[IMPROVED] Subscribe returns error if consumer config does not match

js.go

@@ -973,7 +973,7 @@ func (js *js) PullSubscribe(subj, durable string, opts ...SubOpt) (*Subscription
 	return js.subscribe(subj, _EMPTY_, nil, mch, true, true, append(opts, Durable(durable)))
 }
 
-func processConsInfo(info *ConsumerInfo, isPullMode bool, subj, queue string) (string, error) {
+func processConsInfo(info *ConsumerInfo, userCfg *ConsumerConfig, isPullMode bool, subj, queue string) (string, error) {
 	ccfg := &info.Config
 
 	// Make sure this new subject matches or is a subset.
@@ -990,7 +990,7 @@ func processConsInfo(info *ConsumerInfo, isPullMode bool, subj, queue string) (s
 
 	// If pull mode, nothing else to check here.
 	if isPullMode {
-		return _EMPTY_, nil
+		return _EMPTY_, checkConfig(ccfg, userCfg)
 	}
 
 	// At this point, we know the user wants push mode, and the JS consumer is
@@ -1019,14 +1019,80 @@ func processConsInfo(info *ConsumerInfo, isPullMode bool, subj, queue string) (s
 				queue, dg)
 		}
 	}
+	if err := checkConfig(ccfg, userCfg); err != nil {
+		return _EMPTY_, err
+	}
 	return ccfg.DeliverSubject, nil
 }
 
+func checkConfig(s, u *ConsumerConfig) error {
+	makeErr := func(fieldName string, usrVal, srvVal interface{}) error {
+		return fmt.Errorf("configuration requests %s to be %v, but consumer's value is %v", fieldName, usrVal, srvVal)
+	}
+
+	if u.Durable != _EMPTY_ && u.Durable != s.Durable {
+		return makeErr("durable", u.Durable, s.Durable)
+	}
+	if u.Description != _EMPTY_ && u.Description != s.Description {
+		return makeErr("description", u.Description, s.Description)
+	}
+	if u.DeliverPolicy != deliverPolicyNotSet && u.DeliverPolicy != s.DeliverPolicy {
+		return makeErr("deliver policy", u.DeliverPolicy, s.DeliverPolicy)
+	}
+	if u.OptStartSeq > 0 && u.OptStartSeq != s.OptStartSeq {
+		return makeErr("optional start sequence", u.OptStartSeq, s.OptStartSeq)
+	}
+	if u.OptStartTime != nil && !u.OptStartTime.IsZero() && u.OptStartTime != s.OptStartTime {
+		return makeErr("optional start time", u.OptStartTime, s.OptStartTime)
+	}
+	if u.AckPolicy != ackPolicyNotSet && u.AckPolicy != s.AckPolicy {
+		return makeErr("ack policy", u.AckPolicy, s.AckPolicy)
+	}
+	if u.AckWait > 0 && u.AckWait != s.AckWait {
+		return makeErr("ack wait", u.AckWait, s.AckWait)
+	}
+	if u.MaxDeliver > 0 && u.MaxDeliver != s.MaxDeliver {
+		return makeErr("max deliver", u.MaxDeliver, s.MaxDeliver)
+	}
+	if u.ReplayPolicy != replayPolicyNotSet && u.ReplayPolicy != s.ReplayPolicy {
+		return makeErr("replay policy", u.ReplayPolicy, s.ReplayPolicy)
+	}
+	if u.RateLimit > 0 && u.RateLimit != s.RateLimit {
+		return makeErr("rate limit", u.RateLimit, s.RateLimit)
+	}
+	if u.SampleFrequency != _EMPTY_ && u.SampleFrequency != s.SampleFrequency {
+		return makeErr("sample frequency", u.SampleFrequency, s.SampleFrequency)
+	}
+	if u.MaxWaiting > 0 && u.MaxWaiting != s.MaxWaiting {
+		return makeErr("max waiting", u.MaxWaiting, s.MaxWaiting)
+	}
+	if u.MaxAckPending > 0 && u.MaxAckPending != s.MaxAckPending {
+		return makeErr("max ack pending", u.MaxAckPending, s.MaxAckPending)
+	}
+	// For flow control, we want to fail if the user explicit wanted it, but
+	// it is not set in the existing consumer. If it is not asked by the user,
+	// the library still handles it and so no reason to fail.
+	if u.FlowControl && !s.FlowControl {
+		return makeErr("flow control", u.FlowControl, s.FlowControl)
+	}
+	if u.Heartbeat > 0 && u.Heartbeat != s.Heartbeat {
+		return makeErr("heartbeat", u.Heartbeat, s.Heartbeat)
+	}
+	return nil
+}
+
 func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync, isPullMode bool, opts []SubOpt) (*Subscription, error) {
-	cfg := ConsumerConfig{AckPolicy: ackPolicyNotSet}
+	cfg := ConsumerConfig{
+		DeliverPolicy: deliverPolicyNotSet,
+		AckPolicy:     ackPolicyNotSet,
+		ReplayPolicy:  replayPolicyNotSet,
+	}
 	o := subOpts{cfg: &cfg}
 	if len(opts) > 0 {
 		for _, opt := range opts {
+			if opt == nil {
+				continue
+			}
 			if err := opt.configureSubscribe(&o); err != nil {
 				return nil, err
 			}
@@ -1159,7 +1225,7 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync,
 
