TUN-528: Move cloudflared into a separate repo

vendor/zombiezen.com/go/capnproto2/internal/queue/queue.go

@@ -0,0 +1,70 @@
+// Package queue implements a generic queue using a ring buffer.
+package queue
+
+// A Queue wraps an Interface to provide queue operations.
+type Queue struct {
+	q     Interface
+	start int
+	n     int
+	cap   int
+}
+
+// New creates a new queue that starts with n elements.  The interface's
+// length must not change over the course of the queue's usage.
+func New(q Interface, n int) *Queue {
+	qq := new(Queue)
+	qq.Init(q, n)
+	return qq
+}
+
+// Init initializes a queue.  The old queue is untouched.
+func (q *Queue) Init(r Interface, n int) {
+	q.q = r
+	q.start = 0
+	q.n = n
+	q.cap = r.Len()
+}
+
+// Len returns the length of the queue.  This is different from the
+// underlying interface's length, which is the queue's capacity.
+func (q *Queue) Len() int {
+	return q.n
+}
+
+// Push reserves space for an element on the queue, returning its index.
+// If the queue is full, Push returns -1.
+func (q *Queue) Push() int {
+	if q.n >= q.cap {
+		return -1
+	}
+	i := (q.start + q.n) % q.cap
+	q.n++
+	return i
+}
+
+// Front returns the index of the front of the queue, or -1 if the queue is empty.
+func (q *Queue) Front() int {
+	if q.n == 0 {
+		return -1
+	}
+	return q.start
+}
+
+// Pop pops an element from the queue, returning whether it succeeded.
+func (q *Queue) Pop() bool {
+	if q.n == 0 {
+		return false
+	}
+	q.q.Clear(q.start)
+	q.start = (q.start + 1) % q.cap
+	q.n--
+	return true
+}
+
+// A type implementing Interface can be used to store elements in a Queue.
+type Interface interface {
+	// Len returns the number of elements available.
+	Len() int
+	// Clear removes the element at i.
+	Clear(i int)
+}