crypt: Add --crypt-show-mapping to show encrypted file mapping

Fixes #1004

crypt/crypt.go

@@ -12,6 +12,12 @@ import (
 	"github.com/pkg/errors"
 )
 
+// Globals
+var (
+	// Flags
+	cryptShowMapping = fs.BoolP("crypt-show-mapping", "", false, "For all files listed show how the names encrypt.")
+)
+
 // Register with Fs
 func init() {
 	fs.Register(&fs.RegInfo{
@@ -485,11 +491,14 @@ func (lo *ListOpts) Level() int {
 // Multiple goroutines can safely add objects concurrently.
 func (lo *ListOpts) Add(obj fs.Object) (abort bool) {
 	remote := obj.Remote()
-	_, err := lo.f.cipher.DecryptFileName(remote)
+	decryptedRemote, err := lo.f.cipher.DecryptFileName(remote)
 	if err != nil {
 		fs.Debug(remote, "Skipping undecryptable file name: %v", err)
 		return lo.ListOpts.IsFinished()
 	}
+	if *cryptShowMapping {
+		fs.Log(decryptedRemote, "Encrypts to %q", remote)
+	}
 	return lo.ListOpts.Add(lo.f.newObject(obj))
 }
 
@@ -498,11 +507,14 @@ func (lo *ListOpts) Add(obj fs.Object) (abort bool) {
 // Multiple goroutines can safely add objects concurrently.
 func (lo *ListOpts) AddDir(dir *fs.Dir) (abort bool) {
 	remote := dir.Name
-	_, err := lo.f.cipher.DecryptDirName(remote)
+	decryptedRemote, err := lo.f.cipher.DecryptDirName(remote)
 	if err != nil {
 		fs.Debug(remote, "Skipping undecryptable dir name: %v", err)
 		return lo.ListOpts.IsFinished()
 	}
+	if *cryptShowMapping {
+		fs.Log(decryptedRemote, "Encrypts to %q", remote)
+	}
 	return lo.ListOpts.AddDir(lo.f.newDir(dir))
 }
 

docs/content/crypt.md

@@ -236,6 +236,21 @@ depends on that.
 Hashes are not stored for crypt.  However the data integrity is
 protected by an extremely strong crypto authenticator.
 
+### Specific options ###
+
+Here are the command line options specific to this cloud storage
+system.
+
+#### --crypt-show-mapping ####
+
+If this flag is set then for each file that the remote is asked to
+list, it will log (at level INFO) a line stating the decrypted file
+name and the encrypted file name.
+
+This is so you can work out which encrypted names are which decrypted
+names just in case you need to do something with the encrypted file
+names, or for debugging purposes.
+
 ## File formats ##
 
 ### File encryption ###