 	switch {
 	case info != nil:
-		deliver, err = processConsInfo(info, isPullMode, subj, queue)
+		deliver, err = processConsInfo(info, o.cfg, isPullMode, subj, queue)
 		if err != nil {
 			return nil, err
 		}
@@ -1189,10 +1255,19 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync,
 			cfg.DeliverGroup = queue
 		}
 
-		// If not set default to ack explicit.
+		// If not set, default to deliver all
+		if cfg.DeliverPolicy == deliverPolicyNotSet {
+			cfg.DeliverPolicy = DeliverAllPolicy
+		}
+		// If not set, default to ack explicit.
 		if cfg.AckPolicy == ackPolicyNotSet {
 			cfg.AckPolicy = AckExplicitPolicy
 		}
+		// If not set, default to instant
+		if cfg.ReplayPolicy == replayPolicyNotSet {
+			cfg.ReplayPolicy = ReplayInstantPolicy
+		}
+
 		// If we have acks at all and the MaxAckPending is not set go ahead
 		// and set to the internal max.
 		// TODO(dlc) - We should be able to update this if client updates PendingLimits.
@@ -1303,7 +1378,7 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync,
 				if err != nil {
 					return nil, err
 				}
-				deliver, err = processConsInfo(info, isPullMode, subj, queue)
+				deliver, err = processConsInfo(info, o.cfg, isPullMode, subj, queue)
 				if err != nil {
 					return nil, err
 				}
@@ -1712,6 +1787,14 @@ func ManualAck() SubOpt {
 	})
 }
 
+// Description will set the description for the created consumer.
+func Description(description string) SubOpt {
+	return subOptFn(func(opts *subOpts) error {
+		opts.cfg.Description = description
+		return nil
+	})
+}
+
 // Durable defines the consumer name for JetStream durable subscribers.
 func Durable(consumer string) SubOpt {
 	return subOptFn(func(opts *subOpts) error {
@@ -1836,6 +1919,14 @@ func ReplayOriginal() SubOpt {
 	})
 }
 
+// ReplayInstant replays the messages as fast as possible.
+func ReplayInstant() SubOpt {
+	return subOptFn(func(opts *subOpts) error {
+		opts.cfg.ReplayPolicy = ReplayInstantPolicy
+		return nil
+	})
+}
+
 // RateLimit is the Bits per sec rate limit applied to a push consumer.
 func RateLimit(n uint64) SubOpt {
 	return subOptFn(func(opts *subOpts) error {
@@ -2418,7 +2509,7 @@ const (
 	// AckExplicitPolicy requires ack or nack for all messages.
 	AckExplicitPolicy
 
-	// For setting
+	// For configuration mismatch check
 	ackPolicyNotSet = 99
 )
 
@@ -2478,6 +2569,9 @@ const (
 
 	// ReplayOriginalPolicy will maintain the same timing as the messages were received.
 	ReplayOriginalPolicy
+
+	// For configuration mismatch check
+	replayPolicyNotSet = 99
 )
 
 func (p *ReplayPolicy) UnmarshalJSON(data []byte) error {
@@ -2538,6 +2632,9 @@ const (
 	// DeliverLastPerSubjectPolicy will start the consumer with the last message
 	// for all subjects received.
 	DeliverLastPerSubjectPolicy
+
+	// For configuration mismatch check
+	deliverPolicyNotSet = 99
 )
 
 func (p *DeliverPolicy) UnmarshalJSON(data []byte) error {