Code cleanup & decoupling

main.go

@@ -30,7 +30,8 @@ var (
 	jsonOutput = flag.Bool("json", false, "output all devices in JSON format")
 )
 
-func renderTables(m []Mount, sortCol int) error {
+// renderTables renders all tables.
+func renderTables(m []Mount, columns []int, sortCol int) error {
 	var local, network, fuse, special []Mount
 
 	// sort/filter devices
@@ -72,19 +73,6 @@ func renderTables(m []Mount, sortCol int) error {
 		local = append(local, v)
 	}
 
-	columns, err := parseColumns(*output)
-	if err != nil {
-		return err
-	}
-	if len(columns) == 0 {
-		// no columns supplied, use defaults
-		if *inodes {
-			columns = []int{1, 6, 7, 8, 9, 10, 11}
-		} else {
-			columns = []int{1, 2, 3, 4, 5, 10, 11}
-		}
-	}
-
 	// print tables
 	if !*hideLocal || *all {
 		printTable("local", local, sortCol, columns)
@@ -101,6 +89,7 @@ func renderTables(m []Mount, sortCol int) error {
 	return nil
 }
 
+// renderJSON encodes the JSON output and prints it.
 func renderJSON(m []Mount) error {
 	output, err := json.MarshalIndent(m, "", " ")
 	if err != nil {
@@ -111,6 +100,7 @@ func renderJSON(m []Mount) error {
 	return nil
 }
 
+// parseColumns parses the supplied output flag into a slice of column indices.
 func parseColumns(cols string) ([]int, error) {
 	var i []int
 
@@ -135,6 +125,21 @@ func parseColumns(cols string) ([]int, error) {
 func main() {
 	flag.Parse()
 
+	// validate flags
+	columns, err := parseColumns(*output)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if len(columns) == 0 {
+		// no columns supplied, use defaults
+		if *inodes {
+			columns = []int{1, 6, 7, 8, 9, 10, 11}
+		} else {
+			columns = []int{1, 2, 3, 4, 5, 10, 11}
+		}
+	}
+
 	sortCol, err := stringToSortIndex(*sortBy)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
@@ -160,10 +165,12 @@ func main() {
 		os.Exit(1)
 	}
 
+	// print out warnings
 	for _, warning := range warnings {
 		fmt.Fprintln(os.Stderr, warning)
 	}
 
+	// print JSON
 	if *jsonOutput {
 		err := renderJSON(m)
 		if err != nil {
@@ -173,7 +180,8 @@ func main() {
 		return
 	}
 
-	err = renderTables(m, sortCol)
+	// print tables
+	err = renderTables(m, columns, sortCol)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 	}

mounts.go

@@ -8,6 +8,7 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+// Mount contains all metadata for a single filesystem mount.
 type Mount struct {
 	Device     string        `json:"device"`
 	DeviceType string        `json:"device_type"`

table.go

@@ -43,6 +43,7 @@ var (
 	colorCyan    = term.Color("#66C2CD")
 )
 
+// printTable prints an individual table of mounts.
 func printTable(title string, m []Mount, sortBy int, cols []int) {
 	tab := table.NewWriter()
 	tab.SetAllowedRowLength(int(*width))
@@ -138,10 +139,12 @@ func printTable(title string, m []Mount, sortBy int, cols []int) {
 	tab.Render()
 }
 
+// sizeTransformer makes a size human-readable.
 func sizeTransformer(val interface{}) string {
 	return sizeToString(val.(uint64))
 }
 
+// spaceTransformer makes a size human-readable and applies a color coding.
 func spaceTransformer(val interface{}) string {
 	free := val.(uint64)
 
@@ -158,6 +161,7 @@ func spaceTransformer(val interface{}) string {
 	return s.String()
 }
 
+// barTransformer transforms a percentage into a progress-bar.
 func barTransformer(val interface{}) string {
 	usage := val.(float64)
 	s := termenv.String()
@@ -187,16 +191,19 @@ func barTransformer(val interface{}) string {
 	return s.String()
 }
 
-func inColumns(i []int, j int) bool {
-	for _, v := range i {
-		if v == j {
+// inColumns return true if the column with index i is in the slice of visible
+// columns cols.
+func inColumns(cols []int, i int) bool {
+	for _, v := range cols {
+		if v == i {
 			return true
 		}
 	}
 
 	return false
 }
 
+// barWidth returns the width of progress-bars for the given render width.
 func barWidth() int {
 	switch {
 	case *width < 100:
@@ -208,6 +215,7 @@ func barWidth() int {
 	}
 }
 
+// tableWidth returns the required minimum table width for the given columns.
 func tableWidth(cols []int, separators bool) int {
 	var sw int
 	if separators {
@@ -274,6 +282,7 @@ func stringToSortIndex(s string) (int, error) {
 	return 0, fmt.Errorf("unknown column: %s (valid: %s)", s, strings.Join(columnIDs(), ", "))
 }
 
+// columnsIDs returns a slice of all column IDs.
 func columnIDs() []string {
 	s := make([]string, len(columns))
 	for i, v := range columns {