make the protocol package internal

internal/protocol/packet_number.go

@@ -0,0 +1,56 @@
+package protocol
+
+// InferPacketNumber calculates the packet number based on the received packet number, its length and the last seen packet number
+func InferPacketNumber(packetNumberLength PacketNumberLen, lastPacketNumber PacketNumber, wirePacketNumber PacketNumber) PacketNumber {
+	epochDelta := PacketNumber(1) << (uint8(packetNumberLength) * 8)
+	epoch := lastPacketNumber & ^(epochDelta - 1)
+	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
+}
+
+// GetPacketNumberLengthForPublicHeader 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 GetPacketNumberLengthForPublicHeader(packetNumber PacketNumber, leastUnacked PacketNumber) PacketNumberLen {
+	diff := uint64(packetNumber - leastUnacked)
+	if diff < (2 << (uint8(PacketNumberLen2)*8 - 2)) {
+		return PacketNumberLen2
+	}
+	if diff < (2 << (uint8(PacketNumberLen4)*8 - 2)) {
+		return PacketNumberLen4
+	}
+	// we do not check if there are less than 2^46 packets in flight, since flow control and congestion control will limit this number *a lot* sooner
+	return PacketNumberLen6
+}
+
+// GetPacketNumberLength gets the minimum length needed to fully represent the packet number
+func GetPacketNumberLength(packetNumber PacketNumber) PacketNumberLen {
+	if packetNumber < (1 << (uint8(PacketNumberLen1) * 8)) {
+		return PacketNumberLen1
+	}
+	if packetNumber < (1 << (uint8(PacketNumberLen2) * 8)) {
+		return PacketNumberLen2
+	}
+	if packetNumber < (1 << (uint8(PacketNumberLen4) * 8)) {
+		return PacketNumberLen4
+	}
+	return PacketNumberLen6
+}