feat: add decryption error to the device message about outgoing message decryption failure

src/chat/chat_tests.rs

@@ -2792,7 +2792,7 @@ async fn test_broadcast_members_cant_see_each_other() -> Result<()> {
         assert_eq!(parsed.decoded_data_contains("bob@example.net"), false);
 
         let parsed_by_bob = bob.parse_msg(&vc_pubkey).await;
-        assert!(parsed_by_bob.decrypting_failed);
+        assert!(parsed_by_bob.decryption_error.is_some());
 
         charlie.recv_msg_trash(&vc_pubkey).await;
     }
@@ -2821,7 +2821,7 @@ async fn test_broadcast_members_cant_see_each_other() -> Result<()> {
         assert_eq!(parsed.decoded_data_contains("bob@example.net"), false);
 
         let parsed_by_bob = bob.parse_msg(&member_added).await;
-        assert!(parsed_by_bob.decrypting_failed);
+        assert!(parsed_by_bob.decryption_error.is_some());
 
         let rcvd = charlie.recv_msg(&member_added).await;
         assert_eq!(rcvd.param.get_cmd(), SystemMessage::MemberAddedToGroup);
@@ -2836,7 +2836,7 @@ async fn test_broadcast_members_cant_see_each_other() -> Result<()> {
         assert_eq!(parsed.decoded_data_contains("bob@example.net"), false);
 
         let parsed_by_bob = bob.parse_msg(&hi_msg).await;
-        assert_eq!(parsed_by_bob.decrypting_failed, false);
+        assert!(parsed_by_bob.decryption_error.is_none());
     }
 
     tcm.section("Alice removes Charlie. Bob must not see it.");
@@ -2853,7 +2853,7 @@ async fn test_broadcast_members_cant_see_each_other() -> Result<()> {
         assert_eq!(parsed.decoded_data_contains("bob@example.net"), false);
 
         let parsed_by_bob = bob.parse_msg(&member_removed).await;
-        assert!(parsed_by_bob.decrypting_failed);
+        assert!(parsed_by_bob.decryption_error.is_some());
 
         let rcvd = charlie.recv_msg(&member_removed).await;
         assert_eq!(rcvd.param.get_cmd(), SystemMessage::MemberRemovedFromGroup);

src/mimeparser.rs

@@ -86,7 +86,9 @@ pub(crate) struct MimeMessage {
     /// messages to this address to post them to the list.
     pub list_post: Option<String>,
     pub chat_disposition_notification_to: Option<SingleInfo>,
-    pub decrypting_failed: bool,
+
+    /// Decryption error if decryption of the message has failed.
+    pub decryption_error: Option<String>,
 
     /// Valid signature fingerprint if a message is an
     /// Autocrypt encrypted and signed message and corresponding intended recipient fingerprints
@@ -664,7 +666,7 @@ impl MimeMessage {
             from,
             incoming,
             chat_disposition_notification_to,
-            decrypting_failed: mail.is_err(),
+            decryption_error: mail.err().map(|err| format!("{err:#}")),
 
             // only non-empty if it was a valid autocrypt message
             signature,
@@ -905,7 +907,7 @@ impl MimeMessage {
             && let Some(ref subject) = self.get_subject()
         {
             let mut prepend_subject = true;
-            if !self.decrypting_failed {
+            if self.decryption_error.is_none() {
                 let colon = subject.find(':');
                 if colon == Some(2)
                     || colon == Some(3)
@@ -946,7 +948,7 @@ impl MimeMessage {
         self.parse_attachments();
 
         // See if an MDN is requested from the other side
-        if !self.decrypting_failed
+        if self.decryption_error.is_none()
             && !self.parts.is_empty()
             && let Some(ref dn_to) = self.chat_disposition_notification_to
         {
@@ -1078,7 +1080,7 @@ impl MimeMessage {
     #[cfg(test)]
     /// Returns whether the decrypted data contains the given `&str`.
     pub(crate) fn decoded_data_contains(&self, s: &str) -> bool {
-        assert!(!self.decrypting_failed);
+        assert!(self.decryption_error.is_none());
         let decoded_str = str::from_utf8(&self.decoded_data).unwrap();
         decoded_str.contains(s)
     }

src/receive_imf.rs

@@ -727,7 +727,7 @@ pub(crate) async fn receive_imf_inner(
         let show_emails = ShowEmails::from_i32(context.get_config_int(Config::ShowEmails).await?)
             .unwrap_or_default();
 
