feat: do not run SecureJoin if we are already in the group

src/securejoin/bob.rs

@@ -65,7 +65,21 @@ pub(super) async fn start_protocol(context: &Context, invite: QrInvite) -> Resul
             )
             .await?;
 
-        if has_key
+        // Chat ID of the group we are joining, unused otherwise.
+        let group_chat_id = joining_chat_id(context, &invite, chat_id).await?;
+        if matches!(invite, QrInvite::Group { .. })
+            && is_contact_in_chat(context, group_chat_id, ContactId::SELF).await?
+        {
+            // If QR code is a group invite
+            // and we are already in the chat,
+            // nothing needs to be done.
+            // Even if Alice is not verified, we don't send anything.
+            context.emit_event(EventType::SecurejoinJoinerProgress {
+                contact_id: invite.contact_id(),
+                progress: JoinerProgress::Succeeded.to_usize(),
+            });
+            return Ok(group_chat_id);
+        } else if has_key
             && verify_sender_by_fingerprint(context, invite.fingerprint(), invite.contact_id())
                 .await?
         {

src/securejoin/securejoin_tests.rs

@@ -959,3 +959,46 @@ async fn test_expired_synced_auth_token() -> Result<()> {
 
     Ok(())
 }
+
+/// Tests that attempting to join already joined group does nothing.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_rejoin_group() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+
+    let alice_chat_id = chat::create_group(alice, "the chat").await?;
+
+    let qr = get_securejoin_qr(alice, Some(alice_chat_id)).await?;
+    tcm.exec_securejoin_qr(bob, alice, &qr).await;
+
+    // Bob gets two progress events.
+    for expected_progress in [400, 1000] {
+        let EventType::SecurejoinJoinerProgress { progress, .. } = bob
+            .evtracker
+            .get_matching(|evt| matches!(evt, EventType::SecurejoinJoinerProgress { .. }))
+            .await
+        else {
+            unreachable!();
+        };
+        assert_eq!(progress, expected_progress);
+    }
+
+    // Bob scans the QR code again.
+    join_securejoin(bob, &qr).await?;
+
+    // Bob immediately receives progress 1000 event.
+    let EventType::SecurejoinJoinerProgress { progress, .. } = bob
+        .evtracker
+        .get_matching(|evt| matches!(evt, EventType::SecurejoinJoinerProgress { .. }))
+        .await
+    else {
+        unreachable!();
+    };
+    assert_eq!(progress, 1000);
+
+    // Bob does not send any more messages by scanning the QR code.
+    assert!(bob.pop_sent_msg_opt(Duration::ZERO).await.is_none());
+
+    Ok(())
+}