main: error on startup for attempting to switch between utreexo and

non-utreexo nodes

utreexod.go

@@ -16,6 +16,7 @@ import (
 	"runtime/pprof"
 	"runtime/trace"
 
+	"github.com/utreexo/utreexod/blockchain"
 	"github.com/utreexo/utreexod/blockchain/indexers"
 	"github.com/utreexo/utreexod/database"
 	"github.com/utreexo/utreexod/limits"
@@ -139,6 +140,45 @@ func btcdMain(serverChan chan<- *server) error {
 		return nil
 	}
 
+	// Find out if the user is restarting the node.
+	var chainstateInitialized bool
+	db.View(func(dbTx database.Tx) error {
+		chainstateInitialized = blockchain.ChainstateInitialized(dbTx)
+		return nil
+	})
+
+	// If the node is being re-started, do some checks to prevent the user from switching
+	// between a utreexo node vs a non-utreexo node.
+	if chainstateInitialized {
+		var cacheInitialized bool
+		db.View(func(dbTx database.Tx) error {
+			cacheInitialized = blockchain.UtxoCacheInitialized(dbTx)
+			return nil
+		})
+
+		// If the node has been a non-utreexo node but it was now re-started as a utreexo node.
+		if cacheInitialized && !cfg.NoUtreexo {
+			err = fmt.Errorf("Utreexo enabled but this node has been "+
+				"started as a non-utreexo node previously at datadir of \"%v\". "+
+				"Please completely remove the datadir to start as a utreexo "+
+				"node or pass in a different --datadir.",
+				cfg.DataDir)
+			btcdLog.Error(err)
+			return err
+		}
+
+		// If the node has been a utreexo node but it was now re-started as a non-utreexo node.
+		if !cacheInitialized && cfg.NoUtreexo {
+			err = fmt.Errorf("Utreexo disabled but this node has been previously "+
+				"started as a utreexo node at datadir of \"%v\". Please "+
+				"completely remove the datadir to start as a non-utreexo node "+
+				"or pass in a different --datadir.",
+				cfg.DataDir)
+			btcdLog.Error(err)
+			return err
+		}
+	}
+
 	// Drop indexes and exit if requested.
 	//
 	// NOTE: The order is important here because dropping the tx index also