DeflateStream.EndRead Method

Note: This method is new in the .NET Framework version 2.0.

Waits for the pending asynchronous read to complete.

Namespace: System.IO.Compression
Assembly: System (in system.dll)

Public Overrides Function EndRead ( _
	asyncResult As IAsyncResult _
) As Integer
Dim instance As DeflateStream
Dim asyncResult As IAsyncResult
Dim returnValue As Integer

returnValue = instance.EndRead(asyncResult)
public int EndRead (
	IAsyncResult asyncResult
public override function EndRead (
	asyncResult : IAsyncResult
) : int



The reference to the pending asynchronous request to finish.

Return Value

The number of bytes read from the stream, between zero (0) and the number of bytes you requested. DeflateStream returns zero (0) only at the end of the stream; otherwise, it blocks until at least one byte is available.

Exception typeCondition


asyncResult is a null reference (Nothing in Visual Basic).


asyncResult did not originate from a BeginRead method on the current stream.

Call this method to determine how many bytes were read from the stream. This method can be called once to return the amount of bytes read between calls to BeginRead and EndRead.

This method blocks until the I/O operation has completed.

The following code example shows how to use the DeflateStream class to compress and decompress a file.

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

Public Class DeflateTest
    Shared msg As String
   Public Shared Function ReadAllBytesFromStream(stream As Stream, buffer() As Byte) As Integer
      ' Use this method is used to read all bytes from a stream.
      Dim offset As Integer = 0
      Dim totalCount As Integer = 0
      While True
         Dim bytesRead As Integer = stream.Read(buffer, offset, 100)
         If bytesRead = 0 Then
            Exit While
         End If
         offset += bytesRead
         totalCount += bytesRead
      End While
      Return totalCount
   End Function 'ReadAllBytesFromStream
   Public Shared Function CompareData(buf1() As Byte, len1 As Integer, buf2() As Byte, len2 As Integer) As Boolean
      ' Use this method to compare data from two different buffers.
        If len1 <> len2 Then
            msg = "Number of bytes in two buffer are different" & len1 & ":" & len2
            Return False
        End If
      Dim i As Integer
      For i = 0 To len1 - 1
         If buf1(i) <> buf2(i) Then
                msg = "byte " & i & " is different " & buf1(i) & "|" & buf2(i)
                Return False
         End If
        Next i
        msg = "All bytes compare."
        Return True
   End Function 'CompareData
   Public Shared Sub DeflateCompressDecompress(filename As String)
        msg = "Test compression and decompression on file " & filename

        Dim infile As FileStream
         ' Open the file as a FileStream object.
         infile = New FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read)
            Dim buffer(infile.Length - 1) As Byte
         ' Read the file to ensure it is readable.
            Dim count As Integer = infile.Read(buffer, 0, buffer.Length)
         If count <> buffer.Length Then
                msg = "Test Failed: Unable to read data from file"
         End If
         Dim ms As New MemoryStream()
         ' Use the newly created memory stream for the compressed data.
         Dim compressedzipStream As New DeflateStream(ms, CompressionMode.Compress, True)
         compressedzipStream.Write(buffer, 0, buffer.Length)
         ' Close the stream.

            msg = "Original size: " & buffer.Length & ", Compressed size: " & ms.Length

         ' Reset the memory stream position to begin decompression.
         ms.Position = 0
         Dim zipStream As New DeflateStream(ms, CompressionMode.Decompress)
         Dim decompressedBuffer(buffer.Length + 100) As Byte
         ' Use the ReadAllBytesFromStream to read the stream.
         Dim totalCount As Integer = DeflateTest.ReadAllBytesFromStream(zipStream, decompressedBuffer)
            msg = "Decompressed " & totalCount & " bytes"

         If Not DeflateTest.CompareData(buffer, buffer.Length, decompressedBuffer, totalCount) Then
                msg = "Error. The two buffers did not compare."

