Problem with GzZipStream

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Hi there, can anyone point me in the direction*of where I'm going wrong here.* I have written two functions, basically the same as countless examples on web..

- One is passed an array of bytes as a parameter and returns a compressed array of bytes

- The other (surprise surprise) is passed the compressed array and (is meant to) return an uncompressed array.

 

I have temporarily added code to parallel the compression/decompression to file, curious to see if that worked.

 

The gist of this is, the "compression function" writes the same number of bytes to file as it returns as an array.

The "decompression" function decompresses the file version back to the original size, but the attempt to do simlar on memory is failing.

 

The point that it seems to go awry is documented.**After positioning the underlying MemoryStream position to 0, a read of N bytes returns zero read, and the MemoryStream Position is now at end*of stream.*

 

Any help will*be greatly appreciated.

 

---------------------------------------------------------------------------------------

 

PublicFunction Compress(ByRef inbytes() AsByte) AsByte()

Using mem AsNew MemoryStream, _

g AsNew GZipStream(mem, CompressionMode.Compress), _

fs AsNew FileStream("c:\users\davem\documents\compressedtable.gz", FileMode.OpenOrCreate, FileAccess.Write), _

g2 AsNew GZipStream(fs, CompressionMode.Compress)

Try

'========================================================================

' First compress array of bytes to file

g2.Write(inbytes, 0, inbytes.Length)

'=========================================================================

' Now compress to an array (retVal)

g.Write(inbytes, 0, inbytes.Length)

Dim

retval()

As

Byte

= mem.ToArray

' The compressed bytes in memory (Retval) and and those written to file are same length

Return

retval

Catch

ex

As

Exception

Return

Nothing

Finally

If

Not

g

Is

Nothing

Then

g.Close()

End

If

If

Not

mem

Is

Nothing

Then

mem.Close()

End

If

End

Try

EndUsing

EndFunction

 

----------------------------------------------------------

 

PublicFunction DeCompress(ByRef inbytes() AsByte) AsByte()

Using mem As MemoryStream = New MemoryStream(inbytes), _

mem2 As MemoryStream = New MemoryStream(), _

g As GZipStream = New GZipStream(mem, CompressionMode.Decompress, False), _

fs As FileStream = New FileStream("c:\users\davem\documents\compressedtable.gz", FileMode.Open, FileAccess.Read), _

g2 As GZipStream = New GZipStream(fs, CompressionMode.Decompress, True)

Try

'=============================================================================

' First decompress the file

Dim

filebuffer(1024)

As

Byte

fs.Position = 0

Dim

fileread

As

Integer

= g2.Read(filebuffer, 0, filebuffer.Length)

While

fileread > 0

mem3.Write(filebuffer, 0, fileread)

fileread = g2.Read(filebuffer, 0, filebuffer.Length)

End

While

Dim

decompfile()

As

Byte

= mem3.ToArray

' decompfile array is the same size as original uncompressed byte array

'==============================================================================

' Now try decompressing the array of compressed bytes

mem.Position = 0

Dim

buffer(1024)

As

Byte

Dim

memread

As

Integer

= g.Read(buffer, 0, buffer.Length)

' memread is zero, and the mem.Position is now positioned at end of stream

' so this next loop is of course skipped entirely

While

memread > 0

mem2.Write(buffer, 0, memread)

memread = g.Read(buffer, 0, buffer.Length)

End

While

' therefore retval is empty

Dim

retval()

As

Byte

= mem2.ToArray

Return

retval

Catch

ex

As

Exception

Return

Nothing

Finally

If

Not

mem

Is

Nothing

Then

mem.Close()

End

If

If

Not

mem2

Is

Nothing

Then

mem2.Close()

End

If

If

Not

g

Is

Nothing

Then

g.Flush()

g.Close()

End

If

End

Try

EndUsing

ReturnNothing

EndFunction

 

 

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