From dcc65d7d37f3ad4758667cbed3aff743c15e817d Mon Sep 17 00:00:00 2001
From: Doug Nelson <dougnelson@cloudflare.com>
Date: Wed, 15 Oct 2025 10:42:06 +0100
Subject: [PATCH] fix: question marks are not correctly encoded

---
 src/encode.rs | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/encode.rs b/src/encode.rs
index 889022d..aab92d2 100644
--- a/src/encode.rs
+++ b/src/encode.rs
@@ -72,7 +72,7 @@ fn rfc2047_encode_word(word: &str) -> String {
         if b == ' ' {
             result.push('_');
             at += 1;
-        } else if b.is_ascii() && b != '_' && b != '=' {
+        } else if b.is_ascii() && b != '_' && b != '=' && b != '?' {
             result.push(b);
             at += 1;
         } else {
@@ -98,6 +98,11 @@ mod tests {
         assert_eq!("foo \n bar", rfc2047_encode("foo \n bar"));
     }
 
+    #[test]
+    fn just_ascii_with_qmark() {
+        assert_eq!("foo? bar!", rfc2047_encode("foo? bar!"));
+    }
+
     #[test]
     fn just_whitespace() {
         assert_eq!("   ", rfc2047_encode("   "));
@@ -118,6 +123,14 @@ mod tests {
         assert_eq!("=?utf-8?q?foo=C3=A1bar?=", rfc2047_encode("fooábar"));
     }
 
+    #[test]
+    fn encoded_qmark() {
+        assert_eq!(
+            "=?utf-8?q?c=C3=A1t=3F?=",
+            rfc2047_encode("cát?")
+        );
+    }
+
     #[test]
     fn encoded_at_start() {
         assert_eq!("=?utf-8?q?=C3=A4?=  bar", rfc2047_encode("ä  bar"));