Job handler caching

Caches the last job sent down the wire, and ensures that we can return it, rather than blank.

Fixes #37

lib/pool.js

@@ -202,6 +202,7 @@ function Miner(id, login, pass, ipAddress, startingDiff, messageSender, protoVer
     this.valid_miner = true;
     this.port = port;
     this.portType = portType;
+    this.incremented = false;
     switch (portType) {
         case 'pplns':
             this.poolTypeEnum = global.protos.POOLTYPE.PPLNS;
@@ -320,6 +321,8 @@ function Miner(id, login, pass, ipAddress, startingDiff, messageSender, protoVer
 
     this.validJobs = global.support.circularBuffer(10);
 
+    this.cachedJob = null;
+
     this.invalidShareProto = global.protos.InvalidShare.encode({
         paymentAddress: this.address,
         paymentID: this.paymentID,
@@ -432,12 +435,8 @@ function Miner(id, login, pass, ipAddress, startingDiff, messageSender, protoVer
         };
         this.getJob = function () {
             
-            if (this.lastBlockHeight === activeBlockTemplate.height && !this.newDiff) {
-                return {
-                    blob: '',
-                    job_id: '',
-                    target: ''
-                };
+            if (this.lastBlockHeight === activeBlockTemplate.height && !this.newDiff && this.cachedJob !== null) {
+                return this.cachedJob;
             }
 
             let blob = activeBlockTemplate.nextBlob();
@@ -455,12 +454,12 @@ function Miner(id, login, pass, ipAddress, startingDiff, messageSender, protoVer
             };
 
             this.validJobs.enq(newJob);
-
-            return {
+            this.cachedJob = {
                 blob: blob,
                 job_id: newJob.id,
                 target: target
             };
+            return this.cachedJob;
         };
     }
 }
@@ -522,7 +521,13 @@ function processShare(miner, job, blockTemplate, nonce, resultHash) {
     }
     if (hash.toString('hex') !== resultHash) {
         console.error(threadName + "Bad hash from miner " + miner.logString);
-        miner.newDiff = miner.difficulty + 1;
+        if (miner.incremented === false){
+            miner.newDiff = miner.difficulty + 1;
+            miner.incremented = true;
+        } else {
+            miner.newDiff = miner.difficulty - 1;
+            miner.incremented = false;
+        }
         miner.messageSender('job', miner.getJob());
         return false;
     }
@@ -644,7 +649,13 @@ function handleMinerData(method, params, ip, portData, sendReply, pushMessage) {
 
             if (!blockTemplate) {
                 console.warn(threadName + 'Block expired, Height: ' + job.height + ' from ' + miner.logString);
-                miner.newDiff = miner.difficulty + 1;
+                if (miner.incremented === false){
+                    miner.newDiff = miner.difficulty + 1;
+                    miner.incremented = true;
+                } else {
+                    miner.newDiff = miner.difficulty - 1;
+                    miner.incremented = false;
+                }
                 miner.messageSender('job', miner.getJob());
                 sendReply('Block expired');
                 global.database.storeInvalidShare(miner.invalidShareProto);