From 42a0048119d9a8f99710fa0e971b540fae17de0d Mon Sep 17 00:00:00 2001
From: IKEDA Soji <ikeda@conversion.co.jp>
Date: Tue, 29 Aug 2023 08:31:53 +0900
Subject: [PATCH] Fix broken encodeXtext()

---
 client_test.go | 26 ++++++++++++++++++++++++++
 conn.go        | 12 +++++-------
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/client_test.go b/client_test.go
index 17eac3c..ba8dfe3 100644
--- a/client_test.go
+++ b/client_test.go
@@ -931,3 +931,29 @@ Goodbye.`
 		t.Fatalf("QUIT failed: %s", err)
 	}
 }
+
+func TestClientXtext(t *testing.T) {
+	server := "220 hello world\r\n" +
+		"200 some more"
+	var wrote bytes.Buffer
+	var fake faker
+	fake.ReadWriter = struct {
+		io.Reader
+		io.Writer
+	}{
+		strings.NewReader(server),
+		&wrote,
+	}
+	c, err := NewClient(fake, "fake.host")
+	if err != nil {
+		t.Fatalf("NewClient: %v", err)
+	}
+	c.didHello = true
+	c.ext = map[string]string{"AUTH": "PLAIN"}
+	email := "e=mc2@example.com"
+	c.Mail(email, &MailOptions{Auth: &email})
+	c.Close()
+	if got, want := wrote.String(), "MAIL FROM:<e=mc2@example.com> AUTH=e+3Dmc2@example.com\r\n"; got != want {
+		t.Errorf("wrote %q; want %q", got, want)
+	}
+}
diff --git a/conn.go b/conn.go
index d060bbe..1254175 100644
--- a/conn.go
+++ b/conn.go
@@ -426,16 +426,14 @@ func encodeXtext(raw string) string {
 	out.Grow(len(raw))
 
 	for _, ch := range raw {
-		if ch == '+' || ch == '=' {
+		switch {
+		case ch >= '!' && ch <= '~' && ch != '+' && ch != '=':
+			// printable non-space US-ASCII except '+' and '='
+			out.WriteRune(ch)
+		default:
 			out.WriteRune('+')
 			out.WriteString(strings.ToUpper(strconv.FormatInt(int64(ch), 16)))
 		}
-		if ch > '!' && ch < '~' { // printable non-space US-ASCII
-			out.WriteRune(ch)
-		}
-		// Non-ASCII.
-		out.WriteRune('+')
-		out.WriteString(strings.ToUpper(strconv.FormatInt(int64(ch), 16)))
 	}
 	return out.String()
 }