Reorganize errors

gemini/errors.go

@@ -0,0 +1,52 @@
+package gemini
+
+import (
+	"fmt"
+
+	"gemini-grc/errors"
+)
+
+// GeminiError is used to represent
+// Gemini network protocol errors only.
+// Should be recorded to the snapshot.
+// See https://geminiprotocol.net/docs/protocol-specification.gmi
+type GeminiError struct {
+	Msg    string
+	Code   int
+	Header string
+}
+
+func (e *GeminiError) Error() string {
+	return fmt.Sprintf("gemini error: code %d %s", e.Code, e.Msg)
+}
+
+func NewGeminiError(code int, header string) error {
+	var msg string
+	switch {
+	case code >= 10 && code < 20:
+		msg = "needs input"
+	case code >= 30 && code < 40:
+		msg = "redirect"
+	case code >= 40 && code < 50:
+		msg = "bad request"
+	case code >= 50 && code < 60:
+		msg = "server error"
+	case code >= 60 && code < 70:
+		msg = "TLS error"
+	default:
+		msg = "unexpected Status code"
+	}
+	return &GeminiError{
+		Msg:    msg,
+		Code:   code,
+		Header: header,
+	}
+}
+
+func IsGeminiError(err error) bool {
+	if err == nil {
+		return false
+	}
+	var asError *GeminiError
+	return errors.As(err, &asError)
+}