lnrpc: add StateService

lnd.go

@@ -349,6 +349,17 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 	interceptorChain := rpcperms.NewInterceptorChain(
 		rpcsLog, cfg.NoMacaroons, walletExists,
 	)
+	if err := interceptorChain.Start(); err != nil {
+		return err
+	}
+	defer func() {
+		err := interceptorChain.Stop()
+		if err != nil {
+			ltndLog.Warnf("error stopping RPC interceptor "+
+				"chain: %v", err)
+		}
+	}()
+
 	rpcServerOpts := interceptorChain.CreateServerOpts()
 	serverOpts = append(serverOpts, rpcServerOpts...)
 
@@ -358,6 +369,10 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 	// Register the WalletUnlockerService with the GRPC server.
 	lnrpc.RegisterWalletUnlockerServer(grpcServer, pwService)
 
+	// We'll also register the RPC interceptor chain as the StateServer, as
+	// it can be used to query for the current state of the wallet.
+	lnrpc.RegisterStateServer(grpcServer, interceptorChain)
+
 	// Initialize, and register our implementation of the gRPC interface
 	// exported by the rpcServer.
 	rpcServer := newRPCServer(
@@ -1239,7 +1254,7 @@ func startRestProxy(cfg *Config, rpcServer *rpcServer, restDialOpts []grpc.DialO
 	)
 	mux := proxy.NewServeMux(customMarshalerOption)
 
-	// Register both services with the REST proxy.
+	// Register our services with the REST proxy.
 	err := lnrpc.RegisterWalletUnlockerHandlerFromEndpoint(
 		ctx, mux, restProxyDest, restDialOpts,
 	)
@@ -1247,6 +1262,13 @@ func startRestProxy(cfg *Config, rpcServer *rpcServer, restDialOpts []grpc.DialO
 		return nil, err
 	}
 
+	err = lnrpc.RegisterStateHandlerFromEndpoint(
+		ctx, mux, restProxyDest, restDialOpts,
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	err = rpcServer.RegisterWithRestProxy(
 		ctx, mux, restDialOpts, restProxyDest,
 	)

lnrpc/gen_protos.sh

@@ -6,7 +6,7 @@ set -e
 function generate() {
   echo "Generating root gRPC server protos"
   
-  PROTOS="rpc.proto walletunlocker.proto **/*.proto"
+  PROTOS="rpc.proto walletunlocker.proto stateservice.proto **/*.proto"
   
   # For each of the sub-servers, we then generate their protos, but a restricted
   # set as they don't yet require REST proxies, or swagger docs.

lnrpc/rest-annotations.yaml

@@ -247,6 +247,10 @@ http:
       post: "/v2/signer/sharedkey"
       body: "*"
 
+    # stateservice.proto
+    - selector: lnrpc.State.SubscribeState
+      get: "/v1/state/subscribe"
+
     # verrpc/verrpc.proto
     - selector: verrpc.Versioner.GetVersion
       get: "/v2/versioner/version"

