Class ZlibCodec¶
Namespace: OfficeOpenXml.Packaging.Ionic.Zlib
Assembly: EPPlus.dll
Encoder and Decoder for ZLIB and DEFLATE (IETF RFC1950 and RFC1951).
Inheritance¶
Inherited Members¶
object.Equals(object?, object?)
object.Equals(object?)
object.GetHashCode()
object.GetType()
object.ReferenceEquals(object?, object?)
object.ToString()
Remarks¶
This class compresses and decompresses data according to the Deflate algorithm and optionally, the ZLIB format, as documented in RFC 1950 - ZLIB and RFC 1951 - DEFLATE.
Constructors¶
ZlibCodec()¶
Create a ZlibCodec.
Remarks¶
If you use this default constructor, you will later have to explicitly call InitializeInflate() or InitializeDeflate() before using the ZlibCodec to compress or decompress.
ZlibCodec(CompressionMode)¶
Create a ZlibCodec that either compresses or decompresses.
Parameters¶
mode CompressionMode
Indicates whether the codec should compress (deflate) or decompress (inflate).
Fields¶
AvailableBytesIn¶
The number of bytes available in the InputBuffer, starting at NextIn.
Field Value¶
Remarks¶
Generally you should set this to InputBuffer.Length before the first Inflate() or Deflate() call. The class will update this number as calls to Inflate/Deflate are made.
AvailableBytesOut¶
The number of bytes available in the OutputBuffer, starting at NextOut.
Field Value¶
Remarks¶
Generally you should set this to OutputBuffer.Length before the first Inflate() or Deflate() call. The class will update this number as calls to Inflate/Deflate are made.
CompressLevel¶
The compression level to use in this codec. Useful only in compression mode.
Field Value¶
InputBuffer¶
The buffer from which data is taken.
Field Value¶
byte[]
Message¶
used for diagnostics, when something goes wrong!
Field Value¶
NextIn¶
An index into the InputBuffer array, indicating where to start reading.
Field Value¶
NextOut¶
An index into the OutputBuffer array, indicating where to start writing.
Field Value¶
OutputBuffer¶
Buffer to store output data.
Field Value¶
byte[]
Strategy¶
The compression strategy to use.
Field Value¶
Remarks¶
This is only effective in compression. The theory offered by ZLIB is that different strategies could potentially produce significant differences in compression behavior for different data sets. Unfortunately I don't have any good recommendations for how to set it differently. When I tested changing the strategy I got minimally different compression performance. It's best to leave this property alone if you don't have a good feel for it. Or, you may want to produce a test harness that runs through the different strategy options and evaluates them on different file types. If you do that, let me know your results.
TotalBytesIn¶
Total number of bytes read so far, through all calls to Inflate()/Deflate().
Field Value¶
TotalBytesOut¶
Total number of bytes written to the output so far, through all calls to Inflate()/Deflate().
Field Value¶
WindowBits¶
The number of Window Bits to use.
Field Value¶
Remarks¶
This gauges the size of the sliding window, and hence the compression effectiveness as well as memory consumption. It's best to just leave this setting alone if you don't know what it is. The maximum value is 15 bits, which implies a 32k window.
Properties¶
Adler32¶
The Adler32 checksum on the data transferred through the codec so far. You probably don't need to look at this.
Property Value¶
Methods¶
Deflate(FlushType)¶
Deflate one batch of data.
Parameters¶
flush FlushType
whether to flush all data as you deflate. Generally you will want to use Z_NO_FLUSH here, in a series of calls to Deflate(), and then call EndDeflate() to flush everything.
Returns¶
Z_OK if all goes well.
Examples¶
private void DeflateBuffer(CompressionLevel level)
{
int bufferSize = 1024;
byte[] buffer = new byte[bufferSize];
ZlibCodec compressor = new ZlibCodec();
Console.WriteLine("\n============================================");
Console.WriteLine("Size of Buffer to Deflate: {0} bytes.", UncompressedBytes.Length);
MemoryStream ms = new MemoryStream();
int rc = compressor.InitializeDeflate(level);
compressor.InputBuffer = UncompressedBytes;
compressor.NextIn = 0;
compressor.AvailableBytesIn = UncompressedBytes.Length;
compressor.OutputBuffer = buffer;
// pass 1: deflate
do
{
compressor.NextOut = 0;
compressor.AvailableBytesOut = buffer.Length;
rc = compressor.Deflate(FlushType.None);
if (rc != ZlibConstants.Z_OK && rc != ZlibConstants.Z_STREAM_END)
throw new Exception("deflating: " + compressor.Message);
ms.Write(compressor.OutputBuffer, 0, buffer.Length - compressor.AvailableBytesOut);
}
while (compressor.AvailableBytesIn > 0 || compressor.AvailableBytesOut == 0);
// pass 2: finish and flush
do
{
compressor.NextOut = 0;
compressor.AvailableBytesOut = buffer.Length;
rc = compressor.Deflate(FlushType.Finish);
if (rc != ZlibConstants.Z_STREAM_END && rc != ZlibConstants.Z_OK)
throw new Exception("deflating: " + compressor.Message);
if (buffer.Length - compressor.AvailableBytesOut > 0)
ms.Write(buffer, 0, buffer.Length - compressor.AvailableBytesOut);
}
while (compressor.AvailableBytesIn > 0 || compressor.AvailableBytesOut == 0);
compressor.EndDeflate();
ms.Seek(0, SeekOrigin.Begin);
CompressedBytes = new byte[compressor.TotalBytesOut];
ms.Read(CompressedBytes, 0, CompressedBytes.Length);
}
Remarks¶
You must have set InputBuffer and OutputBuffer before calling this method.
