TUN-8638: Add datagram v3 serializers and deserializers

Closes TUN-8638

quic/v3/request.go

@@ -0,0 +1,72 @@
+package v3
+
+import (
+	"encoding/binary"
+	"errors"
+)
+
+const (
+	datagramRequestIdLen = 16
+)
+
+var (
+	// ErrInvalidRequestIDLen is returned when the provided request id can not be parsed from the provided byte slice.
+	ErrInvalidRequestIDLen error = errors.New("invalid request id length provided")
+	// ErrInvalidPayloadDestLen is returned when the provided destination byte slice cannot fit the whole request id.
+	ErrInvalidPayloadDestLen error = errors.New("invalid payload size provided")
+)
+
+// RequestID is the request-id-v2 identifier, it is used to distinguish between specific flows or sessions proxied
+// from the edge to cloudflared.
+type RequestID uint128
+
+type uint128 struct {
+	hi uint64
+	lo uint64
+}
+
+// RequestIDFromSlice reads a request ID from a byte slice.
+func RequestIDFromSlice(data []byte) (RequestID, error) {
+	if len(data) != datagramRequestIdLen {
+		return RequestID{}, ErrInvalidRequestIDLen
+	}
+
+	return RequestID{
+		hi: binary.BigEndian.Uint64(data[:8]),
+		lo: binary.BigEndian.Uint64(data[8:]),
+	}, nil
+}
+
+// Compare returns an integer comparing two IPs.
+// The result will be 0 if id == id2, -1 if id < id2, and +1 if id > id2.
+// The definition of "less than" is the same as the [RequestID.Less] method.
+func (id RequestID) Compare(id2 RequestID) int {
+	hi1, hi2 := id.hi, id2.hi
+	if hi1 < hi2 {
+		return -1
+	}
+	if hi1 > hi2 {
+		return 1
+	}
+	lo1, lo2 := id.lo, id2.lo
+	if lo1 < lo2 {
+		return -1
+	}
+	if lo1 > lo2 {
+		return 1
+	}
+	return 0
+}
+
+// Less reports whether id sorts before id2.
+func (id RequestID) Less(id2 RequestID) bool { return id.Compare(id2) == -1 }
+
+// MarshalBinaryTo writes the id to the provided destination byte slice; the byte slice must be of at least size 16.
+func (id RequestID) MarshalBinaryTo(data []byte) error {
+	if len(data) < datagramRequestIdLen {
+		return ErrInvalidPayloadDestLen
+	}
+	binary.BigEndian.PutUint64(data[:8], id.hi)
+	binary.BigEndian.PutUint64(data[8:], id.lo)
+	return nil
+}