indexer: support data exporting/forwarding (#103)

To support more effective and flexible blockchain info exploring, we add
`indexer` package, defines the flow of indexer dameon, and integrate
into dex.Dexon fullnode.

For more export options, we use Golang built-in `plugin` package to
support mulitple implementations.

3 files changed, 139 insertions, 0 deletions

diff --git a/indexer/blockhain.go b/indexer/blockhain.go
new file mode 100644
index 000000000..bf9a180ce
--- /dev/null
+++ b/indexer/blockhain.go
@@ -0,0 +1,85 @@
+package indexer
+
+import (
+	"math/big"
+
+	coreCommon "github.com/dexon-foundation/dexon-consensus/common"
+	coreTypes "github.com/dexon-foundation/dexon-consensus/core/types"
+
+	"github.com/dexon-foundation/dexon/common"
+	"github.com/dexon-foundation/dexon/core"
+	"github.com/dexon-foundation/dexon/core/state"
+	"github.com/dexon-foundation/dexon/core/types"
+	"github.com/dexon-foundation/dexon/event"
+	"github.com/dexon-foundation/dexon/rlp"
+)
+
+// ReadOnlyBlockChain defines safe reading blockchain interface by removing write
+// methods of core.BlockChain struct.
+type ReadOnlyBlockChain interface {
+	BadBlocks() []*types.Block
+	CurrentBlock() *types.Block
+	CurrentFastBlock() *types.Block
+	CurrentHeader() *types.Header
+	GasLimit() uint64
+	Genesis() *types.Block
+	GetAncestor(common.Hash, uint64, uint64, *uint64) (common.Hash, uint64)
+	GetAddressInfo(uint32, common.Address) (
+		info struct {
+			Nonce   uint64
+			Cost    *big.Int
+			Counter uint64
+		})
+	GetBlock(common.Hash, uint64) *types.Block
+	GetBlockByHash(common.Hash) *types.Block
+	GetBlockByNumber(uint64) *types.Block
+	GetBlockHashesFromHash(common.Hash, uint64) []common.Hash
+	GetBlocksFromHash(common.Hash, int) (blocks []*types.Block)
+	GetBody(common.Hash) *types.Body
+	GetBodyRLP(common.Hash) rlp.RawValue
+	GetChainLastConfirmedHeight(uint32) uint64
+	GetConfirmedBlockByHash(uint32, coreCommon.Hash) (*coreTypes.Block, types.Transactions)
+	GetCostInConfirmedBlocks(uint32, common.Address) (*big.Int, bool)
+	GetGovStateByHash(common.Hash) (*types.GovState, error)
+	GetGovStateByNumber(uint64) (*types.GovState, error)
+	GetHeader(common.Hash, uint64) *types.Header
+	GetHeaderByHash(common.Hash) *types.Header
+	GetHeaderByNumber(number uint64) *types.Header
+	GetLastNonceInConfirmedBlocks(uint32, common.Address) (uint64, bool)
+	GetPending() (*types.Block, *state.StateDB)
+	GetPendingBlockByNumber(uint64) *types.Block
+	GetPendingHeight() uint64
+	GetReceiptsByHash(common.Hash) types.Receipts
+	GetRoundHeight(uint64) (uint64, bool)
+	GetTd(common.Hash, uint64) *big.Int
+	GetTdByHash(common.Hash) *big.Int
+	GetUnclesInChain(*types.Block, int) []*types.Header
+	HasBlock(common.Hash, uint64) bool
+	HasBlockAndState(common.Hash, uint64) bool
+	HasHeader(common.Hash, uint64) bool
+	HasState(common.Hash) bool
+	PendingBlock() *types.Block
+	State() (*state.StateDB, error)
+	StateAt(root common.Hash) (*state.StateDB, error)
+	SubscribeBlockConfirmedEvent(chan<- core.BlockConfirmedEvent) event.Subscription
+	SubscribeChainEvent(chan<- core.ChainEvent) event.Subscription
+	SubscribeChainHeadEvent(chan<- core.ChainHeadEvent) event.Subscription
+	SubscribeChainSideEvent(chan<- core.ChainSideEvent) event.Subscription
+	SubscribeLogsEvent(chan<- []*types.Log) event.Subscription
+	SubscribeRemovedLogsEvent(chan<- core.RemovedLogsEvent) event.Subscription
+}
+
+// access protection
+type ro interface {
+	ReadOnlyBlockChain
+}
+
+// ROBlockChain struct for safe read.
+type ROBlockChain struct {
+	ro
+}
+
+// NewROBlockChain converts original block chain to readonly interface.
+func NewROBlockChain(bc *core.BlockChain) ReadOnlyBlockChain {
+	return &ROBlockChain{ro: bc}
+}
diff --git a/indexer/config.go b/indexer/config.go
new file mode 100644
index 000000000..3b626272a
--- /dev/null
+++ b/indexer/config.go
@@ -0,0 +1,35 @@
+package indexer
+
+import (
+	"plugin"
+)
+
+// Config is data sources related configs struct.
+type Config struct {
+	// Used by dex/backend init flow.
+	Enable bool
+
+	// Plugin path for building components.
+	Plugin string
+}
+
+// NewIndexerFromConfig initialize exporter according to given config.
+func NewIndexerFromConfig(bc ReadOnlyBlockChain, c Config) (idx Indexer) {
+	if c.Plugin == "" {
+		// default
+		return
+	}
+
+	plug, err := plugin.Open(c.Plugin)
+	if err != nil {
+		panic(err)
+	}
+
+	symbol, err := plug.Lookup(NewIndexerFuncName)
+	if err != nil {
+		panic(err)
+	}
+
+	idx = symbol.(NewIndexerFunc)(bc, c)
+	return
+}
diff --git a/indexer/interfaces.go b/indexer/interfaces.go
new file mode 100644
index 000000000..f35bc6547
--- /dev/null
+++ b/indexer/interfaces.go
@@ -0,0 +1,19 @@
+package indexer
+
+// NewIndexerFuncName plugin looks up name.
+var NewIndexerFuncName = "NewIndexer"
+
+// NewIndexerFunc init function alias.
+type NewIndexerFunc = func(ReadOnlyBlockChain, Config) Indexer
+
+// Indexer defines indexer daemon interface. The daemon would hold a
+// core.Blockhain, passed by initialization function, to receiving latest block
+// event or other information query and interaction.
+type Indexer interface {
+	// Start is called by dex.Dexon if config is set.
+	Start() error
+
+	// Stop is called by dex.Dexon if config is set and procedure is
+	// terminating.
+	Stop() error
+}