swarm/storage/localstore: add godoc package overview

swarm/storage/localstore/doc.go

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+// Copyright 2019 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 localstore provides disk storage layer for Swarm Chunk persistance.
+It uses swarm/shed abstractions on top of github.com/syndtr/goleveldb LevelDB
+implementation.
+
+The main type is DB which manages the storage by providing methods to
+access and add Chunks and to manage their status.
+
+Modes are abstractions that do specific changes to Chunks. There are three
+mode types:
+
+ - ModeGet, for Chunk access
+ - ModePut, for adding Chunks to the database
+ - ModeSet, for changing Chunk statuses
+
+Every mode type has a corresponding type (Getter, Putter and Setter)
+that provides adequate method to perform the opperation and that type
+should be injected into localstore consumers instead the whole DB.
+This provides more clear insight which operations consumer is performing
+on the database.
+
+Getters, Putters and Setters accept different get, put and set modes
+to perform different actions. For example, ModeGet has two different
+variables ModeGetRequest and ModeGetSync and dwo different Getters
+can be constructed with them that are used when the chunk is requested
+or when the chunk is synced as this two events are differently changing
+the database.
+
+Subscription methods are implemented for a specific purpose of
+continuous iterations over Chunks that should be provided to
+Push and Pull syncing.
+*/
+package localstore