/// <summary>
/// Reads one entry from the zip directory structure in the zip file.
/// </summary>
/// <param name="s">the stream from which to read.</param>
/// <returns>the entry read from the archive.</returns>
public static ZipDirEntry Read(Stream s)
{
int signature = Shared.ReadSignature(s);
// return null if this is not a local file header signature
if (IsNotValidSig(signature))
{
s.Seek(-4, SeekOrigin.Current);
// Getting "not a ZipDirEntry signature" here is not always wrong or an error.
// This can happen when walking through a zipfile. After the last ZipDirEntry,
// we expect to read an EndOfCentralDirectorySignature. When we get this is how we
// know we've reached the end of the central directory.
if (signature != ZipConstants.EndOfCentralDirectorySignature)
{
throw new Exception(string.Format(" ZipDirEntry::Read(): Bad signature ({0:X8}) at position 0x{1:X8}", signature, s.Position));
}
return(null);
}
var block = new byte[42];
int n = s.Read(block, 0, block.Length);
if (n != block.Length)
{
return(null);
}
int i = 0;
var zde = new ZipDirEntry();
zde.VersionMadeBy = (short)(block[i++] + block[i++] * 256);
zde.VersionNeeded = (short)(block[i++] + block[i++] * 256);
zde._BitField = (short)(block[i++] + block[i++] * 256);
zde.CompressionMethod = (short)(block[i++] + block[i++] * 256);
zde._LastModDateTime = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
zde._Crc32 = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
zde.CompressedSize = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
zde.UncompressedSize = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
zde.LastModified = Shared.PackedToDateTime(zde._LastModDateTime);
short filenameLength = (short)(block[i++] + block[i++] * 256);
short extraFieldLength = (short)(block[i++] + block[i++] * 256);
short commentLength = (short)(block[i++] + block[i++] * 256);
short diskNumber = (short)(block[i++] + block[i++] * 256);
zde._InternalFileAttrs = (short)(block[i++] + block[i++] * 256);
zde._ExternalFileAttrs = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
int Offset = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
block = new byte[filenameLength];
n = s.Read(block, 0, block.Length);
zde.FileName = Shared.StringFromBuffer(block, 0, block.Length);
if (extraFieldLength > 0)
{
zde._Extra = new byte[extraFieldLength];
n = s.Read(zde._Extra, 0, zde._Extra.Length);
}
if (commentLength > 0)
{
block = new byte[commentLength];
n = s.Read(block, 0, block.Length);
zde.Comment = Shared.StringFromBuffer(block, 0, block.Length);
}
return(zde);
}
private static bool ReadHeader(Stream s, ZipEntry ze)
{
int signature = Shared.ReadSignature(s);
// Return false if this is not a local file header signature.
if (IsNotValidSig(signature))
{
s.Seek(-4, 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);
}
var 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;
}
short filenameLength = (short)(block[i++] + block[i++] * 256);
short 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);
// when creating an entry by reading, the LocalFileName is the same as the FileNameInArchivre
ze.LocalFileName = ze.FileName;
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)
{
long posn = s.Position;
long SizeOfDataRead = 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, SeekOrigin.Begin);
}
return(true);
}
