From 0ec31bb8258ac3677fdd4fffb7b10e00e5834e3b Mon Sep 17 00:00:00 2001
From: Rafael Dantas Justo <rafael@registro.br>
Date: Thu, 16 Jul 2015 13:02:51 -0300
Subject: [PATCH 1/2] encode function should return nil when an invalid
 character is detected and ToPunycode function should return an empty string
 when there's an invalid domain name

---
 idn/punycode.go      | 16 +++++++++++-----
 idn/punycode_test.go |  2 +-
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/idn/punycode.go b/idn/punycode.go
index 28c7dcc7..670dc76d 100644
--- a/idn/punycode.go
+++ b/idn/punycode.go
@@ -27,8 +27,8 @@ const (
 )
 
 // ToPunycode converts unicode domain names to DNS-appropriate punycode names.
-// This function would return incorrect result for strings for non-canonical
-// unicode strings.
+// This function would return an empty string result for domain names with
+// invalid unicode strings. This function expects domain names in lowercase.
 func ToPunycode(s string) string {
 	tokens := dns.SplitDomainName(s)
 	switch {
@@ -41,7 +41,11 @@ func ToPunycode(s string) string {
 	}
 
 	for i := range tokens {
-		tokens[i] = string(encode([]byte(tokens[i])))
+		t := encode([]byte(tokens[i]))
+		if t == nil {
+			return ""
+		}
+		tokens[i] = string(t)
 	}
 	return strings.Join(tokens, ".")
 }
@@ -139,14 +143,16 @@ func tfunc(k, bias rune) rune {
 	return k - bias
 }
 
-// encode transforms Unicode input bytes (that represent DNS label) into punycode bytestream
+// encode transforms Unicode input bytes (that represent DNS label) into
+// punycode bytestream. This function would return nil if there's an invalid
+// character in the label
 func encode(input []byte) []byte {
 	n, bias := _N, _BIAS
 
 	b := bytes.Runes(input)
 	for i := range b {
 		if !isValidRune(b[i]) {
-			return input
+			return nil
 		}
 
 		b[i] = preprune(b[i])
diff --git a/idn/punycode_test.go b/idn/punycode_test.go
index c6b88992..f8b355ca 100644
--- a/idn/punycode_test.go
+++ b/idn/punycode_test.go
@@ -108,7 +108,7 @@ var invalidUnicodes = []string{
 func TestInvalidUnicodes(t *testing.T) {
 	for _, d := range invalidUnicodes {
 		s := ToPunycode(d)
-		if s != d {
+		if s != "" {
 			t.Errorf("Changed invalid name %s to %#v", d, s)
 		}
 	}

From c1abafe6ad7079593170ce82bc7b43607d39bc70 Mon Sep 17 00:00:00 2001
From: Rafael Dantas Justo <rafael@registro.br>
Date: Fri, 17 Jul 2015 07:17:18 -0300
Subject: [PATCH 2/2] add final dot in function comment

---
 idn/punycode.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/idn/punycode.go b/idn/punycode.go
index 670dc76d..09363821 100644
--- a/idn/punycode.go
+++ b/idn/punycode.go
@@ -145,7 +145,7 @@ func tfunc(k, bias rune) rune {
 
 // encode transforms Unicode input bytes (that represent DNS label) into
 // punycode bytestream. This function would return nil if there's an invalid
-// character in the label
+// character in the label.
 func encode(input []byte) []byte {
 	n, bias := _N, _BIAS