feat: imap: Don't prefetch Chat-Version; try to find out message encryption state instead

Instead, prefetch Secure-Join, Content-Type and Subject headers, try to find out if the message is encrypted, i.e.:
- if its Content-Type is "multipart/encrypted"
- or Subject is "..." or "[...]" as Some MUAs use "multipart/mixed"; we can't only look at Subject
  as it's not mandatory;
and depending on this decide on the target folder.

Changed behavior: before, "Chat-Version"-containing messages were moved from INBOX to DeltaChat, now
such encrypted messages may remain in INBOX -- if there's no parent message or it's not
`MessengerMessage`. We can't unconditionally move encrypted messages because the account may be
shared with other software which doesn't and shouldn't look into DeltaChat.

Part of chatmail/scalable-resilient-chat#13.

Author: iequidoo

src/imap.rs

@@ -1964,21 +1964,23 @@ impl Session {
     }
 }
 
+fn is_encrypted(headers: &[mailparse::MailHeader<'_>]) -> bool {
+    // Some MUAs use "multipart/mixed", so look also at Subject. We can't only look at Subject as
+    // it's not mandatory, see <https://datatracker.ietf.org/doc/html/rfc5322#section-3.6>.
+    let mut res = headers
+        .get_header_value(HeaderDef::ContentType)
+        .is_some_and(|v| v.contains("multipart/encrypted"));
+    res |= headers
+        .get_header_value(HeaderDef::Subject)
+        .is_some_and(|v| v == "..." || v == "[...]");
+    res
+}
+
 async fn should_move_out_of_spam(
     context: &Context,
     headers: &[mailparse::MailHeader<'_>],
 ) -> Result<bool> {
-    if headers.get_header_value(HeaderDef::ChatVersion).is_some() {
-        // If this is a chat message (i.e. has a ChatVersion header), then this might be
-        // a securejoin message. We can't find out at this point as we didn't prefetch
-        // the SecureJoin header. So, we always move chat messages out of Spam.
-        // Two possibilities to change this would be:
-        // 1. Remove the `&& !context.is_spam_folder(folder).await?` check from
-        // `fetch_new_messages()`, and then let `receive_imf()` check
-        // if it's a spam message and should be hidden.
-        // 2. Or add a flag to the ChatVersion header that this is a securejoin
-        // request, and return `true` here only if the message has this flag.
-        // `receive_imf()` can then check if the securejoin request is valid.
+    if headers.get_header_value(HeaderDef::SecureJoin).is_some() || is_encrypted(headers) {
         return Ok(true);
     }
 
@@ -2037,7 +2039,8 @@ async fn spam_target_folder_cfg(
         return Ok(None);
     }
 
-    if needs_move_to_mvbox(context, headers).await?
+    if is_encrypted(headers) && context.get_config_bool(Config::MvboxMove).await?
+        || needs_move_to_mvbox(context, headers).await?
         // If OnlyFetchMvbox is set, we don't want to move the message to
         // the inbox where we wouldn't fetch it again:
         || context.get_config_bool(Config::OnlyFetchMvbox).await?
@@ -2090,20 +2093,6 @@ async fn needs_move_to_mvbox(
     context: &Context,
     headers: &[mailparse::MailHeader<'_>],
 ) -> Result<bool> {
-    let has_chat_version = headers.get_header_value(HeaderDef::ChatVersion).is_some();
-    if !context.get_config_bool(Config::IsChatmail).await?
-        && has_chat_version
-        && headers
-            .get_header_value(HeaderDef::AutoSubmitted)
-            .filter(|val| val.eq_ignore_ascii_case("auto-generated"))
-            .is_some()
-    {
-        if let Some(from) = mimeparser::get_from(headers) {
-            if context.is_self_addr(&from.addr).await? {
-                return Ok(true);
-            }
-        }
-    }
     if !context.get_config_bool(Config::MvboxMove).await? {
         return Ok(false);
     }
@@ -2117,7 +2106,7 @@ async fn needs_move_to_mvbox(
         return Ok(false);
     }
 
-    if has_chat_version {
+    if headers.get_header_value(HeaderDef::SecureJoin).is_some() {
         Ok(true)
     } else if let Some(parent) = get_prefetch_parent_message(context, headers).await? {
         match parent.is_dc_message {
@@ -2309,7 +2298,6 @@ pub(crate) async fn prefetch_should_download(
         return Ok(false);
     }
 
