private static bool ReadHeader(Stream s, ZipEntry ze)
{
var signature = Shared.ReadSignature(s);
// return null if this is not a local file header signature
if (SignatureIsNotValid(signature))
{
s.Seek(-4, SeekOrigin.Current);
if (ze._Debug)
{
Console.WriteLine(" ZipEntry::Read(): Bad signature ({0:X8}) at position {1}", signature,
s.Position);
}
return(false);
}
var block = new byte[26];
var n = s.Read(block, 0, block.Length);
if (n != block.Length)
{
return(false);
}
var i = 0;
ze.VersionNeeded = (short)(block[i++] + block[i++] * 256);
ze.BitField = (short)(block[i++] + block[i++] * 256);
ze.CompressionMethod = (short)(block[i++] + block[i++] * 256);
ze._LastModDateTime = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
// the PKZIP spec says that if bit 3 is set (0x0008), then the CRC, Compressed size, and uncompressed size
// come directly after the file data. The only way to find it is to scan the zip archive for the signature of
// the Data Descriptor, and presume that that signature does not appear in the (compressed) data of the compressed file.
if ((ze.BitField & 0x0008) != 0x0008)
{
ze._Crc32 = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
ze.CompressedSize = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 +
block[i++] * 256 * 256 * 256;
ze.UncompressedSize = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 +
block[i++] * 256 * 256 * 256;
}
else
{
// the CRC, compressed size, and uncompressed size are stored later in the stream.
// here, we advance the pointer.
i += 12;
}
var filenameLength = (short)(block[i++] + block[i++] * 256);
var extraFieldLength = (short)(block[i++] + block[i++] * 256);
block = new byte[filenameLength];
n = s.Read(block, 0, block.Length);
ze.FileName = Shared.StringFromBuffer(block, 0, block.Length);
ze._Extra = new byte[extraFieldLength];
n = s.Read(ze._Extra, 0, ze._Extra.Length);
// transform the time data into something usable
ze.LastModified = Shared.PackedToDateTime(ze._LastModDateTime);
// actually get the compressed size and CRC if necessary
if ((ze.BitField & 0x0008) == 0x0008)
{
var posn = s.Position;
var SizeOfDataRead = Shared.FindSignature(s, ZipEntryDataDescriptorSignature);
if (SizeOfDataRead == -1)
{
return(false);
}
// read 3x 4-byte fields (CRC, Compressed Size, Uncompressed Size)
block = new byte[12];
n = s.Read(block, 0, block.Length);
if (n != 12)
{
return(false);
}
i = 0;
ze._Crc32 = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
ze.CompressedSize = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 +
block[i++] * 256 * 256 * 256;
ze.UncompressedSize = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 +
block[i++] * 256 * 256 * 256;
if (SizeOfDataRead != ze.CompressedSize)
{
throw new Exception("Data format error (bit 3 is set)");
}
// seek back to previous position, to read file data
s.Seek(posn, SeekOrigin.Begin);
}
return(true);
}
