Implement --import mode and re-order startup

This commit modifies the startup sequence somewhat, so that OS signals
are only listened for if NodeAtlas is starting up normally.

Ref #62

Author: alexander-bauer

nodeatlas.go

@@ -48,6 +48,7 @@ var (
 
 	fReadOnly = flag.Bool("readonly", false, "disallow database changes")
 
+	fImport = flag.String("import", "", "import a JSON array of nodes")
 	fTestDB = flag.Bool("testdb", false, "test the database")
 )
 
@@ -90,9 +91,6 @@ func main() {
 		os.Exit(1)
 	}
 
-	// Listen for OS signals.
-	go ListenSignal()
-
 	l.Infof("Starting NodeAtlas %s\n", Version)
 
 	// Compile and template the static directory.
@@ -159,6 +157,21 @@ func main() {
 	l.Debug("Initialized database\n")
 	l.Infof("Nodes: %d (%d local)\n", Db.LenNodes(true), Db.LenNodes(false))
 
+	// Check action flags and abandon normal startup if any are set.
+	if len(*fImport) != 0 {
+		err := ImportFile(*fImport)
+		if err != nil {
+			l.Fatalf("Import failed: %s", err)
+		} else {
+			l.Printf("Import successful!")
+		}
+		return
+	}
+
+	// Listen for OS signals.
+	go ListenSignal()
+
+	// Start the Heartbeat.
 	Heartbeat()
 	l.Debug("Heartbeat started\n")