dex: implement downloader for dex

We need governance state to verify block's signature (randomness),
but in ethereum fast sync mode, eth downloader only downloads the whole
state of pivot block, so we don't have governance state to verify the
downloaded block that is before pivot block if we don't processing
transaction.
To avoid running transactions, dex downloader also downloads the
governance state (merkle proof and storage) at snapshot height of each round,
so that we can verify blocks in fast sync mode.

1 files changed, 9 insertions, 1 deletions

diff --git a/dex/protocol.go b/dex/protocol.go
index 04928d2b2..0c271248e 100644
--- a/dex/protocol.go
+++ b/dex/protocol.go
@@ -34,6 +34,7 @@
 package dex
 
 import (
+	"context"
 	"crypto/ecdsa"
 	"fmt"
 	"io"
@@ -60,7 +61,7 @@ var ProtocolName = "dex"
 var ProtocolVersions = []uint{dex64}
 
 // ProtocolLengths are the number of implemented message corresponding to different protocol versions.
-var ProtocolLengths = []uint64{40}
+var ProtocolLengths = []uint64{42}
 
 const ProtocolMaxMsgSize = 10 * 1024 * 1024 // Maximum cap on the size of a protocol message
 
@@ -93,6 +94,9 @@ const (
 	DKGPartialSignatureMsg = 0x25
 	PullBlocksMsg          = 0x26
 	PullVotesMsg           = 0x27
+
+	GetGovStateMsg = 0x28
+	GovStateMsg    = 0x29
 )
 
 type errCode int
@@ -140,6 +144,8 @@ type txPool interface {
 }
 
 type governance interface {
+	GetRoundHeight(context.Context, uint64) (uint64, error)
+
 	GetNumChains(uint64) uint32
 
 	LenCRS() uint64
@@ -184,6 +190,8 @@ type getBlockHeadersData struct {
 	Amount  uint64       // Maximum number of headers to retrieve
 	Skip    uint64       // Blocks to skip between consecutive headers
 	Reverse bool         // Query direction (false = rising towards latest, true = falling towards genesis)
+
+	WithGov bool
 }
 
 // hashOrNumber is a combined field for specifying an origin block.