GZipStream Class

Definition

Namespace:

System.IO.Compression

Assembly:

System.IO.Compression.dll

Source:

GZipStream.cs

Provides methods and properties used to compress and decompress streams by using the GZip data format specification.

public ref class GZipStream : System::IO::Stream

public class GZipStream : System.IO.Stream

type GZipStream = class
    inherit Stream

Public Class GZipStream
Inherits Stream

Inheritance

Object

MarshalByRefObject

Stream

GZipStream

Examples

The following example shows how to use the GZipStream class to compress and decompress a directory of files.

using System;
using System.IO;
using System.IO.Compression;

public class FileCompressionModeExample
{
    private const string Message = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";
    private const string OriginalFileName = "original.txt";
    private const string CompressedFileName = "compressed.gz";
    private const string DecompressedFileName = "decompressed.txt";

    public static void Run()
    {
        CreateFileToCompress();
        CompressFile();
        DecompressFile();
        PrintResults();
        DeleteFiles();

        /*
         Output:

            The original file 'original.txt' is 445 bytes. Contents: "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."

            The compressed file 'compressed.gz' is 283 bytes.

            The decompressed file 'decompressed.txt' is 445 bytes. Contents: "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
         */
    }

    private static void CreateFileToCompress() => File.WriteAllText(OriginalFileName, Message);

    private static void CompressFile()
    {
        using FileStream originalFileStream = File.Open(OriginalFileName, FileMode.Open);
        using FileStream compressedFileStream = File.Create(CompressedFileName);
        using var compressor = new GZipStream(compressedFileStream, CompressionMode.Compress);
        originalFileStream.CopyTo(compressor);
    }

    private static void DecompressFile()
    {
        using FileStream compressedFileStream = File.Open(CompressedFileName, FileMode.Open);
        using FileStream outputFileStream = File.Create(DecompressedFileName);
        using var decompressor = new GZipStream(compressedFileStream, CompressionMode.Decompress);
        decompressor.CopyTo(outputFileStream);
    }

    private static void PrintResults()
    {
        long originalSize = new FileInfo(OriginalFileName).Length;
        long compressedSize = new FileInfo(CompressedFileName).Length;
        long decompressedSize = new FileInfo(DecompressedFileName).Length;

        Console.WriteLine($"The original file '{OriginalFileName}' is {originalSize} bytes. Contents: \"{File.ReadAllText(OriginalFileName)}\"");
        Console.WriteLine($"The compressed file '{CompressedFileName}' is {compressedSize} bytes.");
        Console.WriteLine($"The decompressed file '{DecompressedFileName}' is {decompressedSize} bytes. Contents: \"{File.ReadAllText(DecompressedFileName)}\"");
    }

    private static void DeleteFiles()
    {
        File.Delete(OriginalFileName);
        File.Delete(CompressedFileName);
        File.Delete(DecompressedFileName);
    }
}

Imports System
Imports System.IO
Imports System.IO.Compression

Public Class FileCompressionModeExample
    Private Const Message As String = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
    Private Const OriginalFileName As String = "original.txt"
    Private Const CompressedFileName As String = "compressed.gz"
    Private Const DecompressedFileName As String = "decompressed.txt"

    Public Shared Sub Main()
        CreateFileToCompress()
        CompressFile()
        DecompressFile()
        PrintResults()
        DeleteFiles()

        ' Output:
        '   The original file 'original.txt' weighs 445 bytes. Contents: "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."

        '   The compressed file 'compressed.gz' weighs 283 bytes.

        '   The decompressed file 'decompressed.txt' weighs 445 bytes. Contents: "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
    End Sub

    Private Shared Sub CreateFileToCompress()
        File.WriteAllText(OriginalFileName, Message)
    End Sub

    Private Shared Sub CompressFile()
        Using originalFileStream As FileStream = File.Open(OriginalFileName, FileMode.Open)
            Using compressedFileStream As FileStream = File.Create(CompressedFileName)
                Using compressor = New GZipStream(compressedFileStream, CompressionMode.Compress)
                    originalFileStream.CopyTo(compressor)
                End Using
            End Using
        End Using
    End Sub

    Private Shared Sub DecompressFile()
        Using compressedFileStream As FileStream = File.Open(CompressedFileName, FileMode.Open)
            Using outputFileStream As FileStream = File.Create(DecompressedFileName)
                Using decompressor = New GZipStream(compressedFileStream, CompressionMode.Decompress)
                    decompressor.CopyTo(outputFileStream)
                End Using
            End Using
        End Using
    End Sub

    Private Shared Sub PrintResults()
        Dim originalSize As Long = New FileInfo(OriginalFileName).Length
        Dim compressedSize As Long = New FileInfo(CompressedFileName).Length
        Dim decompressedSize As Long = New FileInfo(DecompressedFileName).Length