-    let is_chat_message = headers.get_header_value(HeaderDef::ChatVersion).is_some();
     let accepted_contact = origin.is_known();
     let is_reply_to_chat_message = get_prefetch_parent_message(context, headers)
         .await?
@@ -2318,16 +2306,13 @@ pub(crate) async fn prefetch_should_download(
             MessengerMessage::Yes | MessengerMessage::Reply => true,
         })
         .unwrap_or_default();
-
-    let show_emails =
-        ShowEmails::from_i32(context.get_config_int(Config::ShowEmails).await?).unwrap_or_default();
-
     let show = is_autocrypt_setup_message
-        || match show_emails {
-            ShowEmails::Off => is_chat_message || is_reply_to_chat_message,
-            ShowEmails::AcceptedContacts => {
-                is_chat_message || is_reply_to_chat_message || accepted_contact
-            }
+        || is_encrypted(headers)
+        || match ShowEmails::from_i32(context.get_config_int(Config::ShowEmails).await?)
+            .unwrap_or_default()
+        {
+            ShowEmails::Off => is_reply_to_chat_message,
+            ShowEmails::AcceptedContacts => is_reply_to_chat_message || accepted_contact,
             ShowEmails::All => true,
         };
 

src/imap/imap_tests.rs

@@ -94,14 +94,14 @@ fn test_build_sequence_sets() {
 async fn check_target_folder_combination(
     folder: &str,
     mvbox_move: bool,
-    chat_msg: bool,
+    is_encrypted: bool,
     expected_destination: &str,
     accepted_chat: bool,
     outgoing: bool,
     setupmessage: bool,
 ) -> Result<()> {
     println!(
-        "Testing: For folder {folder}, mvbox_move {mvbox_move}, chat_msg {chat_msg}, accepted {accepted_chat}, outgoing {outgoing}, setupmessage {setupmessage}"
+        "Testing: For folder {folder}, mvbox_move {mvbox_move}, is_encrypted {is_encrypted}, accepted {accepted_chat}, outgoing {outgoing}, setupmessage {setupmessage}"
     );
 
     let t = TestContext::new_alice().await;
@@ -124,7 +124,6 @@ async fn check_target_folder_combination(
         temp = format!(
             "Received: (Postfix, from userid 1000); Mon, 4 Dec 2006 14:51:39 +0100 (CET)\n\
                     {}\
-                    Subject: foo\n\
                     Message-ID: <[email protected]>\n\
                     {}\
                     Date: Sun, 22 Mar 2020 22:37:57 +0000\n\
@@ -135,7 +134,11 @@ async fn check_target_folder_combination(
             } else {
                 "From: [email protected]\nTo: [email protected]\n"
             },
-            if chat_msg { "Chat-Version: 1.0\n" } else { "" },
+            if is_encrypted {
+                "Subject: [...]\n"
+            } else {
+                "Subject: foo\n"
+            },
         );
         temp.as_bytes()
     };
@@ -157,30 +160,31 @@ async fn check_target_folder_combination(
     assert_eq!(
         expected,
         actual.as_deref(),
-        "For folder {folder}, mvbox_move {mvbox_move}, chat_msg {chat_msg}, accepted {accepted_chat}, outgoing {outgoing}, setupmessage {setupmessage}: expected {expected:?}, got {actual:?}"
+        "For folder {folder}, mvbox_move {mvbox_move}, is_encrypted {is_encrypted}, accepted {accepted_chat}, outgoing {outgoing}, setupmessage {setupmessage}: expected {expected:?}, got {actual:?}"
     );
     Ok(())
 }
 
-// chat_msg means that the message was sent by Delta Chat
-// The tuples are (folder, mvbox_move, chat_msg, expected_destination)
+// The tuples are (folder, mvbox_move, is_encrypted, expected_destination)
 const COMBINATIONS_ACCEPTED_CHAT: &[(&str, bool, bool, &str)] = &[
     ("INBOX", false, false, "INBOX"),
     ("INBOX", false, true, "INBOX"),
     ("INBOX", true, false, "INBOX"),
-    ("INBOX", true, true, "DeltaChat"),
-    ("Spam", false, false, "INBOX"), // Move classical emails in accepted chats from Spam to Inbox, not 100% sure on this, we could also just never move non-chat-msgs
+    ("INBOX", true, true, "INBOX"),
+    ("Spam", false, false, "INBOX"),
     ("Spam", false, true, "INBOX"),
-    ("Spam", true, false, "INBOX"), // Move classical emails in accepted chats from Spam to Inbox, not 100% sure on this, we could also just never move non-chat-msgs
+    // Move unencrypted emails in accepted chats from Spam to INBOX, not 100% sure on this, we could
+    // also not move unencrypted emails or, if mvbox_move=1, move them to DeltaChat.
+    ("Spam", true, false, "INBOX"),
     ("Spam", true, true, "DeltaChat"),
 ];
 
