delegate more work from getOlderHistory to the worker

lib/workers/db-worker.js

@@ -222,10 +222,10 @@ const computeMetadata = function (data, cb) {
 const getOlderHistory = function (data, cb) {
     const oldestKnownHash = data.hash;
     const channelName = data.channel;
+    const desiredMessages = data.desiredMessages;
+    const desiredCheckpoint = data.desiredCheckpoint;
 
-    //const store = Env.store;
-    //const Log = Env.Log;
-    var messageBuffer = [];
+    var messages = [];
     var found = false;
     store.getMessages(channelName, function (msgStr) {
         if (found) { return; }
@@ -246,9 +246,22 @@ const getOlderHistory = function (data, cb) {
         if (hash === oldestKnownHash) {
             found = true;
         }
-        messageBuffer.push(parsed);
+        messages.push(parsed);
     }, function (err) {
-        cb(err, messageBuffer);
+        var toSend = [];
+        if (typeof (desiredMessages) === "number") {
+            toSend = messages.slice(-desiredMessages);
+        } else {
+            let cpCount = 0;
+            for (var i = messages.length - 1; i >= 0; i--) {
+                if (/^cp\|/.test(messages[i][4]) && i !== (messages.length - 1)) {
+                    cpCount++;
+                }
+                toSend.unshift(messages[i]);
+                if (cpCount >= desiredCheckpoint) { break; }
+            }
+        }
+        cb(err, toSend);
     });
 };
 

lib/workers/index.js

@@ -250,12 +250,14 @@ Workers.initialize = function (Env, config, _cb) {
             });
         };
 
-        Env.getOlderHistory = function (channel, oldestKnownHash, cb) {
+        Env.getOlderHistory = function (channel, oldestKnownHash, desiredMessages, desiredCheckpoint, cb) {
             Env.store.getWeakLock(channel, function (next) {
                 sendCommand({
                     channel: channel,
                     command: "GET_OLDER_HISTORY",
                     hash: oldestKnownHash,
+                    desiredMessages: desiredMessages,
+                    desiredCheckpoint: desiredCheckpoint,
                 }, Util.both(next, cb));
             });
         };