check if new template file was modified

internal/app/wwctl/overlay/edit/main.go

@@ -1,7 +1,10 @@
 package edit
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
+	"io"
 	"os"
 	"path"
 	"path/filepath"
@@ -47,34 +50,59 @@ func CobraRunE(cmd *cobra.Command, args []string) error {
 			os.Exit(1)
 		}
 	}
-
+	newFile := false
 	if !util.IsFile(overlayFile) && filepath.Ext(overlayFile) == ".ww" {
 		wwlog.Verbose("This is a new file, creating some default content")
-
+		newFile = true
 		w, err := os.OpenFile(overlayFile, os.O_RDWR|os.O_CREATE, os.FileMode(PermMode))
 		if err != nil {
 			wwlog.Warn("Could not create file for writing: %s", err)
 		}
-
-		fmt.Fprintf(w, "# This is a Warewulf Template file.\n")
-		fmt.Fprintf(w, "#\n")
-		fmt.Fprintf(w, "# This file (suffix '.ww') will be automatically rewritten without the suffix\n")
-		fmt.Fprintf(w, "# when the overlay is rendered for the individual nodes. Here are some examples\n")
-		fmt.Fprintf(w, "# of macros and logic which can be used within this file:\n")
-		fmt.Fprintf(w, "#\n")
-		fmt.Fprintf(w, "# Node FQDN = {{.Id}}\n")
-		fmt.Fprintf(w, "# Node Cluster = {{.ClusterName}}\n")
-		fmt.Fprintf(w, "# Network Config = {{.NetDevs.eth0.Ipaddr}}, {{.NetDevs.eth0.Hwaddr}}, etc.\n")
-		fmt.Fprintf(w, "#\n")
-		fmt.Fprintf(w, "# Goto the documentation pages for more information: http://www.hpcng.org/...\n")
-		fmt.Fprintf(w, "\n")
+		fmtStr := `# This is a Warewulf Template file.
+#
+# This file (suffix '.ww') will be automatically rewritten without the suffix
+# when the overlay is rendered for the individual nodes. Here are some examples
+# of macros and logic which can be used within this file:
+#
+# Node FQDN = {{.Id}}\n")
+# Node Cluster = {{.ClusterName}}\n")
+# Network Config = {{.NetDevs.eth0.Ipaddr}}, {{.NetDevs.eth0.Hwaddr}}, etc.
+#
+# Goto the documentation pages for more information: http://www.hpcng.org/...
+# Keep the following for better reference
+# This file is autogenerated by warewulf 
+# Host:   {{.BuildHost}}
+# Time:   {{.BuildTime}}
+# Source: {{.BuildSource}}
+`
+		fmt.Fprint(w, fmtStr)
 	}
-
-	err := util.ExecInteractive(editor, overlayFile)
+	fileDesc, err := os.OpenFile(overlayFile, os.O_RDWR, os.FileMode(PermMode))
+	defer fileDesc.Close()
+	_, _ = fileDesc.Seek(0, 0)
+	hasher := sha256.New()
+	if _, err := io.Copy(hasher, fileDesc); err != nil {
+		wwlog.Error("Problems getting checksum of file %s\n", err)
+	}
+	sum1 := hex.EncodeToString(hasher.Sum(nil))
+	err = util.ExecInteractive(editor, overlayFile)
 	if err != nil {
 		wwlog.Error("Editor process existed with non-zero")
 		os.Exit(1)
 	}
+	_, _ = fileDesc.Seek(0, 0)
+	hasher.Reset()
+	if _, err := io.Copy(hasher, fileDesc); err != nil {
+		wwlog.Error("Problems getting checksum of file %s\n", err)
+	}
+	sum2 := hex.EncodeToString(hasher.Sum(nil))
+	if sum1 == sum2 && newFile {
+		wwlog.Verbose("New template %s wasn't modified, deleting it", overlayFile)
+		err = os.Remove(overlayFile)
+		if err != nil {
+			wwlog.Warn("Could not delete %s", overlayFile)
+		}
+	}
 
 	return nil
 }