refactors app specific to return an error

pubsub.go

@@ -173,8 +173,9 @@ type PubSub struct {
 
 	// appSpecificRpcInspector is an auxiliary that may be set by the application to inspect incoming RPCs prior to
 	// processing them. The inspector is invoked on an accepted RPC right prior to handling it.
-	// The return value of the inspector function is a boolean indicating whether the RPC should be processed or not.
-	appSpecificRpcInspector func(peer.ID, *RPC) bool
+	// The return value of the inspector function is an error indicating whether the RPC should be processed or not.
+	// If the error is nil, the RPC is processed as usual. If the error is non-nil, the RPC is dropped.
+	appSpecificRpcInspector func(peer.ID, *RPC) error
 }
 
 // PubSubRouter is the message router component of PubSub.
@@ -532,7 +533,7 @@ func WithSeenMessagesTTL(ttl time.Duration) Option {
 	}
 }
 
-func WithAppSpecificRpcInspector(inspector func(peer.ID, *RPC) bool) Option {
+func WithAppSpecificRpcInspector(inspector func(peer.ID, *RPC) error) Option {
 	return func(ps *PubSub) error {
 		ps.appSpecificRpcInspector = inspector
 		return nil
@@ -1020,7 +1021,8 @@ func (p *PubSub) handleIncomingRPC(rpc *RPC) {
 	// pass the rpc through app specific validation (if any available).
 	if p.appSpecificRpcInspector != nil {
 		// check if the RPC is allowed by the external inspector
-		if accept := p.appSpecificRpcInspector(rpc.from, rpc); !accept {
+		if err := p.appSpecificRpcInspector(rpc.from, rpc); err != nil {
+			log.Debugf("application-specific inspection failed, rejecting incoming rpc: %s", err)
 			return // reject the RPC
 		}
 	}