lnrpc/stateservice.pb.go

@@ -0,0 +1,265 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// source: stateservice.proto
+
+package lnrpc
+
+import (
+	context "context"
+	fmt "fmt"
+	proto "github.com/golang/protobuf/proto"
+	grpc "google.golang.org/grpc"
+	codes "google.golang.org/grpc/codes"
+	status "google.golang.org/grpc/status"
+	math "math"
+)
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.ProtoPackageIsVersion3 // please upgrade the proto package
+
+type WalletState int32
+
+const (
+	WalletState_NON_EXISTING WalletState = 0
+	WalletState_LOCKED       WalletState = 1
+	WalletState_UNLOCKED     WalletState = 2
+	WalletState_RPC_ACTIVE   WalletState = 3
+)
+
+var WalletState_name = map[int32]string{
+	0: "NON_EXISTING",
+	1: "LOCKED",
+	2: "UNLOCKED",
+	3: "RPC_ACTIVE",
+}
+
+var WalletState_value = map[string]int32{
+	"NON_EXISTING": 0,
+	"LOCKED":       1,
+	"UNLOCKED":     2,
+	"RPC_ACTIVE":   3,
+}
+
+func (x WalletState) String() string {
+	return proto.EnumName(WalletState_name, int32(x))
+}
+
+func (WalletState) EnumDescriptor() ([]byte, []int) {
+	return fileDescriptor_9cd64a11048f05dd, []int{0}
+}
+
+type SubscribeStateRequest struct {
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *SubscribeStateRequest) Reset()         { *m = SubscribeStateRequest{} }
+func (m *SubscribeStateRequest) String() string { return proto.CompactTextString(m) }
+func (*SubscribeStateRequest) ProtoMessage()    {}
+func (*SubscribeStateRequest) Descriptor() ([]byte, []int) {
+	return fileDescriptor_9cd64a11048f05dd, []int{0}
+}
+
+func (m *SubscribeStateRequest) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_SubscribeStateRequest.Unmarshal(m, b)
+}
+func (m *SubscribeStateRequest) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_SubscribeStateRequest.Marshal(b, m, deterministic)
+}
+func (m *SubscribeStateRequest) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_SubscribeStateRequest.Merge(m, src)
+}
+func (m *SubscribeStateRequest) XXX_Size() int {
+	return xxx_messageInfo_SubscribeStateRequest.Size(m)
+}
+func (m *SubscribeStateRequest) XXX_DiscardUnknown() {
+	xxx_messageInfo_SubscribeStateRequest.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_SubscribeStateRequest proto.InternalMessageInfo
+
+type SubscribeStateResponse struct {
+	State                WalletState `protobuf:"varint,1,opt,name=State,proto3,enum=lnrpc.WalletState" json:"State,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}    `json:"-"`
+	XXX_unrecognized     []byte      `json:"-"`
+	XXX_sizecache        int32       `json:"-"`
+}
+
+func (m *SubscribeStateResponse) Reset()         { *m = SubscribeStateResponse{} }
+func (m *SubscribeStateResponse) String() string { return proto.CompactTextString(m) }
+func (*SubscribeStateResponse) ProtoMessage()    {}
+func (*SubscribeStateResponse) Descriptor() ([]byte, []int) {
+	return fileDescriptor_9cd64a11048f05dd, []int{1}
+}
+
+func (m *SubscribeStateResponse) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_SubscribeStateResponse.Unmarshal(m, b)
