private static bool ReadHeader(System.IO.Stream s, ZipEntry ze)
{
int signature = ZForge.Zip.Shared.ReadSignature(s);
// Return false if this is not a local file header signature.
if (ZipEntry.IsNotValidSig(signature))
{
s.Seek(-4, System.IO.SeekOrigin.Current); // unread the signature
// Getting "not a ZipEntry signature" is not always wrong or an error.
// This can happen when walking through a zipfile. After the last compressed entry,
// we expect to read a ZipDirEntry signature. When we get this is how we
// know we've reached the end of the compressed entries.
if (ZipDirEntry.IsNotValidSig(signature))
{
throw new Exception(String.Format(" ZipEntry::Read(): Bad signature ({0:X8}) at position 0x{1:X8}", signature, s.Position));
}
return false;
}
byte[] block = new byte[26];
int n = s.Read(block, 0, block.Length);
if (n != block.Length) return false;
int 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;
}
Int16 filenameLength = (short)(block[i++] + block[i++] * 256);
Int16 extraFieldLength = (short)(block[i++] + block[i++] * 256);
block = new byte[filenameLength];
n = s.Read(block, 0, block.Length);
ze._FileNameInArchive = ZForge.Zip.Shared.StringFromBuffer(block, 0, block.Length);
// when creating an entry by reading, the LocalFileName is the same as the FileNameInArchivre
ze._LocalFileName = ze._FileNameInArchive;
ze._Extra = new byte[extraFieldLength];
n = s.Read(ze._Extra, 0, ze._Extra.Length);
// transform the time data into something usable
ze._LastModified = ZForge.Zip.Shared.PackedToDateTime(ze._LastModDateTime);
// actually get the compressed size and CRC if necessary
if ((ze._BitField & 0x0008) == 0x0008)
{
long posn = s.Position;
long SizeOfDataRead = ZForge.Zip.Shared.FindSignature(s, ZipConstants.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, System.IO.SeekOrigin.Begin);
}
return true;
}
