add a function to tell if a packet is a 0-RTT packet

internal/wire/header.go

@@ -2,6 +2,7 @@ package wire
 
 import (
 	"bytes"
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"io"
@@ -43,6 +44,21 @@ func IsVersionNegotiationPacket(b []byte) bool {
 	return b[0]&0x80 > 0 && b[1] == 0 && b[2] == 0 && b[3] == 0 && b[4] == 0
 }
 
+// Is0RTTPacket says if this is a 0-RTT packet.
+// A packet sent with a version we don't understand can never be a 0-RTT packet.
+func Is0RTTPacket(b []byte) bool {
+	if len(b) < 5 {
+		return false
+	}
+	if b[0]&0x80 == 0 {
+		return false
+	}
+	if !protocol.IsSupportedVersion(protocol.SupportedVersions, protocol.VersionNumber(binary.BigEndian.Uint32(b[1:5]))) {
+		return false
+	}
+	return b[0]&0x30>>4 == 0x1
+}
+
 var ErrUnsupportedVersion = errors.New("unsupported version")
 
 // The Header is the version independent part of the header