Initial QSfera import

Server/vendor/github.com/nats-io/nats-server/v2/server/sdm.go

@@ -0,0 +1,80 @@
+// Copyright 2025 The NATS Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package server
+
+import (
+	"bytes"
+	"time"
+)
+
+// SDMMeta holds pending/proposed data for subject delete markers or message removals.
+type SDMMeta struct {
+	totals  map[string]uint64
+	pending map[uint64]SDMBySeq
+}
+
+// SDMBySeq holds data for a message with a specific sequence.
+type SDMBySeq struct {
+	last bool  // Whether the message for this sequence was the last for this subject.
+	ts   int64 // Last timestamp we proposed a removal/sdm.
+}
+
+func newSDMMeta() *SDMMeta {
+	return &SDMMeta{
+		totals:  make(map[string]uint64, 1),
+		pending: make(map[uint64]SDMBySeq, 1),
+	}
+}
+
+// isSubjectDeleteMarker returns whether the headers indicate this message is a subject delete marker.
+// Either it's a usual marker with JSMarkerReason, or it's a KV Purge marker as the KVOperation.
+func isSubjectDeleteMarker(hdr []byte) bool {
+	return len(sliceHeader(JSMarkerReason, hdr)) != 0 || bytes.Equal(sliceHeader(KVOperation, hdr), KVOperationValuePurge)
+}
+
+// empty clears all data.
+func (sdm *SDMMeta) empty() {
+	if sdm == nil {
+		return
+	}
+	clear(sdm.totals)
+	clear(sdm.pending)
+}
+
+// trackPending caches the given seq and subj and whether it's the last message for that subject.
+func (sdm *SDMMeta) trackPending(seq uint64, subj string, last bool) bool {
+	if p, ok := sdm.pending[seq]; ok {
+		return p.last
+	}
+	sdm.pending[seq] = SDMBySeq{last, time.Now().UnixNano()}
+	sdm.totals[subj]++
+	return last
+}
+
+// removeSeqAndSubject clears the seq and subj from the cache.
+func (sdm *SDMMeta) removeSeqAndSubject(seq uint64, subj string) {
+	if sdm == nil {
+		return
+	}
+	if _, ok := sdm.pending[seq]; ok {
+		delete(sdm.pending, seq)
+		if msgs, ok := sdm.totals[subj]; ok {
+			if msgs <= 1 {
+				delete(sdm.totals, subj)
+			} else {
+				sdm.totals[subj] = msgs - 1
+			}
+		}
+	}
+}