lnwire: modify Alias to only track the non-zero portion of wire msg

This commit modifies the Alias type to only hold the non-zero portion
of the alias as encoded on the wire. Previously the entire 32-bytes
would be read and stored, including the zeroes at the end used as
padding. Within the constructor, we now parse the alias properly,
discarding the trailing zeroes within the passed byte slice.
Additionally, the .String() method of Alias will now also only print
the non-zero prefix of the decoded alias.

lnwire/lnwire.go

@@ -6,12 +6,13 @@ import (
 	"fmt"
 	"io"
 
+	"net"
+
 	"github.com/go-errors/errors"
 	"github.com/roasbeef/btcd/btcec"
 	"github.com/roasbeef/btcd/txscript"
 	"github.com/roasbeef/btcd/wire"
 	"github.com/roasbeef/btcutil"
-	"net"
 )
 
 // MaxSliceLength is the maximum allowed lenth for any opaque byte slices in
@@ -379,7 +380,7 @@ func writeElement(w io.Writer, element interface{}) error {
 			return err
 		}
 	case Alias:
-		if err := writeElements(w, ([32]byte)(e)); err != nil {
+		if err := writeElements(w, ([32]byte)(e.data)); err != nil {
 			return err
 		}
 
@@ -720,8 +721,11 @@ func readElement(r io.Reader, element interface{}) error {
 		if err := readElements(r, &a); err != nil {
 			return err
 		}
-		*e = (Alias)(a)
 
+		*e, err = newAlias(a[:])
+		if err != nil {
+			return err
+		}
 	default:
 		return fmt.Errorf("Unknown type in readElement: %T", e)
 	}

lnwire/node_announcement.go

@@ -24,39 +24,51 @@ type RGB struct {
 	blue  uint8
 }
 
-// Alias a hex encoded UTF-8 string that may be displayed
-// as an alternative to the node's ID. Notice that aliases are not
-// unique and may be freely chosen by the node operators.
-type Alias [32]byte
+// Alias a hex encoded UTF-8 string that may be displayed as an alternative to
+// the node's ID. Notice that aliases are not unique and may be freely chosen
+// by the node operators.
+type Alias struct {
+	data     [32]byte
+	aliasLen int
+}
 
 // NewAlias create the alias from string and also checks spec requirements.
 func NewAlias(s string) (Alias, error) {
-	var a Alias
-
 	data := []byte(s)
-	if len(data) > aliasSpecLen {
-		return a, errors.Errorf("alias too long the size "+
-			"must be less than %v", aliasSpecLen)
+	return newAlias(data)
+}
+
+func newAlias(data []byte) (Alias, error) {
+	var a [32]byte
+
+	aliasEnd := len(data)
+	for data[aliasEnd-1] == 0 && aliasEnd > 0 {
+		aliasEnd--
 	}
 
-	copy(a[:], data)
-	return a, nil
+	copy(a[:aliasEnd], data[:aliasEnd])
+
+	return Alias{
+		data:     a,
+		aliasLen: aliasEnd,
+	}, nil
 }
 
 func (a *Alias) String() string {
-	return string(a[:])
+	return string(a.data[:a.aliasLen])
 }
 
-// Validate check that alias data lenght is lower than spec size.
+// Validate check that alias data length is lower than spec size.
 func (a *Alias) Validate() error {
-	nonzero := len(a)
-	for a[nonzero-1] == 0 && nonzero > 0 {
+	nonzero := len(a.data)
+	for a.data[nonzero-1] == 0 && nonzero > 0 {
 		nonzero--
 	}
 
 	if nonzero > aliasSpecLen {
 		return errors.New("alias should be less then 21 bytes")
 	}
+
 	return nil
 }