Add MaxRequestMaxBytes consumer option

js.go

@@ -1037,8 +1037,9 @@ type ConsumerConfig struct {
 	HeadersOnly     bool            `json:"headers_only,omitempty"`
 
 	// Pull based options.
-	MaxRequestBatch   int           `json:"max_batch,omitempty"`
-	MaxRequestExpires time.Duration `json:"max_expires,omitempty"`
+	MaxRequestBatch    int           `json:"max_batch,omitempty"`
+	MaxRequestExpires  time.Duration `json:"max_expires,omitempty"`
+	MaxRequestMaxBytes int           `json:"max_bytes,omitempty"`
 
 	// Push based consumers.
 	DeliverSubject string `json:"deliver_subject,omitempty"`
@@ -1084,9 +1085,10 @@ type SequencePair struct {
 
 // nextRequest is for getting next messages for pull based consumers from JetStream.
 type nextRequest struct {
-	Expires time.Duration `json:"expires,omitempty"`
-	Batch   int           `json:"batch,omitempty"`
-	NoWait  bool          `json:"no_wait,omitempty"`
+	Expires  time.Duration `json:"expires,omitempty"`
+	Batch    int           `json:"batch,omitempty"`
+	NoWait   bool          `json:"no_wait,omitempty"`
+	MaxBytes int           `json:"max_bytes,omitempty"`
 }
 
 // jsSub includes JetStream subscription info.
@@ -2445,6 +2447,15 @@ func MaxRequestExpires(max time.Duration) SubOpt {
 	})
 }
 
+// MaxRequesMaxBytes sets the maximum pull consumer request bytes that a
+// Fetch() can receive.
+func MaxRequestMaxBytes(bytes int) SubOpt {
+	return subOptFn(func(opts *subOpts) error {
+		opts.cfg.MaxRequestMaxBytes = bytes
+		return nil
+	})
+}
+
 // InactiveThreshold indicates how long the server should keep an ephemeral
 // after detecting loss of interest.
 func InactiveThreshold(threshold time.Duration) SubOpt {
@@ -2485,8 +2496,9 @@ func (sub *Subscription) ConsumerInfo() (*ConsumerInfo, error) {
 }
 
 type pullOpts struct {
-	ttl time.Duration
-	ctx context.Context
+	maxBytes int
+	ttl      time.Duration
+	ctx      context.Context
 }
 
 // PullOpt are the options that can be passed when pulling a batch of messages.
@@ -2502,6 +2514,14 @@ func PullMaxWaiting(n int) SubOpt {
 	})
 }
 
+// PullMaxBytes defines the max bytes allowed for a fetch request.
+type PullMaxBytes int
+
+func (n PullMaxBytes) configurePull(opts *pullOpts) error {
+	opts.maxBytes = int(n)
+	return nil
+}
+
 var (
 	// errNoMessages is an error that a Fetch request using no_wait can receive to signal
 	// that there are no more messages available.
@@ -2677,6 +2697,7 @@ func (sub *Subscription) Fetch(batch int, opts ...PullOpt) ([]*Msg, error) {
 		// For batch real size of 1, it does not make sense to set no_wait in
 		// the request.
 		noWait := batch-len(msgs) > 1
+
 		var nr nextRequest
 
 		sendReq := func() error {
@@ -2701,6 +2722,7 @@ func (sub *Subscription) Fetch(batch int, opts ...PullOpt) ([]*Msg, error) {
 			nr.Batch = batch - len(msgs)
 			nr.Expires = expires
 			nr.NoWait = noWait
+			nr.MaxBytes = o.maxBytes
 			req, _ := json.Marshal(nr)
 			return nc.PublishRequest(nms, rply, req)
 		}

test/js_test.go

@@ -1411,6 +1411,8 @@ func TestJetStreamManagement(t *testing.T) {
 		expected.HeadersOnly = true
 		expected.MaxRequestBatch = 10
 		expected.MaxRequestExpires = 2 * time.Second
+		expected.MaxRequestMaxBytes = 1024
+
 		ci, err = js.UpdateConsumer("foo", &expected)
 		if err != nil {
 			t.Fatalf("Error on update: %v", err)
@@ -5870,6 +5872,20 @@ func testJetStreamFetchOptions(t *testing.T, srvs ...*jsServer) {
 		}
 	})
 
+	t.Run("max request max bytes", func(t *testing.T) {
+		defer js.PurgeStream(subject)
+
+		sub, err := js.PullSubscribe(subject, "max-request-max-bytes", nats.MaxRequestMaxBytes(100))
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer sub.Unsubscribe()
+
+		if _, err := sub.Fetch(10, nats.PullMaxBytes(200)); err == nil || !strings.Contains(err.Error(), "MaxRequestMaxBytes of 100") {
+			t.Fatalf("Expected error about max request max bytes, got %v", err)
+		}
+	})
+
 	t.Run("max request expires", func(t *testing.T) {
 		defer js.PurgeStream(subject)