ext4: Build working, args parsing

1 files changed, 68 insertions, 15 deletions

diff --git a/ext4/ext4.go b/ext4/ext4.go
index cbe87da..401d208 100644
--- a/ext4/ext4.go
+++ b/ext4/ext4.go
@@ -1,37 +1,90 @@
 package main
 
 import (
+	"flag"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 )
 
-func printUsage(w io.Writer, name string) {
-	fmt.Fprintf(w, "Usage: %s [enable|disable] <device> [--force]\n\n", name)
-	fmt.Fprintln(w, "Enable or disable encryption on an ext4 filesystem.")
-	fmt.Fprintln(w, "  <device> - Path to the filesystem device")
-	fmt.Fprintln(w, "  --force  - Automatically proceed with the operation")
+var (
+	// Setup command parsing
+	cmdName = os.Args[0]
+	set     = flag.NewFlagSet(cmdName, flag.ContinueOnError)
+	// Flags for our command
+	forceFlag   = set.Bool("force", false, "Suppress all warnings and do not prompt")
+	versionFlag = set.Bool("version", false, "Print the fscrypt version.")
+	helpFlag    = set.Bool("help", false, "Print this help text.")
+	// fscrypt's version (set by Makefile)
+	version string
+)
+
+const (
+	manPage  = "fscrypt-ext4(8)"
+	manBrief = "enable or disable encryption on an ext4 filesystem"
+	usageFmt = `
+Usage:
+	%[1]s [enable | disable] <mountpoint> [--force]
+	%[1]s --help
+	%[1]s --version
+
+Arguments:
+  	<mountpoint> - path to an ext4 filesystem
+`
+)
+
+func printUsageAndExit(err error) {
+	var w io.Writer
+	var rc int
+	if err == nil {
+		w = os.Stdout
+		rc = 0
+		fmt.Fprintf(w, "%s - %s\n", cmdName, manBrief)
+	} else {
+		w = os.Stderr
+		rc = 1
+		fmt.Fprintf(w, "%s: %v\n", cmdName, err)
+	}
+
+	fmt.Fprintf(w, usageFmt, cmdName)
+	fmt.Fprintln(w, "\nOptions:")
+	set.VisitAll(func(f *flag.Flag) {
+		fmt.Fprintf(w, "\t--%s\n\t\t%s\n", f.Name, f.Usage)
+	})
+	fmt.Fprintf(w, "\nSee the %s man page for more info.\n", manPage)
+	os.Exit(rc)
 }
 
 func main() {
-	if len(os.Args) != 3 {
-		printUsage(os.Stderr, os.Args[0])
-		os.Exit(1)
+	set.SetOutput(ioutil.Discard)
+	if err := set.Parse(os.Args[1:]); err != nil {
+		printUsageAndExit(err)
+	}
+	if *helpFlag {
+		printUsageAndExit(nil)
 	}
-	switch os.Args[1] {
+	if *versionFlag {
+		fmt.Println(version)
+		return
+	}
+	if set.NArg() != 2 {
+		printUsageAndExit(fmt.Errorf("expected 2 arguments, got %d", set.NArg()))
+	}
+
+	command, mountpoint := set.Arg(0), set.Arg(1)
+	switch command {
 	case "enable":
 		fmt.Println("Enabling encryption!!")
 	case "disable":
 		fmt.Println("Disabling encryption!!")
 	default:
-		fmt.Fprintf(os.Stderr, "%s: invalid command %q\n", os.Args[0], os.Args[1])
-		printUsage(os.Stderr, os.Args[0])
-		os.Exit(1)
+		printUsageAndExit(fmt.Errorf("invalid command %q", command))
 	}
 
-	if isExt4EncryptionEnabled(os.Args[2]) {
-		fmt.Printf("%q has encryption\n", os.Args[2])
+	if isExt4EncryptionEnabled(mountpoint) {
+		fmt.Printf("%q has encryption\n", mountpoint)
 	} else {
-		fmt.Printf("%q doesn't have encryption\n", os.Args[2])
+		fmt.Printf("%q doesn't have encryption\n", mountpoint)
 	}
 }