Include hash of template in the maptoken returned from instanciation

Doing so basically removes the need to include the template identifier
in the surrogate keys of the responses for resources fetched via
the instance whenever template is updated. See #105

NEWS.md

@@ -11,6 +11,8 @@ New features:
 Enhancements:
 
  * Allow specifying fixed sqlapi host address (#117)
+ * Include template hash in template instance response, to keep caches
+   of different instances separated (#105)
 
 Bug fixes:
 

lib/cartodb/cartodb_windshaft.js

@@ -484,7 +484,8 @@ var CartodbWindshaft = function(serverOptions) {
           if ( err ) throw err;
           //console.log("Response from createLayergroup: "); console.dir(response);
           // Add the signature part to the token!
-          response.layergroupid = cdbuser + '@' + response.layergroupid;
+          var tplhash = templateMaps.fingerPrint(template).substring(0,8);
+          response.layergroupid = cdbuser + '@' + tplhash + '@' + response.layergroupid;
           return response;
         },
         callback

lib/cartodb/server_options.js

@@ -613,9 +613,12 @@ console.log("Checking authorization from signer " + signer + " for resource " +
           if ( tksplit.length > 1 ) req.params.cache_buster= tksplit[1];
           tksplit = req.params.token.split('@');
           if ( tksplit.length > 1 ) {
-            req.params.signer = this.userByReq(req);
-            if ( tksplit[0] ) req.params.signer = tksplit[0];
-            req.params.token = tksplit[1];
+            req.params.signer = tksplit.shift();
+            if ( ! req.params.signer ) req.params.signer = this.userByReq(req);
+            if ( tksplit.length > 1 ) {
+              var template_hash = tksplit.shift(); // unused
+            }
+            req.params.token = tksplit.shift(); 
             //console.log("Request for token " + req.params.token + " with signature from " + req.params.signer);
           }
         }

lib/cartodb/template_maps.js

@@ -588,4 +588,12 @@ o.instance = function(template, params) {
   return layergroup;
 };
 
+// Return a fingerPrint of the object
+o.fingerPrint = function(template) {
+  return crypto.createHash('md5')
+    .update(JSON.stringify(template))
+    .digest('hex')
+  ;
+};
+
 module.exports = TemplateMaps;