.map(response => response.json())
.subscribe(
data => {
console.log(data);
//this.image = data.body;
},
err => console.log('Error is..:' + err)
);;
}