github.com/sagernet/quic-go@v0.43.1-beta.1/internal/wire/version_negotiation.go (about)

     1  package wire
     2  
     3  import (
     4  	"crypto/rand"
     5  	"encoding/binary"
     6  	"errors"
     7  
     8  	"github.com/sagernet/quic-go/internal/protocol"
     9  )
    10  
    11  // ParseVersionNegotiationPacket parses a Version Negotiation packet.
    12  func ParseVersionNegotiationPacket(b []byte) (dest, src protocol.ArbitraryLenConnectionID, _ []protocol.Version, _ error) {
    13  	n, dest, src, err := ParseArbitraryLenConnectionIDs(b)
    14  	if err != nil {
    15  		return nil, nil, nil, err
    16  	}
    17  	b = b[n:]
    18  	if len(b) == 0 {
    19  		//nolint:stylecheck
    20  		return nil, nil, nil, errors.New("Version Negotiation packet has empty version list")
    21  	}
    22  	if len(b)%4 != 0 {
    23  		//nolint:stylecheck
    24  		return nil, nil, nil, errors.New("Version Negotiation packet has a version list with an invalid length")
    25  	}
    26  	versions := make([]protocol.Version, len(b)/4)
    27  	for i := 0; len(b) > 0; i++ {
    28  		versions[i] = protocol.Version(binary.BigEndian.Uint32(b[:4]))
    29  		b = b[4:]
    30  	}
    31  	return dest, src, versions, nil
    32  }
    33  
    34  // ComposeVersionNegotiation composes a Version Negotiation
    35  func ComposeVersionNegotiation(destConnID, srcConnID protocol.ArbitraryLenConnectionID, versions []protocol.Version) []byte {
    36  	greasedVersions := protocol.GetGreasedVersions(versions)
    37  	expectedLen := 1 /* type byte */ + 4 /* version field */ + 1 /* dest connection ID length field */ + destConnID.Len() + 1 /* src connection ID length field */ + srcConnID.Len() + len(greasedVersions)*4
    38  	buf := make([]byte, 1+4 /* type byte and version field */, expectedLen)
    39  	_, _ = rand.Read(buf[:1]) // ignore the error here. It is not critical to have perfect random here.
    40  	// Setting the "QUIC bit" (0x40) is not required by the RFC,
    41  	// but it allows clients to demultiplex QUIC with a long list of other protocols.
    42  	// See RFC 9443 and https://mailarchive.ietf.org/arch/msg/quic/oR4kxGKY6mjtPC1CZegY1ED4beg/ for details.
    43  	buf[0] |= 0xc0
    44  	// The next 4 bytes are left at 0 (version number).
    45  	buf = append(buf, uint8(destConnID.Len()))
    46  	buf = append(buf, destConnID.Bytes()...)
    47  	buf = append(buf, uint8(srcConnID.Len()))
    48  	buf = append(buf, srcConnID.Bytes()...)
    49  	for _, v := range greasedVersions {
    50  		buf = binary.BigEndian.AppendUint32(buf, uint32(v))
    51  	}
    52  	return buf
    53  }