+}
+func (m *SubscribeStateResponse) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_SubscribeStateResponse.Marshal(b, m, deterministic)
+}
+func (m *SubscribeStateResponse) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_SubscribeStateResponse.Merge(m, src)
+}
+func (m *SubscribeStateResponse) XXX_Size() int {
+	return xxx_messageInfo_SubscribeStateResponse.Size(m)
+}
+func (m *SubscribeStateResponse) XXX_DiscardUnknown() {
+	xxx_messageInfo_SubscribeStateResponse.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_SubscribeStateResponse proto.InternalMessageInfo
+
+func (m *SubscribeStateResponse) GetState() WalletState {
+	if m != nil {
+		return m.State
+	}
+	return WalletState_NON_EXISTING
+}
+
+func init() {
+	proto.RegisterEnum("lnrpc.WalletState", WalletState_name, WalletState_value)
+	proto.RegisterType((*SubscribeStateRequest)(nil), "lnrpc.SubscribeStateRequest")
+	proto.RegisterType((*SubscribeStateResponse)(nil), "lnrpc.SubscribeStateResponse")
+}
+
+func init() { proto.RegisterFile("stateservice.proto", fileDescriptor_9cd64a11048f05dd) }
+
+var fileDescriptor_9cd64a11048f05dd = []byte{
+	// 244 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xe2, 0x12, 0x2a, 0x2e, 0x49, 0x2c,
+	0x49, 0x2d, 0x4e, 0x2d, 0x2a, 0xcb, 0x4c, 0x4e, 0xd5, 0x2b, 0x28, 0xca, 0x2f, 0xc9, 0x17, 0x62,
+	0xcd, 0xc9, 0x2b, 0x2a, 0x48, 0x56, 0x12, 0xe7, 0x12, 0x0d, 0x2e, 0x4d, 0x2a, 0x4e, 0x2e, 0xca,
+	0x4c, 0x4a, 0x0d, 0x06, 0xa9, 0x0a, 0x4a, 0x2d, 0x2c, 0x4d, 0x2d, 0x2e, 0x51, 0x72, 0xe2, 0x12,
+	0x43, 0x97, 0x28, 0x2e, 0xc8, 0xcf, 0x2b, 0x4e, 0x15, 0xd2, 0xe0, 0x62, 0x05, 0x0b, 0x48, 0x30,
+	0x2a, 0x30, 0x6a, 0xf0, 0x19, 0x09, 0xe9, 0x81, 0x4d, 0xd2, 0x0b, 0x4f, 0xcc, 0xc9, 0x49, 0x2d,
+	0x81, 0x28, 0x85, 0x28, 0xd0, 0xf2, 0xe4, 0xe2, 0x46, 0x12, 0x15, 0x12, 0xe0, 0xe2, 0xf1, 0xf3,
+	0xf7, 0x8b, 0x77, 0x8d, 0xf0, 0x0c, 0x0e, 0xf1, 0xf4, 0x73, 0x17, 0x60, 0x10, 0xe2, 0xe2, 0x62,
+	0xf3, 0xf1, 0x77, 0xf6, 0x76, 0x75, 0x11, 0x60, 0x14, 0xe2, 0xe1, 0xe2, 0x08, 0xf5, 0x83, 0xf2,
+	0x98, 0x84, 0xf8, 0xb8, 0xb8, 0x82, 0x02, 0x9c, 0xe3, 0x1d, 0x9d, 0x43, 0x3c, 0xc3, 0x5c, 0x05,
+	0x98, 0x8d, 0x22, 0xa0, 0x96, 0x0a, 0xf9, 0x73, 0xf1, 0xa1, 0xba, 0x4b, 0x48, 0x06, 0xea, 0x00,
+	0xac, 0xfe, 0x90, 0x92, 0xc5, 0x21, 0x0b, 0xf1, 0x8c, 0x01, 0xa3, 0x93, 0x7a, 0x94, 0x6a, 0x7a,
+	0x66, 0x49, 0x46, 0x69, 0x92, 0x5e, 0x72, 0x7e, 0xae, 0x7e, 0x4e, 0x66, 0x7a, 0x46, 0x49, 0x5e,
+	0x66, 0x5e, 0x7a, 0x5e, 0x6a, 0x49, 0x79, 0x7e, 0x51, 0xb6, 0x7e, 0x4e, 0x5e, 0x8a, 0x3e, 0xd8,
+	0x84, 0x24, 0x36, 0x70, 0xc0, 0x19, 0x03, 0x02, 0x00, 0x00, 0xff, 0xff, 0x05, 0xd6, 0xa9, 0xb4,
+	0x4e, 0x01, 0x00, 0x00,
+}
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ context.Context
+var _ grpc.ClientConn
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the grpc package it is being compiled against.
+const _ = grpc.SupportPackageIsVersion4
+
+// StateClient is the client API for State service.
+//
+// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://godoc.org/google.golang.org/grpc#ClientConn.NewStream.
+type StateClient interface {
+	// SubscribeState subscribes to the state of the wallet. The current wallet
+	// state will always be delivered immediately.
+	SubscribeState(ctx context.Context, in *SubscribeStateRequest, opts ...grpc.CallOption) (State_SubscribeStateClient, error)
+}
+
+type stateClient struct {
+	cc *grpc.ClientConn
+}
+
+func NewStateClient(cc *grpc.ClientConn) StateClient {
+	return &stateClient{cc}
+}
+
+func (c *stateClient) SubscribeState(ctx context.Context, in *SubscribeStateRequest, opts ...grpc.CallOption) (State_SubscribeStateClient, error) {
+	stream, err := c.cc.NewStream(ctx, &_State_serviceDesc.Streams[0], "/lnrpc.State/SubscribeState", opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &stateSubscribeStateClient{stream}
+	if err := x.ClientStream.SendMsg(in); err != nil {
+		return nil, err
+	}
+	if err := x.ClientStream.CloseSend(); err != nil {
+		return nil, err
+	}
+	return x, nil
+}
+
+type State_SubscribeStateClient interface {
+	Recv() (*SubscribeStateResponse, error)
+	grpc.ClientStream
+}
+
+type stateSubscribeStateClient struct {
+	grpc.ClientStream
+}
+
+func (x *stateSubscribeStateClient) Recv() (*SubscribeStateResponse, error) {
+	m := new(SubscribeStateResponse)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+// StateServer is the server API for State service.
+type StateServer interface {
+	// SubscribeState subscribes to the state of the wallet. The current wallet
+	// state will always be delivered immediately.
+	SubscribeState(*SubscribeStateRequest, State_SubscribeStateServer) error
+}
+
+// UnimplementedStateServer can be embedded to have forward compatible implementations.
+type UnimplementedStateServer struct {
+}
+
+func (*UnimplementedStateServer) SubscribeState(req *SubscribeStateRequest, srv State_SubscribeStateServer) error {
+	return status.Errorf(codes.Unimplemented, "method SubscribeState not implemented")
+}
+
+func RegisterStateServer(s *grpc.Server, srv StateServer) {
+	s.RegisterService(&_State_serviceDesc, srv)
+}
+
+func _State_SubscribeState_Handler(srv interface{}, stream grpc.ServerStream) error {
+	m := new(SubscribeStateRequest)
+	if err := stream.RecvMsg(m); err != nil {
+		return err
+	}
+	return srv.(StateServer).SubscribeState(m, &stateSubscribeStateServer{stream})
+}
+
+type State_SubscribeStateServer interface {
+	Send(*SubscribeStateResponse) error
+	grpc.ServerStream
+}
+
+type stateSubscribeStateServer struct {
+	grpc.ServerStream
+}
+
+func (x *stateSubscribeStateServer) Send(m *SubscribeStateResponse) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+var _State_serviceDesc = grpc.ServiceDesc{
+	ServiceName: "lnrpc.State",
+	HandlerType: (*StateServer)(nil),
+	Methods:     []grpc.MethodDesc{},
+	Streams: []grpc.StreamDesc{
+		{
+			StreamName:    "SubscribeState",
+			Handler:       _State_SubscribeState_Handler,
+			ServerStreams: true,
+		},
+	},
+	Metadata: "stateservice.proto",
+}

