add support for inline (synchronous) validators

pubsub.go

@@ -696,11 +696,29 @@ func (p *PubSub) validate(vals []*topicVal, src peer.ID, msg *Message) {
 		return
 	}
 
-	if len(vals) > 0 {
+	var inline, async []*topicVal
+	for _, val := range vals {
+		if val.validateInline {
+			inline = append(inline, val)
+		} else {
+			async = append(async, val)
+		}
+	}
+
+	// apply inline (synchronous) validators
+	for _, val := range inline {
+		if !val.validateMsg(p.ctx, src, msg) {
+			log.Debugf("message validation failed; dropping message from %s", src)
+			return
+		}
+	}
+
+	// apply async validators
+	if len(async) > 0 {
 		select {
 		case p.validateThrottle <- struct{}{}:
 			go func() {
-				p.doValidateTopic(vals, src, msg)
+				p.doValidateTopic(async, src, msg)
 				<-p.validateThrottle
 			}()
 		default:
@@ -709,7 +727,7 @@ func (p *PubSub) validate(vals []*topicVal, src peer.ID, msg *Message) {
 		return
 	}
 
-	// no user validators and the signature was valid, send the message
+	// no async validators, send the message
 	p.sendMsg <- &sendReq{
 		from: src,
 		msg:  msg,
@@ -945,6 +963,7 @@ type addValReq struct {
 	validate Validator
 	timeout  time.Duration
 	throttle int
+	inline   bool
 	resp     chan error
 }
 
@@ -958,6 +977,7 @@ type topicVal struct {
 	validate         Validator
 	validateTimeout  time.Duration
 	validateThrottle chan struct{}
+	validateInline   bool
 }
 
 // Validator is a function that validates a message.
@@ -984,6 +1004,16 @@ func WithValidatorConcurrency(n int) ValidatorOpt {
 	}
 }
 
+// WithValidatorInline is an option that sets the validation disposition to synchronous:
+// it will be executed inline in validation front-end, without spawning a new goroutine.
+// This is suitable for simple or cpu-bound validators that do not block.
+func WithValidatorInline(inline bool) ValidatorOpt {
+	return func(addVal *addValReq) error {
+		addVal.inline = inline
+		return nil
+	}
+}
+
 // RegisterTopicValidator registers a validator for topic.
 // By default validators are asynchronous, which means they will run in a separate goroutine.
 // The number of active goroutines is controlled by global and per topic validator
@@ -1020,6 +1050,7 @@ func (ps *PubSub) addValidator(req *addValReq) {
 		validate:         req.validate,
 		validateTimeout:  0,
 		validateThrottle: make(chan struct{}, defaultValidateConcurrency),
+		validateInline:   req.inline,
 	}
 
 	if req.timeout > 0 {