feat(ffi) Room::members returns a RoomMembersIterator.

This patch updates `Room::members` to return
`Result<Arc<RoomMembersIterator>, ClientError>`. This
`RoomMembersIterator` type is new, and is implemented in this patch too.

The idea behind this patch is to allow the bindings to “paginate” over
the list of members for a particular room, in case the room has 17k
members for example.

bindings/matrix-sdk-ffi/src/room.rs

@@ -42,6 +42,7 @@ use uuid::Uuid;
 
 use super::RUNTIME;
 use crate::{
+    chunk_iterator::ChunkIterator,
     client::ProgressWatcher,
     error::{ClientError, RoomError},
     room_info::RoomInfo,
@@ -197,14 +198,8 @@ impl Room {
         })
     }
 
-    pub async fn members(&self) -> Result<Vec<Arc<RoomMember>>, ClientError> {
-        Ok(self
-            .inner
-            .members(RoomMemberships::empty())
-            .await?
-            .iter()
-            .map(|m| Arc::new(RoomMember::new(m.clone())))
-            .collect())
+    pub async fn members(&self) -> Result<Arc<RoomMembersIterator>, ClientError> {
+        Ok(Arc::new(RoomMembersIterator::new(self.inner.members(RoomMemberships::empty()).await?)))
     }
 
     pub async fn member(&self, user_id: String) -> Result<Arc<RoomMember>, ClientError> {
@@ -1142,3 +1137,27 @@ impl From<AssetType> for RumaAssetType {
         }
     }
 }
+
+#[derive(uniffi::Object)]
+pub struct RoomMembersIterator {
+    chunk_iterator: ChunkIterator<matrix_sdk::room::RoomMember>,
+}
+
+impl RoomMembersIterator {
+    fn new(members: Vec<matrix_sdk::room::RoomMember>) -> Self {
+        Self { chunk_iterator: ChunkIterator::new(members) }
+    }
+}
+
+#[uniffi::export]
+impl RoomMembersIterator {
+    fn len(&self) -> u32 {
+        self.chunk_iterator.len()
+    }
+
+    fn next_chunk(&self, chunk_size: u32) -> Option<Vec<Arc<RoomMember>>> {
+        self.chunk_iterator
+            .next(chunk_size)
+            .map(|members| members.into_iter().map(RoomMember::new).map(Arc::new).collect())
+    }
+}