lnrpc/stateservice.pb.gw.go

@@ -0,0 +1,133 @@
+// Code generated by protoc-gen-grpc-gateway. DO NOT EDIT.
+// source: stateservice.proto
+
+/*
+Package lnrpc is a reverse proxy.
+
+It translates gRPC into RESTful JSON APIs.
+*/
+package lnrpc
+
+import (
+	"context"
+	"io"
+	"net/http"
+
+	"github.com/golang/protobuf/descriptor"
+	"github.com/golang/protobuf/proto"
+	"github.com/grpc-ecosystem/grpc-gateway/runtime"
+	"github.com/grpc-ecosystem/grpc-gateway/utilities"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/status"
+)
+
+// Suppress "imported and not used" errors
+var _ codes.Code
+var _ io.Reader
+var _ status.Status
+var _ = runtime.String
+var _ = utilities.NewDoubleArray
+var _ = descriptor.ForMessage
+
+func request_State_SubscribeState_0(ctx context.Context, marshaler runtime.Marshaler, client StateClient, req *http.Request, pathParams map[string]string) (State_SubscribeStateClient, runtime.ServerMetadata, error) {
+	var protoReq SubscribeStateRequest
+	var metadata runtime.ServerMetadata
+
+	stream, err := client.SubscribeState(ctx, &protoReq)
+	if err != nil {
+		return nil, metadata, err
+	}
+	header, err := stream.Header()
+	if err != nil {
+		return nil, metadata, err
+	}
+	metadata.HeaderMD = header
+	return stream, metadata, nil
+
+}
+
+// RegisterStateHandlerServer registers the http handlers for service State to "mux".
+// UnaryRPC     :call StateServer directly.
+// StreamingRPC :currently unsupported pending https://github.com/grpc/grpc-go/issues/906.
+func RegisterStateHandlerServer(ctx context.Context, mux *runtime.ServeMux, server StateServer) error {
+
+	mux.Handle("GET", pattern_State_SubscribeState_0, func(w http.ResponseWriter, req *http.Request, pathParams map[string]string) {
+		err := status.Error(codes.Unimplemented, "streaming calls are not yet supported in the in-process transport")
+		_, outboundMarshaler := runtime.MarshalerForRequest(mux, req)
+		runtime.HTTPError(ctx, mux, outboundMarshaler, w, req, err)
+		return
+	})
+
+	return nil
+}
+
+// RegisterStateHandlerFromEndpoint is same as RegisterStateHandler but
+// automatically dials to "endpoint" and closes the connection when "ctx" gets done.
+func RegisterStateHandlerFromEndpoint(ctx context.Context, mux *runtime.ServeMux, endpoint string, opts []grpc.DialOption) (err error) {
+	conn, err := grpc.Dial(endpoint, opts...)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if err != nil {
+			if cerr := conn.Close(); cerr != nil {
+				grpclog.Infof("Failed to close conn to %s: %v", endpoint, cerr)
+			}
+			return
+		}
+		go func() {
+			<-ctx.Done()
+			if cerr := conn.Close(); cerr != nil {
+				grpclog.Infof("Failed to close conn to %s: %v", endpoint, cerr)
+			}
+		}()
+	}()
+
+	return RegisterStateHandler(ctx, mux, conn)
+}
+
+// RegisterStateHandler registers the http handlers for service State to "mux".
+// The handlers forward requests to the grpc endpoint over "conn".
+func RegisterStateHandler(ctx context.Context, mux *runtime.ServeMux, conn *grpc.ClientConn) error {
+	return RegisterStateHandlerClient(ctx, mux, NewStateClient(conn))
+}
+
+// RegisterStateHandlerClient registers the http handlers for service State
+// to "mux". The handlers forward requests to the grpc endpoint over the given implementation of "StateClient".
+// Note: the gRPC framework executes interceptors within the gRPC handler. If the passed in "StateClient"
+// doesn't go through the normal gRPC flow (creating a gRPC client etc.) then it will be up to the passed in
+// "StateClient" to call the correct interceptors.
+func RegisterStateHandlerClient(ctx context.Context, mux *runtime.ServeMux, client StateClient) error {
+
+	mux.Handle("GET", pattern_State_SubscribeState_0, func(w http.ResponseWriter, req *http.Request, pathParams map[string]string) {
+		ctx, cancel := context.WithCancel(req.Context())
+		defer cancel()
+		inboundMarshaler, outboundMarshaler := runtime.MarshalerForRequest(mux, req)
+		rctx, err := runtime.AnnotateContext(ctx, mux, req)
+		if err != nil {
+			runtime.HTTPError(ctx, mux, outboundMarshaler, w, req, err)
+			return
+		}
+		resp, md, err := request_State_SubscribeState_0(rctx, inboundMarshaler, client, req, pathParams)
+		ctx = runtime.NewServerMetadataContext(ctx, md)
+		if err != nil {
+			runtime.HTTPError(ctx, mux, outboundMarshaler, w, req, err)
+			return
+		}
+
+		forward_State_SubscribeState_0(ctx, mux, outboundMarshaler, w, req, func() (proto.Message, error) { return resp.Recv() }, mux.GetForwardResponseOptions()...)
+
+	})
+
+	return nil
+}
+
+var (
+	pattern_State_SubscribeState_0 = runtime.MustPattern(runtime.NewPattern(1, []int{2, 0, 2, 1, 2, 2}, []string{"v1", "state", "subscribe"}, "", runtime.AssumeColonVerbOpt(true)))
+)
+
+var (
+	forward_State_SubscribeState_0 = runtime.ForwardResponseStream
+)

lnrpc/stateservice.proto

@@ -0,0 +1,46 @@
+syntax = "proto3";
+
+package lnrpc;
+
+option go_package = "github.com/lightningnetwork/lnd/lnrpc";
+
+/*
+ * Comments in this file will be directly parsed into the API
+ * Documentation as descriptions of the associated method, message, or field.
+ * These descriptions should go right above the definition of the object, and
+ * can be in either block or // comment format.
+ *
+ * An RPC method can be matched to an lncli command by placing a line in the
+ * beginning of the description in exactly the following format:
+ * lncli: `methodname`
+ *
+ * Failure to specify the exact name of the command will cause documentation
+ * generation to fail.
+ *
+ * More information on how exactly the gRPC documentation is generated from
+ * this proto file can be found here:
+ * https://github.com/lightninglabs/lightning-api
+ */
+
+// State service is a always running service that exposes the current state of
+// the wallet and RPC server.
+service State {
+    // SubscribeState subscribes to the state of the wallet. The current wallet
+    // state will always be delivered immediately.
+    rpc SubscribeState (SubscribeStateRequest)
+        returns (stream SubscribeStateResponse);
+}
+
+enum WalletState {
+    NON_EXISTING = 0;
+    LOCKED = 1;
+    UNLOCKED = 2;
+    RPC_ACTIVE = 3;
+}
+
+message SubscribeStateRequest {
+}
+
+message SubscribeStateResponse {
+    WalletState State = 1;
+}

