invoicesrpc: add HtlcModifier RPC endpoint and modifier RPC server

This commit introduces a singleton invoice HTLC modifier RPC server and
an endpoint to activate it. The server interfaces with the internal
invoice HTLC modifier interpreter, handling the marshalling between RPC
types and internal formats.

lnrpc/invoicesrpc/invoices_grpc.pb.go

@@ -36,9 +36,14 @@ type InvoicesClient interface {
 	// SettleInvoice settles an accepted invoice. If the invoice is already
 	// settled, this call will succeed.
 	SettleInvoice(ctx context.Context, in *SettleInvoiceMsg, opts ...grpc.CallOption) (*SettleInvoiceResp, error)
-	// LookupInvoiceV2 attempts to look up at invoice. An invoice can be refrenced
+	// LookupInvoiceV2 attempts to look up at invoice. An invoice can be referenced
 	// using either its payment hash, payment address, or set ID.
 	LookupInvoiceV2(ctx context.Context, in *LookupInvoiceMsg, opts ...grpc.CallOption) (*lnrpc.Invoice, error)
+	// HtlcModifier is a bidirectional streaming RPC that allows a client to
+	// intercept and modify the HTLCs that attempt to settle the given invoice. The
+	// server will send HTLCs of invoices to the client and the client can modify
+	// some aspects of the HTLC in order to pass the invoice acceptance tests.
+	HtlcModifier(ctx context.Context, opts ...grpc.CallOption) (Invoices_HtlcModifierClient, error)
 }
 
 type invoicesClient struct {
@@ -117,6 +122,37 @@ func (c *invoicesClient) LookupInvoiceV2(ctx context.Context, in *LookupInvoiceM
 	return out, nil
 }
 
+func (c *invoicesClient) HtlcModifier(ctx context.Context, opts ...grpc.CallOption) (Invoices_HtlcModifierClient, error) {
+	stream, err := c.cc.NewStream(ctx, &Invoices_ServiceDesc.Streams[1], "/invoicesrpc.Invoices/HtlcModifier", opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &invoicesHtlcModifierClient{stream}
+	return x, nil
+}
+
+type Invoices_HtlcModifierClient interface {
+	Send(*HtlcModifyResponse) error
+	Recv() (*HtlcModifyRequest, error)
+	grpc.ClientStream
+}
+
+type invoicesHtlcModifierClient struct {
+	grpc.ClientStream
+}
+
+func (x *invoicesHtlcModifierClient) Send(m *HtlcModifyResponse) error {
+	return x.ClientStream.SendMsg(m)
+}
+
+func (x *invoicesHtlcModifierClient) Recv() (*HtlcModifyRequest, error) {
+	m := new(HtlcModifyRequest)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
 // InvoicesServer is the server API for Invoices service.
 // All implementations must embed UnimplementedInvoicesServer
 // for forward compatibility
@@ -138,9 +174,14 @@ type InvoicesServer interface {
 	// SettleInvoice settles an accepted invoice. If the invoice is already
 	// settled, this call will succeed.
 	SettleInvoice(context.Context, *SettleInvoiceMsg) (*SettleInvoiceResp, error)
-	// LookupInvoiceV2 attempts to look up at invoice. An invoice can be refrenced
+	// LookupInvoiceV2 attempts to look up at invoice. An invoice can be referenced
 	// using either its payment hash, payment address, or set ID.
 	LookupInvoiceV2(context.Context, *LookupInvoiceMsg) (*lnrpc.Invoice, error)
+	// HtlcModifier is a bidirectional streaming RPC that allows a client to
+	// intercept and modify the HTLCs that attempt to settle the given invoice. The
+	// server will send HTLCs of invoices to the client and the client can modify
+	// some aspects of the HTLC in order to pass the invoice acceptance tests.
+	HtlcModifier(Invoices_HtlcModifierServer) error
 	mustEmbedUnimplementedInvoicesServer()
 }
 
@@ -163,6 +204,9 @@ func (UnimplementedInvoicesServer) SettleInvoice(context.Context, *SettleInvoice
 func (UnimplementedInvoicesServer) LookupInvoiceV2(context.Context, *LookupInvoiceMsg) (*lnrpc.Invoice, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method LookupInvoiceV2 not implemented")
 }
+func (UnimplementedInvoicesServer) HtlcModifier(Invoices_HtlcModifierServer) error {
+	return status.Errorf(codes.Unimplemented, "method HtlcModifier not implemented")
+}
 func (UnimplementedInvoicesServer) mustEmbedUnimplementedInvoicesServer() {}
 
 // UnsafeInvoicesServer may be embedded to opt out of forward compatibility for this service.
@@ -269,6 +313,32 @@ func _Invoices_LookupInvoiceV2_Handler(srv interface{}, ctx context.Context, dec
 	return interceptor(ctx, in, info, handler)
 }
 
+func _Invoices_HtlcModifier_Handler(srv interface{}, stream grpc.ServerStream) error {
+	return srv.(InvoicesServer).HtlcModifier(&invoicesHtlcModifierServer{stream})
+}
+
+type Invoices_HtlcModifierServer interface {
+	Send(*HtlcModifyRequest) error
+	Recv() (*HtlcModifyResponse, error)
+	grpc.ServerStream
+}
+
+type invoicesHtlcModifierServer struct {
+	grpc.ServerStream
+}
+
+func (x *invoicesHtlcModifierServer) Send(m *HtlcModifyRequest) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+func (x *invoicesHtlcModifierServer) Recv() (*HtlcModifyResponse, error) {
+	m := new(HtlcModifyResponse)
+	if err := x.ServerStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
 // Invoices_ServiceDesc is the grpc.ServiceDesc for Invoices service.
 // It's only intended for direct use with grpc.RegisterService,
 // and not to be introspected or modified (even as a copy)
@@ -299,6 +369,12 @@ var Invoices_ServiceDesc = grpc.ServiceDesc{
 			Handler:       _Invoices_SubscribeSingleInvoice_Handler,
 			ServerStreams: true,
 		},
+		{
+			StreamName:    "HtlcModifier",
+			Handler:       _Invoices_HtlcModifier_Handler,
+			ServerStreams: true,
+			ClientStreams: true,
+		},
 	},
 	Metadata: "invoicesrpc/invoices.proto",
 }