fix arithmetic side-effects

Signed-off-by: Jason Volk <jason@zemos.net>

src/admin/debug/commands.rs

@@ -58,7 +58,7 @@ pub(super) async fn parse_pdu(body: Vec<&str>) -> Result<RoomMessageEventContent
 		));
 	}
 
-	let string = body[1..body.len() - 1].join("\n");
+	let string = body[1..body.len().saturating_sub(1)].join("\n");
 	match serde_json::from_str(&string) {
 		Ok(value) => match ruma::signatures::reference_hash(&value, &RoomVersionId::V6) {
 			Ok(hash) => {

src/admin/room/room_moderation_commands.rs

@@ -191,7 +191,10 @@ async fn ban_list_of_rooms(body: Vec<&str>, force: bool, disable_federation: boo
 		));
 	}
 
-	let rooms_s = body.clone().drain(1..body.len() - 1).collect::<Vec<_>>();
+	let rooms_s = body
+		.clone()
+		.drain(1..body.len().saturating_sub(1))
+		.collect::<Vec<_>>();
 
 	let admin_room_alias = &services().globals.admin_alias;
 

src/admin/user/commands.rs

@@ -23,7 +23,7 @@ pub(super) async fn list(_body: Vec<&str>) -> Result<RoomMessageEventContent> {
 	match services().users.list_local_users() {
 		Ok(users) => {
 			let mut plain_msg = format!("Found {} local user account(s):\n```\n", users.len());
-			plain_msg += &users.join("\n");
+			plain_msg += users.join("\n").as_str();
 			plain_msg += "\n```";
 
 			Ok(RoomMessageEventContent::notice_markdown(plain_msg))
@@ -195,7 +195,10 @@ pub(super) async fn deactivate_all(
 		));
 	}
 
-	let usernames = body.clone().drain(1..body.len() - 1).collect::<Vec<_>>();
+	let usernames = body
+		.clone()
+		.drain(1..body.len().saturating_sub(1))
+		.collect::<Vec<_>>();
 
 	let mut user_ids: Vec<OwnedUserId> = Vec::with_capacity(usernames.len());
 	let mut admins = Vec::new();