-// These are the same as above, but non-chat messages in Spam stay in Spam
+// These are the same as above, but unencrypted messages in Spam stay in Spam.
 const COMBINATIONS_REQUEST: &[(&str, bool, bool, &str)] = &[
     ("INBOX", false, false, "INBOX"),
     ("INBOX", false, true, "INBOX"),
     ("INBOX", true, false, "INBOX"),
-    ("INBOX", true, true, "DeltaChat"),
+    ("INBOX", true, true, "INBOX"),
     ("Spam", false, false, "Spam"),
     ("Spam", false, true, "INBOX"),
     ("Spam", true, false, "Spam"),
@@ -189,11 +193,11 @@ const COMBINATIONS_REQUEST: &[(&str, bool, bool, &str)] = &[
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_target_folder_incoming_accepted() -> Result<()> {
-    for (folder, mvbox_move, chat_msg, expected_destination) in COMBINATIONS_ACCEPTED_CHAT {
+    for (folder, mvbox_move, is_encrypted, expected_destination) in COMBINATIONS_ACCEPTED_CHAT {
         check_target_folder_combination(
             folder,
             *mvbox_move,
-            *chat_msg,
+            *is_encrypted,
             expected_destination,
             true,
             false,
@@ -206,11 +210,11 @@ async fn test_target_folder_incoming_accepted() -> Result<()> {
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_target_folder_incoming_request() -> Result<()> {
-    for (folder, mvbox_move, chat_msg, expected_destination) in COMBINATIONS_REQUEST {
+    for (folder, mvbox_move, is_encrypted, expected_destination) in COMBINATIONS_REQUEST {
         check_target_folder_combination(
             folder,
             *mvbox_move,
-            *chat_msg,
+            *is_encrypted,
             expected_destination,
             false,
             false,
@@ -224,11 +228,11 @@ async fn test_target_folder_incoming_request() -> Result<()> {
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_target_folder_outgoing() -> Result<()> {
     // Test outgoing emails
-    for (folder, mvbox_move, chat_msg, expected_destination) in COMBINATIONS_ACCEPTED_CHAT {
+    for (folder, mvbox_move, is_encrypted, expected_destination) in COMBINATIONS_ACCEPTED_CHAT {
         check_target_folder_combination(
             folder,
             *mvbox_move,
-            *chat_msg,
+            *is_encrypted,
             expected_destination,
             true,
             true,
@@ -242,11 +246,11 @@ async fn test_target_folder_outgoing() -> Result<()> {
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_target_folder_setupmsg() -> Result<()> {
     // Test setupmessages
-    for (folder, mvbox_move, chat_msg, _expected_destination) in COMBINATIONS_ACCEPTED_CHAT {
+    for (folder, mvbox_move, is_encrypted, _expected_destination) in COMBINATIONS_ACCEPTED_CHAT {
         check_target_folder_combination(
             folder,
             *mvbox_move,
-            *chat_msg,
+            *is_encrypted,
             if folder == &"Spam" { "INBOX" } else { folder }, // Never move setup messages, except if they are in "Spam"
             false,
             true,

src/imap/session.rs

@@ -14,16 +14,20 @@ use crate::tools;
 /// Prefetch:
 /// - Message-ID to check if we already have the message.
 /// - In-Reply-To and References to check if message is a reply to chat message.
-/// - Chat-Version to check if a message is a chat message
 /// - Autocrypt-Setup-Message to check if a message is an autocrypt setup message,
 ///   not necessarily sent by Delta Chat.
+///
+/// NB: We don't look at Chat-Version as we don't want any "better" handling for unencrypted
+/// messages.
 const PREFETCH_FLAGS: &str = "(UID INTERNALDATE RFC822.SIZE BODY.PEEK[HEADER.FIELDS (\
                               MESSAGE-ID \
                               DATE \
                               X-MICROSOFT-ORIGINAL-MESSAGE-ID \
                               FROM \
                               IN-REPLY-TO REFERENCES \
-                              CHAT-VERSION \
+                              CONTENT-TYPE \
+                              SECURE-JOIN \
+                              SUBJECT \
                               AUTO-SUBMITTED \
                               AUTOCRYPT-SETUP-MESSAGE\
                               )])";

src/receive_imf.rs

@@ -1005,7 +1005,7 @@ pub(crate) async fn receive_imf_inner(
     if let Some(is_bot) = mime_parser.is_bot {
         // If the message is auto-generated and was generated by Delta Chat,
         // mark the contact as a bot.
-        if mime_parser.get_header(HeaderDef::ChatVersion).is_some() {
+        if mime_parser.has_chat_version() {
             from_id.mark_bot(context, is_bot).await?;
         }
     }
@@ -2947,7 +2947,7 @@ async fn apply_group_changes(
             }
 
             // Allow non-Delta Chat MUAs to add members.
-            if mime_parser.get_header(HeaderDef::ChatVersion).is_none() {
+            if !mime_parser.has_chat_version() {
                 // Don't delete any members locally, but instead add absent ones to provide group
                 // membership consistency for all members:
                 new_members.extend(to_ids_flat.iter());