Initial QSfera import

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

@@ -0,0 +1,77 @@
+// Copyright 2018-2025 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
+
+// We wrap to hold onto optional items for /connz.
+type closedClient struct {
+	ConnInfo
+	subs []SubDetail
+	user string
+	acc  string
+}
+
+// Fixed sized ringbuffer for closed connections.
+type closedRingBuffer struct {
+	total uint64
+	conns []*closedClient
+}
+
+// Create a new ring buffer with at most max items.
+func newClosedRingBuffer(max int) *closedRingBuffer {
+	rb := &closedRingBuffer{}
+	rb.conns = make([]*closedClient, max)
+	return rb
+}
+
+// Adds in a new closed connection. If there is no more room,
+// remove the oldest.
+func (rb *closedRingBuffer) append(cc *closedClient) {
+	rb.conns[rb.next()] = cc
+	rb.total++
+}
+
+func (rb *closedRingBuffer) next() int {
+	return int(rb.total % uint64(cap(rb.conns)))
+}
+
+func (rb *closedRingBuffer) len() int {
+	if rb.total > uint64(cap(rb.conns)) {
+		return cap(rb.conns)
+	}
+	return int(rb.total)
+}
+
+func (rb *closedRingBuffer) totalConns() uint64 {
+	return rb.total
+}
+
+// This will return a sorted copy of the list which recipient can
+// modify. If the contents of the client itself need to be modified,
+// meaning swapping in any optional items, a copy should be made. We
+// could introduce a new lock and hold that but since we return this
+// list inside monitor which allows programatic access, we do not
+// know when it would be done.
+func (rb *closedRingBuffer) closedClients() []*closedClient {
+	dup := make([]*closedClient, rb.len())
+	head := rb.next()
+	if rb.total <= uint64(cap(rb.conns)) || head == 0 {
+		copy(dup, rb.conns[:rb.len()])
+	} else {
+		fp := rb.conns[head:]
+		sp := rb.conns[:head]
+		copy(dup, fp)
+		copy(dup[len(fp):], sp)
+	}
+	return dup
+}