Correct state handling for split updates

- Always merge state again, so that we keep the missing information from the not updated protocol

service/updaterequest.go

@@ -6,6 +6,7 @@ import (
 	"io/ioutil"
 	"log"
 	"net"
+	"os"
 )
 
 type UpdateRequest struct {
@@ -30,13 +31,41 @@ func (ur *UpdateRequest) PrettyPrint() string {
 	return string(s)
 }
 
+func (ur *UpdateRequest) MergeOldStateFile() {
+	filename := ur.Config.GetStateFileName()
+
+	if _, err := os.Stat(filename); err != nil {
+		log.Printf("No old state file %s found, skip merging: %v", filename, err)
+	}
+
+	// We have a state file present, load it and merge into current state
+	// so that we don't loose any IPv4/v6 data during partial updates.
+
+	oldState, err := LoadStateFile(ur.Config)
+	if err != nil {
+		log.Printf("Failed to load old state file %s to merge while saving, skipping it: %v",
+			filename, err)
+		return
+	}
+
+	if ur.IPv4 == nil {
+		ur.IPv4 = oldState.IPv4
+	}
+	if ur.IPv6 == nil {
+		ur.IPv6 = oldState.IPv6
+		ur.IPv6Net = oldState.IPv6Net
+	}
+}
+
 func (ur *UpdateRequest) SaveStateFile() error {
+	ur.MergeOldStateFile()
+
+	filename := ur.Config.GetStateFileName()
 	data, err := json.MarshalIndent(ur, "", " ")
 	if err != nil {
 		return fmt.Errorf("failed to convert state for user %s to JSON: %v",
 			ur.UserName, err)
 	}
-	filename := ur.Config.GetStateFileName()
 	if err = ioutil.WriteFile(filename, data, 0640); err != nil {
 		return fmt.Errorf("failed to to write sate file for user %s to file %s: %v",
 			ur.UserName, filename, err)