EndDeflate()¶
End a deflation session.
Returns¶
Z_OK if all goes well.
Remarks¶
Call this after making a series of one or more calls to Deflate(). All buffers are flushed.
EndInflate()¶
Ends an inflation session.
Returns¶
Z_OK if everything goes well.
Remarks¶
Call this after successively calling Inflate(). This will cause all buffers to be flushed. After calling this you cannot call Inflate() without a intervening call to one of the InitializeInflate() overloads.
Inflate(FlushType)¶
Inflate the data in the InputBuffer, placing the result in the OutputBuffer.
Parameters¶
flush FlushType
The flush to use when inflating.
Returns¶
Z_OK if everything goes well.
Examples¶
private void InflateBuffer()
{
int bufferSize = 1024;
byte[] buffer = new byte[bufferSize];
ZlibCodec decompressor = new ZlibCodec();
Console.WriteLine("\n============================================");
Console.WriteLine("Size of Buffer to Inflate: {0} bytes.", CompressedBytes.Length);
MemoryStream ms = new MemoryStream(DecompressedBytes);
int rc = decompressor.InitializeInflate();
decompressor.InputBuffer = CompressedBytes;
decompressor.NextIn = 0;
decompressor.AvailableBytesIn = CompressedBytes.Length;
decompressor.OutputBuffer = buffer;
// pass 1: inflate
do
{
decompressor.NextOut = 0;
decompressor.AvailableBytesOut = buffer.Length;
rc = decompressor.Inflate(FlushType.None);
if (rc != ZlibConstants.Z_OK && rc != ZlibConstants.Z_STREAM_END)
throw new Exception("inflating: " + decompressor.Message);
ms.Write(decompressor.OutputBuffer, 0, buffer.Length - decompressor.AvailableBytesOut);
}
while (decompressor.AvailableBytesIn > 0 || decompressor.AvailableBytesOut == 0);
// pass 2: finish and flush
do
{
decompressor.NextOut = 0;
decompressor.AvailableBytesOut = buffer.Length;
rc = decompressor.Inflate(FlushType.Finish);
if (rc != ZlibConstants.Z_STREAM_END && rc != ZlibConstants.Z_OK)
throw new Exception("inflating: " + decompressor.Message);
if (buffer.Length - decompressor.AvailableBytesOut > 0)
ms.Write(buffer, 0, buffer.Length - decompressor.AvailableBytesOut);
}
while (decompressor.AvailableBytesIn > 0 || decompressor.AvailableBytesOut == 0);
decompressor.EndInflate();
}
Remarks¶
You must have set InputBuffer and OutputBuffer, NextIn and NextOut, and AvailableBytesIn and AvailableBytesOut before calling this method.
InitializeDeflate()¶
Initialize the ZlibCodec for deflation operation.
Returns¶
Z_OK if all goes well. You generally don't need to check the return code.
Examples¶
int bufferSize = 40000;
byte[] CompressedBytes = new byte[bufferSize];
byte[] DecompressedBytes = new byte[bufferSize];
ZlibCodec compressor = new ZlibCodec();
compressor.InitializeDeflate(CompressionLevel.Default);
compressor.InputBuffer = System.Text.ASCIIEncoding.ASCII.GetBytes(TextToCompress);
compressor.NextIn = 0;
compressor.AvailableBytesIn = compressor.InputBuffer.Length;
compressor.OutputBuffer = CompressedBytes;
compressor.NextOut = 0;
compressor.AvailableBytesOut = CompressedBytes.Length;
while (compressor.TotalBytesIn != TextToCompress.Length && compressor.TotalBytesOut < bufferSize)
{
compressor.Deflate(FlushType.None);
}
while (true)
{
int rc= compressor.Deflate(FlushType.Finish);
if (rc == ZlibConstants.Z_STREAM_END) break;
}
compressor.EndDeflate();
Remarks¶
The codec will use the MAX window bits and the default level of compression.
