/// <summary>
/// Computes the CRC32 hash of a given stream
/// </summary>
/// <param name="data"></param>
/// <returns>CRC32 hash, as a string</returns>
/// <remarks></remarks>
private static string ComputeCRC32Hash(Stream data)
{
var crc = Crc32.Crc(data);
var crcString = string.Format("{0:X8}", crc);
return(crcString);
}
/// <inheritdoc />
public override void Write(byte[] buffer, int offset, int count)
{
// Implementation caveat:
// The .NET GZipStream/DeflateStream implementation, as of .NET 4.7.1, writes the entire header at once.
// This method depends on that functionality.
if (Position == 0 && count >= 10)
{
var modifiedBuffer = new List <byte>();
var i = offset;
modifiedBuffer.Add(buffer[i++]); // should be 31/0x1f (GZIP constant)
modifiedBuffer.Add(buffer[i++]); // should be 139/0x8b (GZIP constant)
modifiedBuffer.Add(buffer[i++]); // should be 8 (deflate)
var flags = (GzipFlags)buffer[i++];
var writeFileName = false;
if (!flags.HasFlag(GzipFlags.FNAME) && !string.IsNullOrWhiteSpace(InternalFilename))
{
writeFileName = true;
flags = flags | GzipFlags.FNAME;
}
var writeComment = false;
if (!flags.HasFlag(GzipFlags.FCOMMENT) && !string.IsNullOrWhiteSpace(InternalComment))
{
writeComment = true;
flags = flags | GzipFlags.FCOMMENT;
}
var addingHeaderCrc = true;
if (AddOrCheckHeaderCrc)
{
if (flags.HasFlag(GzipFlags.FHCRC))
{
addingHeaderCrc = false;
}
flags = flags | GzipFlags.FHCRC;
}
modifiedBuffer.Add((byte)flags);
var unixTimeStart = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
if (InternalLastModified.ToUniversalTime() > unixTimeStart)
{
i += 4;
var utc = InternalLastModified.ToUniversalTime();
var timestampUnix = (long)utc.Subtract(unixTimeStart).TotalSeconds;
modifiedBuffer.Add((byte)((timestampUnix & 0x000000FF)));
modifiedBuffer.Add((byte)((timestampUnix & 0x0000FF00) >> 8));
modifiedBuffer.Add((byte)((timestampUnix & 0x00FF0000) >> 16));
modifiedBuffer.Add((byte)((timestampUnix & 0xFF000000) >> 24));
}
else
{
modifiedBuffer.Add(buffer[i++]);
modifiedBuffer.Add(buffer[i++]);
modifiedBuffer.Add(buffer[i++]);
modifiedBuffer.Add(buffer[i++]);
}
modifiedBuffer.Add(buffer[i++]); // Extra Fields byte
modifiedBuffer.Add(buffer[i++]); // OS byte
if (flags.HasFlag(GzipFlags.FEXTRA))
{
int length = buffer[i];
modifiedBuffer.Add(buffer[i++]);
length += buffer[i] << 8;
modifiedBuffer.Add(buffer[i++]);
for (var j = 0; j < length && i < offset + count; j++)
{
modifiedBuffer.Add(buffer[i++]);
}
}
var iso8859Encoding = Encoding.GetEncoding("ISO-8859-1");
if (writeFileName)
{
var bytes = iso8859Encoding.GetBytes(InternalFilename);
modifiedBuffer.AddRange(bytes);
modifiedBuffer.Add(0); // add zero-byte terminator
}
if (writeComment)
{
var bytes = iso8859Encoding.GetBytes(InternalComment);
modifiedBuffer.AddRange(bytes);
modifiedBuffer.Add(0); // add zero-byte terminator
}
if (flags.HasFlag(GzipFlags.FHCRC))
{
if (!addingHeaderCrc)
{
i += 2;
}
// Least two significant bytes of the CRC32 for all bytes of the gzip header, up to (but not including) the CRC16
var crc = Crc32.Crc(modifiedBuffer.ToArray());
modifiedBuffer.Add((byte)(crc & 0x000000FF));
modifiedBuffer.Add((byte)((crc & 0x0000FF00) >> 8));
HeaderCrc = (ushort)crc;
}
for (var j = i; j < offset + count; j++)
{
modifiedBuffer.Add(buffer[j]);
}
BaseStream.Write(modifiedBuffer.ToArray(), 0, modifiedBuffer.Count);
}
else
{
BaseStream.Write(buffer, offset, count);
}
}
private bool ReadMetadata()
{
if (!CanSeek)
{
// Can't seek, so don't read metadata, because it will cause the GZipStream to fail.
