attr: add default error reasons

attribute_errorcode.go

@@ -0,0 +1,34 @@
+package stun
+
+// ErrorCode is code for ERROR-CODE attribute.
+type ErrorCode int
+
+// Possible error codes.
+const (
+	CodeTryAlternate     ErrorCode = 300
+	CodeBadRequest       ErrorCode = 400
+	CodeUnauthorised     ErrorCode = 401
+	CodeUnknownAttribute ErrorCode = 420
+	CodeStaleNonce       ErrorCode = 428
+	CodeServerError      ErrorCode = 500
+)
+
+// Reason returns recommended reason string.
+func (c ErrorCode) Reason() string {
+	switch c {
+	case CodeTryAlternate:
+		return "Try Alternate"
+	case CodeBadRequest:
+		return "Bad Request"
+	case CodeUnauthorised:
+		return "Unauthorised"
+	case CodeUnknownAttribute:
+		return "Unknown attribute"
+	case CodeStaleNonce:
+		return "Stale Nonce"
+	case CodeServerError:
+		return "Server Error"
+	default:
+		return "Unknown Error"
+	}
+}

attributes.go

@@ -140,6 +140,13 @@ func (m *Message) AddErrorCode(code int, reason string) {
 	m.Add(AttrErrorCode, value)
 }
 
+// AddErrorCodeDefault is wrapper for AddErrorCode that uses recommended
+// reason string from RFC. If error code is unknown, reason will be "Unknown
+// Error".
+func (m *Message) AddErrorCodeDefault(code int) {
+	m.AddErrorCode(code, ErrorCode(code).Reason())
+}
+
 // GetErrorCode returns ERROR-CODE code, reason and decode error if any.
 func (m *Message) GetErrorCode() (int, []byte, error) {
 	v := m.getAttrValue(AttrErrorCode)