Implements a new jsm function StreamContainedSubjects()` to get the…

… list of (matching) subjects for the messages currently in the stream and the number of messages for each subject, using the pagination API for Stream Info (see nats-io/nats-server#3454)

js_test.go

@@ -1096,3 +1096,36 @@ func TestJetStreamConvertDirectMsgResponseToMsg(t *testing.T) {
 		t.Fatalf("Wrong header: %v", r.Header)
 	}
 }
+
+func TestJetStreamStreamInfoSubjectDetails(t *testing.T) {
+	s := RunBasicJetStreamServer()
+	defer shutdownJSServerAndRemoveStorage(t, s)
+
+	nc, js := jsClient(t, s)
+	defer nc.Close()
+
+	var err error
+
+	_, err = js.AddStream(&StreamConfig{
+		Name:     "TEST",
+		Subjects: []string{"test.*"},
+	})
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+
+	// Publish on enough subjects to exercise the pagination
+	payload := make([]byte, 10)
+	for i := 0; i < 100001; i++ {
+		nc.Publish(fmt.Sprintf("test.%d", i), payload)
+	}
+
+	result, err := js.StreamContainedSubjects("TEST", "test.*")
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+
+	if len(result) != 100001 {
+		t.Fatalf("expected 100001 subjects in the stream, but got %d instead", len(result))
+	}
+}

jsm.go

@@ -37,6 +37,9 @@ type JetStreamManager interface {
 	// StreamInfo retrieves information from a stream.
 	StreamInfo(stream string, opts ...JSOpt) (*StreamInfo, error)
 
+	// StreamContainedSubjects queries the stream for the subjects it holds with optional filter
+	StreamContainedSubjects(stream string, filter ...string) (map[string]uint64, error)
+
 	// PurgeStream purges a stream messages.
 	PurgeStream(name string, opts ...JSOpt) error
 
@@ -682,12 +685,17 @@ func (js *js) AddStream(cfg *StreamConfig, opts ...JSOpt) (*StreamInfo, error) {
 type (
 	// StreamInfoRequest contains additional option to return
 	StreamInfoRequest struct {
+		apiPagedRequest
 		// DeletedDetails when true includes information about deleted messages
 		DeletedDetails bool `json:"deleted_details,omitempty"`
 		// SubjectsFilter when set, returns information on the matched subjects
 		SubjectsFilter string `json:"subjects_filter,omitempty"`
 	}
-	streamInfoResponse = streamCreateResponse
+	streamInfoResponse = struct {
+		apiResponse
+		apiPaged
+		*StreamInfo
+	}
 )
 
 func (js *js) StreamInfo(stream string, opts ...JSOpt) (*StreamInfo, error) {
@@ -727,6 +735,78 @@ func (js *js) StreamInfo(stream string, opts ...JSOpt) (*StreamInfo, error) {
 	return resp.StreamInfo, nil
 }
 
+func (js *js) StreamContainedSubjects(stream string, filter ...string) (map[string]uint64, error) {
+	if err := checkStreamName(stream); err != nil {
+		return nil, err
+	}
+
+	if len(filter) > 1 {
+		return nil, fmt.Errorf("only 1 filter supported")
+	}
+
+	f := ">"
+	if len(filter) == 1 && filter[0] != "" {
+		f = filter[0]
+	}
+
+	var i int
+	var subjectMessagesMap map[string]uint64 = nil
+
+	o, cancel, err := getJSContextOpts(js.opts)
+	if err != nil {
+		return nil, err
+	}
+	if cancel != nil {
+		defer cancel()
+	}
+
+	for {
+		var req []byte
+
+		if req, err = json.Marshal(StreamInfoRequest{SubjectsFilter: f, apiPagedRequest: apiPagedRequest{Offset: i}}); err != nil {
+			return nil, err
+		}
+
+		r, err := js.apiRequestWithContext(o.ctx, js.apiSubj(fmt.Sprintf(apiStreamInfoT, stream)), req)
+		if err != nil {
+			return nil, err
+		}
+
+		var resp streamInfoResponse
+		if err := json.Unmarshal(r.Data, &resp); err != nil {
+			return nil, err
+		}
+		if resp.Error != nil {
+			if errors.Is(resp.Error, ErrStreamNotFound) {
+				return nil, ErrStreamNotFound
+			}
+			return nil, resp.Error
+		}
+
+		// for backwards compatibility
+		var total int
+		if resp.Total != 0 {
+			total = resp.Total
+		} else {
+			total = len(resp.State.Subjects)
+		}
+
+		if subjectMessagesMap == nil {
+			subjectMessagesMap = make(map[string]uint64, total)
+		}
+
+		for k, j := range resp.State.Subjects {
+			subjectMessagesMap[k] = j
+			i++
+		}
+		if i == total {
+			break
+		}
+	}
+
+	return subjectMessagesMap, nil
+}
+
 // StreamInfo shows config and current state for this stream.
 type StreamInfo struct {
 	Config  StreamConfig        `json:"config"`