HeaderRead = false;
return(false);
}
// ReSharper disable UnusedVariable
var id1 = BaseStream.ReadByte(); // should be 31/0x1f (GZIP constant)
var id2 = BaseStream.ReadByte(); // should be 139/0x8b (GZIP constant)
var compressionMethod = BaseStream.ReadByte(); // should be 8 (deflate)
// ReSharper restore UnusedVariable
// ReSharper disable CommentTypo
// Bit flags:
// &0x1 = FTEXT (probably ASCII)
// &0x2 = CRC16 for gzip header present
// &0x4 = FEXTRA (extra fields)
// &0x8 = FNAME (name)
// &0x10 = FCOMMENT (comment)
// &0x20, &0x40, &0x80 = reserved
var flags = (GzipFlags)BaseStream.ReadByte();
// ReSharper restore CommentTypo
uint timestamp = 0;
for (var x = 0; x < 4; x++)
{
timestamp += (uint)BaseStream.ReadByte() << (8 * x);
}
// If timestamp == 0, no timestamp is available; use the compressed file timestamp
if (timestamp > 0)
{
InternalLastModified = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc).AddSeconds(timestamp); // Gzip times are stored in universal time
}
else
{
InternalLastModified = DateTime.MinValue;
}
// ReSharper disable UnusedVariable
var extraFlags = BaseStream.ReadByte();
var osId = BaseStream.ReadByte();
// ReSharper restore UnusedVariable
if (flags.HasFlag(GzipFlags.FEXTRA))
{
var length = BaseStream.ReadByte();
length += BaseStream.ReadByte() << 8;
BaseStream.Seek(length, SeekOrigin.Current);
}
// ReSharper disable CommentTypo
/*
* FNAME and FCOMMENT both must be written (and read) as ISO-8859-1 (LATIN-1) characters
* FNAME is filename only (no path), and if written on case-insensitive file system, lower-case only,
*/
// ReSharper restore CommentTypo
var iso8859Encoding = Encoding.GetEncoding("ISO-8859-1");
if (flags.HasFlag(GzipFlags.FNAME))
{
var nameBytes = new List <byte>();
int c;
while ((c = BaseStream.ReadByte()) > 0)
{
nameBytes.Add((byte)c);
}
InternalFilename = iso8859Encoding.GetString(nameBytes.ToArray());
}
if (flags.HasFlag(GzipFlags.FCOMMENT))
{
var commentBytes = new List <byte>();
int c;
while ((c = BaseStream.ReadByte()) > 0)
{
commentBytes.Add((byte)c);
}
InternalComment = iso8859Encoding.GetString(commentBytes.ToArray());
}
var headerCorrupted = false;
if (flags.HasFlag(GzipFlags.FHCRC))
{
var headerCrcPosition = (int)BaseStream.Position;
// Applies to all bytes prior to this item
var headerCrcBytes = new byte[2];
headerCrcBytes[0] = (byte)BaseStream.ReadByte();
headerCrcBytes[1] = (byte)BaseStream.ReadByte();
HeaderCrc = (ushort)(headerCrcBytes[0] + (headerCrcBytes[1] << 8));
BaseStream.Seek(0, SeekOrigin.Begin);
var bytes = new byte[headerCrcPosition];
BaseStream.Read(bytes, 0, headerCrcPosition);
var crc = Crc32.Crc(bytes);
var crc16 = (ushort)crc;
headerCorrupted = HeaderCrc != crc16;
}
// Then compressed data
// ReSharper disable once CommentTypo
// Then 4 CRC32 bytes, then 4 ISIZE bytes
// Reset stream position before decompressing file
BaseStream.Seek(0, SeekOrigin.Begin);
HeaderRead = true;
return(headerCorrupted);
}