briefly cache server metadata in-memory to avoid repeated reads

lib/commands/metadata.js

@@ -17,7 +17,14 @@ Data.getMetadataRaw = function (Env, channel /* channelName */, _cb) {
     }
 
     Env.batchMetadata(channel, cb, function (done) {
-        Env.computeMetadata(channel, done);
+        Env.computeMetadata(channel, function (err, meta) {
+            if (!err && meta && meta.channel) {
+                Env.metadata_cache[channel] = meta;
+                // clear metadata after a delay if nobody has joined the channel within 30s
+                Env.checkCache(channel);
+            }
+            done(err, meta);
+        });
     });
 };
 

lib/env.js

@@ -42,6 +42,8 @@ module.exports.create = function (config) {
 
         metadata_cache: {},
         channel_cache: {},
+        cache_checks: {},
+
         queueStorage: WriteQueue(),
         queueDeletes: WriteQueue(),
         queueValidation: WriteQueue(),
@@ -117,8 +119,14 @@ module.exports.create = function (config) {
         }
     }());
 
-
+    Env.checkCache = function (channel) {
-
+        var f = Env.cache_checks[channel] || Util.throttle(function () {
+            if (Env.channel_cache[channel]) { return; }
+            delete Env.metadata_cache[channel];
+            delete Env.cache_checks[channel];
+        }, 30000);
+        f();
+    };
 
     (function () {
         var custom = config.customLimits;