Set Last-Modified header to allow for 304 responses

NEWS.md

@@ -1,5 +1,6 @@
 1.3.3
 ------
+* Set Last-Modified header to allow for 304 responses
 
 1.3.2
 ------

lib/cartodb/server_options.js

@@ -215,10 +215,17 @@ module.exports = function(){
           res.header('Cache-Control', 'public,max-age=31536000'); // 1 year
         } else {
           var ttl = global.environment.varnish.ttl || 86400;
-          res.header('Last-Modified', new Date().toUTCString());
           res.header('Cache-Control', 'no-cache,max-age='+ttl+',must-revalidate, public');
         }
 
+        // Set Last-Modified header
+        //
+        // Currently sets it to NOW
+        //
+        // TODO: find out a real value, querying for most recent change in
+        //       any of the source tables
+        res.header('Last-Modified', new Date().toUTCString());
+
         me.generateCacheChannel(req, function(err, channel){
             if ( ! err ) {
               res.header('X-Cache-Channel', channel);