Support SameSite value "None" cookie attribute (#581)

* Support SameSite value "None" cookie attribute

* Fix typo in CookieSameSiteNoneMode comment

* fix comment for SameSite None

cookie.go

@@ -31,6 +31,9 @@ const (
 	CookieSameSiteLaxMode
 	// CookieSameSiteStrictMode sets the SameSite flag with the "Strict" parameter
 	CookieSameSiteStrictMode
+	// CookieSameSiteNoneMode sets the SameSite flag with the "None" parameter
+	// see https://tools.ietf.org/html/draft-west-cookie-incrementalism-00
+	CookieSameSiteNoneMode
 )
 
 // AcquireCookie returns an empty Cookie object from the pool.
@@ -119,8 +122,12 @@ func (c *Cookie) SameSite() CookieSameSite {
 }
 
 // SetSameSite sets the cookie's SameSite flag to the given value.
+// set value CookieSameSiteNoneMode will set Secure to true also to avoid browser rejection
 func (c *Cookie) SetSameSite(mode CookieSameSite) {
 	c.sameSite = mode
+	if mode == CookieSameSiteNoneMode {
+		c.SetSecure(true)
+	}
 }
 
 // Path returns cookie path.
@@ -288,6 +295,11 @@ func (c *Cookie) AppendBytes(dst []byte) []byte {
 		dst = append(dst, strCookieSameSite...)
 		dst = append(dst, '=')
 		dst = append(dst, strCookieSameSiteStrict...)
+	case CookieSameSiteNoneMode:
+		dst = append(dst, ';', ' ')
+		dst = append(dst, strCookieSameSite...)
+		dst = append(dst, '=')
+		dst = append(dst, strCookieSameSiteNone...)
 	}
 	return dst
 }
@@ -386,6 +398,10 @@ func (c *Cookie) ParseBytes(src []byte) error {
 						if caseInsensitiveCompare(strCookieSameSiteStrict, kv.value) {
 							c.sameSite = CookieSameSiteStrictMode
 						}
+					case 'n': // "none"
+						if caseInsensitiveCompare(strCookieSameSiteNone, kv.value) {
+							c.sameSite = CookieSameSiteNoneMode
+						}
 					}
 				}
 			}

cookie_test.go

@@ -121,6 +121,29 @@ func TestCookieSameSite(t *testing.T) {
 		t.Fatalf("missing SameSite flag in cookie %q", s)
 	}
 
+	if err := c.Parse("foo=bar; samesite=none"); err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	if c.SameSite() != CookieSameSiteNoneMode {
+		t.Fatalf("SameSite None Mode must be set")
+	}
+	s = c.String()
+	if !strings.Contains(s, "; SameSite=None") {
+		t.Fatalf("missing SameSite flag in cookie %q", s)
+	}
+
+	if err := c.Parse("foo=bar"); err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	c.SetSameSite(CookieSameSiteNoneMode)
+	s = c.String()
+	if !strings.Contains(s, "; SameSite=None") {
+		t.Fatalf("missing SameSite flag in cookie %q", s)
+	}
+	if !strings.Contains(s, "; secure") {
+		t.Fatalf("missing Secure flag in cookie %q", s)
+	}
+
 	if err := c.Parse("foo=bar"); err != nil {
 		t.Fatalf("unexpected error: %s", err)
 	}

strings.go

@@ -62,6 +62,7 @@ var (
 	strCookieSameSite       = []byte("SameSite")
 	strCookieSameSiteLax    = []byte("Lax")
 	strCookieSameSiteStrict = []byte("Strict")
+	strCookieSameSiteNone   = []byte("None")
 
 	strClose               = []byte("close")
 	strGzip                = []byte("gzip")