code: function middleware(req, res, next) {
  		//Check to see if req.url matches a fingerprinted URL
  		var info = fingerprints[req.originalUrl];
  		//If this request matches a fingerprint
  		if(info)
  		{
  			//Set headers
  			if(info.lastModified)
  				res.setHeader("Last-Modified", info.lastModified.toUTCString() );
  			if(info.etag)
  				res.setHeader("ETag", info.etag);
  			if(info.expires)
  			{
  				res.setHeader("Expires", info.expires.toUTCString() );
  				res.setHeader("Cache-Control", "public; max-age=" +
  					Math.floor((info.expires.getTime() - new Date().getTime() ) / 1000) );
  			}
  			//Check If-Modified-Since and If-None-Match headers and return 304, if appropriate
  			if((req.headers["if-none-match"] && info.etag == req.headers["if-none-match"]) ||
  				(req.headers["if-modified-since"] && info.lastModified.toUTCString() ==
  					req.headers["if-modified-since"]) )
  				return (res.sendStatus || res.send).call(res, 304);
  		}
  		//If req.assetFingerprint is already there, do nothing.
  		if(!req.assetFingerprint)
  		{
  			//Create req.assetFingerprint
  			req.assetFingerprint = assetFingerprint;
  			//Expose req.assetFingerprint in Express helper
  			res.locals.assetFingerprint = function() {
  				return assetFingerprint.apply(req, arguments);
  			};
  		}
  		//Run next middleware
  		next();
  	}
docs: Express middleware