func GetMinAcraStructLength() int {
	return len(TagBegin) + KeyBlockLength + DataLengthSize
}
GetMinAcraStructLength returns minimal length of AcraStruct
because in golang we can't declare byte array as constant we need to calculate length of TagBegin in runtime
or hardcode as constant and maintain len(TagBegin) == CONST_VALUE
package base
import (
	"bytes"
	"encoding/binary"
	"errors"
	"github.com/cossacklabs/acra/keystore"
	"github.com/cossacklabs/acra/utils"
	"github.com/cossacklabs/themis/gothemis/cell"
	"github.com/cossacklabs/themis/gothemis/keys"
	"github.com/cossacklabs/themis/gothemis/message"
)
func GetDataLengthFromAcraStruct(data []byte) int {
	dataLengthBlock := data[GetMinAcraStructLength()-DataLengthSize : GetMinAcraStructLength()]
	return int(binary.LittleEndian.Uint64(dataLengthBlock))
}