added the wwctl overlay parse command

The `wwctl overlay parse -n NODE FILE` will interpret the given overlay file and print it stdout, via wwlog.PRINTF.
The overlay code had to be refactored for this, but hopefully this makes the code a bit more readable. Also the tstruct has not its own initilization code.

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

@@ -0,0 +1,83 @@
+package parse
+
+import (
+	"bufio"
+	"bytes"
+	"os"
+	"path/filepath"
+	"regexp"
+
+	"github.com/hpcng/warewulf/internal/pkg/node"
+	"github.com/hpcng/warewulf/internal/pkg/overlay"
+	"github.com/hpcng/warewulf/internal/pkg/util"
+	"github.com/hpcng/warewulf/internal/pkg/wwlog"
+	"github.com/spf13/cobra"
+)
+
+func CobraRunE(cmd *cobra.Command, args []string) error {
+	var host node.NodeInfo
+	if NodeName == "" {
+		host.Kernel = new(node.KernelEntry)
+		host.Ipmi = new(node.IpmiEntry)
+		var idEntry node.Entry
+		hostname, _ := os.Hostname()
+		idEntry.Set(hostname)
+		host.Id = idEntry
+	} else {
+		nodeDB, err := node.New()
+		if err != nil {
+			wwlog.Printf(wwlog.ERROR, "Could not open node configuration: %s\n", err)
+			os.Exit(1)
+		}
+		nodes, err := nodeDB.FindAllNodes()
+		if err != nil {
+			wwlog.Printf(wwlog.ERROR, "Could not get node list: %s\n", err)
+			os.Exit(1)
+		}
+		node := node.FilterByName(nodes, []string{NodeName})
+		if len(node) != 1 {
+			wwlog.Printf(wwlog.ERROR, "%v does not identify a single node\n", NodeName)
+			os.Exit(1)
+		}
+		host = node[0]
+	}
+	if !util.IsFile(args[0]) {
+		wwlog.Printf(wwlog.ERROR, "%s is not a file\n", args[0])
+	}
+	tstruct := overlay.InitStruct(host)
+	buffer, backupFile, writeFile, err := overlay.RenderTemplateFile(args[0], tstruct)
+	if err != nil {
+		return err
+	}
+	if filepath.Ext(args[0]) != ".ww" {
+		wwlog.Printf(wwlog.WARN, "%s has not the '.ww' so wont be rendered if in overlay\n", args[0])
+	}
+	wwlog.Printf(wwlog.INFO, "backupFile: %v\nwriteFile: %v\n", backupFile, writeFile)
+	var outBuffer bytes.Buffer
+	// search for magic file name comment
+	bufferScanner := bufio.NewScanner(bytes.NewReader(buffer.Bytes()))
+	bufferScanner.Split(overlay.ScanLines)
+	reg := regexp.MustCompile(`.*{{\s*/\*\s*file\s*["'](.*)["']\s*\*/\s*}}.*`)
+	foundFileComment := false
+	destFileName := args[0]
+	for bufferScanner.Scan() {
+		line := bufferScanner.Text()
+		filenameFromTemplate := reg.FindAllStringSubmatch(line, -1)
+		if len(filenameFromTemplate) != 0 {
+			wwlog.Printf(wwlog.DEBUG, "Found multifile comment, new filename %s\n", filenameFromTemplate[0][1])
+			if foundFileComment {
+				wwlog.Printf(wwlog.INFO, "%s", outBuffer.String())
+				outBuffer.Reset()
+			}
+			destFileName = filenameFromTemplate[0][1]
+			wwlog.Printf(wwlog.INFO, "Filename: %s\n\n", destFileName)
+			wwlog.Printf(wwlog.INFO, "%s", outBuffer.String())
+			foundFileComment = true
+		} else {
+			_, _ = outBuffer.WriteString(line)
+		}
+	}
+	wwlog.Printf(wwlog.INFO, "Filename: %s\n\n", destFileName)
+	wwlog.Printf(wwlog.INFO, "%s", outBuffer.String())
+	return nil
+}

