feat: Add Limit on Groups in Add Member method (#554)

* feat: Add Limit on Groups in Add Member method

Added limit in config
Added check to determine if adding memebers would add too many users

* feat: Group Limit

Added tests for verifiying group limit
Added group limit error

* Fix Format

Fixed formatting

---------

Co-authored-by: Alex Risch <[email protected]>

xmtp_mls/src/configuration.rs

@@ -16,3 +16,5 @@ pub const MAX_INTENT_PUBLISH_ATTEMPTS: usize = 3;
 const NANOSECONDS_IN_HOUR: i64 = 3_600_000_000_000;
 
 pub const UPDATE_INSTALLATIONS_INTERVAL_NS: i64 = NANOSECONDS_IN_HOUR / 2; // 30 min
+
+pub const MAX_GROUP_SIZE: u8 = 250;

xmtp_mls/src/groups/mod.rs

@@ -17,7 +17,7 @@ use self::{
 };
 use crate::{
     client::{deserialize_welcome, ClientError, MessageProcessingError},
-    configuration::CIPHERSUITE,
+    configuration::{CIPHERSUITE, MAX_GROUP_SIZE},
     hpke::{decrypt_welcome, HpkeError},
     identity::{Identity, IdentityError},
     retry::RetryableError,
@@ -59,6 +59,8 @@ use xmtp_proto::{
 pub enum GroupError {
     #[error("group not found")]
     GroupNotFound,
+    #[error("Max user limit exceeded.")]
+    UserLimitExceeded,
     #[error("api error: {0}")]
     Api(#[from] xmtp_proto::api_client::Error),
     #[error("storage error: {0}")]
@@ -272,6 +274,12 @@ where
         account_addresses_to_add: Vec<String>,
     ) -> Result<(), GroupError> {
         let account_addresses = sanitize_evm_addresses(account_addresses_to_add)?;
+        // get current number of users in group
+        let member_count = self.members()?.len();
+        if member_count + account_addresses.len() > MAX_GROUP_SIZE as usize {
+            return Err(GroupError::UserLimitExceeded);
+        }
+
         let conn = &mut self.client.store.conn()?;
         let intent_data: Vec<u8> =
             AddMembersIntentData::new(account_addresses.into()).try_into()?;
@@ -878,4 +886,23 @@ mod tests {
             .await
             .is_err(),);
     }
+
+    #[tokio::test]
+    async fn test_max_limit_add() {
+        let amal = ClientBuilder::new_test_client(&generate_local_wallet()).await;
+        let amal_group = amal
+            .create_group(Some(PreconfiguredPolicies::GroupCreatorIsAdmin))
+            .unwrap();
+        let mut clients = Vec::new();
+        for _ in 0..249 {
+            let client: Client<_> = ClientBuilder::new_test_client(&generate_local_wallet()).await;
+            clients.push(client.account_address());
+        }
+        amal_group.add_members(clients).await.unwrap();
+        let bola = ClientBuilder::new_test_client(&generate_local_wallet()).await;
+        assert!(amal_group
+            .add_members(vec![bola.account_address()])
+            .await
+            .is_err(),);
+    }
 }