use a ring buffer in the framer (#3857)

* implement and use ringbuffer in framer

* Add comments for ring buffer

Co-authored-by: Marten Seemann <martenseemann@gmail.com>

---------

Co-authored-by: Marten Seemann <martenseemann@gmail.com>

internal/utils/ringbuffer/ringbuffer.go

@@ -0,0 +1,86 @@
+package ringbuffer
+
+// A RingBuffer is a ring buffer.
+// It acts as a heap that doesn't cause any allocations.
+type RingBuffer[T any] struct {
+	ring             []T
+	headPos, tailPos int
+	full             bool
+}
+
+// Init preallocs a buffer with a certain size.
+func (r *RingBuffer[T]) Init(size int) {
+	r.ring = make([]T, size)
+}
+
+// Len returns the number of elements in the ring buffer.
+func (r *RingBuffer[T]) Len() int {
+	if r.full {
+		return len(r.ring)
+	}
+	if r.tailPos >= r.headPos {
+		return r.tailPos - r.headPos
+	}
+	return r.tailPos - r.headPos + len(r.ring)
+}
+
+// Empty says if the ring buffer is empty.
+func (r *RingBuffer[T]) Empty() bool {
+	return !r.full && r.headPos == r.tailPos
+}
+
+// PushBack adds a new element.
+// If the ring buffer is full, its capacity is increased first.
+func (r *RingBuffer[T]) PushBack(t T) {
+	if r.full || len(r.ring) == 0 {
+		r.grow()
+	}
+	r.ring[r.tailPos] = t
+	r.tailPos++
+	if r.tailPos == len(r.ring) {
+		r.tailPos = 0
+	}
+	if r.tailPos == r.headPos {
+		r.full = true
+	}
+}
+
+// PopFront returns the next element.
+// It must not be called when the buffer is empty, that means that
+// callers might need to check if there are elements in the buffer first.
+func (r *RingBuffer[T]) PopFront() T {
+	if r.Empty() {
+		panic("github.com/quic-go/quic-go/internal/utils/ringbuffer: pop from an empty queue")
+	}
+	r.full = false
+	t := r.ring[r.headPos]
+	r.ring[r.headPos] = *new(T)
+	r.headPos++
+	if r.headPos == len(r.ring) {
+		r.headPos = 0
+	}
+	return t
+}
+
+// Grow the maximum size of the queue.
+// This method assume the queue is full.
+func (r *RingBuffer[T]) grow() {
+	oldRing := r.ring
+	newSize := len(oldRing) * 2
+	if newSize == 0 {
+		newSize = 1
+	}
+	r.ring = make([]T, newSize)
+	headLen := copy(r.ring, oldRing[r.headPos:])
+	copy(r.ring[headLen:], oldRing[:r.headPos])
+	r.headPos, r.tailPos, r.full = 0, len(oldRing), false
+}
+
+// Clear removes all elements.
+func (r *RingBuffer[T]) Clear() {
+	var zeroValue T
+	for i := range r.ring {
+		r.ring[i] = zeroValue
+	}
+	r.headPos, r.tailPos, r.full = 0, 0, false
+}

internal/utils/ringbuffer/ringbuffer_bench_test.go

@@ -0,0 +1,12 @@
+package ringbuffer
+
+import "testing"
+
+func BenchmarkRingBuffer(b *testing.B) {
+	r := RingBuffer[int]{}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.PushBack(i)
+		r.PopFront()
+	}
+}

internal/utils/ringbuffer/ringbuffer_suite_test.go

@@ -0,0 +1,13 @@
+package ringbuffer
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestTestdata(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "ringbuffer suite")
+}

internal/utils/ringbuffer/ringbuffer_test.go

@@ -0,0 +1,38 @@
+package ringbuffer
+
+import (
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("RingBuffer", func() {
+	It("push and pop", func() {
+		r := RingBuffer[int]{}
+		Expect(len(r.ring)).To(Equal(0))
+		Expect(func() { r.PopFront() }).To(Panic())
+		r.PushBack(1)
+		r.PushBack(2)
+		r.PushBack(3)
+		Expect(r.PopFront()).To(Equal(1))
+		Expect(r.PopFront()).To(Equal(2))
+		r.PushBack(4)
+		r.PushBack(5)
+		Expect(r.Len()).To(Equal(3))
+		r.PushBack(6)
+		Expect(r.Len()).To(Equal(4))
+		Expect(r.PopFront()).To(Equal(3))
+		Expect(r.PopFront()).To(Equal(4))
+		Expect(r.PopFront()).To(Equal(5))
+		Expect(r.PopFront()).To(Equal(6))
+	})
+	It("clear", func() {
+		r := RingBuffer[int]{}
+		r.Init(2)
+		r.PushBack(1)
+		r.PushBack(2)
+		Expect(r.full).To(BeTrue())
+		r.Clear()
+		Expect(r.full).To(BeFalse())
+		Expect(r.Len()).To(Equal(0))
+	})
+})