-        let allow_creation = if mime_parser.decrypting_failed {
+        let allow_creation = if mime_parser.decryption_error.is_some() {
             false
         } else if is_dc_message == MessengerMessage::No
             && !context.get_config_bool(Config::IsChatmail).await?
@@ -1211,14 +1211,18 @@ async fn decide_chat_assignment(
     {
         info!(context, "Call state changed (TRASH).");
         true
-    } else if mime_parser.decrypting_failed && !mime_parser.incoming {
+    } else if let Some(ref decryption_error) = mime_parser.decryption_error
+        && !mime_parser.incoming
+    {
         // Outgoing undecryptable message.
         let last_time = context
             .get_config_i64(Config::LastCantDecryptOutgoingMsgs)
             .await?;
         let now = tools::time();
         let update_config = if last_time.saturating_add(24 * 60 * 60) <= now {
-            let txt = "⚠️ It seems you are using Delta Chat on multiple devices that cannot decrypt each other's outgoing messages. To fix this, on the older device use \"Settings / Add Second Device\" and follow the instructions.";
+            let txt = format!(
+                "⚠️ It seems you are using Delta Chat on multiple devices that cannot decrypt each other's outgoing messages. To fix this, on the older device use \"Settings / Add Second Device\" and follow the instructions. (Error: {decryption_error}, {rfc724_mid})."
+            );
             let mut msg = Message::new_text(txt.to_string());
             chat::add_device_msg(context, None, Some(&mut msg))
                 .await
@@ -2290,7 +2294,7 @@ RETURNING id
                     if trash { 0 } else { ephemeral_timestamp },
                     if trash {
                         DownloadState::Done
-                    } else if mime_parser.decrypting_failed {
+                    } else if mime_parser.decryption_error.is_some() {
                         DownloadState::Undecipherable
                     } else if let PreMessageMode::Pre {..} = mime_parser.pre_message {
                         DownloadState::Available
@@ -2703,7 +2707,7 @@ async fn lookup_or_create_adhoc_group(
     allow_creation: bool,
     create_blocked: Blocked,
 ) -> Result<Option<(ChatId, Blocked, bool)>> {
-    if mime_parser.decrypting_failed {
+    if mime_parser.decryption_error.is_some() {
         warn!(
             context,
             "Not creating ad-hoc group for message that cannot be decrypted."
@@ -2925,7 +2929,7 @@ async fn create_group(
 
     if let Some(chat_id) = chat_id {
         Ok(Some((chat_id, chat_id_blocked)))
-    } else if mime_parser.decrypting_failed {
+    } else if mime_parser.decryption_error.is_some() {
         // It is possible that the message was sent to a valid,
         // yet unknown group, which was rejected because
         // Chat-Group-Name, which is in the encrypted part, was

src/receive_imf/receive_imf_tests.rs

@@ -3327,7 +3327,7 @@ async fn test_outgoing_undecryptable() -> Result<()> {
     assert!(
         dev_msg
             .text
-            .contains("⚠️ It seems you are using Delta Chat on multiple devices that cannot decrypt each other's outgoing messages. To fix this, on the older device use \"Settings / Add Second Device\" and follow the instructions.")
+            .starts_with("⚠️ It seems you are using Delta Chat on multiple devices that cannot decrypt each other's outgoing messages. To fix this, on the older device use \"Settings / Add Second Device\" and follow the instructions. (Error:")
     );
 
     let raw = include_bytes!("../../test-data/message/thunderbird_encrypted_signed.eml");

src/tests/pre_messages/sending.rs

@@ -79,7 +79,7 @@ async fn test_sending_pre_message() -> Result<()> {
     );
 
     let decrypted_post_message = bob.parse_msg(post_message).await;
-    assert_eq!(decrypted_post_message.decrypting_failed, false);
+    assert!(decrypted_post_message.decryption_error.is_none());
     assert_eq!(
         decrypted_post_message.header_exists(HeaderDef::ChatPostMessageId),
         false