guard against empty strings

multibase.go

@@ -31,6 +31,10 @@ func Encode(base int, data []byte) (string, error) {
 }
 
 func Decode(data string) (int, []byte, error) {
+	if len(data) == 0 {
+		return 0, nil, fmt.Errorf("cannot decode multibase for zero length string")
+	}
+
 	switch data[0] {
 	case Base58BTC:
 		return Base58BTC, b58.DecodeAlphabet(data[1:], b58.BTCAlphabet), nil

multibase_test.go

@@ -27,4 +27,9 @@ func TestBase58RoundTrip(t *testing.T) {
 	if !bytes.Equal(buf, out) {
 		t.Fatal("input wasnt the same as output", buf, out)
 	}
+
+	_, _, err = Decode("")
+	if err == nil {
+		t.Fatal("shouldnt be able to decode empty string")
+	}
 }