Compression to stream - vb.net

Question

I'm attempting to compress a file to stream which is sent over wcf and decompressed. However with the following code the I'm get not a valid exe when attempting to execute the decompressed exe. Any decompressed exe is around 211-212 bytes lower that the original.
Sub Main()
Dim strm As Stream = CompressToStream("c:\rje\Launcher.exe")
DecompressToFile(strm)
End Sub
Compression Routine
Private Function CompressToStream(ByVal strFullFilename As String) As Stream
If File.Exists(strFullFilename) Then
Dim uncompressedfile As New MemoryStream(File.ReadAllBytes(strFullFilename))
Dim compressedStream As New MemoryStream
Dim compressionStream As New GZipStream(compressedStream, CompressionMode.Compress)
uncompressedfile.CopyToStream(compressionStream)
compressionStream.Flush()
compressedStream.Position = 0
Return compressedStream
End If
Return Nothing
End Function
Extension method to copy streams as using .net3.5
<System.Runtime.CompilerServices.Extension()> _
Private Sub CopyToStream(ByVal input As Stream, ByRef output As Stream)
Dim Buffer(4096) As Byte
Dim numRead As Integer = input.Read(Buffer, 0, Buffer.Length)
Do While numRead <> 0
output.Write(Buffer, 0, numRead)
numRead = input.Read(Buffer, 0, Buffer.Length)
Loop
End Sub
Finally Decompression
Private Sub DecompressToFile(ByVal strmDownload As Stream)
Dim spath As String = "c:\rje\text.exe"
Using outFile As FileStream = File.Create(spath)
Using Decompress As GZipStream = New GZipStream(strmDownload, CompressionMode.Decompress)
' Copy the compressed file into the decompression stream.
Dim buffer(4096) As Byte
Dim numRead As Integer = Decompress.Read(buffer, 0, buffer.Length)
Do While numRead <> 0
outFile.Write(buffer, 0, numRead)
numRead = Decompress.Read(buffer, 0, buffer.Length)
Loop
End Using
outFile.Close()
End Using
End Sub
If someone could point out where I'm going wrong that would be great.

Answer 1

The error was with CompressToStream, amending as follows functions correctly
Private Function CompressToStream(ByVal strFullFilename As String) As Stream
If File.Exists(strFullFilename) Then
Dim compressedStream As New MemoryStream()
Using uncompressedfile As New MemoryStream(File.ReadAllBytes(strFullFilename))
Using compressionStream As New GZipStream(compressedStream, CompressionMode.Compress, True)
uncompressedfile.CopyToStream(compressionStream)
End Using
End Using
compressedStream.Seek(0, SeekOrigin.Begin)
Return compressedStream
End If
Return Nothing
End Function
I still don't have an answer as to why I shouldn't use File.Exists()?

Answer 2

Here are adapted Compress()/Decompress() methods from the sample in the link I posted in my comment:
Private Function Compress(ByVal strFullFilename As FileInfo) As Stream
' Get the stream of the source file.
Dim fi as New FileInfo(strFullFilename)
Dim result As New MemoryStream()
Using inFile As FileStream = fi.OpenRead()
' Compressing:
' Prevent compressing hidden and already compressed files.
If (File.GetAttributes(fi.FullName) And FileAttributes.Hidden) _
<> FileAttributes.Hidden And fi.Extension <> ".gz" Then
' Create the compressed file.
Using Compress As GZipStream = New GZipStream(result, CompressionMode.Compress)
' Copy the source file into the compression stream.
Dim buffer As Byte() = New Byte(4096) {}
Dim numRead As Integer = inFile.Read(buffer, 0, buffer.Length)
Do While numRead <> 0
Compress.Write(buffer, 0, numRead)
numRead = inFile.Read(buffer, 0, buffer.Length)
Loop
'Console.WriteLine("Compressed {0} from {1} to {2} bytes.", fi.Name, fi.Length.ToString(), result.Length.ToString())
End Using
End If
End Using
Return result
End Sub
' Method to decompress.
Private Sub Decompress(ByVal strmDownload As Stream, ByVal resultFileName As String)
' Create the decompressed file.
Using outFile As FileStream = File.Create(resultFileName)
Using Decomp As GZipStream = New GZipStream(strmDownload, CompressionMode.Decompress)
' Copy the compressed file into the decompression stream.
Dim buffer As Byte() = New Byte(4096) {}
Dim numRead As Integer = Decompress.Read(buffer, 0, buffer.Length)
Do While numRead <> 0
outFile.Write(buffer, 0, numRead)
numRead = Decomp.Read(buffer, 0, buffer.Length)
Loop
'Console.WriteLine("Decompressed: {0}", fi.Name)
End Using
End Using
End Using
End Sub