TUN-4597: Add a QUIC server skeleton

- Added a QUIC server to accept streams
- Unit test for this server also tests ALPN
- Temporary echo capability for HTTP ConnectionType

vendor/github.com/lucas-clemente/quic-go/buffer_pool.go

@@ -0,0 +1,80 @@
+package quic
+
+import (
+	"sync"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+)
+
+type packetBuffer struct {
+	Data []byte
+
+	// refCount counts how many packets Data is used in.
+	// It doesn't support concurrent use.
+	// It is > 1 when used for coalesced packet.
+	refCount int
+}
+
+// Split increases the refCount.
+// It must be called when a packet buffer is used for more than one packet,
+// e.g. when splitting coalesced packets.
+func (b *packetBuffer) Split() {
+	b.refCount++
+}
+
+// Decrement decrements the reference counter.
+// It doesn't put the buffer back into the pool.
+func (b *packetBuffer) Decrement() {
+	b.refCount--
+	if b.refCount < 0 {
+		panic("negative packetBuffer refCount")
+	}
+}
+
+// MaybeRelease puts the packet buffer back into the pool,
+// if the reference counter already reached 0.
+func (b *packetBuffer) MaybeRelease() {
+	// only put the packetBuffer back if it's not used any more
+	if b.refCount == 0 {
+		b.putBack()
+	}
+}
+
+// Release puts back the packet buffer into the pool.
+// It should be called when processing is definitely finished.
+func (b *packetBuffer) Release() {
+	b.Decrement()
+	if b.refCount != 0 {
+		panic("packetBuffer refCount not zero")
+	}
+	b.putBack()
+}
+
+// Len returns the length of Data
+func (b *packetBuffer) Len() protocol.ByteCount {
+	return protocol.ByteCount(len(b.Data))
+}
+
+func (b *packetBuffer) putBack() {
+	if cap(b.Data) != int(protocol.MaxPacketBufferSize) {
+		panic("putPacketBuffer called with packet of wrong size!")
+	}
+	bufferPool.Put(b)
+}
+
+var bufferPool sync.Pool
+
+func getPacketBuffer() *packetBuffer {
+	buf := bufferPool.Get().(*packetBuffer)
+	buf.refCount = 1
+	buf.Data = buf.Data[:0]
+	return buf
+}
+
+func init() {
+	bufferPool.New = func() interface{} {
+		return &packetBuffer{
+			Data: make([]byte, 0, protocol.MaxPacketBufferSize),
+		}
+	}
+}