internal/app/wwctl/overlay/parse/root.go

@@ -0,0 +1,41 @@
+package parse
+
+import (
+	"log"
+
+	"github.com/hpcng/warewulf/internal/pkg/node"
+	"github.com/spf13/cobra"
+)
+
+var (
+	baseCmd = &cobra.Command{
+		DisableFlagsInUseLine: true,
+		Use:                   "parse [OPTIONS] FILE_NAME",
+		Short:                 "parses interprets the given file as warewulf template",
+		Long:                  "This command tries to parse a given file as warewulf template, it needs not to be in overlay folder.",
+		RunE:                  CobraRunE,
+		Aliases:               []string{"parse"},
+		Args:                  cobra.ExactArgs(1),
+	}
+	NodeName string
+)
+
+func init() {
+	baseCmd.PersistentFlags().StringVarP(&NodeName, "node", "n", "", "node used for the variables in the template")
+	if err := baseCmd.RegisterFlagCompletionFunc("node", func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		nodeDB, _ := node.New()
+		nodes, _ := nodeDB.FindAllNodes()
+		var node_names []string
+		for _, node := range nodes {
+			node_names = append(node_names, node.Id.Get())
+		}
+		return node_names, cobra.ShellCompDirectiveNoFileComp
+	}); err != nil {
+		log.Println(err)
+	}
+}
+
+// GetRootCommand returns the root cobra.Command for the application.
+func GetCommand() *cobra.Command {
+	return baseCmd
+}

internal/app/wwctl/overlay/root.go

@@ -10,6 +10,7 @@ import (
 	"github.com/hpcng/warewulf/internal/app/wwctl/overlay/imprt"
 	"github.com/hpcng/warewulf/internal/app/wwctl/overlay/list"
 	"github.com/hpcng/warewulf/internal/app/wwctl/overlay/mkdir"
+	"github.com/hpcng/warewulf/internal/app/wwctl/overlay/parse"
 	"github.com/hpcng/warewulf/internal/app/wwctl/overlay/show"
 	"github.com/spf13/cobra"
 )
@@ -17,9 +18,9 @@ import (
 var (
 	baseCmd = &cobra.Command{
 		DisableFlagsInUseLine: true,
-		Use:   "overlay COMMAND [OPTIONS]",
+		Use:                   "overlay COMMAND [OPTIONS]",
-		Short: "Warewulf Overlay Management",
+		Short:                 "Warewulf Overlay Management",
-		Long:  "Management interface for Warewulf overlays",
+		Long:                  "Management interface for Warewulf overlays",
 	}
 )
 
@@ -34,6 +35,8 @@ func init() {
 	baseCmd.AddCommand(imprt.GetCommand())
 	baseCmd.AddCommand(chmod.GetCommand())
 	baseCmd.AddCommand(chown.GetCommand())
+	baseCmd.AddCommand(parse.GetCommand())
+
 }
 
 // GetRootCommand returns the root cobra.Command for the application.

internal/pkg/overlay/overlay.go

@@ -243,12 +243,15 @@ func BuildOverlayIndir(nodeInfo node.NodeInfo, overlayNames []string, outputDir
 				destFile := strings.TrimSuffix(location, ".ww")
 
 				buffer, backupFile, writeFile, err := RenderTemplateFile(location, tstruct)
+				if err != nil {
+					return errors.Wrap(err, fmt.Sprintf("Failed to render template %s", location))
+				}
 				if writeFile {
 					destFileName := destFile
 					var fileBuffer bytes.Buffer
 					// search for magic file name comment
 					fileScanner := bufio.NewScanner(bytes.NewReader(buffer.Bytes()))
-					fileScanner.Split(scanLines)
+					fileScanner.Split(ScanLines)
 					reg := regexp.MustCompile(`.*{{\s*/\*\s*file\s*["'](.*)["']\s*\*/\s*}}.*`)
 					foundFileComment := false
 					for fileScanner.Scan() {
@@ -346,7 +349,11 @@ Parses the template with the given filename, variables must be in data. Returns
 parsed template as bytes.Buffer, and the bool variables for backupFile and writeFile.
 If something goes wrong an error is returned.
 */
-func RenderTemplateFile(fileName string, data TemplateStruct) (buffer bytes.Buffer, backupFile bool, writeFile bool, err error) {
+func RenderTemplateFile(fileName string, data TemplateStruct) (
+	buffer bytes.Buffer,
+	backupFile bool,
+	writeFile bool,
+	err error) {
 	backupFile = true
 	writeFile = true
 	tmpl, err := template.New(path.Base(fileName)).Option("missingkey=default").Funcs(template.FuncMap{
@@ -385,7 +392,7 @@ func RenderTemplateFile(fileName string, data TemplateStruct) (buffer bytes.Buff
 }
 
 // Simple version of ScanLines, but include the line break
-func scanLines(data []byte, atEOF bool) (advance int, token []byte, err error) {
+func ScanLines(data []byte, atEOF bool) (advance int, token []byte, err error) {
 	if atEOF && len(data) == 0 {
 		return 0, nil, nil
 	}