How to serve a file not saved in folder, stored in postgresql database, and to be rendered to HTML by expressjs?

We first sent the file to be posted as following:

router.post('/savefile', multer().single('filesource'), (q,s) => {  
     db.query("insert into filesource  (filerefid, source) values ($1, $2) returning filerefid",   [ q.body.filerefid,  q.file ])
      .then (r=> s.send(r.rows[0]))
  })

And then tried to show that as following to the HTML:

<object type="application/pdf" data="http://localhost:3000/getsource/1"></object>

Which is requested by:

router.get('/getsource/:i', (q,s) => {
      db.query('select source from  filesource  where  filerefid = $1;',
               [q.params.i])
        .then (r=> s.send(Buffer.from(r.rows[0].source.buffer)))
    
})

However the files cant be showed or downloaded correctly like that, What is the best way of doing that, without saving file in any directory?

I suppose you are missing content type header in the response.

res.set('Content-Type', 'application/pdf');

Also consider setting Content-Disposition header to present a correct file name. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Disposition

Content-Type: application/pdf
Content-Disposition: attachment; filename="file.pdf"

Update

file property which is provided by multer is a js object, which contains buffer property with binary data of the file. In http get method this binary data should be returned decorated by the required http headers mentioned above.