properly handle json file missing case

database/database.go

@@ -3,12 +3,20 @@
 
 package database
 
-import "github.com/ava-labs/avalanchego/ids"
+import (
+	"github.com/ava-labs/avalanchego/ids"
+	"github.com/pkg/errors"
+)
 
 const (
 	LatestSeenBlockKey = "latestSeenBlock"
 )
 
+var (
+	ErrKeyNotFound   = errors.New("key not found")
+	ErrChainNotFound = errors.New("no database for chain")
+)
+
 // RelayerDatabase is a key-value store for relayer state, with each chainID maintaining its own state
 type RelayerDatabase interface {
 	Get(chainID ids.ID, key []byte) ([]byte, error)

database/json_file_storage.go

@@ -67,7 +67,7 @@ func NewJSONFileStorage(logger logging.Logger, dir string, networks []ids.ID) (*
 func (s *JSONFileStorage) Get(chainID ids.ID, key []byte) ([]byte, error) {
 	mutex, ok := s.mutexes[chainID]
 	if !ok {
-		return nil, errors.New("network does not exist")
+		return nil, errors.New("database not configured for chain")
 	}
 
 	mutex.RLock()
@@ -83,14 +83,14 @@ func (s *JSONFileStorage) Get(chainID ids.ID, key []byte) ([]byte, error) {
 		return nil, err
 	}
 	if !fileExists {
-		return nil, errors.Errorf("file does not exist. chainID: %s", chainID)
+		return nil, ErrChainNotFound
 	}
 
 	if val, ok := currentState[string(key)]; ok {
 		return []byte(val), nil
 	}
 
-	return nil, errors.Errorf("key does not exist. chainID: %s key: %s", chainID, key)
+	return nil, ErrKeyNotFound
 }
 
 // Put the value into the json database. Read the current chain state and overwrite the key, if it exists

relayer/relayer.go

@@ -4,6 +4,7 @@
 package relayer
 
 import (
+	"errors"
 	"math/big"
 	"math/rand"
 	"sync"
@@ -124,8 +125,16 @@ func NewRelayer(
 		return nil, nil, err
 	}
 
-	// Get the latest processed block height from the database.
+	// Get the latest processed block height from the database. If the database doesn't have a value for the latest block height,
+	// for this chain, return here without an error. This will cause the subscriber to begin processing new incoming warp messages.
 	latestSeenBlockData, err := r.db.Get(r.sourceChainID, []byte(database.LatestSeenBlockKey))
+	if errors.Is(err, database.ErrChainNotFound) {
+		logger.Info(
+			"Latest seen block not found in database. Starting from latest block.",
+			zap.String("chainID", r.sourceChainID.String()),
+		)
+		return &r, sub, nil
+	}
 	if err != nil {
 		r.logger.Warn("failed to get latest block from database", zap.Error(err))
 		return nil, nil, err