dot/rpc: implement chain_subscribeFinalizedHeads RPC method

dot/rpc/modules/api.go

@@ -29,6 +29,8 @@ type BlockAPI interface {
 	GetFinalizedHash(uint64, uint64) (common.Hash, error)
 	RegisterImportedChannel(ch chan<- *types.Block) (byte, error)
 	UnregisterImportedChannel(id byte)
+	RegisterFinalizedChannel(ch chan<- *types.Header) (byte, error)
+	UnregisterFinalizedChannel(id byte)
 }
 
 // NetworkAPI interface for network state methods

dot/rpc/websocket.go

@@ -170,6 +170,12 @@ func (c *WSConn) handleComm() {
 				}
 				c.startListener(scl)
 			case "chain_subscribeFinalizedHeads":
+				bfl, err3 := c.initBlockFinalizedListener(reqid)
+				if err3 != nil {
+					logger.Warn("failed to create block finalized", "error", err)
+					continue
+				}
+				c.startListener(bfl)
 			}
 			continue
 		}
@@ -368,3 +374,61 @@ func (l *BlockListener) Listen() {
 
 	}
 }
+
+// BlockFinalizedListener to handle listening for finalized blocks
+type BlockFinalizedListener struct {
+	channel chan *types.Header
+	wsconn  *WSConn
+	chanID  byte
+	subID   int
+}
+
+func (c *WSConn) initBlockFinalizedListener(reqID float64) (int, error) {
+	bfl := &BlockFinalizedListener{
+		channel: make(chan *types.Header),
+		wsconn:  c,
+	}
+
+	if c.blockAPI == nil {
+		err := c.safeSendError(reqID, nil, "error BlockAPI not set")
+		if err != nil {
+			logger.Warn("error sending error message", "error", err)
+		}
+		return 0, fmt.Errorf("error BlockAPI not set")
+	}
+	chanID, err := c.blockAPI.RegisterFinalizedChannel(bfl.channel)
+	if err != nil {
+		return 0, err
+	}
+	bfl.chanID = chanID
+	c.qtyListeners++
+	bfl.subID = c.qtyListeners
+	c.subscriptions[bfl.subID] = bfl
+	c.blockSubChannels[bfl.subID] = chanID
+	initRes := newSubscriptionResponseJSON(bfl.subID, reqID)
+	err = c.safeSend(initRes)
+	if err != nil {
+		return 0, err
+	}
+	return bfl.subID, nil
+}
+
+// Listen implementation of Listen interface to listen for channel changes
+func (l *BlockFinalizedListener) Listen() {
+	for header := range l.channel {
+		if header == nil {
+			continue
+		}
+		head := modules.HeaderToJSON(*header)
+		headM := make(map[string]interface{})
+		headM["result"] = head
+		headM["subscription"] = l.subID
+		res := newSubcriptionBaseResponseJSON()
+		res.Method = "chain_finalizedHead"
+		res.Params = headM
+		err := l.wsconn.safeSend(res)
+		if err != nil {
+			logger.Error("error sending websocket message", "error", err)
+		}
+	}
+}

dot/rpc/websocket_test.go

@@ -97,6 +97,10 @@ func (m *MockBlockAPI) RegisterImportedChannel(ch chan<- *types.Block) (byte, er
 }
 func (m *MockBlockAPI) UnregisterImportedChannel(id byte) {
 }
+func (m *MockBlockAPI) RegisterFinalizedChannel(ch chan<- *types.Header) (byte, error) {
+	return 0, nil
+}
+func (m *MockBlockAPI) UnregisterFinalizedChannel(id byte) {}
 
 type MockStorageAPI struct{}
 

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/docker/docker v1.13.1
 	github.com/ethereum/go-ethereum v1.9.6
 	github.com/go-interpreter/wagon v0.6.1-0.20200227184901-6803234760a6
+	github.com/golangci/golangci-lint v1.23.1 // indirect
 	github.com/gorilla/mux v1.7.4
 	github.com/gorilla/rpc v1.2.0
 	github.com/gorilla/websocket v1.4.2