check config file keys for validity (#296)

* check config file keys for validity, use setValue instead of direct access
* Update config.d
  Add 'drive_id' to be initialised, set to an empty string
* exit application if there is a configuration file error
* Issue #293 was caused by a spelling error in the configuration file. 
  If the configuration file has errors, we should not load it or run
  using the application defaults as this may have undesirable consequences
  for users data
* missed returning false on key issue
* Missed this edit of the file

src/config.d

@@ -24,7 +24,7 @@ final class Config
 		syncListFilePath = configDirName ~ "/sync_list";
 	}
 
-	void init()
+	bool init()
 	{
 		// Default configuration directory
 		setValue("sync_dir", "~/OneDrive");
@@ -39,10 +39,20 @@ final class Config
 		setValue("monitor_interval", "45");
 		// Configure the default logging directory to be /var/log/onedrive/
 		setValue("log_dir", "/var/log/onedrive/");
+		// Configure a default empty value for drive_id
+		setValue("drive_id", "");
 
 		if (!load(userConfigFilePath)) {
-			log.vlog("No config file found, using defaults");
+			// What was the reason for failure?
+			if (!exists(userConfigFilePath)) {
+				log.vlog("No config file found, using application defaults");
+				return true;
+			} else {
+				log.log("Configuration file has errors - please check your configuration");
+				return false;
+			}
 		}
+		return true;
 	}
 
 	string getValue(string key)
@@ -82,10 +92,17 @@ final class Config
 			if (!c.empty) {
 				c.popFront(); // skip the whole match
 				string key = c.front.dup;
-				c.popFront();
-				values[key] = c.front.dup;
+				auto p = key in values;
+				if (p) {
+					c.popFront();
+					setValue(key, c.front.dup);
+				} else {
+					log.log("Unknown key in config file: ", key);
+					return false;
+				}
 			} else {
 				log.log("Malformed config line: ", line);
+				return false;
 			}
 		}
 		return true;

src/main.d

@@ -155,7 +155,11 @@ int main(string[] args)
 	log.vlog("Using Config Dir: ", configDirName);
 	if (!exists(configDirName)) mkdirRecurse(configDirName);
 	auto cfg = new config.Config(configDirName);
-	cfg.init();
+	if(!cfg.init()){
+		// There was an error loading the configuration
+		// Error message already printed
+		return EXIT_FAILURE;
+	}
 
 	// Set the local path OneDrive root
 	string syncDir;