lnrpc/stateservice.swagger.json

@@ -0,0 +1,125 @@
+{
+  "swagger": "2.0",
+  "info": {
+    "title": "stateservice.proto",
+    "version": "version not set"
+  },
+  "consumes": [
+    "application/json"
+  ],
+  "produces": [
+    "application/json"
+  ],
+  "paths": {
+    "/v1/state/subscribe": {
+      "get": {
+        "summary": "SubscribeState subscribes to the state of the wallet. The current wallet\nstate will always be delivered immediately.",
+        "operationId": "SubscribeState",
+        "responses": {
+          "200": {
+            "description": "A successful response.(streaming responses)",
+            "schema": {
+              "type": "object",
+              "properties": {
+                "result": {
+                  "$ref": "#/definitions/lnrpcSubscribeStateResponse"
+                },
+                "error": {
+                  "$ref": "#/definitions/runtimeStreamError"
+                }
+              },
+              "title": "Stream result of lnrpcSubscribeStateResponse"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response",
+            "schema": {
+              "$ref": "#/definitions/runtimeError"
+            }
+          }
+        },
+        "tags": [
+          "State"
+        ]
+      }
+    }
+  },
+  "definitions": {
+    "lnrpcSubscribeStateResponse": {
+      "type": "object",
+      "properties": {
+        "State": {
+          "$ref": "#/definitions/lnrpcWalletState"
+        }
+      }
+    },
+    "lnrpcWalletState": {
+      "type": "string",
+      "enum": [
+        "NON_EXISTING",
+        "LOCKED",
+        "UNLOCKED",
+        "RPC_ACTIVE"
+      ],
+      "default": "NON_EXISTING"
+    },
+    "protobufAny": {
+      "type": "object",
+      "properties": {
+        "type_url": {
+          "type": "string"
+        },
+        "value": {
+          "type": "string",
+          "format": "byte"
+        }
+      }
+    },
+    "runtimeError": {
+      "type": "object",
+      "properties": {
+        "error": {
+          "type": "string"
+        },
+        "code": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "message": {
+          "type": "string"
+        },
+        "details": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/protobufAny"
+          }
+        }
+      }
+    },
+    "runtimeStreamError": {
+      "type": "object",
+      "properties": {
+        "grpc_code": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "http_code": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "message": {
+          "type": "string"
+        },
+        "http_status": {
+          "type": "string"
+        },
+        "details": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/protobufAny"
+          }
+        }
+      }
+    }
+  }
+}

rpcperms/interceptor.go

@@ -10,6 +10,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/macaroons"
 	"github.com/lightningnetwork/lnd/monitoring"
+	"github.com/lightningnetwork/lnd/subscribe"
 	"google.golang.org/grpc"
 	"gopkg.in/macaroon-bakery.v2/bakery"
 )
@@ -66,6 +67,10 @@ var (
 		"/lnrpc.WalletUnlocker/InitWallet":     {},
 		"/lnrpc.WalletUnlocker/UnlockWallet":   {},
 		"/lnrpc.WalletUnlocker/ChangePassword": {},
+
+		// The State service must be available at all times, even
+		// before we can check macaroons, so we whitelist it.
+		"/lnrpc.State/SubscribeState": {},
 	}
 )
 
@@ -73,9 +78,16 @@ var (
 // intercepting API calls. This is useful for logging, enforcing permissions
 // etc.
 type InterceptorChain struct {
+	started sync.Once
+	stopped sync.Once
+
 	// state is the current RPC state of our RPC server.
 	state rpcState
 
+	// ntfnServer is a subscription server we use to notify clients of the
+	// State service when the state changes.
+	ntfnServer *subscribe.Server
+
 	// noMacaroons should be set true if we don't want to check macaroons.
 	noMacaroons bool
 
@@ -89,9 +101,14 @@ type InterceptorChain struct {
 	// rpcsLog is the logger used to log calles to the RPCs intercepted.
 	rpcsLog btclog.Logger
 
