Implement blackbox in Golang (#250)

* Initial release

pkg/bbutil/shred.go

@@ -0,0 +1,109 @@
+package bbutil
+
+// Pick an appropriate secure erase command for this operating system
+// or just delete the file with os.Remove().
+
+// Code rewritten based https://codereview.stackexchange.com/questions/245072
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+)
+
+var shredCmds = []struct {
+	name, opts string
+}{
+	{"sdelete", "-a"},
+	{"shred", "-u"},
+	{"srm", "-f"},
+	{"rm", "-Pf"},
+}
+
+func shredTemp(path, opts string) error {
+	file, err := ioutil.TempFile("", "shredTemp.")
+	if err != nil {
+		return err
+	}
+	filename := file.Name()
+	defer os.Remove(filename)
+	defer file.Close()
+
+	err = file.Close()
+	if err != nil {
+		return err
+	}
+	err = RunBash(path, opts, filename)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+var shredPath, shredOpts = func() (string, string) {
+	for _, cmd := range shredCmds {
+		path, err := exec.LookPath(cmd.name)
+		if err != nil {
+			continue
+		}
+		err = shredTemp(path, cmd.opts)
+		if err == nil {
+			return path, cmd.opts
+		}
+	}
+	return "", ""
+}()
+
+// ShredInfo reveals the shred command and flags (for "blackbox info")
+func ShredInfo() string {
+	return shredPath + " " + shredOpts
+}
+
+// shredFile shreds one file.
+func shredFile(filename string) error {
+	fi, err := os.Stat(filename)
+	if err != nil {
+		return err
+	}
+	if !fi.Mode().IsRegular() {
+		err := fmt.Errorf("filename is not mode regular")
+		return err
+	}
+
+	if shredPath == "" {
+		// No secure erase command found.  Default to a normal file delete.
+		// TODO(tlim): Print a warning? Have a flag that causes this to be an error?
+		return os.Remove(filename)
+	}
+
+	err = RunBash(shredPath, shredOpts, filename)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// ShredFiles securely erases a list of files.
+func ShredFiles(names []string) error {
+
+	// TODO(tlim) DO the shredding in parallel like in v1.
+
+	var eerr error
+	for _, n := range names {
+		_, err := os.Stat(n)
+		if err != nil {
+			if os.IsNotExist(err) {
+				fmt.Printf("======= already gone: %q\n", n)
+				continue
+			}
+		}
+		fmt.Printf("========== SHREDDING: %q\n", n)
+		e := shredFile(n)
+		if e != nil {
+			eerr = e
+			fmt.Printf("ERROR: %v\n", e)
+		}
+	}
+	return eerr
+}