        Console.WriteLine($"The original file '{OriginalFileName}' weighs {originalSize} bytes. Contents: ""{File.ReadAllText(OriginalFileName)}""")
        Console.WriteLine($"The compressed file '{CompressedFileName}' weighs {compressedSize} bytes.")
        Console.WriteLine($"The decompressed file '{DecompressedFileName}' weighs {decompressedSize} bytes. Contents: ""{File.ReadAllText(DecompressedFileName)}""")
    End Sub

    Private Shared Sub DeleteFiles()
        File.Delete(OriginalFileName)
        File.Delete(CompressedFileName)
        File.Delete(DecompressedFileName)
    End Sub
End Class

Remarks

This class represents the gzip data format, which uses an industry-standard algorithm for lossless file compression and decompression. The format includes a cyclic redundancy check value for detecting data corruption. The gzip data format uses the same algorithm as the DeflateStream class, but can be extended to use other compression formats. The format can be readily implemented in a manner not covered by patents.

Starting with .NET Framework 4.5, the DeflateStream class uses the zlib library for compression. As a result, it provides a better compression algorithm and, in most cases, a smaller compressed file than it provides in earlier versions of .NET Framework.

Compressed GZipStream objects written to a file with an extension of .gz can be decompressed using many common compression tools; however, this class does not inherently provide functionality for adding files to or extracting files from zip archives.

The compression functionality in DeflateStream and GZipStream is exposed as a stream. Data is read on a byte-by-byte basis, so it's not possible to perform multiple passes to determine the best method for compressing entire files or large blocks of data. The DeflateStream and GZipStream classes are best used on uncompressed sources of data. If the source data is already compressed, using these classes may actually increase the size of the stream.

Notes to Inheritors

When you inherit from GZipStream, you must override the following members: CanSeek, CanWrite, and CanRead.

Constructors

GZipStream(Stream, CompressionLevel)	Initializes a new instance of the GZipStream class by using the specified stream and compression level.
GZipStream(Stream, CompressionLevel, Boolean)	Initializes a new instance of the GZipStream class by using the specified stream and compression level, and optionally leaves the stream open.
GZipStream(Stream, CompressionMode)	Initializes a new instance of the GZipStream class by using the specified stream and compression mode.
GZipStream(Stream, CompressionMode, Boolean)	Initializes a new instance of the GZipStream class by using the specified stream and compression mode, and optionally leaves the stream open.

Properties

BaseStream	Gets a reference to the underlying stream.
CanRead	Gets a value indicating whether the stream supports reading while decompressing a file.
CanSeek	Gets a value indicating whether the stream supports seeking.
CanTimeout	Gets a value that determines whether the current stream can time out. (Inherited from Stream)
CanWrite	Gets a value indicating whether the stream supports writing.
Length	This property is not supported and always throws a NotSupportedException.
Position	This property is not supported and always throws a NotSupportedException.
ReadTimeout	Gets or sets a value, in milliseconds, that determines how long the stream will attempt to read before timing out. (Inherited from Stream)
WriteTimeout	Gets or sets a value, in milliseconds, that determines how long the stream will attempt to write before timing out. (Inherited from Stream)

