GZipStream machine dependence

问题

I'm running into some strange machine/OS dependent GZipStream behavior in .NET 4.0. This is the relevant code:

public static string Compress(string input) {
    using(var ms = new MemoryStream(Encoding.UTF8.GetBytes(input)))
    using(var os = new MemoryStream()) {
        using(var gz = new GZipStream(os,CompressionMode.Compress,true)) {
            ms.CopyTo(gz);
        }
        return string.Join("",os.ToArray().Select(b=>b.ToString("X2")));
    }
}

Running Compress("freek") gives me

1F8B08000000000004004B2B4A4DCD06001E33909D05000000

on Windows 7 and

1F8B0800000000000400ECBD07601C499625262F6DCA7B7F4AF54AD7E074A10880601324D8904010ECC188CDE692EC1D69472329AB2A81CA6556655D661640CCED9DBCF7DE7BEFBDF7DE7BEFBDF7BA3B9D4E27F7DFFF3F5C6664016CF6CE4ADAC99E2180AAC81F3F7E7C1F3F22CEEB3C7FFBFF040000FFFF1E33909D05000000

on Windows Server 2008R2. Both are 64bit. I would expect the results to be the same.

Both machines give the correct result when I decompress either result. I already found out that on W7 ms.Length == 25 while on W2K8R2 ms.Length==128, but no clue why.

What's going on?

回答1:

It was announced that .NET 4.5 Beta includes zip compression improvements to reduce the size:

Starting with the .NET Framework 4.5 RC, 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 the .NET Framework.

Do you perhaps have .Net 4.5+ installed on the Win7 machine?

回答2:

It seems there is a change in the algorithm used by DeflateStream in .NET 4.5:

Starting with the .NET Framework 4.5 Beta, 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 the .NET Framework.

Since I had 4.5 installed, this was causing the problem.

回答3:

As opposed to Abel's answer, I get the result of

1F8B08000000000004004B2B4A4DCD06001E33909D05000000

on my Windows 7 x64 Ultimate SP1. Perhaps there's a .NET Framework update you don't have on one of the boxes? The version of my mscorlib.dll is 4.0.30319.17379.

ETA: If I retarget to .NET 2 (and change the .NET 4-specific constructs to their .NET 2 equivalents), I do get the result of

1F8B0800000000000400EDBD07601C499625262F6DCA7B7F4AF54AD7E074A10880601324D8904010ECC188CDE692EC1D69472329AB2A81CA6556655D661640CCED9DBCF7DE7BEFBDF7DE7BEFBDF7BA3B9D4E27F7DFFF3F5C6664016CF6CE4ADAC99E2180AAC81F3F7E7C1F3F22CEEB3C7FFBFF001E33909D05000000

on the same machine/OS.

回答4:

I ran your code on my Windows 7 64 bit machine and got the following, which equals your Win2k8SP2:

1F8B0800000000000400ECBD07601C499625262F6DCA7B7F4AF54AD7E074A10880601324D8904010ECC188CDE692EC1D69472329AB2A81CA6556655D661640CCED9DBCF7DE7BEFBDF7DE7BEFBDF7BA3B9D4E27F7DFFF3F5C6664016CF6CE4ADAC99E2180AAC81F3F7E7C1F3F229ED579FEF6FF090000FFFF1A1C515C05000000

Essentially, I think the result has to do with the word-length of the machine. I.e., your windows-7 machine is perhaps 32 bit?

NOTE: I wrote a little decompress for your strings and I have to second that they indeed decompress well. I ran my version in both 32 bit and 64 bit and the outcome was equal. Only possible difference remains: different runtimes?

EDIT: