cln+lnd: liveness check

add a plugin hook in the case of core lightning and
an interceptor in the case of lnd, and pre-install
a dead/alive monitor for each daemon.

clightning/clightning.go

@@ -131,6 +131,7 @@ func NewClightningClient(ctx context.Context) (*ClightningClient, <-chan interfa
 	cl.Plugin = glightning.NewPlugin(cl.onInit)
 	err := cl.Plugin.RegisterHooks(&glightning.Hooks{
 		CustomMsgReceived: cl.OnCustomMsg,
+		RpcCommand:        cl.OnRPCCommand,
 	})
 	if err != nil {
 		return nil, nil, err
@@ -408,6 +409,28 @@ func (cl *ClightningClient) OnCustomMsg(event *glightning.CustomMsgReceivedEvent
 	return event.Continue(), nil
 }
 
+func (cl *ClightningClient) OnRPCCommand(event *glightning.RpcCommandEvent) (*glightning.RpcCommandResponse, error) {
+	if cl.gbitcoin != nil {
+		ok, err := cl.gbitcoin.Ping()
+		if err != nil {
+			return event.ReturnError(err.Error(), 0)
+		}
+		if !ok {
+			return event.ReturnError("failed to ping", 0)
+		}
+	}
+	if cl.liquidWallet != nil {
+		ok, err := cl.liquidWallet.Ping()
+		if err != nil {
+			return event.ReturnError(err.Error(), 0)
+		}
+		if !ok {
+			return event.ReturnError("failed to ping", 0)
+		}
+	}
+	return event.Continue(), nil
+}
+
 // AddMessageHandler adds a listener for incoming peermessages
 func (cl *ClightningClient) AddMessageHandler(f func(peerId string, msgType string, payload []byte) error) {
 	cl.msgHandlers = append(cl.msgHandlers, f)

cmd/peerswaplnd/peerswapd/main.go

@@ -397,7 +397,9 @@ func run() error {
 	}
 	defer lis.Close()
 
-	grpcSrv := grpc.NewServer()
+	grpcSrv := grpc.NewServer(
+		grpc.UnaryInterceptor(livenessCheckInterceptor(liquidCli)),
+	)
 
 	peerswaprpc.RegisterPeerSwapServer(grpcSrv, peerswaprpcServer)
 
@@ -439,6 +441,21 @@ func run() error {
 	return nil
 }
 
+func livenessCheckInterceptor(liquidCli *gelements.Elements) grpc.UnaryServerInterceptor {
+	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
+		if liquidCli != nil {
+			ok, err := liquidCli.Ping()
+			if err != nil {
+				return nil, err
+			}
+			if !ok {
+				return nil, errors.New("liquid rpc not reachable")
+			}
+		}
+		return handler(ctx, req)
+	}
+}
+
 func getBitcoinChain(ctx context.Context, li lnrpc.LightningClient) (*chaincfg.Params, error) {
 	gi, err := li.GetInfo(ctx, &lnrpc.GetInfoRequest{})
 	if err != nil {

electrum/client.go

@@ -84,3 +84,7 @@ func (c *electrumClient) GetFee(ctx context.Context, target uint32) (float32, er
 	}
 	return c.client.GetFee(ctx, target)
 }
+
+func (c *electrumClient) Ping(ctx context.Context) error {
+	return c.reconnect(ctx)
+}

electrum/electrum.go

@@ -12,4 +12,5 @@ type RPC interface {
 	GetRawTransaction(ctx context.Context, txHash string) (string, error)
 	BroadcastTransaction(ctx context.Context, rawTx string) (string, error)
 	GetFee(ctx context.Context, target uint32) (float32, error)
+	Ping(ctx context.Context) error
 }

lwk/lwkwallet.go

@@ -280,3 +280,10 @@ func (r *LWKRpcWallet) SetLabel(txID, address, label string) error {
 	// TODO: call set label
 	return nil
 }
+
+func (r *LWKRpcWallet) Ping() (bool, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), defaultContextTimeout)
+	defer cancel()
+	err := r.electrumClient.Ping(ctx)
+	return err == nil, err
+}

wallet/elementsrpcwallet.go

@@ -31,6 +31,7 @@ type RpcClient interface {
 	SendRawTx(txHex string) (string, error)
 	EstimateFee(blocks uint32, mode string) (*gelements.FeeResponse, error)
 	SetLabel(address, label string) error
+	Ping() (bool, error)
 }
 
 // ElementsRpcWallet uses the elementsd rpc wallet
@@ -191,3 +192,7 @@ func satsToAmountString(sats uint64) string {
 	bitcoinAmt := float64(sats) / 100000000
 	return fmt.Sprintf("%f", bitcoinAmt)
 }
+
+func (r *ElementsRpcWallet) Ping() (bool, error) {
+	return r.rpcClient.Ping()
+}

wallet/wallet.go

@@ -22,4 +22,5 @@ type Wallet interface {
 	SendRawTx(rawTx string) (txid string, err error)
 	GetFee(txSize int64) (uint64, error)
 	SetLabel(txID, address, label string) error
+	Ping() (bool, error)
 }