Using GZipStream not behaving how I would expect

Question

I have the following code:

string testString = "test abc";
var bytes = Encoding.UTF8.GetBytes(testString);

using var memoryStream = new MemoryStream();
using var gzipStream = new GZipStream(memoryStream, CompressionLevel.SmallestSize);
gzipStream.Write(bytes, 0, bytes.Length);

var dbytes = memoryStream.ToArray();

My understanding is that this code will compress the string. However, when I try to decompress this, it returns an empty byte array:

using var memoryStream2 = new MemoryStream(dbytes);
using var outputStream = new MemoryStream();
using var decompressStream = new GZipStream(memoryStream2, CompressionMode.Decompress);
decompressStream.CopyTo(outputStream);
var returnBytes = outputStream.ToArray();

string stest2 = Encoding.UTF8.GetString(returnBytes)!;
Console.WriteLine(stest2); // empty

It also seems to actually make the byte array bigger after compression, but I guess this is because the string is so small the overhead of compression causes the size to increase.

Please can someone point me to what I'm doing wrong here.

You need to flush (or close) the GZipStream after write. – Poul Bak Sep 06 '22 at 07:46 — Poul Bak, Sep 06 '22 at 07:46

score 0 · Accepted Answer · answered Sep 06 '22 at 08:09

0

string testString = "test abc";
var bytes = Encoding.UTF8.GetBytes(testString);

using var memoryStream = new MemoryStream();
using var gzipStream = new GZipStream(memoryStream, CompressionMode.Compress, true);
gzipStream.Write(bytes, 0, bytes.Length);
gzipStream.Close();

var dbytes = memoryStream.ToArray();

using var memoryStream2 = new MemoryStream(dbytes);
using var outputStream = new MemoryStream();
using var decompressStream = new GZipStream(memoryStream2, CompressionMode.Decompress);
decompressStream.CopyTo(outputStream);
var returnBytes = outputStream.ToArray();

string stest2 = Encoding.UTF8.GetString(returnBytes)!;
Console.WriteLine(stest2); // works well

Thanks.

answered Sep 06 '22 at 08:09

ThrowDevNull

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5

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When the code is several lines long, and you change only a small part of the original code, you should highlight the part that makes up the solution. And possibly explain what you changed. – Rubidium 37 Sep 06 '22 at 09:31
Wow - can't believe I missed that - thanks! – sid Sep 06 '22 at 17:35
Thanks Rubidium. But I don't know how to highlight the sentence in the code. Could you tell me the way to highlight? – ThrowDevNull Sep 07 '22 at 02:49

Using GZipStream not behaving how I would expect

1 Answers1