// 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_test
import (
"bytes"
"context"
"encoding/binary"
"fmt"
"io/ioutil"
"log"
"os"
"time"
"github.com/dexon-foundation/dexon/swarm/shed"
"github.com/dexon-foundation/dexon/swarm/storage"
"github.com/syndtr/goleveldb/leveldb"
)
// Store holds fields and indexes (including their encoding functions)
// and defines operations on them by composing data from them.
// It implements storage.ChunkStore interface.
// It is just an example without any support for parallel operations
// or real world implementation.
type Store struct {
db *shed.DB
// fields and indexes
schemaName shed.StringField
sizeCounter shed.Uint64Field
accessCounter shed.Uint64Field
retrievalIndex shed.Index
accessIndex shed.Index
gcIndex shed.Index
}
// New returns new Store. All fields and indexes are initialized
// and possible conflicts with schema from existing database is checked
// automatically.
func New(path string) (s *Store, err error) {
db, err := shed.NewDB(path, "")
if err != nil {
return nil, err
}
s = &Store{
db: db,
}
// Identify current storage schema by arbitrary name.
s.schemaName, err = db.NewStringField("schema-name")
if err != nil {
return nil, err
}
// Global ever incrementing index of chunk accesses.
s.accessCounter, err = db.NewUint64Field("access-counter")
if err != nil {
return nil, err
}
// Index storing actual chunk address, data and store timestamp.
s.retrievalIndex, err = db.NewIndex("Address->StoreTimestamp|Data", shed.IndexFuncs{
EncodeKey: func(fields shed.Item) (key []byte, err error) {
return fields.Address, nil
},
DecodeKey: func(key []byte) (e shed.Item, err error) {
e.Address = key
return e, nil
},
EncodeValue: func(fields shed.Item) (value []byte, err error) {
b := make([]byte, 8)
binary.BigEndian.PutUint64(b, uint64(fields.StoreTimestamp))
value = append(b, fields.Data...)
return value, nil
},
DecodeValue: func(keyItem shed.Item, value []byte) (e shed.Item, err error) {
e.StoreTimestamp = int64(binary.BigEndian.Uint64(value[:8]))
e.Data = value[8:]
return e, nil
},
})
if err != nil {
return nil, err
}
// Index storing access timestamp for a particular address.
// It is needed in order to update gc index keys for iteration order.
s.accessIndex, err = db.NewIndex("Address->AccessTimestamp", shed.IndexFuncs{
EncodeKey: func(fields shed.Item) (key []byte, err error) {
return fields.Address, nil
},
DecodeKey: func(key []byte) (e shed.Item, err error) {
e.Address = key
return e, nil
},
EncodeValue: func(fields shed.Item) (value []byte, err error) {
b := make([]byte, 8)
binary.BigEndian.PutUint64(b, uint64(fields.AccessTimestamp))
return b, nil
},
DecodeValue: func(keyItem shed.Item, value []byte) (e shed.Item, err error) {
e.AccessTimestamp = int64(binary.BigEndian.Uint64(value))
return e, nil
},
})
if err != nil {
return nil, err
}
// Index with keys ordered by access timestamp for garbage collection prioritization.
s.gcIndex, err = db.NewIndex("AccessTimestamp|StoredTimestamp|Address->nil", shed.IndexFuncs{
EncodeKey: func(fields shed.Item) (key []byte, err error) {
b := make([]byte, 16, 16+len(fields.Address))
binary.BigEndian.PutUint64(b[:8], uint64(fields.AccessTimestamp))
binary.BigEndian.PutUint64(b[8:16], uint64(fields.StoreTimestamp))
key = append(b, fields.Address...)
return key, nil
},
DecodeKey: func(key []byte) (e shed.Item, err error) {
e.AccessTimestamp = int64(binary.BigEndian.Uint64(key[:8]))
e.StoreTimestamp = int64(binary.BigEndian.Uint64(key[8:16]))
e.Address = key[16:]
return e, nil
},
EncodeValue: func(fields shed.Item) (value []byte, err error) {
return nil, nil
},
DecodeValue: func(keyItem shed.Item, value []byte) (e shed.Item, err error) {
return e, nil
},
})
if err != nil {
return nil, err
}
return s, nil
}
// Put stores the chunk and sets it store timestamp.
func (s *Store) Put(_ context.Context, ch storage.Chunk) (err error) {
return s.retrievalIndex.Put(shed.Item{
Address: ch.Address(),
Data: ch.Data(),
StoreTimestamp: time.Now().UTC().UnixNano(),
})
}
// Get retrieves a chunk with the provided address.
