multi: refactor external subserver config

As a preparation for making more and more implementation details
configurable, we add a new ImplementationCfg struct that houses all the
interfaces that can be defined externally.

config_builder.go

@@ -0,0 +1,115 @@
+package lnd
+
+import (
+	"context"
+	"fmt"
+
+	proxy "github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
+	"github.com/lightningnetwork/lnd/macaroons"
+	"google.golang.org/grpc"
+	"gopkg.in/macaroon-bakery.v2/bakery"
+)
+
+// GrpcRegistrar is an interface that must be satisfied by an external subserver
+// that wants to be able to register its own gRPC server onto lnd's main
+// grpc.Server instance.
+type GrpcRegistrar interface {
+	// RegisterGrpcSubserver is called for each net.Listener on which lnd
+	// creates a grpc.Server instance. External subservers implementing this
+	// method can then register their own gRPC server structs to the main
+	// server instance.
+	RegisterGrpcSubserver(*grpc.Server) error
+}
+
+// RestRegistrar is an interface that must be satisfied by an external subserver
+// that wants to be able to register its own REST mux onto lnd's main
+// proxy.ServeMux instance.
+type RestRegistrar interface {
+	// RegisterRestSubserver is called after lnd creates the main
+	// proxy.ServeMux instance. External subservers implementing this method
+	// can then register their own REST proxy stubs to the main server
+	// instance.
+	RegisterRestSubserver(context.Context, *proxy.ServeMux, string,
+		[]grpc.DialOption) error
+}
+
+// ExternalValidator is an interface that must be satisfied by an external
+// macaroon validator.
+type ExternalValidator interface {
+	macaroons.MacaroonValidator
+
+	// Permissions returns the permissions that the external validator is
+	// validating. It is a map between the full HTTP URI of each RPC and its
+	// required macaroon permissions. If multiple action/entity tuples are
+	// specified per URI, they are all required. See rpcserver.go for a list
+	// of valid action and entity values.
+	Permissions() map[string][]bakery.Op
+}
+
+// ImplementationCfg is a struct that holds all configuration items for
+// components that can be implemented outside lnd itself.
+type ImplementationCfg struct {
+	// GrpcRegistrar is a type that can register additional gRPC subservers
+	// before the main gRPC server is started.
+	GrpcRegistrar
+
+	// RestRegistrar is a type that can register additional REST subservers
+	// before the main REST proxy is started.
+	RestRegistrar
+
+	// ExternalValidator is a type that can provide external macaroon
+	// validation.
+	ExternalValidator
+}
+
+// DefaultWalletImpl is the default implementation of our normal, btcwallet
+// backed configuration.
+type DefaultWalletImpl struct {
+}
+
+// RegisterRestSubserver is called after lnd creates the main proxy.ServeMux
+// instance. External subservers implementing this method can then register
+// their own REST proxy stubs to the main server instance.
+//
+// NOTE: This is part of the GrpcRegistrar interface.
+func (d *DefaultWalletImpl) RegisterRestSubserver(context.Context,
+	*proxy.ServeMux, string, []grpc.DialOption) error {
+
+	return nil
+}
+
+// RegisterGrpcSubserver is called for each net.Listener on which lnd creates a
+// grpc.Server instance. External subservers implementing this method can then
+// register their own gRPC server structs to the main server instance.
+//
+// NOTE: This is part of the GrpcRegistrar interface.
+func (d *DefaultWalletImpl) RegisterGrpcSubserver(*grpc.Server) error {
+	return nil
+}
+
+// ValidateMacaroon extracts the macaroon from the context's gRPC metadata,
+// checks its signature, makes sure all specified permissions for the called
+// method are contained within and finally ensures all caveat conditions are
+// met. A non-nil error is returned if any of the checks fail.
+//
+// NOTE: This is part of the ExternalValidator interface.
+func (d *DefaultWalletImpl) ValidateMacaroon(ctx context.Context,
+	requiredPermissions []bakery.Op, fullMethod string) error {
+
+	// Because the default implementation does not return any permissions,
+	// we shouldn't be registered as an external validator at all and this
+	// should never be invoked.
+	return fmt.Errorf("default implementation does not support external " +
+		"macaroon validation")
+}
+
+// Permissions returns the permissions that the external validator is
+// validating. It is a map between the full HTTP URI of each RPC and its
+// required macaroon permissions. If multiple action/entity tuples are specified
+// per URI, they are all required. See rpcserver.go for a list of valid action
+// and entity values.
+//
+// NOTE: This is part of the ExternalValidator interface.
+func (d *DefaultWalletImpl) Permissions() map[string][]bakery.Op {
+	return nil
+}