Read/Write/Upgrade config.json with settings module

src/common/settings.js

@@ -0,0 +1,39 @@
+'use strict';
+
+const fs = require('fs');
+const version = 1;
+
+var upgradeV0toV1 = function(config_v0) {
+  return {
+    url: [config_v0.url],
+    version: 1
+  };
+};
+
+var upgrade = function(config) {
+  var config_version = config.version ? config.version : 0;
+  switch (config_version) {
+    case 0:
+      return upgrade(upgradeV0toV1(config));
+    default:
+      return config;
+  }
+};
+
+module.exports = {
+  version: version,
+
+  upgrade: upgrade,
+
+  readFileSync: function(configFile) {
+    return JSON.parse(fs.readFileSync(configFile, 'utf8'));
+  },
+
+  writeFileSync: function(configFile, config) {
+    if (config.version != version) {
+      throw 'version ' + config.version + ' is not equal to ' + version;
+    }
+    var data = JSON.stringify(config, null, '  ');
+    fs.writeFileSync(configFile, data, 'utf8');
+  }
+};