feat: Use Quoted-Printable for the text part (#3986)

This is needed to protect from ESPs (such as gmx.at) doing their own Quoted-Printable encoding and
thus breaking messages and signatures. It's unlikely that the reader uses a MUA not supporting
Quoted-Printable encoding. And RFC 2646 "4.6" also recommends it for encrypted messages.

Cargo.lock

@@ -1136,6 +1136,7 @@ dependencies = [
  "proptest",
  "qrcodegen",
  "quick-xml",
+ "quoted_printable",
  "rand 0.8.5",
  "ratelimit",
  "regex",

Cargo.toml

@@ -76,6 +76,7 @@ pin-project = "1"
 pretty_env_logger = { version = "0.5", optional = true }
 qrcodegen = "1.7.0"
 quick-xml = "0.31"
+quoted_printable = "0.4"
 rand = "0.8"
 regex = "1.9"
 reqwest = { version = "0.11.23", features = ["json"] }

src/e2ee.rs

@@ -52,7 +52,7 @@ impl EncryptHelper {
         &self,
         context: &Context,
         e2ee_guaranteed: bool,
-        peerstates: &[(Option<Peerstate>, &str)],
+        peerstates: &[(Option<Peerstate>, String)],
     ) -> Result<bool> {
         let mut prefer_encrypt_count = if self.prefer_encrypt == EncryptPreference::Mutual {
             1
@@ -94,7 +94,7 @@ impl EncryptHelper {
         context: &Context,
         verified: bool,
         mail_to_encrypt: lettre_email::PartBuilder,
-        peerstates: Vec<(Option<Peerstate>, &str)>,
+        peerstates: Vec<(Option<Peerstate>, String)>,
     ) -> Result<String> {
         let mut keyring: Vec<SignedPublicKey> = Vec::new();
 
@@ -117,7 +117,7 @@ impl EncryptHelper {
         // Encrypt to secondary verified keys
         // if we also encrypt to the introducer ("verifier") of the key.
         if verified {
-            for (peerstate, _addr) in peerstates {
+            for (peerstate, _addr) in &peerstates {
                 if let Some(peerstate) = peerstate {
                     if let (Some(key), Some(verifier)) = (
                         peerstate.secondary_verified_key.as_ref(),
@@ -293,7 +293,7 @@ Sent with my Delta Chat Messenger: https://delta.chat";
         Ok(())
     }
 
-    fn new_peerstates(prefer_encrypt: EncryptPreference) -> Vec<(Option<Peerstate>, &'static str)> {
+    fn new_peerstates(prefer_encrypt: EncryptPreference) -> Vec<(Option<Peerstate>, String)> {
         let addr = "bob@foo.bar";
         let pub_key = bob_keypair().public;
         let peerstate = Peerstate {
@@ -315,7 +315,7 @@ Sent with my Delta Chat Messenger: https://delta.chat";
             backward_verified_key_id: None,
             fingerprint_changed: false,
         };
-        vec![(Some(peerstate), addr)]
+        vec![(Some(peerstate), addr.to_string())]
     }
 
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
@@ -340,7 +340,7 @@ Sent with my Delta Chat Messenger: https://delta.chat";
         assert!(encrypt_helper.should_encrypt(&t, false, &ps).unwrap());
 
         // test with missing peerstate
-        let ps = vec![(None, "bob@foo.bar")];
+        let ps = vec![(None, "bob@foo.bar".to_string())];
         assert!(encrypt_helper.should_encrypt(&t, true, &ps).is_err());
         assert!(!encrypt_helper.should_encrypt(&t, false, &ps).unwrap());
     }

src/mimefactory.rs

@@ -277,7 +277,7 @@ impl<'a> MimeFactory<'a> {
     async fn peerstates_for_recipients(
         &self,
         context: &Context,
-    ) -> Result<Vec<(Option<Peerstate>, &str)>> {
+    ) -> Result<Vec<(Option<Peerstate>, String)>> {
         let self_addr = context.get_primary_self_addr().await?;
 
         let mut res = Vec::new();
@@ -286,7 +286,7 @@ impl<'a> MimeFactory<'a> {
             .iter()
             .filter(|(_, addr)| addr != &self_addr)
         {
-            res.push((Peerstate::from_addr(context, addr).await?, addr.as_str()));
+            res.push((Peerstate::from_addr(context, addr).await?, addr.clone()));
         }
 