Methods

BeginRead(Byte[], Int32, Int32, AsyncCallback, Object)	Begins an asynchronous read operation. (Consider using the ReadAsync(Byte[], Int32, Int32) method instead.)
BeginWrite(Byte[], Int32, Int32, AsyncCallback, Object)	Begins an asynchronous write operation. (Consider using the WriteAsync(Byte[], Int32, Int32) method instead.)
Close()	Closes the current stream and releases any resources (such as sockets and file handles) associated with the current stream. Instead of calling this method, ensure that the stream is properly disposed. (Inherited from Stream)
CopyTo(Stream)	Reads the bytes from the current stream and writes them to another stream. Both streams positions are advanced by the number of bytes copied. (Inherited from Stream)
CopyTo(Stream, Int32)	Reads the bytes from the current GZip stream and writes them to another stream, using the specified buffer size.
CopyToAsync(Stream)	Asynchronously reads the bytes from the current stream and writes them to another stream. Both streams positions are advanced by the number of bytes copied. (Inherited from Stream)
CopyToAsync(Stream, CancellationToken)	Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified cancellation token. Both streams positions are advanced by the number of bytes copied. (Inherited from Stream)
CopyToAsync(Stream, Int32)	Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified buffer size. Both streams positions are advanced by the number of bytes copied. (Inherited from Stream)
CopyToAsync(Stream, Int32, CancellationToken)	Asynchronously reads the bytes from the current GZip stream and writes them to another stream, using a specified buffer size.
CreateObjRef(Type)	Creates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject)
CreateWaitHandle()	Obsolete. Allocates a WaitHandle object. (Inherited from Stream)
Dispose()	Releases all resources used by the Stream. (Inherited from Stream)
Dispose(Boolean)	Releases the unmanaged resources used by the GZipStream and optionally releases the managed resources.
DisposeAsync()	Asynchronously releases the unmanaged resources used by the GZipStream.
EndRead(IAsyncResult)	Waits for the pending asynchronous read to complete. (Consider using the ReadAsync(Byte[], Int32, Int32) method instead.)
EndWrite(IAsyncResult)	Handles the end of an asynchronous write operation. (Consider using the WriteAsync(Byte[], Int32, Int32) method instead.)
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
Flush()	Flushes the internal buffers.
FlushAsync()	Asynchronously clears all buffers for this stream and causes any buffered data to be written to the underlying device. (Inherited from Stream)
FlushAsync(CancellationToken)	Asynchronously clears all buffers for this GZip stream, causes any buffered data to be written to the underlying device, and monitors cancellation requests.
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetLifetimeService()	Obsolete. Retrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject)
GetType()	Gets the Type of the current instance. (Inherited from Object)
InitializeLifetimeService()	Obsolete. Obtains a lifetime service object to control the lifetime policy for this instance. (Inherited from MarshalByRefObject)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
MemberwiseClone(Boolean)	Creates a shallow copy of the current MarshalByRefObject object. (Inherited from MarshalByRefObject)
ObjectInvariant()	Obsolete. Provides support for a Contract. (Inherited from Stream)
Read(Byte[], Int32, Int32)	Reads a number of decompressed bytes into the specified byte array.
Read(Span<Byte>)	Reads a sequence of bytes from the current GZip stream into a byte span and advances the position within the GZip stream by the number of bytes read.
ReadAsync(Byte[], Int32, Int32)	Asynchronously reads a sequence of bytes from the current stream and advances the position within the stream by the number of bytes read. (Inherited from Stream)
ReadAsync(Byte[], Int32, Int32, CancellationToken)	Asynchronously reads a sequence of bytes from the current GZip stream into a byte array, advances the position within the GZip stream by the number of bytes read, and monitors cancellation requests.
ReadAsync(Memory<Byte>, CancellationToken)	Asynchronously reads a sequence of bytes from the current GZip stream into a byte memory region, advances the position within the GZip stream by the number of bytes read, and monitors cancellation requests.
ReadAtLeast(Span<Byte>, Int32, Boolean)	Reads at least a minimum number of bytes from the current stream and advances the position within the stream by the number of bytes read. (Inherited from Stream)
ReadAtLeastAsync(Memory<Byte>, Int32, Boolean, CancellationToken)	Asynchronously reads at least a minimum number of bytes from the current stream, advances the position within the stream by the number of bytes read, and monitors cancellation requests. (Inherited from Stream)
ReadByte()	Reads a byte from the GZip stream and advances the position within the stream by one byte, or returns -1 if at the end of the GZip stream.
ReadExactly(Byte[], Int32, Int32)	Reads count number of bytes from the current stream and advances the position within the stream. (Inherited from Stream)
ReadExactly(Span<Byte>)	Reads bytes from the current stream and advances the position within the stream until the buffer is filled. (Inherited from Stream)
ReadExactlyAsync(Byte[], Int32, Int32, CancellationToken)	Asynchronously reads count number of bytes from the current stream, advances the position within the stream, and monitors cancellation requests. (Inherited from Stream)
ReadExactlyAsync(Memory<Byte>, CancellationToken)	Asynchronously reads bytes from the current stream, advances the position within the stream until the buffer is filled, and monitors cancellation requests. (Inherited from Stream)
Seek(Int64, SeekOrigin)	This property is not supported and always throws a NotSupportedException.
SetLength(Int64)	This property is not supported and always throws a NotSupportedException.
ToString()	Returns a string that represents the current object. (Inherited from Object)
Write(Byte[], Int32, Int32)	Writes compressed bytes to the underlying GZip stream from the specified byte array.
Write(ReadOnlySpan<Byte>)	Writes a sequence of bytes to the current GZip stream from a read-only byte span and advances the current position within this GZip stream by the number of bytes written.
WriteAsync(Byte[], Int32, Int32)	Asynchronously writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written. (Inherited from Stream)
WriteAsync(Byte[], Int32, Int32, CancellationToken)	Asynchronously writes compressed bytes to the underlying GZip stream from the specified byte array.
WriteAsync(ReadOnlyMemory<Byte>, CancellationToken)	Asynchronously writes compressed bytes to the underlying GZip stream from the specified read-only byte memory region.
WriteByte(Byte)	Writes a byte to the current GZip stream and advances the current position within this GZip stream by one.

Extension Methods

CopyToAsync(Stream, PipeWriter, CancellationToken)	Asynchronously reads the bytes from the Stream and writes them to the specified PipeWriter, using a cancellation token.
ConfigureAwait(IAsyncDisposable, Boolean)	Configures how awaits on the tasks returned from an async disposable will be performed.

See also

• Partial and zero-byte reads in DeflateStream, GZipStream, and CryptoStream