From 489b34a01f47211e39705af6fe7621dcb4803ad4 Mon Sep 17 00:00:00 2001
From: Potuz <potuz@prysmaticlabs.com>
Date: Fri, 22 Sep 2023 16:48:24 -0300
Subject: [PATCH] Use headstate when requesting current epochs (#12940)

* Use headstate when requesting current epochs

* gazelle

* review requests
---
 beacon-chain/rpc/eth/validator/BUILD.bazel |  1 +
 beacon-chain/rpc/eth/validator/handlers.go | 32 +++++++++++++++++++---
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/beacon-chain/rpc/eth/validator/BUILD.bazel b/beacon-chain/rpc/eth/validator/BUILD.bazel
index 32054be99..18903e880 100644
--- a/beacon-chain/rpc/eth/validator/BUILD.bazel
+++ b/beacon-chain/rpc/eth/validator/BUILD.bazel
@@ -18,6 +18,7 @@ go_library(
         "//beacon-chain/cache:go_default_library",
         "//beacon-chain/core/feed/operation:go_default_library",
         "//beacon-chain/core/helpers:go_default_library",
+        "//beacon-chain/core/transition:go_default_library",
         "//beacon-chain/db:go_default_library",
         "//beacon-chain/db/kv:go_default_library",
         "//beacon-chain/operations/attestations:go_default_library",
diff --git a/beacon-chain/rpc/eth/validator/handlers.go b/beacon-chain/rpc/eth/validator/handlers.go
index 0b0d4215e..ffb9b6522 100644
--- a/beacon-chain/rpc/eth/validator/handlers.go
+++ b/beacon-chain/rpc/eth/validator/handlers.go
@@ -19,6 +19,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/builder"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/cache"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/core/helpers"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/core/transition"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/db/kv"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/rpc/core"
 	rpchelpers "github.com/prysmaticlabs/prysm/v4/beacon-chain/rpc/eth/helpers"
@@ -804,10 +805,33 @@ func (s *Server) GetProposerDuties(w http.ResponseWriter, r *http.Request) {
 		http2.HandleError(w, fmt.Sprintf("Could not get start slot of epoch %d: %v", requestedEpoch, err), http.StatusInternalServerError)
 		return
 	}
-	st, err := s.Stater.StateBySlot(ctx, epochStartSlot)
-	if err != nil {
-		http2.HandleError(w, fmt.Sprintf("Could not get state for slot %d: %v ", epochStartSlot, err), http.StatusInternalServerError)
-		return
+	var st state.BeaconState
+	// if the requested epoch is new, use the head state and the next slot cache
+	if requestedEpoch < currentEpoch {
+		st, err = s.Stater.StateBySlot(ctx, epochStartSlot)
+		if err != nil {
+			http2.HandleError(w, fmt.Sprintf("Could not get state for slot %d: %v ", epochStartSlot, err), http.StatusInternalServerError)
+			return
+		}
+	} else {
+		st, err = s.HeadFetcher.HeadState(ctx)
+		if err != nil {
+			http2.HandleError(w, fmt.Sprintf("Could not get head state: %v ", err), http.StatusInternalServerError)
+			return
+		}
+		// Advance state with empty transitions up to the requested epoch start slot.
+		if st.Slot() < epochStartSlot {
+			headRoot, err := s.HeadFetcher.HeadRoot(ctx)
+			if err != nil {
+				http2.HandleError(w, fmt.Sprintf("Could not get head root: %v ", err), http.StatusInternalServerError)
+				return
+			}
+			st, err = transition.ProcessSlotsUsingNextSlotCache(ctx, st, headRoot, epochStartSlot)
+			if err != nil {
+				http2.HandleError(w, fmt.Sprintf("Could not process slots up to %d: %v ", epochStartSlot, err), http.StatusInternalServerError)
+				return
+			}
+		}
 	}
 
 	var proposals map[primitives.ValidatorIndex][]primitives.Slot