1 files changed, 72 insertions, 0 deletions
diff --git a/src/vendor/golang.org/x/net/quic/packet_number.go b/src/vendor/golang.org/x/net/quic/packet_number.go
new file mode 100644
index 0000000000..9e9f0ad003
--- /dev/null
+++ b/src/vendor/golang.org/x/net/quic/packet_number.go
@@ -0,0 +1,72 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package quic
+
+// A packetNumber is a QUIC packet number.
+// Packet numbers are integers in the range [0, 2^62-1].
+//
+// https://www.rfc-editor.org/rfc/rfc9000.html#section-12.3
+type packetNumber int64
+
+const maxPacketNumber = 1<<62 - 1 // https://www.rfc-editor.org/rfc/rfc9000.html#section-17.1-1
+
+// decodePacketNumber decodes a truncated packet number, given
+// the largest acknowledged packet number in this number space,
+// the truncated number received in a packet, and the size of the
+// number received in bytes.
+//
+// https://www.rfc-editor.org/rfc/rfc9000.html#section-17.1
+// https://www.rfc-editor.org/rfc/rfc9000.html#section-a.3
+func decodePacketNumber(largest, truncated packetNumber, numLenInBytes int) packetNumber {
+	expected := largest + 1
+	win := packetNumber(1) << (uint(numLenInBytes) * 8)
+	hwin := win / 2
+	mask := win - 1
+	candidate := (expected &^ mask) | truncated
+	if candidate <= expected-hwin && candidate < (1<<62)-win {
+		return candidate + win
+	}
+	if candidate > expected+hwin && candidate >= win {
+		return candidate - win
+	}
+	return candidate
+}
+
+// appendPacketNumber appends an encoded packet number to b.
+// The packet number must be larger than the largest acknowledged packet number.
+// When no packets have been acknowledged yet, largestAck is -1.
+//
+// https://www.rfc-editor.org/rfc/rfc9000.html#section-17.1-5
+func appendPacketNumber(b []byte, pnum, largestAck packetNumber) []byte {
+	switch packetNumberLength(pnum, largestAck) {
+	case 1:
+		return append(b, byte(pnum))
+	case 2:
+		return append(b, byte(pnum>>8), byte(pnum))
+	case 3:
+		return append(b, byte(pnum>>16), byte(pnum>>8), byte(pnum))
+	default:
+		return append(b, byte(pnum>>24), byte(pnum>>16), byte(pnum>>8), byte(pnum))
+	}
+}
+
+// packetNumberLength returns the minimum length, in bytes, needed to encode
+// a packet number given the largest acknowledged packet number.
+// The packet number must be larger than the largest acknowledged packet number.
+//
+// https://www.rfc-editor.org/rfc/rfc9000.html#section-17.1-5
+func packetNumberLength(pnum, largestAck packetNumber) int {
+	d := pnum - largestAck
+	switch {
+	case d < 0x80:
+		return 1
+	case d < 0x8000:
+		return 2
+	case d < 0x800000:
+		return 3
+	default:
+		return 4
+	}
+}