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package dmpkg
import (
"bytes"
"fmt"
"github.com/lunixbochs/struc"
)
func DecodeExchange(data []byte) (exc DanmakuExchange, err error) {
if ln := len(data); ln < HeaderLength {
err = fmt.Errorf("incomplete datagram: length = %v < %v", ln, HeaderLength)
return
}
// unpack header
var exchangeHeader DanmakuExchangeHeader
err = struc.Unpack(bytes.NewReader(data[:HeaderLength]), &exchangeHeader)
if err != nil {
err = fmt.Errorf("cannot unpack exchange header: %w", err)
return
}
headerLength := exchangeHeader.HeaderLength
// validate header length, fail fast if not match
if headerLength != HeaderLength {
err = fmt.Errorf("invalid header length, "+
"the protocol implementation might be obsolete: %v != %v", headerLength, HeaderLength)
return
}
// special process
// TODO decouple this
// The server OpHeartbeatAck contains an extra 4-bytes header entry in the body, maybe a heat value
var body []byte
// copy body
body = make([]byte, exchangeHeader.Length-uint32(headerLength))
copy(body, data[headerLength:])
exc = DanmakuExchange{
DanmakuExchangeHeader: exchangeHeader,
Body: body,
}
return
}
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