Don't open a raft snapshot file until we have a successful snapshot response. (#9894)

* Don't open the snapshot file until we have a successful response

* Check the success of Close if nothing else errors

command/operator_raft_snapshot_save.go

@@ -2,6 +2,7 @@ package command
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"strings"
 
@@ -71,24 +72,54 @@ func (c *OperatorRaftSnapshotSaveCommand) Run(args []string) int {
 		return 1
 	}
 
-	snapFile, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
-	if err != nil {
-		c.UI.Error(fmt.Sprintf("Error opening output file: %s", err))
-		return 2
+	w := &lazyOpenWriter{
+		openFunc: func() (io.WriteCloser, error) {
+			return os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+		},
 	}
-	defer snapFile.Close()
 
 	client, err := c.Client()
 	if err != nil {
+		w.Close()
 		c.UI.Error(err.Error())
 		return 2
 	}
 
-	err = client.Sys().RaftSnapshot(snapFile)
+	err = client.Sys().RaftSnapshot(w)
+	if err != nil {
+		w.Close()
+		c.UI.Error(fmt.Sprintf("Error taking the snapshot: %s", err))
+		return 2
+	}
+	
+	err = w.Close()
 	if err != nil {
 		c.UI.Error(fmt.Sprintf("Error taking the snapshot: %s", err))
 		return 2
 	}
-
 	return 0
 }
+
+type lazyOpenWriter struct {
+	openFunc func() (io.WriteCloser, error)
+	writer io.WriteCloser
+}
+
+
+func (l *lazyOpenWriter) Write(p []byte) (n int, err error) {
+	if l.writer == nil {
+		var err error
+		l.writer, err = l.openFunc()
+		if err != nil {
+			return 0, err
+		}
+	}
+	return l.writer.Write(p)
+}
+
+func (l *lazyOpenWriter) Close() error {
+	if l.writer != nil {
+		return l.writer.Close()
+	}
+	return nil
+}