From d4f94f3091230bed0e7651d86dc795e54e60f96a Mon Sep 17 00:00:00 2001
From: ansuz <ansuz@transitiontech.ca>
Date: Tue, 8 Dec 2020 16:34:28 +0530
Subject: [PATCH] briefly cache server metadata in-memory to avoid repeated
 reads

---
 lib/commands/metadata.js |  9 ++++++++-
 lib/env.js               | 12 ++++++++++--
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/lib/commands/metadata.js b/lib/commands/metadata.js
index 3d20f36e6..b189d73be 100644
--- a/lib/commands/metadata.js
+++ b/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);
+        });
     });
 };
 
diff --git a/lib/env.js b/lib/env.js
index 3a876f1f7..066fcd115 100644
--- a/lib/env.js
+++ b/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;