From 9f2b58a57ca61bf059bb4fe37072be78a2bc732c Mon Sep 17 00:00:00 2001
From: Ferran Borreguero <ferran.borreguero@gmail.com>
Date: Fri, 26 Dec 2025 08:48:10 +0100
Subject: [PATCH] Load specs from beacon node

---
 beaconclient/prod_beacon_instance.go |  5 +++
 cmd/api.go                           | 52 ++++++++++++++++++++++++----
 common/types.go                      |  3 ++
 3 files changed, 53 insertions(+), 7 deletions(-)

diff --git a/beaconclient/prod_beacon_instance.go b/beaconclient/prod_beacon_instance.go
index a69a622f6..39fca1c13 100644
--- a/beaconclient/prod_beacon_instance.go
+++ b/beaconclient/prod_beacon_instance.go
@@ -324,6 +324,11 @@ type GetSpecResponse struct {
 	DomainAggregateAndProof         string `json:"DOMAIN_AGGREGATE_AND_PROOF"`         //nolint:tagliatelle
 	InactivityPenaltyQuotient       string `json:"INACTIVITY_PENALTY_QUOTIENT"`        //nolint:tagliatelle
 	InactivityPenaltyQuotientAltair string `json:"INACTIVITY_PENALTY_QUOTIENT_ALTAIR"` //nolint:tagliatelle
+	BellatrixForkVersion            string `json:"BELLATRIX_FORK_VERSION"`             //nolint:tagliatelle
+	CapellaForkVersion              string `json:"CAPELLA_FORK_VERSION"`               //nolint:tagliatelle
+	DenebForkVersion                string `json:"DENEB_FORK_VERSION"`                 //nolint:tagliatelle
+	ElectraForkVersion              string `json:"ELECTRA_FORK_VERSION"`               //nolint:tagliatelle
+	FuluForkVersion                 string `json:"FULU_FORK_VERSION"`                  //nolint:tagliatelle
 }
 
 // GetSpec - https://ethereum.github.io/beacon-APIs/#/Config/getSpec
diff --git a/cmd/api.go b/cmd/api.go
index ef23a3d16..116d5f7d0 100644
--- a/cmd/api.go
+++ b/cmd/api.go
@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"fmt"
 	"net/url"
 	"os"
 	"os/signal"
@@ -90,13 +91,6 @@ var apiCmd = &cobra.Command{
 		}
 		log.Infof("boost-relay %s", Version)
 
-		networkInfo, err := common.NewEthNetworkDetails(network)
-		if err != nil {
-			log.WithError(err).Fatalf("error getting network details")
-		}
-		log.Infof("Using network: %s", networkInfo.Name)
-		log.Debug(networkInfo.String())
-
 		// Connect to beacon clients and ensure it's synced
 		if len(beaconNodeURIs) == 0 {
 			log.Fatalf("no beacon endpoints specified")
@@ -117,6 +111,19 @@ var apiCmd = &cobra.Command{
 		}
 		beaconClient := beaconclient.NewMultiBeaconClient(log, beaconInstances)
 
+		if network == "" {
+			if err := loadSpecFromBeaconClient(beaconClient); err != nil {
+				log.WithError(err).Fatalf("error loading spec from beacon client")
+			}
+		}
+
+		networkInfo, err := common.NewEthNetworkDetails(network)
+		if err != nil {
+			log.WithError(err).Fatalf("error getting network details")
+		}
+		log.Infof("Using network: %s", networkInfo.Name)
+		log.Debug(networkInfo.String())
+
 		// Connect to Redis
 		if redisReadonlyURI == "" {
 			log.Infof("Connecting to Redis at %s ...", redisURI)
@@ -217,3 +224,34 @@ var apiCmd = &cobra.Command{
 		log.Info("bye")
 	},
 }
+
+// loadSpecFromBeaconClient fetches the chain spec and genesis data from the beacon client
+// and sets the corresponding environment variables for fork versions and genesis info.
+// This allows the relay to automatically configure network parameters without manual specification.
+func loadSpecFromBeaconClient(beaconClient *beaconclient.MultiBeaconClient) error {
+	spec, err := beaconClient.GetSpec()
+	if err != nil {
+		return err
+	}
+
+	genesis, err := beaconClient.GetGenesis()
+	if err != nil {
+		return err
+	}
+
+	envs := map[string]string{
+		"GENESIS_FORK_VERSION":    genesis.Data.GenesisForkVersion,
+		"GENESIS_VALIDATORS_ROOT": genesis.Data.GenesisValidatorsRoot,
+		"BELLATRIX_FORK_VERSION":  spec.BellatrixForkVersion,
+		"CAPELLA_FORK_VERSION":    spec.CapellaForkVersion,
+		"DENEB_FORK_VERSION":      spec.DenebForkVersion,
+		"ELECTRA_FORK_VERSION":    spec.ElectraForkVersion,
+		"FULU_FORK_VERSION":       spec.FuluForkVersion,
+	}
+	for k, v := range envs {
+		if err := os.Setenv(k, v); err != nil {
+			return fmt.Errorf("failed to set env var %s: %w", k, err)
+		}
+	}
+	return nil
+}
diff --git a/common/types.go b/common/types.go
index 59f72a27c..efe2f8b9f 100644
--- a/common/types.go
+++ b/common/types.go
@@ -31,6 +31,7 @@ var (
 	EthNetworkHoodi   = "hoodi"
 	EthNetworkMainnet = "mainnet"
 	EthNetworkCustom  = "custom"
+	EthNetworkBeacon  = ""
 
 	GenesisForkVersionHolesky = "0x01017000"
 	GenesisForkVersionSepolia = "0x90000069"
@@ -155,6 +156,8 @@ func NewEthNetworkDetails(networkName string) (ret *EthNetworkDetails, err error
 		denebForkVersion = DenebForkVersionMainnet
 		electraForkVersion = ElectraForkVersionMainnet
 		fuluForkVersion = FuluForkVersionMainnet
+	case EthNetworkBeacon:
+		fallthrough
 	case EthNetworkCustom:
 		genesisForkVersion = os.Getenv("GENESIS_FORK_VERSION")
 		genesisValidatorsRoot = os.Getenv("GENESIS_VALIDATORS_ROOT")