initial implementation of banning room IDs

takes a full room ID, evicts all our users from that room,
adds room ID to banned room IDs metadata db table, and
forbids any new local users from attempting to join it.

Signed-off-by: strawberry <strawberry@puppygock.gay>

src/database/key_value/rooms/metadata.rs

@@ -1,4 +1,5 @@
 use ruma::{OwnedRoomId, RoomId};
+use tracing::error;
 
 use crate::{database::KeyValueDatabase, service, services, utils, Error, Result};
 
@@ -42,4 +43,37 @@ impl service::rooms::metadata::Data for KeyValueDatabase {
 
         Ok(())
     }
+
+    fn is_banned(&self, room_id: &RoomId) -> Result<bool> {
+        Ok(self.bannedroomids.get(room_id.as_bytes())?.is_some())
+    }
+
+    fn ban_room(&self, room_id: &RoomId, banned: bool) -> Result<()> {
+        if banned {
+            self.bannedroomids.insert(room_id.as_bytes(), &[])?;
+        } else {
+            self.bannedroomids.remove(room_id.as_bytes())?;
+        }
+
+        Ok(())
+    }
+
+    fn list_banned_rooms<'a>(&'a self) -> Box<dyn Iterator<Item = Result<OwnedRoomId>> + 'a> {
+        Box::new(self.bannedroomids.iter().map(
+            |(room_id_bytes, _ /* non-banned rooms should not be in this table */)| {
+                let room_id = utils::string_from_bytes(&room_id_bytes)
+                    .map_err(|e| {
+                        error!("Invalid room_id bytes in bannedroomids: {e}");
+                        Error::bad_database("Invalid room_id in bannedroomids.")
+                    })?
+                    .try_into()
+                    .map_err(|e| {
+                        error!("Invalid room_id in bannedroomids: {e}");
+                        Error::bad_database("Invalid room_id in bannedroomids")
+                    })?;
+
+                Ok(room_id)
+            },
+        ))
+    }
 }