Add support for cache_policy=persistent

When cache_policy=persistent is given the response will contain
a Cache-Control header requesting for 1 year lifetime caching

README.md

@@ -80,8 +80,16 @@ Args:
 
 * sql - plain SQL arguments
 * interactivity - specify the column to use in UTFGrid
-* cache_buster - if needed you can add a cachebuster to make sure you're
-  rendering new
+* cache_buster - Specify an identifier for the internal tile cache.
+                 Requesting tiles with the same cache_buster value may
+                 result in being served a cached version of the tile
+                 (even when requesting a tile for the first time, as tiles
+                 can be prepared in advance)
+* cache_policy - Set to "persist" to have the server send an Cache-Control
+                 header requesting caching devices to keep the response
+                 cached as much as possible. This is best used with a
+                 timestamp value in cache_buster for manual control of
+                 updates.
 * geom_type - override the cartodb default
 * style - override the default map style with Carto
 

lib/cartodb/server_options.js

@@ -45,8 +45,13 @@ module.exports = function(){
         var ttl = global.environment.varnish.ttl || 86400;
         Cache.generateCacheChannel(req, function(channel){
             res.header('X-Cache-Channel', channel);
-            res.header('Last-Modified', new Date().toUTCString());
-            res.header('Cache-Control', 'no-cache,max-age='+ttl+',must-revalidate, public');
+            var cache_policy = req.query.cache_policy;
+            if ( cache_policy == 'persist' ) {
+              res.header('Cache-Control', 'public,max-age=31536000'); // 1 year
+            } else {
+              res.header('Last-Modified', new Date().toUTCString());
+              res.header('Cache-Control', 'no-cache,max-age='+ttl+',must-revalidate, public');
+            }
             cb(null, channel); // add last-modified too ?
         });
     }
@@ -60,7 +65,7 @@ module.exports = function(){
     me.req2params = function(req, callback){
 
         // Whitelist query parameters and attach format
-        var good_query = ['sql', 'geom_type', 'cache_buster','callback', 'interactivity', 'map_key', 'api_key', 'style'];
+        var good_query = ['sql', 'geom_type', 'cache_buster', 'cache_policy', 'callback', 'interactivity', 'map_key', 'api_key', 'style'];
         var bad_query  = _.difference(_.keys(req.query), good_query);
 
         _.each(bad_query, function(key){ delete req.query[key]; });

test/acceptance/server.js

@@ -535,7 +535,40 @@ suite('server', function() {
     // GET TILE
     //
     /////////////////////////////////////////////////////////////////////////////////
-    
+
+    test("should send Cache-Control header with short expiration by default", function(done){
+        assert.response(server, {
+            headers: {host: 'localhost'},
+            url: '/tiles/gadm4/6/31/24.png',
+            method: 'GET'
+        },{
+            status: 200,
+        }, function(res) {
+          var cc = res.headers['cache-control'];
+          assert.ok(cc);
+          //assert.equal(cc, 'public,max-age=31536000');  // 1 year
+          assert.ok(cc.match('no-cache'), cc);
+          assert.ok(cc.match('must-revalidate'), cc);
+          assert.ok(cc.match('public'), cc);
+          done();
+        });
+    });
+
+    test("should send Cache-Control header with long expiration when requested", function(done){
+        assert.response(server, {
+            headers: {host: 'localhost'},
+            url: '/tiles/gadm4/6/31/24.png?cache_policy=persist',
+            method: 'GET'
+        },{
+            status: 200,
+        }, function(res) {
+          var cc = res.headers['cache-control'];
+          assert.ok(cc);
+          assert.equal(cc, 'public,max-age=31536000');  // 1 year
+          done();
+        });
+    });
+
     test("get'ing a tile with default style should return an image", function(done){
         assert.response(server, {
             headers: {host: 'localhost'},