core: move blockdb into core package and minor change on governance interface (#110)

Since third party apps will possibly implement their only blockdb class,
it make sense for the interface to be in core.
Also add GetNumShards into the governance interface.

1 files changed, 179 insertions, 0 deletions

diff --git a/core/blockdb/memory.go b/core/blockdb/memory.go
new file mode 100644
index 0000000..eeda477
--- /dev/null
+++ b/core/blockdb/memory.go
@@ -0,0 +1,179 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core 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 dexon-consensus-core 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 dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package blockdb
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"os"
+	"sync"
+
+	"github.com/dexon-foundation/dexon-consensus-core/common"
+	"github.com/dexon-foundation/dexon-consensus-core/core/types"
+)
+
+type seqIterator struct {
+	idx int
+	db  *MemBackedBlockDB
+}
+
+func (seq *seqIterator) Next() (types.Block, error) {
+	curIdx := seq.idx
+	seq.idx++
+	return seq.db.getByIndex(curIdx)
+}
+
+// MemBackedBlockDB is a memory backed BlockDB implementation.
+type MemBackedBlockDB struct {
+	blocksMutex        sync.RWMutex
+	blockHashSequence  common.Hashes
+	blocksByHash       map[common.Hash]*types.Block
+	persistantFilePath string
+}
+
+// NewMemBackedBlockDB initialize a memory-backed block database.
+func NewMemBackedBlockDB(persistantFilePath ...string) (db *MemBackedBlockDB, err error) {
+	db = &MemBackedBlockDB{
+		blockHashSequence: common.Hashes{},
+		blocksByHash:      make(map[common.Hash]*types.Block),
+	}
+	if len(persistantFilePath) == 0 || len(persistantFilePath[0]) == 0 {
+		return
+	}
+	db.persistantFilePath = persistantFilePath[0]
+	buf, err := ioutil.ReadFile(db.persistantFilePath)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			// Something unexpected happened.
+			return
+		}
+		// It's expected behavior that file doesn't exists, we should not
+		// report error on it.
+		err = nil
+		return
+	}
+
+	// Init this instance by file content, it's a temporary way
+	// to export those private field for JSON encoding.
+	toLoad := struct {
+		Sequence common.Hashes
+		ByHash   map[common.Hash]*types.Block
+	}{}
+	err = json.Unmarshal(buf, &toLoad)
+	if err != nil {
+		return
+	}
+	db.blockHashSequence = toLoad.Sequence
+	db.blocksByHash = toLoad.ByHash
+	return
+}
+
+// Has returns wheter or not the DB has a block identified with the hash.
+func (m *MemBackedBlockDB) Has(hash common.Hash) bool {
+	m.blocksMutex.RLock()
+	defer m.blocksMutex.RUnlock()
+
+	_, ok := m.blocksByHash[hash]
+	return ok
+}
+
+// Get returns a block given a hash.
+func (m *MemBackedBlockDB) Get(hash common.Hash) (types.Block, error) {
+	m.blocksMutex.RLock()
+	defer m.blocksMutex.RUnlock()
+
+	return m.internalGet(hash)
+}
+
+func (m *MemBackedBlockDB) internalGet(hash common.Hash) (types.Block, error) {
+	b, ok := m.blocksByHash[hash]
+	if !ok {
+		return types.Block{}, ErrBlockDoesNotExist
+	}
+	return *b, nil
+}
+
+// Put inserts a new block into the database.
+func (m *MemBackedBlockDB) Put(block types.Block) error {
+	if m.Has(block.Hash) {
+		return ErrBlockExists
+	}
+
+	m.blocksMutex.Lock()
+	defer m.blocksMutex.Unlock()
+
+	m.blockHashSequence = append(m.blockHashSequence, block.Hash)
+	m.blocksByHash[block.Hash] = &block
+	return nil
+}
+
+// Update updates a block in the database.
+func (m *MemBackedBlockDB) Update(block types.Block) error {
+	m.blocksMutex.Lock()
+	defer m.blocksMutex.Unlock()
+
+	m.blocksByHash[block.Hash] = &block
+	return nil
+}
+
+// Close implement Closer interface, which would release allocated resource.
+func (m *MemBackedBlockDB) Close() (err error) {
+	// Save internal state to a pretty-print json file. It's a temporary way
+	// to dump private file via JSON encoding.
+	if len(m.persistantFilePath) == 0 {
+		return
+	}
+
+	m.blocksMutex.RLock()
+	defer m.blocksMutex.RUnlock()
+
+	toDump := struct {
+		Sequence common.Hashes
+		ByHash   map[common.Hash]*types.Block
+	}{
+		Sequence: m.blockHashSequence,
+		ByHash:   m.blocksByHash,
+	}
+
+	// Dump to JSON with 2-space indent.
+	buf, err := json.Marshal(&toDump)
+	if err != nil {
+		return
+	}
+
+	err = ioutil.WriteFile(m.persistantFilePath, buf, 0644)
+	return
+}
+
+func (m *MemBackedBlockDB) getByIndex(idx int) (types.Block, error) {
+	m.blocksMutex.RLock()
+	defer m.blocksMutex.RUnlock()
+
+	if idx >= len(m.blockHashSequence) {
+		return types.Block{}, ErrIterationFinished
+	}
+
+	hash := m.blockHashSequence[idx]
+	return m.internalGet(hash)
+}
+
+// GetAll implement Reader.GetAll method, which allows caller
+// to retrieve all blocks in DB.
+func (m *MemBackedBlockDB) GetAll() (BlockIterator, error) {
+	return &seqIterator{db: m}, nil
+}