/// <summary>
/// Reads an ICU data header, checks the data format, and returns the data version.
/// </summary>
/// <remarks>
/// Assumes that the <see cref="ByteBuffer"/> position is 0 on input.
/// <para/>
/// The buffer byte order is set according to the data.
/// The buffer position is advanced past the header (including UDataInfo and comment).
/// <para/>
/// See C++ ucmndata.h and unicode/udata.h.
/// </remarks>
/// <returns>dataVersion</returns>
/// <exception cref="IOException">If this is not a valid ICU data item of the expected dataFormat.</exception>
public static int ReadHeader(ByteBuffer bytes, int dataFormat, IAuthenticate authenticate)
{
Debug.Assert(bytes != null && bytes.Position == 0);
byte magic1 = bytes.Get(2);
byte magic2 = bytes.Get(3);
if (magic1 != MAGIC1 || magic2 != MAGIC2)
{
throw new IOException(MAGIC_NUMBER_AUTHENTICATION_FAILED_);
}
byte isBigEndian = bytes.Get(8);
byte charsetFamily = bytes.Get(9);
byte sizeofUChar = bytes.Get(10);
if (isBigEndian < 0 || 1 < isBigEndian ||
charsetFamily != CHAR_SET_ || sizeofUChar != CHAR_SIZE_)
{
throw new IOException(HEADER_AUTHENTICATION_FAILED_);
}
bytes.Order = isBigEndian != 0 ? ByteOrder.BIG_ENDIAN : ByteOrder.LITTLE_ENDIAN;
int headerSize = bytes.GetChar(0);
int sizeofUDataInfo = bytes.GetChar(4);
if (sizeofUDataInfo < 20 || headerSize < (sizeofUDataInfo + 4))
{
throw new IOException("Internal Error: Header size error");
}
// TODO: Change Authenticate to take int major, int minor, int milli, int micro
// to avoid array allocation.
byte[] formatVersion = new byte[] {
bytes.Get(16), bytes.Get(17), bytes.Get(18), bytes.Get(19)
};
if (bytes.Get(12) != (byte)(dataFormat >> 24) ||
bytes.Get(13) != (byte)(dataFormat >> 16) ||
bytes.Get(14) != (byte)(dataFormat >> 8) ||
bytes.Get(15) != (byte)dataFormat ||
(authenticate != null && !authenticate.IsDataVersionAcceptable(formatVersion)))
{
// "; data format %02x%02x%02x%02x, format version %d.%d.%d.%d"
throw new IOException(HEADER_AUTHENTICATION_FAILED_ +
string.Format("; data format {0:x2}{1:x2}{2:x2}{3:x2}, format version {4}.{5}.{6}.{7}",
bytes.Get(12), bytes.Get(13), bytes.Get(14), bytes.Get(15),
formatVersion[0] & 0xff, formatVersion[1] & 0xff,
formatVersion[2] & 0xff, formatVersion[3] & 0xff));
}
bytes.Position = headerSize;
return // dataVersion
((bytes.Get(20) << 24) |
((bytes.Get(21) & 0xff) << 16) |
((bytes.Get(22) & 0xff) << 8) |
(bytes.Get(23) & 0xff));
}
