lnwire: when reading node aliases, properly check validity

In this commit, we ensure that when we read node aliases from the wire,
we ensure that they're valid. Before this commit, we would read the raw
bytes without checking for validity which could result in us writing in
invalid node alias to disk. We've fixed this, and also updated the
quickcheck tests to generate valid strings.

lnwire/lnwire_test.go

@@ -41,6 +41,17 @@ var (
 	_, _ = testSig.S.SetString("18801056069249825825291287104931333862866033135609736119018462340006816851118", 10)
 )
 
+const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+func randAlias(r *rand.Rand) NodeAlias {
+	var a NodeAlias
+	for i := range a {
+		a[i] = letterBytes[r.Intn(len(letterBytes))]
+	}
+
+	return a
+}
+
 func randPubKey() (*btcec.PublicKey, error) {
 	priv, err := btcec.NewPrivateKey(btcec.S256())
 	if err != nil {
@@ -551,17 +562,11 @@ func TestLightningWireProtocol(t *testing.T) {
 			v[0] = reflect.ValueOf(req)
 		},
 		MsgNodeAnnouncement: func(v []reflect.Value, r *rand.Rand) {
-			var a [32]byte
-			if _, err := r.Read(a[:]); err != nil {
-				t.Fatalf("unable to generate alias: %v", err)
-				return
-			}
-
 			var err error
 			req := NodeAnnouncement{
 				Features:  randRawFeatureVector(r),
 				Timestamp: uint32(r.Int31()),
-				Alias:     a,
+				Alias:     randAlias(r),
 				RGBColor: color.RGBA{
 					R: uint8(r.Int31()),
 					G: uint8(r.Int31()),