github.com/daeuniverse/quic-go@v0.0.0-20240413031024-943f218e0810/internal/wire/datagram_frame.go (about)

     1  package wire
     2  
     3  import (
     4  	"bytes"
     5  	"io"
     6  
     7  	"github.com/daeuniverse/quic-go/internal/protocol"
     8  	"github.com/daeuniverse/quic-go/quicvarint"
     9  )
    10  
    11  // MaxDatagramSize is the maximum size of a DATAGRAM frame (RFC 9221).
    12  // By setting it to a large value, we allow all datagrams that fit into a QUIC packet.
    13  // The value is chosen such that it can still be encoded as a 2 byte varint.
    14  // This is a var and not a const so it can be set in tests.
    15  var MaxDatagramSize protocol.ByteCount = 1200
    16  
    17  // A DatagramFrame is a DATAGRAM frame
    18  type DatagramFrame struct {
    19  	DataLenPresent bool
    20  	Data           []byte
    21  }
    22  
    23  func parseDatagramFrame(r *bytes.Reader, typ uint64, _ protocol.Version) (*DatagramFrame, error) {
    24  	f := &DatagramFrame{}
    25  	f.DataLenPresent = typ&0x1 > 0
    26  
    27  	var length uint64
    28  	if f.DataLenPresent {
    29  		var err error
    30  		len, err := quicvarint.Read(r)
    31  		if err != nil {
    32  			return nil, err
    33  		}
    34  		if len > uint64(r.Len()) {
    35  			return nil, io.EOF
    36  		}
    37  		length = len
    38  	} else {
    39  		length = uint64(r.Len())
    40  	}
    41  	f.Data = make([]byte, length)
    42  	if _, err := io.ReadFull(r, f.Data); err != nil {
    43  		return nil, err
    44  	}
    45  	return f, nil
    46  }
    47  
    48  func (f *DatagramFrame) Append(b []byte, _ protocol.Version) ([]byte, error) {
    49  	typ := uint8(0x30)
    50  	if f.DataLenPresent {
    51  		typ ^= 0b1
    52  	}
    53  	b = append(b, typ)
    54  	if f.DataLenPresent {
    55  		b = quicvarint.Append(b, uint64(len(f.Data)))
    56  	}
    57  	b = append(b, f.Data...)
    58  	return b, nil
    59  }
    60  
    61  // MaxDataLen returns the maximum data length
    62  func (f *DatagramFrame) MaxDataLen(maxSize protocol.ByteCount, version protocol.Version) protocol.ByteCount {
    63  	headerLen := protocol.ByteCount(1)
    64  	if f.DataLenPresent {
    65  		// pretend that the data size will be 1 bytes
    66  		// if it turns out that varint encoding the length will consume 2 bytes, we need to adjust the data length afterwards
    67  		headerLen++
    68  	}
    69  	if headerLen > maxSize {
    70  		return 0
    71  	}
    72  	maxDataLen := maxSize - headerLen
    73  	if f.DataLenPresent && quicvarint.Len(uint64(maxDataLen)) != 1 {
    74  		maxDataLen--
    75  	}
    76  	return maxDataLen
    77  }
    78  
    79  // Length of a written frame
    80  func (f *DatagramFrame) Length(_ protocol.Version) protocol.ByteCount {
    81  	length := 1 + protocol.ByteCount(len(f.Data))
    82  	if f.DataLenPresent {
    83  		length += quicvarint.Len(uint64(len(f.Data)))
    84  	}
    85  	return length
    86  }