add pre-fund when there are less than three validators

gateway/src/lib.rs

@@ -685,9 +685,23 @@ impl Actor {
         validator_set: ValidatorSet,
     ) -> Result<RawBytes, ActorError> {
         rt.validate_immediate_caller_is([&SYSTEM_ACTOR_ADDR as &Address])?;
-        let network_name = rt.transaction(|st: &mut State, _| {
+        let (network_name, pre_fund) = rt.transaction(|st: &mut State, _| {
             st.set_membership(validator_set.clone());
-            Ok(st.network_name.clone())
+            // Get validators that are different from the existing validator set
+            let mut pre_fund = vec![];
+            for v in validator_set.validators().iter() {
+                if !st
+                    .validators
+                    .validators
+                    .validators()
+                    .iter()
+                    .any(|x| x.addr == v.addr)
+                {
+                    pre_fund.push(v.addr);
+                }
+            }
+
+            Ok((st.network_name.clone(), pre_fund))
         })?;
 
         // initial validators need to be conveniently funded with at least
@@ -699,12 +713,24 @@ impl Actor {
         // to be committed. This doesn't apply to the root.
         // TODO: Once account abstraction is conveniently supported, there will be
         // no need for this initial funding of validators.
+        if network_name != *ROOTNET_ID {
+            if rt.curr_epoch() == 1 {
+                for v in validator_set.validators().iter() {
+                    rt.send(&v.addr, METHOD_SEND, None, INITIAL_VALIDATOR_FUNDS.clone())?;
+                }
+            }
 
-        if rt.curr_epoch() == 1 && network_name != *ROOTNET_ID {
-            for v in validator_set.validators().iter() {
-                rt.send(&v.addr, METHOD_SEND, None, INITIAL_VALIDATOR_FUNDS.clone())?;
+            // to prevent top-down checkpoint submissions from being stuck when the number of validators
+            // is too small (< 3), where if a new validator join and it doesn't have funds
+            // no new top-down checkpoints can be submitted, we add some balance also for
+            // non-initial validators.
+            if rt.curr_epoch() > 1 && validator_set.validators().len() < 4 {
+                for v in pre_fund.iter() {
+                    rt.send(v, METHOD_SEND, None, INITIAL_VALIDATOR_FUNDS.clone())?;
+                }
             }
         }
+
         Ok(RawBytes::default())
     }