// It updates access and gc indexes by removing the previous
// items from them and adding new items as keys of index entries
// are changed.
func (s *Store) Get(_ context.Context, addr storage.Address) (c storage.Chunk, err error) {
batch := new(leveldb.Batch)
// Get the chunk data and storage timestamp.
item, err := s.retrievalIndex.Get(shed.Item{
Address: addr,
})
if err != nil {
if err == leveldb.ErrNotFound {
return nil, storage.ErrChunkNotFound
}
return nil, err
}
// Get the chunk access timestamp.
accessItem, err := s.accessIndex.Get(shed.Item{
Address: addr,
})
switch err {
case nil:
// Remove gc index entry if access timestamp is found.
err = s.gcIndex.DeleteInBatch(batch, shed.Item{
Address: item.Address,
StoreTimestamp: accessItem.AccessTimestamp,
AccessTimestamp: item.StoreTimestamp,
})
if err != nil {
return nil, err
}
case leveldb.ErrNotFound:
// Access timestamp is not found. Do not do anything.
// This is the firs get request.
default:
return nil, err
}
// Specify new access timestamp
accessTimestamp := time.Now().UTC().UnixNano()
// Put new access timestamp in access index.
err = s.accessIndex.PutInBatch(batch, shed.Item{
Address: addr,
AccessTimestamp: accessTimestamp,
})
if err != nil {
return nil, err
}
// Put new access timestamp in gc index.
err = s.gcIndex.PutInBatch(batch, shed.Item{
Address: item.Address,
AccessTimestamp: accessTimestamp,
StoreTimestamp: item.StoreTimestamp,
})
if err != nil {
return nil, err
}
// Increment access counter.
// Currently this information is not used anywhere.
_, err = s.accessCounter.IncInBatch(batch)
if err != nil {
return nil, err
}
// Write the batch.
err = s.db.WriteBatch(batch)
if err != nil {
return nil, err
}
// Return the chunk.
return storage.NewChunk(item.Address, item.Data), nil
}
// CollectGarbage is an example of index iteration.
// It provides no reliable garbage collection functionality.
func (s *Store) CollectGarbage() (err error) {
const maxTrashSize = 100
maxRounds := 10 // arbitrary number, needs to be calculated
// Run a few gc rounds.
for roundCount := 0; roundCount < maxRounds; roundCount++ {
var garbageCount int
// New batch for a new cg round.
trash := new(leveldb.Batch)
// Iterate through all index items and break when needed.
err = s.gcIndex.Iterate(func(item shed.Item) (stop bool, err error) {
// Remove the chunk.
err = s.retrievalIndex.DeleteInBatch(trash, item)
if err != nil {
return false, err
}
// Remove the element in gc index.
err = s.gcIndex.DeleteInBatch(trash, item)
if err != nil {
return false, err
}
// Remove the relation in access index.
err = s.accessIndex.DeleteInBatch(trash, item)
if err != nil {
return false, err
}
garbageCount++
if garbageCount >= maxTrashSize {
return true, nil
}
return false, nil
}, nil)
if err != nil {
return err
}
if garbageCount == 0 {
return nil
}
err = s.db.WriteBatch(trash)
if err != nil {
return err
}
}
return nil
}
// GetSchema is an example of retrieveing the most simple
// string from a database field.
func (s *Store) GetSchema() (name string, err error) {
name, err = s.schemaName.Get()
if err == leveldb.ErrNotFound {
return "", nil
}
return name, err
}
// GetSchema is an example of storing the most simple
// string in a database field.
func (s *Store) PutSchema(name string) (err error) {
return s.schemaName.Put(name)
}
// Close closes the underlying database.
func (s *Store) Close() error {
return s.db.Close()
}
// Example_store constructs a simple storage implementation using shed package.
func Example_store() {
dir, err := ioutil.TempDir("", "ephemeral")
if err != nil {
log.Fatal(err)
}
defer os.RemoveAll(dir)
s, err := New(dir)
if err != nil {
log.Fatal(err)
}
defer s.Close()
ch := storage.GenerateRandomChunk(1024)
err = s.Put(context.Background(), ch)
if err != nil {
log.Fatal(err)
}
got, err := s.Get(context.Background(), ch.Address())
if err != nil {
log.Fatal(err)
}
fmt.Println(bytes.Equal(got.Data(), ch.Data()))
//Output: true
}
