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Asked: 2026-05-25T16:19:14+00:00

I am using the following code to uncompress a GZipStream (using DotNetZip library ),

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I am using the following code to uncompress a GZipStream (using DotNetZip library), where fs is a filestream pointing to a gz file (with FileMode.Open, FileAccess.Read, FileShare.ReadWrite):

using (var gz = new GZipStream(fs, CompressionMode.Decompress)) {
    using (var sr = new StreamReader(gz)) {
         header = sr.ReadLine();
    }
}

But if the file is not read till the end (which I prefer to do when not needed as the file can be huge), it throws

ZlibException("Bad CRC32 in GZIP trailer. (actual(EC084966)!=expected(8FC3EF16))")

on the first closing bracket (actually when trying to Close() the StreamReader.

Now if call ReadToEnd() before closing the streamreader (or I read all lines using a while(!sr.EndOfStream) loop), it works.
I have observed the same behaviour with a 500 MB and 200 kB compressed file, so it seems it is not related to the file size.

Your insight is very welcome!

Here is a link to a simple dedicated test project.

It works with the System.IO.GZipStream library, so this is very strange.

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1 Answer

  1. Editorial Team

    As a conjecture, I suspect that if the CRC block is at the end of the file, then if I abort reading the stream, it cannot have verified the integrity while disposing the stream and therefore throws the exception.

    However this would not explain why it works when using System.IO.GzipStream.

    I found the relevant part of the source code of DotNetZip here, but it seems they are checking that the stream is read to the end (see // Make sure we have read to the end of the stream). Then, they do compute a CRC32 as the exception message shows one.

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