config+sample-lnd.conf+lncfg: add RPC middleware config

config.go

@@ -380,6 +380,8 @@ type Config struct {
 
 	Cluster *lncfg.Cluster `group:"cluster" namespace:"cluster"`
 
+	RPCMiddleware *lncfg.RPCMiddleware `group:"rpcmiddleware" namespace:"rpcmiddleware"`
+
 	// LogWriter is the root logger that all of the daemon's subloggers are
 	// hooked up to.
 	LogWriter *build.RotatingLogWriter
@@ -550,6 +552,7 @@ func DefaultConfig() Config {
 		LogWriter:               build.NewRotatingLogWriter(),
 		DB:                      lncfg.DefaultDB(),
 		Cluster:                 lncfg.DefaultCluster(),
+		RPCMiddleware:           lncfg.DefaultRPCMiddleware(),
 		registeredChains:        chainreg.NewChainRegistry(),
 		ActiveNetParams:         chainreg.BitcoinTestNetParams,
 		ChannelCommitInterval:   defaultChannelCommitInterval,
@@ -639,6 +642,7 @@ func LoadConfig(interceptor signal.Interceptor) (*Config, error) {
 // normalized. The cleaned up config is returned on success.
 func ValidateConfig(cfg Config, usageMessage string,
 	interceptor signal.Interceptor) (*Config, error) {
+
 	// If the provided lnd directory is not the default, we'll modify the
 	// path to all of the files and directories that will live within it.
 	lndDir := CleanAndExpandPath(cfg.LndDir)
@@ -1477,6 +1481,7 @@ func ValidateConfig(cfg Config, usageMessage string,
 		cfg.DB,
 		cfg.Cluster,
 		cfg.HealthChecks,
+		cfg.RPCMiddleware,
 	)
 	if err != nil {
 		return nil, err

lncfg/rpcmiddleware.go

@@ -0,0 +1,40 @@
+package lncfg
+
+import (
+	"fmt"
+	"time"
+)
+
+const (
+	// defaultRPCMiddlewareTimeout is the time after which a request sent to
+	// a gRPC interception middleware times out. This value is chosen very
+	// low since in a worst case scenario that time is added to a request's
+	// full duration twice (request and response interception) if a
+	// middleware is very slow.
+	defaultRPCMiddlewareTimeout = 2 * time.Second
+)
+
+// RPCMiddleware holds the configuration for RPC interception middleware.
+type RPCMiddleware struct {
+	Enable           bool          `long:"enable" description:"Enable the RPC middleware interceptor functionality."`
+	InterceptTimeout time.Duration `long:"intercepttimeout" description:"Time after which a RPC middleware intercept request will time out and return an error if it hasn't yet received a response."`
+	Mandatory        []string      `long:"addmandatory" description:"Add the named middleware to the list of mandatory middlewares. All RPC requests are blocked/denied if any of the mandatory middlewares is not registered. Can be specified multiple times."`
+}
+
+// Validate checks the values configured for the RPC middleware.
+func (r *RPCMiddleware) Validate() error {
+	if r.InterceptTimeout < 0 {
+		return fmt.Errorf("RPC middleware intercept timeout cannot " +
+			"be negative")
+	}
+
+	return nil
+}
+
+// DefaultRPCMiddleware returns the default values for the RPC interception
+// middleware configuration.
+func DefaultRPCMiddleware() *RPCMiddleware {
+	return &RPCMiddleware{
+		InterceptTimeout: defaultRPCMiddlewareTimeout,
+	}
+}

sample-lnd.conf

@@ -1151,6 +1151,20 @@ litecoin.node=ltcd
 ; Defaults to the hostname.
 ; cluster.id=example.com
 
+[rpcmiddleware]
+
+; Enable the RPC middleware interceptor functionality.
+; rpcmiddleware.enable=true
+
+; Time after which a RPC middleware intercept request will time out and return
+; an error if it hasn't yet received a response.
+; rpcmiddleware.intercepttimeout=2s
+
+; Add the named middleware to the list of mandatory middlewares. All RPC
+; requests are blocked/denied if any of the mandatory middlewares is not
+; registered. Can be specified multiple times.
+; rpcmiddleware.addmandatory=my-example-middleware
+; rpcmiddleware.addmandatory=other-mandatory-middleware
 
 [bolt]