add override function for loading & saving blockchain

blockchain/blockchain.js

@@ -5,7 +5,6 @@ const SensorRegistration = require('./sensor-registration');
 const BrokerRegistration = require('./broker-registration');
 const Integration = require('./integration');
 const Compensation = require('./compensation');
-const fs = require('fs');
 const ChainUtil = require('../util/chain-util');
 const RdsStore = require('./rds-store');
 const {
@@ -984,21 +983,9 @@ function findBlocksDifference(oldBlocks, newBlocks) {
   };
 }
 
-function saveToDisk(blockchain, location) {
-  try {
-    fs.writeFileSync(
-      location,
-      blockchain.serialize());
-  } catch (err) {
-    console.log(`Couldn't save blockchain to disk: ${err}`);
-    return false;
-  }
-  return true;
-}
-
 function onChange(blockchain, newBlocks, oldBlocks, difference) {
   if (blockchain.persisting !== null) {
-    saveToDisk(blockchain, blockchain.persisting);
+    Blockchain.saveToDisk(blockchain, blockchain.persisting);
   }
   for (const listener of blockchain.listeners) {
     listener(newBlocks, oldBlocks, difference);
@@ -1053,6 +1040,7 @@ class Blockchain {
   }
 
   static loadFromDisk(location) {
+    const fs = require('fs');
     //possible race if deleted after check, but we live with it I guess
 
     const returning = new Blockchain();
@@ -1072,6 +1060,40 @@ class Blockchain {
     return returning;
   }
 
+  static saveToDisk(blockchain, location) {
+    const fs = require('fs');
+    try {
+      fs.writeFileSync(
+        location,
+        blockchain.serialize());
+    } catch (err) {
+      console.log(`Couldn't save blockchain to disk: ${err}`);
+      return false;
+    }
+    return true;
+  }
+
+  static loadFromDiskOverrideFS(location, saveChain, loadChain) {
+    Blockchain.saveToDisk = (blockchain, location) => {
+      saveChain(location, blockchain.serialize()); // async call, no result can be returned; must assume success.
+      return true;
+    }
+    Blockchain.loadFromDisk = (location) => {
+      const returning = new Blockchain();
+      returning.persisting = location;
+      const rawPersistedChain = loadChain(location); // sync call, because application has already loaded file,
+                                                     //   this simply retrieves it from memory
+      // TODO: Could add check for empty string to prevent error, however, result is the same so leaving for now.
+      const deserialized = Blockchain.deserialize(rawPersistedChain);
+      const replaceResult = returning.replaceChain(deserialized);
+      if (!replaceResult.result) {
+        console.log(`Couldn't deserialize chain at '${location}', starting from genesis: ${replaceResult.reason}`);
+      }
+      return returning;
+    }
+    return Blockchain.loadFromDisk(location);
+  }
+
   //adds an existing block to the blockchain, returns false if the block can't be added, true if it was added
   addBlock(newBlock) {
 
@@ -1160,4 +1182,4 @@ class Blockchain {
   }    
 }
 
-module.exports = Blockchain;
+module.exports = Blockchain;