+	quit chan struct{}
 	sync.RWMutex
 }
 
+// A compile time check to ensure that InterceptorChain fully implements the
+// StateServer gRPC service.
+var _ lnrpc.StateServer = (*InterceptorChain)(nil)
+
 // NewInterceptorChain creates a new InterceptorChain.
 func NewInterceptorChain(log btclog.Logger, noMacaroons,
 	walletExists bool) *InterceptorChain {
@@ -103,12 +120,36 @@ func NewInterceptorChain(log btclog.Logger, noMacaroons,
 
 	return &InterceptorChain{
 		state:         startState,
+		ntfnServer:    subscribe.NewServer(),
 		noMacaroons:   noMacaroons,
 		permissionMap: make(map[string][]bakery.Op),
 		rpcsLog:       log,
+		quit:          make(chan struct{}),
 	}
 }
 
+// Start starts the InterceptorChain, which is needed to start the state
+// subscription server it powers.
+func (r *InterceptorChain) Start() error {
+	var err error
+	r.started.Do(func() {
+		err = r.ntfnServer.Start()
+	})
+
+	return err
+}
+
+// Stop stops the InterceptorChain and its internal state subscription server.
+func (r *InterceptorChain) Stop() error {
+	var err error
+	r.stopped.Do(func() {
+		close(r.quit)
+		err = r.ntfnServer.Stop()
+	})
+
+	return err
+}
+
 // SetWalletUnlocked moves the RPC state from either walletNotCreated or
 // walletLocked to walletUnlocked.
 func (r *InterceptorChain) SetWalletUnlocked() {
@@ -116,6 +157,7 @@ func (r *InterceptorChain) SetWalletUnlocked() {
 	defer r.Unlock()
 
 	r.state = walletUnlocked
+	_ = r.ntfnServer.SendUpdate(r.state)
 }
 
 // SetRPCActive moves the RPC state from walletUnlocked to rpcActive.
@@ -124,6 +166,75 @@ func (r *InterceptorChain) SetRPCActive() {
 	defer r.Unlock()
 
 	r.state = rpcActive
+	_ = r.ntfnServer.SendUpdate(r.state)
+}
+
+// SubscribeState subscribes to the state of the wallet. The current wallet
+// state will always be delivered immediately.
+//
+// NOTE: Part of the StateService interface.
+func (r *InterceptorChain) SubscribeState(req *lnrpc.SubscribeStateRequest,
+	stream lnrpc.State_SubscribeStateServer) error {
+
+	sendStateUpdate := func(state rpcState) error {
+		resp := &lnrpc.SubscribeStateResponse{}
+		switch state {
+		case walletNotCreated:
+			resp.State = lnrpc.WalletState_NON_EXISTING
+		case walletLocked:
+			resp.State = lnrpc.WalletState_LOCKED
+		case walletUnlocked:
+			resp.State = lnrpc.WalletState_UNLOCKED
+		case rpcActive:
+			resp.State = lnrpc.WalletState_RPC_ACTIVE
+
+		default:
+			return fmt.Errorf("unknown wallet "+
+				"state %v", state)
+		}
+
+		return stream.Send(resp)
+	}
+
+	// Subscribe to state updates.
+	client, err := r.ntfnServer.Subscribe()
+	if err != nil {
+		return err
+	}
+	defer client.Cancel()
+
+	// Always start by sending the current state.
+	r.RLock()
+	state := r.state
+	r.RUnlock()
+
+	if err := sendStateUpdate(state); err != nil {
+		return err
+	}
+
+	for {
+		select {
+		case e := <-client.Updates():
+			newState := e.(rpcState)
+
+			// Ignore already sent state.
+			if newState == state {
+				continue
+			}
+
+			state = newState
+			err := sendStateUpdate(state)
+			if err != nil {
+				return err
+			}
+
+		case <-stream.Context().Done():
+			return stream.Context().Err()
+
+		case <-r.quit:
+			return fmt.Errorf("server exiting")
+		}
+	}
 }
 
 // AddMacaroonService adds a macaroon service to the interceptor. After this is
@@ -335,6 +446,13 @@ func (r *InterceptorChain) MacaroonStreamServerInterceptor() grpc.StreamServerIn
 // checkRPCState checks whether a call to the given server is allowed in the
 // current RPC state.
 func (r *InterceptorChain) checkRPCState(srv interface{}) error {
+	// The StateService is being accessed, we allow the call regardless of
+	// the current state.
+	_, ok := srv.(lnrpc.StateServer)
+	if ok {
+		return nil
+	}
+
 	r.RLock()
 	state := r.state
 	r.RUnlock()