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package wire
import (
"io"
"github.com/quic-go/quic-go/internal/protocol"
"github.com/quic-go/quic-go/quicvarint"
)
// MaxDatagramSize is the maximum size of a DATAGRAM frame (RFC 9221).
// By setting it to a large value, we allow all datagrams that fit into a QUIC packet.
// The value is chosen such that it can still be encoded as a 2 byte varint.
// This is a var and not a const so it can be set in tests.
var MaxDatagramSize protocol.ByteCount = 16383
// A DatagramFrame is a DATAGRAM frame
type DatagramFrame struct {
DataLenPresent bool
Data []byte
}
func parseDatagramFrame(b []byte, typ FrameType, _ protocol.Version) (*DatagramFrame, int, error) {
startLen := len(b)
f := &DatagramFrame{}
f.DataLenPresent = uint64(typ)&0x1 > 0
var length uint64
if f.DataLenPresent {
var err error
var l int
length, l, err = quicvarint.Parse(b)
if err != nil {
return nil, 0, replaceUnexpectedEOF(err)
}
b = b[l:]
if length > uint64(len(b)) {
return nil, 0, io.EOF
}
} else {
length = uint64(len(b))
}
f.Data = make([]byte, length)
copy(f.Data, b)
return f, startLen - len(b) + int(length), nil
}
func (f *DatagramFrame) Append(b []byte, _ protocol.Version) ([]byte, error) {
typ := uint8(0x30)
if f.DataLenPresent {
typ ^= 0b1
}
b = append(b, typ)
if f.DataLenPresent {
b = quicvarint.Append(b, uint64(len(f.Data)))
}
b = append(b, f.Data...)
return b, nil
}
// MaxDataLen returns the maximum data length
func (f *DatagramFrame) MaxDataLen(maxSize protocol.ByteCount, version protocol.Version) protocol.ByteCount {
headerLen := protocol.ByteCount(1)
if f.DataLenPresent {
// pretend that the data size will be 1 bytes
// if it turns out that varint encoding the length will consume 2 bytes, we need to adjust the data length afterwards
headerLen++
}
if headerLen > maxSize {
return 0
}
maxDataLen := maxSize - headerLen
if f.DataLenPresent && quicvarint.Len(uint64(maxDataLen)) != 1 {
maxDataLen--
}
return maxDataLen
}
// Length of a written frame
func (f *DatagramFrame) Length(_ protocol.Version) protocol.ByteCount {
length := 1 + protocol.ByteCount(len(f.Data))
if f.DataLenPresent {
length += protocol.ByteCount(quicvarint.Len(uint64(len(f.Data))))
}
return length
}
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