handle the packet length before parsing the extended header

internal/wire/extended_header.go

@@ -30,7 +30,7 @@ func (h *ExtendedHeader) parse(b *bytes.Reader, v protocol.VersionNumber) (*Exte
 	if err != nil {
 		return nil, err
 	}
-	if _, err := b.Seek(int64(h.len)-1, io.SeekCurrent); err != nil {
+	if _, err := b.Seek(int64(h.ParsedLen())-1, io.SeekCurrent); err != nil {
 		return nil, err
 	}
 	if h.IsLongHeader {

internal/wire/header.go

@@ -24,8 +24,8 @@ type Header struct {
 	SupportedVersions    []protocol.VersionNumber // sent in a Version Negotiation Packet
 	OrigDestConnectionID protocol.ConnectionID    // sent in the Retry packet
 
-	typeByte byte
-	len      int // how many bytes were read while parsing this header
+	typeByte  byte
+	parsedLen protocol.ByteCount // how many bytes were read while parsing this header
 }
 
 // ParseHeader parses the header.
@@ -39,7 +39,7 @@ func ParseHeader(b *bytes.Reader, shortHeaderConnIDLen int) (*Header, error) {
 	if err != nil {
 		return nil, err
 	}
-	h.len = startLen - b.Len()
+	h.parsedLen = protocol.ByteCount(startLen - b.Len())
 	return h, nil
 }
 
@@ -171,6 +171,11 @@ func (h *Header) IsVersionNegotiation() bool {
 	return h.IsLongHeader && h.Version == 0
 }
 
+// ParsedLen returns the number of bytes that were consumed when parsing the header
+func (h *Header) ParsedLen() protocol.ByteCount {
+	return h.parsedLen
+}
+
 // ParseExtended parses the version dependent part of the header.
 // The Reader has to be set such that it points to the first byte of the header.
 func (h *Header) ParseExtended(b *bytes.Reader, ver protocol.VersionNumber) (*ExtendedHeader, error) {

internal/wire/header_test.go

@@ -74,6 +74,7 @@ var _ = Describe("Header Parsing", func() {
 			data = append(data, encodeVarInt(6)...)      // token length
 			data = append(data, []byte("foobar")...)     // token
 			data = append(data, encodeVarInt(0x1337)...) // length
+			hdrLen := len(data)
 			data = append(data, []byte{0, 0, 0xbe, 0xef}...)
 
 			hdr, err := ParseHeader(bytes.NewReader(data), 0)
@@ -92,6 +93,7 @@ var _ = Describe("Header Parsing", func() {
 			Expect(extHdr.PacketNumber).To(Equal(protocol.PacketNumber(0xbeef)))
 			Expect(extHdr.PacketNumberLen).To(Equal(protocol.PacketNumberLen4))
 			Expect(b.Len()).To(BeZero())
+			Expect(hdr.ParsedLen()).To(BeEquivalentTo(hdrLen))
 		})
 
 		It("errors if 0x40 is not set", func() {