         End If
        Catch e As Exception
            msg = "Error: The file being read contains invalid data."
        End Try

   End Sub 'DeflateCompressDecompress
    Public Shared Sub Main(ByVal args() As String)
        Dim usageText As String = "Usage: DeflateTest <inputfilename>"
        'If no file name is specified, write usage text.
        If args.Length = 0 Then
            If File.Exists(args(0)) Then
            End If
        End If
    End Sub 'Main
End Class 'DeflateTest 

import System.*;
import System.IO.*;
import System.IO.Compression.*;

public class DeflateTest
    public static int ReadAllBytesFromStream(Stream stream, ubyte buffer[])
        // Use this method is used to read all bytes from a stream.
        int offSet = 0;
        int totalCount = 0;
        while (true) {
            int bytesRead = stream.Read(buffer, offSet, 100);
            if (bytesRead == 0) {
            offSet += bytesRead;
            totalCount += bytesRead;
        return totalCount;
    } //ReadAllBytesFromStream

    public static boolean CompareData(ubyte buf1[], int len1, 
        ubyte buf2[], int len2)
        // Use this method to compare data from two different buffers.
        if (len1 != len2) {
            Console.WriteLine("Number of bytes in two buffer are "
                + "different {0}:{1}", System.Convert.ToString(len1), 
            return false;
        for (int i = 0; i < len1; i++) {
            if (!(buf1.get_Item(i).Equals(buf2.get_Item(i)))) {
                Console.WriteLine("byte {0} is different {1}|{2}", 
                return false;
        Console.WriteLine("All bytes compare.");
        return true;
    } //CompareData

    public static void DeflateCompressDecompress(String fileName)
        Console.WriteLine("Test compression and decompression on file {0}",
        FileStream inFile;
        try {
            // Open the file as a FileStream object.
            inFile = new FileStream(fileName, FileMode.Open, FileAccess.Read, 
            ubyte buffer[] = new ubyte[(ubyte)inFile.get_Length()];

            // Read the file to ensure it is readable.
            int count = inFile.Read(buffer, 0, buffer.length);
            if (count != buffer.length) {
                Console.WriteLine("Test Failed: Unable to read data from file");
            MemoryStream ms = new MemoryStream();

            // Use the newly created memory stream for the compressed data.
            DeflateStream compressedZipStream = 
                new DeflateStream(ms, CompressionMode.Compress, true);
            compressedZipStream.Write(buffer, 0, buffer.length);

            // Close the stream.
            Console.WriteLine("Original size: {0}, Compressed size: {1}", 

            // Reset the memory stream position to begin decompression.
            DeflateStream zipStream = 
                new DeflateStream(ms, CompressionMode.Decompress);
            ubyte decompressedBuffer[] = new ubyte[buffer.length + 100];

            // Use the ReadAllBytesFromStream to read the stream.
            int totalCount = DeflateTest.ReadAllBytesFromStream(zipStream, 
            Console.WriteLine("Decompressed {0} bytes", 

            if (!(DeflateTest.CompareData(buffer, buffer.length, 
                decompressedBuffer, totalCount))) {
                Console.WriteLine("Error. The two buffers did not compare.");
        catch (InvalidDataException exp) {
            Console.WriteLine("Error: The file being read contains"
                + " invalid data.");
        catch (FileNotFoundException exp) {
            Console.WriteLine("Error:The file specified was not found.");
        catch (ArgumentException exp) {
            Console.WriteLine("Error: path is a zero-length string, contains"
                + " only white space, or contains one or more "
                + "invalid characters");
        catch (PathTooLongException exp) {
            Console.WriteLine("Error: The specified path, file name, or both"
                + " exceed the system-defined maximum length. For example, "
                + "on Windows-based platforms, paths must be less than 248 "
                + "characters, and file names must be less than 260 "
                + "characters.");
        catch (DirectoryNotFoundException exp) {
            Console.WriteLine("Error: The specified path is invalid, such"
                + " as being on an unmapped drive.");
        catch (IOException exp) {
            Console.WriteLine("Error: An I/O error occurred while "
                + "opening the file.");
        catch (UnauthorizedAccessException exp) {
            Console.WriteLine("Error: path specified a file that is read-only,"
                + " the path is a directory, or caller does not have the"
                + " required permissions.");
        catch (IndexOutOfRangeException exp) {
            Console.WriteLine("Error: You must provide parameters for MyGZIP.");
    } //DeflateCompressDecompress

    public static void main(String[] args)
        String usageText = "Usage: DeflateTest <inputfilename>";

        //If no file name is specified, write usage text.
        if (args.length == 0) {
        else {
            if (File.Exists(args[0])) {
    } //main
} //DeflateTest

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

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