fix: add explicit limit for adding relays (5 at the moment) (#7611)

closes https://github.com/chatmail/core/issues/7608

deltachat-rpc-client/tests/test_multitransport.py

@@ -221,3 +221,25 @@ def test_recognize_self_address(acfactory) -> None:
     bob_chat.send_text("Hello!")
     msg = alice.wait_for_incoming_msg().get_snapshot()
     assert msg.chat == alice.create_chat(bob)
+
+
+def test_transport_limit(acfactory) -> None:
+    """Test transports limit."""
+    account = acfactory.get_online_account()
+    qr = acfactory.get_account_qr()
+
+    limit = 5
+
+    for _ in range(1, limit):
+        account.add_transport_from_qr(qr)
+
+    assert len(account.list_transports()) == limit
+
+    with pytest.raises(JsonRpcError):
+        account.add_transport_from_qr(qr)
+
+    second_addr = account.list_transports()[1]["addr"]
+    account.delete_transport(second_addr)
+
+    # test that adding a transport after deleting one works again
+    account.add_transport_from_qr(qr)

src/configure.rs

@@ -45,6 +45,10 @@ use crate::transport::{
 use crate::{EventType, stock_str};
 use crate::{chat, provider};
 
+/// Maximum number of relays
+/// see <https://github.com/chatmail/core/issues/7608>
+pub(crate) const MAX_TRANSPORT_RELAYS: usize = 5;
+
 macro_rules! progress {
     ($context:tt, $progress:expr, $comment:expr) => {
         assert!(
@@ -283,6 +287,18 @@ impl Context {
                     "To use additional relays, set the legacy option \"Settings / Advanced / Show Classic Emails\" to \"All\"."
                 );
             }
+
+            if self
+                .sql
+                .count("SELECT COUNT(*) FROM transports", ())
+                .await?
+                >= MAX_TRANSPORT_RELAYS
+            {
+                bail!(
+                    "You have reached the maximum number of relays ({}).",
+                    MAX_TRANSPORT_RELAYS
+                )
+            }
         }
 
         let provider = match configure(self, param).await {