analyzer: make http3/quic handling more reliable

analyzer/udp/internal/quic/header.go

@@ -9,6 +9,8 @@ import (
 	"github.com/quic-go/quic-go/quicvarint"
 )
 
+var ErrNotInitialPacket = errors.New("not initial packet")
+
 // The Header represents a QUIC header.
 type Header struct {
 	Type             uint8
@@ -36,6 +38,9 @@ func parseLongHeader(b *bytes.Reader) (*Header, error) {
 	if err != nil {
 		return nil, err
 	}
+	if !isLongHeader(typeByte) {
+		return nil, ErrNotInitialPacket
+	}
 	h := &Header{}
 	ver, err := beUint32(b)
 	if err != nil {
@@ -66,18 +71,19 @@ func parseLongHeader(b *bytes.Reader) (*Header, error) {
 	if h.Version == V2 {
 		initialPacketType = 0b01
 	}
-	if (typeByte >> 4 & 0b11) == initialPacketType {
-		tokenLen, err := quicvarint.Read(b)
-		if err != nil {
-			return nil, err
-		}
-		if tokenLen > uint64(b.Len()) {
-			return nil, io.EOF
-		}
-		h.Token = make([]byte, tokenLen)
-		if _, err := io.ReadFull(b, h.Token); err != nil {
-			return nil, err
-		}
+	if (typeByte>>4)&0b11 != initialPacketType {
+		return nil, ErrNotInitialPacket
+	}
+	tokenLen, err := quicvarint.Read(b)
+	if err != nil {
+		return nil, err
+	}
+	if tokenLen > uint64(b.Len()) {
+		return nil, io.EOF
+	}
+	h.Token = make([]byte, tokenLen)
+	if _, err := io.ReadFull(b, h.Token); err != nil {
+		return nil, err
 	}
 
 	pl, err := quicvarint.Read(b)