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/internal/protocol/packet_number.go

@@ -0,0 +1,79 @@
+package protocol
+
+// A PacketNumber in QUIC
+type PacketNumber int64
+
+// InvalidPacketNumber is a packet number that is never sent.
+// In QUIC, 0 is a valid packet number.
+const InvalidPacketNumber PacketNumber = -1
+
+// PacketNumberLen is the length of the packet number in bytes
+type PacketNumberLen uint8
+
+const (
+	// PacketNumberLen1 is a packet number length of 1 byte
+	PacketNumberLen1 PacketNumberLen = 1
+	// PacketNumberLen2 is a packet number length of 2 bytes
+	PacketNumberLen2 PacketNumberLen = 2
+	// PacketNumberLen3 is a packet number length of 3 bytes
+	PacketNumberLen3 PacketNumberLen = 3
+	// PacketNumberLen4 is a packet number length of 4 bytes
+	PacketNumberLen4 PacketNumberLen = 4
+)
+
+// DecodePacketNumber calculates the packet number based on the received packet number, its length and the last seen packet number
+func DecodePacketNumber(
+	packetNumberLength PacketNumberLen,
+	lastPacketNumber PacketNumber,
+	wirePacketNumber PacketNumber,
+) PacketNumber {
+	var epochDelta PacketNumber
+	switch packetNumberLength {
+	case PacketNumberLen1:
+		epochDelta = PacketNumber(1) << 8
+	case PacketNumberLen2:
+		epochDelta = PacketNumber(1) << 16
+	case PacketNumberLen3:
+		epochDelta = PacketNumber(1) << 24
+	case PacketNumberLen4:
+		epochDelta = PacketNumber(1) << 32
+	}
+	epoch := lastPacketNumber & ^(epochDelta - 1)
+	var prevEpochBegin PacketNumber
+	if epoch > epochDelta {
+		prevEpochBegin = epoch - epochDelta
+	}
+	nextEpochBegin := epoch + epochDelta
+	return closestTo(
+		lastPacketNumber+1,
+		epoch+wirePacketNumber,
+		closestTo(lastPacketNumber+1, prevEpochBegin+wirePacketNumber, nextEpochBegin+wirePacketNumber),
+	)
+}
+
+func closestTo(target, a, b PacketNumber) PacketNumber {
+	if delta(target, a) < delta(target, b) {
+		return a
+	}
+	return b
+}
+
+func delta(a, b PacketNumber) PacketNumber {
+	if a < b {
+		return b - a
+	}
+	return a - b
+}
+
+// GetPacketNumberLengthForHeader gets the length of the packet number for the public header
+// it never chooses a PacketNumberLen of 1 byte, since this is too short under certain circumstances
+func GetPacketNumberLengthForHeader(packetNumber, leastUnacked PacketNumber) PacketNumberLen {
+	diff := uint64(packetNumber - leastUnacked)
+	if diff < (1 << (16 - 1)) {
+		return PacketNumberLen2
+	}
+	if diff < (1 << (24 - 1)) {
+		return PacketNumberLen3
+	}
+	return PacketNumberLen4
+}