Wrapping the static mw to add a custom header entry.

staticWrapper.js

var myStatic = express.static(__dirname + '/my/static/path');

app.use(function(req,res,next){
  //We set the custom header here.
  res.setHeader('My-header-name','my-header-value');
  //We call the static middleware here, if the middleware calls "next", it means
  //it didn't serve the file so we replace the static mw's "next" with a custom 
  //function that removes the header entry and calls the real "next" from the 
  //wrapper. This ensure we don't pollute subsequent middleware/route's response 
  //with that custom header.
  myStatic(req,res,function(param){
    res.removeHeader('My-header-name');
    next(param);
  });
});