fix: do not create a group if the sender includes self in the To field

src/receive_imf.rs

@@ -1217,17 +1217,21 @@ async fn decide_chat_assignment(
     //
     // The chat may not exist yet, i.e. there may be
     // no database row and ChatId yet.
-    let mut num_recipients = mime_parser.recipients.len();
-    if from_id != ContactId::SELF {
-        let mut has_self_addr = false;
-        for recipient in &mime_parser.recipients {
-            if context.is_self_addr(&recipient.addr).await? {
-                has_self_addr = true;
-            }
+    let mut num_recipients = 0;
+    let mut has_self_addr = false;
+    for recipient in &mime_parser.recipients {
+        if addr_cmp(&recipient.addr, &mime_parser.from.addr) {
+            continue;
         }
-        if !has_self_addr {
-            num_recipients += 1;
+
+        if context.is_self_addr(&recipient.addr).await? {
+            has_self_addr = true;
         }
+
+        num_recipients += 1;
+    }
+    if from_id != ContactId::SELF && !has_self_addr {
+        num_recipients += 1;
     }
 
     let chat_assignment = if should_trash {

src/receive_imf/receive_imf_tests.rs

@@ -5500,6 +5500,38 @@ async fn test_small_unencrypted_group() -> Result<()> {
     Ok(())
 }
 
+/// Tests that if the sender includes self
+/// in the `To` field, we do not count
+/// it as a third recipient in addition to ourselves
+/// and the sender and do not create a group chat.
+///
+/// This is a regression test.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_bcc_not_a_group() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+
+    let received = receive_imf(
+        alice,
+        b"From: \"\"<foobar@example.org>\n\
+          To: <foobar@example.org>\n\
+          Subject: Hello, this is not a group\n\
+          Message-ID: <abcdef@example.org>\n\
+          Chat-Version: 1.0\n\
+          Date: Sun, 22 Mar 2020 22:37:57 +0000\n\
+          \n\
+          hello\n",
+        false,
+    )
+    .await?
+    .unwrap();
+
+    let received_chat = Chat::load_from_db(alice, received.chat_id).await?;
+    assert_eq!(received_chat.typ, Chattype::Single);
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_lookup_key_contact_by_address_self() -> Result<()> {
     let mut tcm = TestContextManager::new();