fix: do not fail to send encrypted quotes to unencrypted chats

Replace quote text with "..." instead.

python/tests/test_1_online.py

@@ -1343,7 +1343,6 @@ def test_quote_encrypted(acfactory, lp):
 
     for quoted_msg in msg1, msg3:
         # Save the draft with a quote.
-        # It should be encrypted if quoted message is encrypted.
         msg_draft = Message.new_empty(ac1, "text")
         msg_draft.set_text("message reply")
         msg_draft.quote = quoted_msg
@@ -1357,10 +1356,14 @@ def test_quote_encrypted(acfactory, lp):
         chat.set_draft(None)
         assert chat.get_draft() is None
 
+        # Quote should be replaced with "..." if quoted message is encrypted.
         msg_in = ac2._evtracker.wait_next_incoming_message()
         assert msg_in.text == "message reply"
+        assert not msg_in.is_encrypted()
+        if quoted_msg.is_encrypted():
+            assert msg_in.quoted_text == "..."
+        else:
             assert msg_in.quoted_text == quoted_msg.text
-        assert msg_in.is_encrypted() == quoted_msg.is_encrypted()
 
 
 def test_quote_attachment(tmp_path, acfactory, lp):

src/message.rs

@@ -1127,7 +1127,7 @@ impl Message {
                 .get_bool(Param::GuaranteeE2ee)
                 .unwrap_or_default()
             {
-                self.param.set(Param::GuaranteeE2ee, "1");
+                self.param.set(Param::ProtectQuote, "1");
             }
 
             let text = quote.get_text();
@@ -2015,7 +2015,9 @@ mod tests {
     use num_traits::FromPrimitive;
 
     use super::*;
-    use crate::chat::{self, marknoticed_chat, send_text_msg, ChatItem};
+    use crate::chat::{
+        self, add_contact_to_chat, marknoticed_chat, send_text_msg, ChatItem, ProtectionStatus,
+    };
     use crate::chatlist::Chatlist;
     use crate::config::Config;
     use crate::reaction::send_reaction;
@@ -2211,6 +2213,42 @@ mod tests {
         assert_eq!(quoted_msg.get_text(), msg2.quoted_text().unwrap());
     }
 
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_unencrypted_quote_encrypted_message() -> Result<()> {
+        let mut tcm = TestContextManager::new();
+
+        let alice = &tcm.alice().await;
+        let bob = &tcm.bob().await;
+
+        let alice_group = alice
+            .create_group_with_members(ProtectionStatus::Unprotected, "Group chat", &[bob])
+            .await;
+        let sent = alice.send_text(alice_group, "Hi! I created a group").await;
+        let bob_received_message = bob.recv_msg(&sent).await;
+
+        let bob_group = bob_received_message.chat_id;
+        bob_group.accept(bob).await?;
+        let sent = bob.send_text(bob_group, "Encrypted message").await;
+        let alice_received_message = alice.recv_msg(&sent).await;
+        assert!(alice_received_message.get_showpadlock());
+
+        // Alice adds contact without key so chat becomes unencrypted.
+        let alice_flubby_contact_id =
+            Contact::create(alice, "Flubby", "flubby@example.org").await?;
+        add_contact_to_chat(alice, alice_group, alice_flubby_contact_id).await?;
+
+        // Alice quotes encrypted message in unencrypted chat.
+        let mut msg = Message::new(Viewtype::Text);
+        msg.set_quote(alice, Some(&alice_received_message)).await?;
+        chat::send_msg(alice, alice_group, &mut msg).await?;
+
+        let bob_received_message = bob.recv_msg(&alice.pop_sent_msg().await).await;
+        assert_eq!(bob_received_message.quoted_text().unwrap(), "...");
+        assert_eq!(bob_received_message.get_showpadlock(), false);
+
+        Ok(())
+    }
+
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_get_chat_id() {
         // Alice receives a message that pops up as a contact request

src/mimefactory.rs

@@ -669,19 +669,19 @@ impl<'a> MimeFactory<'a> {
 
         let mut is_gossiped = false;
 
-        let (main_part, parts) = match self.loaded {
-            Loaded::Message { .. } => {
-                self.render_message(context, &mut headers, &grpimage)
-                    .await?
-            }
-            Loaded::Mdn { .. } => (self.render_mdn(context).await?, Vec::new()),
-        };
-
         let peerstates = self.peerstates_for_recipients(context).await?;
         let should_encrypt =
             encrypt_helper.should_encrypt(context, e2ee_guaranteed, &peerstates)?;
         let is_encrypted = should_encrypt && !force_plaintext;
 
+        let (main_part, parts) = match self.loaded {
+            Loaded::Message { .. } => {
+                self.render_message(context, &mut headers, &grpimage, is_encrypted)
+                    .await?
+            }
+            Loaded::Mdn { .. } => (self.render_mdn(context).await?, Vec::new()),
+        };
+
         let message = if parts.is_empty() {
             // Single part, render as regular message.
             main_part
@@ -960,6 +960,7 @@ impl<'a> MimeFactory<'a> {
         context: &Context,
         headers: &mut MessageHeaders,
         grpimage: &Option<String>,
+        is_encrypted: bool,
     ) -> Result<(PartBuilder, Vec<PartBuilder>)> {
         let chat = match &self.loaded {
             Loaded::Message { chat } => chat,
@@ -1221,6 +1222,16 @@ impl<'a> MimeFactory<'a> {
             .msg
             .quoted_text()
             .map(|quote| format_flowed_quote(&quote) + "\r\n\r\n");
+        if !is_encrypted
+            && self
+                .msg
+                .param
+                .get_bool(Param::ProtectQuote)
+                .unwrap_or_default()
+        {
+            // Message is not encrypted but quotes encrypted message.
+            quoted_text = Some("> ...\r\n\r\n".to_string());
+        }
         if quoted_text.is_none() && final_text.starts_with('>') {
             // Insert empty line to avoid receiver treating user-sent quote as topquote inserted by
             // Delta Chat.

src/param.rs

@@ -48,6 +48,11 @@ pub enum Param {
     /// For Messages: message is encrypted, outgoing: guarantee E2EE or the message is not send
     GuaranteeE2ee = b'c',
 
+    /// For Messages: quoted message is encrypted.
+    ///
+    /// If this message is sent unencrypted, quote text should be replaced.
+    ProtectQuote = b'0',
+
     /// For Messages: decrypted with validation errors or without mutual set, if neither
     /// 'c' nor 'e' are preset, the messages is only transport encrypted.
     ErroneousE2ee = b'e',