sdk: actually no, let's store all relay urls together in the same kvdb key.

sdk/kvstore/badger/store.go

@@ -58,27 +58,31 @@ func (s *Store) Close() error {
 	return s.db.Close()
 }
 
-func (s *Store) Scan(prefix []byte, fn func(key []byte, value []byte) bool) error {
-	return s.db.View(func(txn *badger.Txn) error {
-		it := txn.NewIterator(badger.DefaultIteratorOptions)
-		defer it.Close()
-
-		for it.Seek(prefix); it.ValidForPrefix(prefix); it.Next() {
-			item := it.Item()
-			err := item.Value(func(v []byte) error {
-				k := item.Key()
-				if !fn(k, v) {
-					return badger.ErrStopIteration
-				}
+func (s *Store) Update(key []byte, f func([]byte) ([]byte, error)) error {
+	return s.db.Update(func(txn *badger.Txn) error {
+		var val []byte
+		item, err := txn.Get(key)
+		if err == nil {
+			err = item.Value(func(v []byte) error {
+				val = make([]byte, len(v))
+				copy(val, v)
 				return nil
 			})
-			if err == badger.ErrStopIteration {
-				break
-			}
 			if err != nil {
 				return err
 			}
+		} else if err != badger.ErrKeyNotFound {
+			return err
 		}
-		return nil
+
+		newVal, err := f(val)
+		if err != nil {
+			return err
+		}
+
+		if newVal == nil {
+			return txn.Delete(key)
+		}
+		return txn.Set(key, newVal)
 	})
 }

sdk/kvstore/interface.go

@@ -14,7 +14,9 @@ type KVStore interface {
 	// Close releases any resources held by the store
 	Close() error
 
-	// Scan iterates through all keys with the given prefix.
-	// For each key-value pair, fn is called. If fn returns false, iteration stops.
-	Scan(prefix []byte, fn func(key []byte, value []byte) bool) error
+	// Update atomically modifies a value for a given key.
+	// The function f receives the current value (nil if not found)
+	// and returns the new value to be set.
+	// If f returns nil, the key is deleted.
+	Update(key []byte, f func([]byte) ([]byte, error)) error
 }

sdk/kvstore/lmdb/store.go

@@ -91,22 +91,26 @@ func (s *Store) Close() error {
 	return nil
 }
 
-func (s *Store) Scan(prefix []byte, fn func(key []byte, value []byte) bool) error {
-	return s.env.View(func(txn *lmdb.Txn) error {
-		cursor, err := txn.OpenCursor(s.dbi)
+func (s *Store) Update(key []byte, f func([]byte) ([]byte, error)) error {
+	return s.env.Update(func(txn *lmdb.Txn) error {
+		var val []byte
+		v, err := txn.Get(s.dbi, key)
+		if err == nil {
+			// make a copy since v is only valid during the transaction
+			val = make([]byte, len(v))
+			copy(val, v)
+		} else if !lmdb.IsNotFound(err) {
+			return err
+		}
+
+		newVal, err := f(val)
 		if err != nil {
 			return err
 		}
-		defer cursor.Close()
 
-		for k, v, err := cursor.Get(prefix, nil, lmdb.SetRange); err == nil; k, v, err = cursor.Get(nil, nil, lmdb.Next) {
-			if !bytes.HasPrefix(k, prefix) {
-				break
-			}
-			if !fn(k, v) {
-				break
-			}
+		if newVal == nil {
+			return txn.Del(s.dbi, key, nil)
 		}
-		return nil
+		return txn.Put(s.dbi, key, newVal, 0)
 	})
 }

sdk/kvstore/memory/store.go

@@ -57,17 +57,29 @@ func (s *Store) Close() error {
 	return nil
 }
 
-func (s *Store) Scan(prefix []byte, fn func(key []byte, value []byte) bool) error {
-	s.RLock()
-	defer s.RUnlock()
+func (s *Store) Update(key []byte, f func([]byte) ([]byte, error)) error {
+	s.Lock()
+	defer s.Unlock()
 
-	prefixStr := string(prefix)
-	for k, v := range s.data {
-		if strings.HasPrefix(k, prefixStr) {
-			if !fn([]byte(k), v) {
-				break
-			}
-		}
+	var val []byte
+	if v, ok := s.data[string(key)]; ok {
+		// Return a copy to prevent modification of stored data
+		val = make([]byte, len(v))
+		copy(val, v)
+	}
+
+	newVal, err := f(val)
+	if err != nil {
+		return err
+	}
+
+	if newVal == nil {
+		delete(s.data, string(key))
+	} else {
+		// Store a copy to prevent modification of stored data
+		cp := make([]byte, len(newVal))
+		copy(cp, newVal)
+		s.data[string(key)] = cp
 	}
 	return nil
 }