lnrpc: add "waiting to start" state to state service

This commit adds a new "waiting to start" state which may be used to
query if we're still waiting to become the cluster leader. Once leader
we advance the state to "wallet not exist" or "wallet locked" given
wallet availablity.

rpcperms/interceptor.go

@@ -21,10 +21,16 @@ import (
 type rpcState uint8
 
 const (
+	// waitingToStart indicates that we're at the beginning of the startup
+	// process. In a cluster evironment this may mean that we're waiting to
+	// become the leader in which case RPC calls will be disabled until
+	// this instance has been elected as leader.
+	waitingToStart rpcState = iota
+
 	// walletNotCreated is the starting state if the RPC server is active,
 	// but the wallet is not yet created. In this state we'll only allow
 	// calls to the WalletUnlockerService.
-	walletNotCreated rpcState = iota
+	walletNotCreated
 
 	// walletLocked indicates the RPC server is active, but the wallet is
 	// locked. In this state we'll only allow calls to the
@@ -40,6 +46,11 @@ const (
 )
 
 var (
+	// ErrWaitingToStart is returned if LND is still wating to start,
+	// possibly blocked until elected as the leader.
+	ErrWaitingToStart = fmt.Errorf("waiting to start, RPC services not " +
+		"available")
+
 	// ErrNoWallet is returned if the wallet does not exist.
 	ErrNoWallet = fmt.Errorf("wallet not created, create one to enable " +
 		"full RPC access")
@@ -110,16 +121,9 @@ type InterceptorChain struct {
 var _ lnrpc.StateServer = (*InterceptorChain)(nil)
 
 // NewInterceptorChain creates a new InterceptorChain.
-func NewInterceptorChain(log btclog.Logger, noMacaroons,
-	walletExists bool) *InterceptorChain {
-
-	startState := walletNotCreated
-	if walletExists {
-		startState = walletLocked
-	}
-
+func NewInterceptorChain(log btclog.Logger, noMacaroons bool) *InterceptorChain {
 	return &InterceptorChain{
-		state:         startState,
+		state:         waitingToStart,
 		ntfnServer:    subscribe.NewServer(),
 		noMacaroons:   noMacaroons,
 		permissionMap: make(map[string][]bakery.Op),
@@ -150,6 +154,26 @@ func (r *InterceptorChain) Stop() error {
 	return err
 }
 
+// SetWalletNotCreated moves the RPC state from either waitingToStart to
+// walletNotCreated.
+func (r *InterceptorChain) SetWalletNotCreated() {
+	r.Lock()
+	defer r.Unlock()
+
+	r.state = walletNotCreated
+	_ = r.ntfnServer.SendUpdate(r.state)
+}
+
+// SetWalletLocked moves the RPC state from either walletNotCreated to
+// walletLocked.
+func (r *InterceptorChain) SetWalletLocked() {
+	r.Lock()
+	defer r.Unlock()
+
+	r.state = walletLocked
+	_ = r.ntfnServer.SendUpdate(r.state)
+}
+
 // SetWalletUnlocked moves the RPC state from either walletNotCreated or
 // walletLocked to walletUnlocked.
 func (r *InterceptorChain) SetWalletUnlocked() {
@@ -179,6 +203,8 @@ func (r *InterceptorChain) SubscribeState(req *lnrpc.SubscribeStateRequest,
 	sendStateUpdate := func(state rpcState) error {
 		resp := &lnrpc.SubscribeStateResponse{}
 		switch state {
+		case waitingToStart:
+			resp.State = lnrpc.WalletState_WAITING_TO_START
 		case walletNotCreated:
 			resp.State = lnrpc.WalletState_NON_EXISTING
 		case walletLocked:
@@ -189,8 +215,7 @@ func (r *InterceptorChain) SubscribeState(req *lnrpc.SubscribeStateRequest,
 			resp.State = lnrpc.WalletState_RPC_ACTIVE
 
 		default:
-			return fmt.Errorf("unknown wallet "+
-				"state %v", state)
+			return fmt.Errorf("unknown wallet state %v", state)
 		}
 
 		return stream.Send(resp)
@@ -459,6 +484,11 @@ func (r *InterceptorChain) checkRPCState(srv interface{}) error {
 
 	switch state {
 
+	// Do not accept any RPC calls (unless to the state service) until LND
+	// has not started.
+	case waitingToStart:
+		return ErrWaitingToStart
+
 	// If the wallet does not exists, only calls to the WalletUnlocker are
 	// accepted.
 	case walletNotCreated: