fix: receive_imf: Look up key contact by intended recipient fingerprint (#7661)

For now, do this only for `OneOneChat` and `MailingListOrBroadcast`, this is enough to correctly
support messages from modern Delta Chat versions sending Intended Recipient Fingerprint subpackets
and single-recipient messages from modern versions of other MUAs.

src/pgp.rs

@@ -196,7 +196,13 @@ pub async fn pk_encrypt(
                 hashed.push(Subpacket::critical(SubpacketData::SignatureCreationTime(
                     chrono::Utc::now().trunc_subsecs(0),
                 ))?);
+                // Test "elena" uses old Delta Chat.
+                let skip = private_key_for_signing.dc_fingerprint().hex()
+                    == "B86586B6DEF437D674BFAFC02A6B2EBC633B9E82";
                 for key in &public_keys_for_encryption {
+                    if skip {
+                        break;
+                    }
                     let data = SubpacketData::IntendedRecipientFingerprint(key.fingerprint());
                     let subpkt = match private_key_for_signing.version() < KeyVersion::V6 {
                         true => Subpacket::regular(data)?,

src/receive_imf.rs

@@ -27,7 +27,9 @@ use crate::events::EventType;
 use crate::headerdef::{HeaderDef, HeaderDefMap};
 use crate::imap::{GENERATED_PREFIX, markseen_on_imap_table};
 use crate::key::{DcKey, Fingerprint};
-use crate::key::{load_self_public_key_opt, self_fingerprint, self_fingerprint_opt};
+use crate::key::{
+    load_self_public_key, load_self_public_key_opt, self_fingerprint, self_fingerprint_opt,
+};
 use crate::log::{LogExt as _, warn};
 use crate::message::{
     self, Message, MessageState, MessengerMessage, MsgId, Viewtype, rfc724_mid_exists,
@@ -386,8 +388,30 @@ async fn get_to_and_past_contact_ids(
                 // This is an encrypted 1:1 chat.
                 to_ids = pgp_to_ids
             } else {
-                let ids = match mime_parser.was_encrypted() {
-                    true => {
+                let ids = if mime_parser.was_encrypted() {
+                    let mut recipient_fps = mime_parser
+                        .signature
+                        .as_ref()
+                        .map(|(_, recipient_fps)| recipient_fps.iter().cloned().collect::<Vec<_>>())
+                        .unwrap_or_default();
+                    // If there are extra recipient fingerprints, it may be a non-chat "implicit
+                    // Bcc" message. Fall back to in-chat lookup if so.
+                    if !recipient_fps.is_empty() && recipient_fps.len() <= 2 {
+                        let self_fp = load_self_public_key(context).await?.dc_fingerprint();
+                        recipient_fps.retain(|fp| *fp != self_fp);
+                        if recipient_fps.is_empty() {
+                            vec![Some(ContactId::SELF)]
+                        } else {
+                            add_or_lookup_key_contacts(
+                                context,
+                                &mime_parser.recipients,
+                                &mime_parser.gossiped_keys,
+                                &recipient_fps,
+                                Origin::Hidden,
+                            )
+                            .await?
+                        }
+                    } else {
                         lookup_key_contacts_fallback_to_chat(
                             context,
                             &mime_parser.recipients,
@@ -396,7 +420,8 @@ async fn get_to_and_past_contact_ids(
                         )
                         .await?
                     }
-                    false => vec![],
+                } else {
+                    vec![]
                 };
                 if mime_parser.was_encrypted() && !ids.contains(&None)
                 // Prefer creating PGP chats if there are any key-contacts. At least this prevents

src/receive_imf/receive_imf_tests.rs

@@ -5111,9 +5111,9 @@ async fn test_dont_verify_by_verified_by_unknown() -> Result<()> {
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_recv_outgoing_msg_before_securejoin() -> Result<()> {
     let mut tcm = TestContextManager::new();
-    let a0 = &tcm.alice().await;
-    let a1 = &tcm.alice().await;
     let bob = &tcm.bob().await;
+    let a0 = &tcm.elena().await;
+    let a1 = &tcm.elena().await;
 
     tcm.execute_securejoin(bob, a0).await;
     let chat_id_a0_bob = a0.create_chat_id(bob).await;
@@ -5154,14 +5154,31 @@ async fn test_recv_outgoing_msg_before_securejoin() -> Result<()> {
         chat_a1.why_cant_send(a1).await?,
         Some(CantSendReason::ContactRequest)
     );
+
+    let a0 = &tcm.alice().await;
+    let a1 = &tcm.alice().await;
+    tcm.execute_securejoin(bob, a0).await;
+    let chat_id_a0_bob = a0.create_chat_id(bob).await;
+    let sent_msg = a0.send_text(chat_id_a0_bob, "Hi").await;
+    bob.recv_msg(&sent_msg).await;
+    let msg_a1 = a1.recv_msg(&sent_msg).await;
+    assert!(msg_a1.get_showpadlock());
+    let chat_a1 = Chat::load_from_db(a1, msg_a1.chat_id).await?;
+    assert_eq!(chat_a1.typ, Chattype::Single);
+    assert!(chat_a1.is_encrypted(a1).await?);
+    assert_eq!(
+        chat::get_chat_contacts(a1, chat_a1.id).await?,
+        [a1.add_or_lookup_contact_id(bob).await]
+    );
+    assert!(chat_a1.can_send(a1).await?);
     Ok(())
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_recv_outgoing_msg_before_having_key_and_after() -> Result<()> {
     let mut tcm = TestContextManager::new();
-    let a0 = &tcm.alice().await;
-    let a1 = &tcm.alice().await;
+    let a0 = &tcm.elena().await;
+    let a1 = &tcm.elena().await;
     let bob = &tcm.bob().await;
 
     tcm.execute_securejoin(bob, a0).await;
@@ -5174,9 +5191,9 @@ async fn test_recv_outgoing_msg_before_having_key_and_after() -> Result<()> {
     assert!(!chat_a1.is_encrypted(a1).await?);
 
     // Device a1 somehow learns Bob's key and creates the corresponding chat. However, this doesn't
-    // help currently because we only look up key contacts by address in a particular chat and the
-    // new chat isn't referenced by the received message. This should be fixed by sending and
-    // receiving Intended Recipient Fingerprint subpackets.
+    // help because we only look up key contacts by address in a particular chat and the new chat
+    // isn't referenced by the received message. This is fixed by sending and receiving Intended
+    // Recipient Fingerprint subpackets which elena doesn't send.
     a1.create_chat_id(bob).await;
     let sent_msg = a0.send_text(chat_id_a0_bob, "Hi again").await;
     let msg_a1 = a1.recv_msg(&sent_msg).await;

src/test_utils.rs

@@ -117,6 +117,8 @@ impl TestContextManager {
             .await
     }
 
+    /// Returns new elena's "device".
+    /// Elena doesn't send Intended Recipient Fingerprint subpackets to simulate old Delta Chat.
     pub async fn elena(&mut self) -> TestContext {
         TestContext::builder()
             .configure_elena()