Correct IDisposable implementation for this code

Question

I have the following code

public static byte[] Compress(byte[] CompressMe)
{
    using (MemoryStream ms = new MemoryStream())
    {
        using (GZipStream gz = new GZipStream(ms, CompressionMode.Compress,true))
        {
            gz.Write(CompressMe, 0, CompressMe.Length);
            ms.Position = 0;
            byte[] Result = new byte[ms.Length];
            ms.Read(Result, 0, (int)ms.Length);
            return Result;
        }
    }
}

This works fine, but when I run code analysis on it, it comes up with the following message

CA2202 : Microsoft.Usage : Object 'ms' can be disposed more than once in 
method 'Compression.Compress(byte[])'. To avoid generating a 
System.ObjectDisposedException you should not call Dispose more than one 
time on an object.

As far as I'm concerned, when the GZipStream is Disposed, it leaves the underlying Stream (ms) open, due to the last parameter of the constructor (leaveOpen=true).

If I change my code slightly.. remove the 'using' block around the MemoryStream and change the 'leaveOpen' parameter to false..

public static byte[] Compress(byte[] CompressMe)
{
    MemoryStream ms = new MemoryStream();
    using (GZipStream gz = new GZipStream(ms, CompressionMode.Compress, false))
    {
        gz.Write(CompressMe, 0, CompressMe.Length);
        ms.Position = 0;
        byte[] Result = new byte[ms.Length];
        ms.Read(Result, 0, (int)ms.Length);
        return Result;
    }
}

This then comes up with..

CA2000 : Microsoft.Reliability : In method 'Compression.Compress(byte[])',
object 'ms' is not disposed along all exception paths. Call 
System.IDisposable.Dispose on object 'ms' before all references to 
it are out of scope.

I can't win.. (unless I'm missing something obvious) I've tried various things, like putting a try/finally around the block, and Disposing of the MemoryStream in there, but it either says that I'm disposing of it twice, or not at all !!

Answer 1

Apart from the disposing issue, your code is also broken. You should close the zip stream before reading back the data.

Also there is already a ToArray() method on MemoryStream, no need to implement that yourself.

using (MemoryStream ms = new MemoryStream())
{
    using (GZipStream gz = new GZipStream(ms, CompressionMode.Compress,true))
    {
        gz.Write(CompressMe, 0, CompressMe.Length);
    }
    return ms.ToArray();
}

I'd simply suppress the warning, since it's a false positive. Code analysis is there to serve you, not the other way round.