swarm: add database abstractions (shed package) (#18183)

swarm/shed/field_string.go

@@ -0,0 +1,66 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package shed
+
+import (
+	"github.com/syndtr/goleveldb/leveldb"
+)
+
+// StringField is the most simple field implementation
+// that stores an arbitrary string under a specific LevelDB key.
+type StringField struct {
+	db  *DB
+	key []byte
+}
+
+// NewStringField retruns a new Instance of StringField.
+// It validates its name and type against the database schema.
+func (db *DB) NewStringField(name string) (f StringField, err error) {
+	key, err := db.schemaFieldKey(name, "string")
+	if err != nil {
+		return f, err
+	}
+	return StringField{
+		db:  db,
+		key: key,
+	}, nil
+}
+
+// Get returns a string value from database.
+// If the value is not found, an empty string is returned
+// an no error.
+func (f StringField) Get() (val string, err error) {
+	b, err := f.db.Get(f.key)
+	if err != nil {
+		if err == leveldb.ErrNotFound {
+			return "", nil
+		}
+		return "", err
+	}
+	return string(b), nil
+}
+
+// Put stores a string in the database.
+func (f StringField) Put(val string) (err error) {
+	return f.db.Put(f.key, []byte(val))
+}
+
+// PutInBatch stores a string in a batch that can be
+// saved later in database.
+func (f StringField) PutInBatch(batch *leveldb.Batch, val string) {
+	batch.Put(f.key, []byte(val))
+}