         Ok(res)
@@ -917,6 +917,16 @@ impl<'a> MimeFactory<'a> {
         Ok(Some(part))
     }
 
+    fn add_message_text(&self, part: PartBuilder, mut text: String) -> PartBuilder {
+        // This is needed to protect from ESPs (such as gmx.at) doing their own Quoted-Printable
+        // encoding and thus breaking messages and signatures. It's unlikely that the reader uses a
+        // MUA not supporting Quoted-Printable encoding. And RFC 2646 "4.6" also recommends it for
+        // encrypted messages.
+        let part = part.header(("Content-Transfer-Encoding", "quoted-printable"));
+        text = quoted_printable::encode_to_str(text);
+        part.body(text)
+    }
+
     #[allow(clippy::cognitive_complexity)]
     async fn render_message(
         &mut self,
@@ -1214,13 +1224,11 @@ impl<'a> MimeFactory<'a> {
             footer
         );
 
-        // Message is sent as text/plain, with charset = utf-8
+        let mut main_part = PartBuilder::new().header((
-        let mut main_part = PartBuilder::new()
+            "Content-Type",
-            .header((
+            "text/plain; charset=utf-8; format=flowed; delsp=no",
-                "Content-Type".to_string(),
+        ));
-                "text/plain; charset=utf-8; format=flowed; delsp=no".to_string(),
+        main_part = self.add_message_text(main_part, message_text);
-            ))
-            .body(message_text);
 
         if is_reaction {
             main_part = main_part.header(("Content-Disposition", "reaction"));
@@ -1347,15 +1355,12 @@ impl<'a> MimeFactory<'a> {
         };
         let p2 = stock_str::read_rcpt_mail_body(context, &p1).await;
         let message_text = format!("{}\r\n", format_flowed(&p2));
-        message = message.child(
+        let text_part = PartBuilder::new().header((
-            PartBuilder::new()
-                .header((
             "Content-Type".to_string(),
             "text/plain; charset=utf-8; format=flowed; delsp=no".to_string(),
-                ))
+        ));
-                .body(message_text)
+        let text_part = self.add_message_text(text_part, message_text);
-                .build(),
+        message = message.child(text_part.build());
-        );
 
         // second body part: machine-readable, always REQUIRED by RFC 6522
         let message_text2 = format!(
@@ -2198,6 +2203,7 @@ mod tests {
         assert_eq!(inner.match_indices("Message-ID:").count(), 1);
         assert_eq!(inner.match_indices("Chat-User-Avatar:").count(), 1);
         assert_eq!(inner.match_indices("Subject:").count(), 0);
+        assert_eq!(inner.match_indices("quoted-printable").count(), 1);
 
         assert_eq!(body.match_indices("this is the text!").count(), 1);
 
@@ -2218,6 +2224,7 @@ mod tests {
         assert_eq!(inner.match_indices("Message-ID:").count(), 1);
         assert_eq!(inner.match_indices("Chat-User-Avatar:").count(), 0);
         assert_eq!(inner.match_indices("Subject:").count(), 0);
+        assert_eq!(inner.match_indices("quoted-printable").count(), 1);
 
         assert_eq!(body.match_indices("this is the text!").count(), 1);
 
@@ -2274,6 +2281,7 @@ mod tests {
         assert_eq!(part.match_indices("Message-ID:").count(), 1);
         assert_eq!(part.match_indices("Chat-User-Avatar:").count(), 1);
         assert_eq!(part.match_indices("Subject:").count(), 0);
+        assert_eq!(part.match_indices("quoted-printable").count(), 1);
 
         let body = payload.next().unwrap();
         assert_eq!(body.match_indices("this is the text!").count(), 1);
@@ -2321,6 +2329,7 @@ mod tests {
         assert_eq!(part.match_indices("Message-ID:").count(), 1);
         assert_eq!(part.match_indices("Chat-User-Avatar:").count(), 0);
         assert_eq!(part.match_indices("Subject:").count(), 0);
+        assert_eq!(part.match_indices("quoted-printable").count(), 1);
 
         let body = payload.next().unwrap();
         assert_eq!(body.match_indices("this is the text!").count(), 1);