InitializeDeflate(CompressionLevel)¶
Initialize the ZlibCodec for deflation operation, using the specified CompressionLevel.
Parameters¶
level CompressionLevel
The compression level for the codec.
Returns¶
Z_OK if all goes well.
Remarks¶
The codec will use the maximum window bits (15) and the specified CompressionLevel. It will emit a ZLIB stream as it compresses.
InitializeDeflate(CompressionLevel, bool)¶
Initialize the ZlibCodec for deflation operation, using the specified CompressionLevel, and the explicit flag governing whether to emit an RFC1950 header byte pair.
Parameters¶
level CompressionLevel
The compression level for the codec.
wantRfc1950Header bool
whether to emit an initial RFC1950 byte pair in the compressed stream.
Returns¶
Z_OK if all goes well.
Remarks¶
The codec will use the maximum window bits (15) and the specified CompressionLevel. If you want to generate a zlib stream, you should specify true for wantRfc1950Header. In this case, the library will emit a ZLIB header, as defined in RFC 1950, in the compressed stream.
InitializeDeflate(CompressionLevel, int)¶
Initialize the ZlibCodec for deflation operation, using the specified CompressionLevel, and the specified number of window bits.
Parameters¶
level CompressionLevel
The compression level for the codec.
bits int
the number of window bits to use. If you don't know what this means, don't use this method.
Returns¶
Z_OK if all goes well.
Remarks¶
The codec will use the specified number of window bits and the specified CompressionLevel.
InitializeDeflate(CompressionLevel, int, bool)¶
Initialize the ZlibCodec for deflation operation, using the specified CompressionLevel, the specified number of window bits, and the explicit flag governing whether to emit an RFC1950 header byte pair.
Parameters¶
level CompressionLevel
The compression level for the codec.
bits int
the number of window bits to use. If you don't know what this means, don't use this method.
wantRfc1950Header bool
whether to emit an initial RFC1950 byte pair in the compressed stream.
Returns¶
Z_OK if all goes well.
InitializeInflate()¶
Initialize the inflation state.
Returns¶
Z_OK if everything goes well.
Remarks¶
It is not necessary to call this before using the ZlibCodec to inflate data; It is implicitly called when you call the constructor.
InitializeInflate(bool)¶
Initialize the inflation state with an explicit flag to govern the handling of RFC1950 header bytes.
Parameters¶
expectRfc1950Header bool
whether to expect an RFC1950 header byte pair when reading the stream of data to be inflated.
Returns¶
Z_OK if everything goes well.
Remarks¶
By default, the ZLIB header defined in RFC 1950 is expected. If you want to read a zlib stream you should specify true for expectRfc1950Header. If you have a deflate stream, you will want to specify false. It is only necessary to invoke this initializer explicitly if you want to specify false.
InitializeInflate(int)¶
Initialize the ZlibCodec for inflation, with the specified number of window bits.
Parameters¶
windowBits int
The number of window bits to use. If you need to ask what that is, then you shouldn't be calling this initializer.
Returns¶
Z_OK if all goes well.
InitializeInflate(int, bool)¶
Initialize the inflation state with an explicit flag to govern the handling of RFC1950 header bytes.
Parameters¶
windowBits int
The number of window bits to use. If you need to ask what that is, then you shouldn't be calling this initializer.
expectRfc1950Header bool
whether to expect an RFC1950 header byte pair when reading the stream of data to be inflated.
Returns¶
Z_OK if everything goes well.
Remarks¶
If you want to read a zlib stream you should specify true for expectRfc1950Header. In this case, the library will expect to find a ZLIB header, as defined in RFC 1950, in the compressed stream. If you will be reading a DEFLATE or GZIP stream, which does not have such a header, you will want to specify false.
ResetDeflate()¶
Reset a codec for another deflation session.
Remarks¶
Call this to reset the deflation state. For example if a thread is deflating non-consecutive blocks, you can call Reset() after the Deflate(Sync) of the first block and before the next Deflate(None) of the second block.
SetDeflateParams(CompressionLevel, CompressionStrategy)¶
Set the CompressionStrategy and CompressionLevel for a deflation session.
Parameters¶
level CompressionLevel
the level of compression to use.
strategy CompressionStrategy
the strategy to use for compression.
Returns¶
Z_OK if all goes well.
SetDictionary(byte[])¶
Set the dictionary to be used for either Inflation or Deflation.
Parameters¶
dictionary byte[]
The dictionary bytes to use.
Returns¶
Z_OK if all goes well.
SyncInflate()¶
I don't know what this does!
Returns¶
Z_OK if everything goes well.