404 error when using response.sendfile in Express.js

I have an Express Node.js application. The structure is the following:

myapp
  +-- node_modules
  +-- public
         |-- htmls
               |-- myhtml.html
  +-- routes
         |-- index.js
  |-- app.js

My app.js is as follows:

var express = require('express')
  , routes = require('./routes')
  , user = require('./routes/user')
  , http = require('http')
  , path = require('path');

var app = express();

// all environments
// some stuff...
app.use(express.static(path.join(__dirname, 'public')));
app.use('/public', express.static(path.join(__dirname, 'public')));

app.get('/', routes.index);
app.get('/content/:file', routes.plainhtml);

http.createServer(app).listen(app.get('port'), function(){
  console.log('Express server listening on port ' + app.get('port'));
});

My routes/index.js is as follows:

// Some stuff...
exports.plainhtml = function(req, res) {
  res.sendfile('/public/htmls/' + req.params.file);
};

I open my browser and try to get the following address: http://localhost:3000/content/myhtml.html and I get 404 error:

Express 404 Error: ENOENT, stat '/public/htmls/myhtml.html'

The routing is done and the function is called... the problem is when I try to use res.sendfile. What address should I pass there???

What to do?