title: how does a etag work in expressjs
body: <p>Expressjs automatically send etags. I would like to know how the etag is generated..is it based on the content that is generated dynamically by the get routine. or is there way I can mainpulate it, by not even going through the process of generating the content(dynamic content - from DB) and pass back etag as same.</p>
  
  <p>may be a middleware which start with just checking if it is valid session id and pass back the same etag that the client gives or may be based of the url + session id..that way it will be unique. and end the request there rather going through the whole db call and all those stuff. in which case I would need to know the client is making a 304 call.</p>
  
  <p>I could go with the expires tag.but when the session is over. if somebody is opening the url it should not allow. so I am thinking the etag should be based of the session id as well. how does if modified can work in this dynamic content scenario. can it be used.</p>