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If Zip file has normal file header AND a post-descriptor header AND the file is attempted to be skipped by a ZipReader, then the data is attempted to be skipped twice. #210

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opened 2026-01-29 22:08:24 +00:00 by claunia · 5 comments
claunia commented 2026-01-29 22:08:24 +00:00
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Originally created by @KvanTTT on GitHub (Jul 7, 2017).

Originally assigned to: @adamhathcock on GitHub.

I have the following BadStateArchive.zip.

I want to ignore files that start with the dot: .DS_Store. But if I just ignore such file I get the exception
Bad state (invalid stored block lengths) in reader.MoveToNextEntry() method. I use the following code for reading:

using (Stream stream = File.OpenRead(sourceArchiveFileName))
{
    using (IReader reader = ReaderFactory.Open(stream))
    {  
        while (reader.MoveToNextEntry())
        {
           ...
        }
    }
}

If such files writing to DummyStream exception does not occur:

using (var dummyStream = new DummyStream())
{
    reader.WriteEntryTo(dummyStream);
}

where DummyStream is

public class DummyStream : Stream
{
    public override bool CanRead => true;

    public override bool CanSeek => true;

    public override bool CanWrite => true;

    public override long Length => 0;

    public override long Position { get; set; } = 0;

    public override void Flush()
    {
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        return 0;
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        return 0;
    }

    public override void SetLength(long value)
    {
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
    }
}
Originally created by @KvanTTT on GitHub (Jul 7, 2017). Originally assigned to: @adamhathcock on GitHub. I have the following [BadStateArchive.zip](https://github.com/adamhathcock/sharpcompress/files/1130352/BadStateArchive.zip). I want to ignore files that start with the dot: `.DS_Store`. But if I just ignore such file I get the exception `Bad state (invalid stored block lengths)` in `reader.MoveToNextEntry()` method. I use the following code for reading: ```CSharp using (Stream stream = File.OpenRead(sourceArchiveFileName)) { using (IReader reader = ReaderFactory.Open(stream)) { while (reader.MoveToNextEntry()) { ... } } } ``` If such files writing to `DummyStream` exception does not occur: ```CSharp using (var dummyStream = new DummyStream()) { reader.WriteEntryTo(dummyStream); } ``` where `DummyStream` is ```CSharp public class DummyStream : Stream { public override bool CanRead => true; public override bool CanSeek => true; public override bool CanWrite => true; public override long Length => 0; public override long Position { get; set; } = 0; public override void Flush() { } public override int Read(byte[] buffer, int offset, int count) { return 0; } public override long Seek(long offset, SeekOrigin origin) { return 0; } public override void SetLength(long value) { } public override void Write(byte[] buffer, int offset, int count) { } } ```
claunia added the bug label 2026-01-29 22:08:24 +00:00
claunia commented 2026-01-29 22:08:25 +00:00
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@adamhathcock commented on GitHub (Jul 7, 2017):

It's probably because you're returning 0 on Read which means the stream is empty. I don't think decompression likes trying to operation on a zero byte stream.

@adamhathcock commented on GitHub (Jul 7, 2017): It's probably because you're returning 0 on Read which means the stream is empty. I don't think decompression likes trying to operation on a zero byte stream.
claunia commented 2026-01-29 22:08:25 +00:00
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@KvanTTT commented on GitHub (Jul 8, 2017):

But I should not use WriteEntryTo method for getting rid of exception.

@KvanTTT commented on GitHub (Jul 8, 2017): But I should not use `WriteEntryTo` method for getting rid of exception.
claunia commented 2026-01-29 22:08:25 +00:00
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@adamhathcock commented on GitHub (Jul 8, 2017):

I don’t know offhand but I may just have a try/catch that’s hiding that exception in that extension.

@adamhathcock commented on GitHub (Jul 8, 2017): I don’t know offhand but I may just have a try/catch that’s hiding that exception in that extension.
claunia commented 2026-01-29 22:08:26 +00:00
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@KvanTTT commented on GitHub (Jul 8, 2017):

I tried to wrap a reader.MoveToNextEntry() to try/catch block. But in this case, not all files being processed. Although they should.

@KvanTTT commented on GitHub (Jul 8, 2017): I tried to wrap a `reader.MoveToNextEntry()` to try/catch block. But in this case, not all files being processed. Although they should.
claunia commented 2026-01-29 22:08:26 +00:00
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@adamhathcock commented on GitHub (Jul 8, 2017):

Sorry. I finally understand what you're trying to: just skip a .DS_Store file but it isn't working. I've reproduced it.

The dummy stream stuff you mentioned doesn't have anything to do with it.

@adamhathcock commented on GitHub (Jul 8, 2017): Sorry. I finally understand what you're trying to: just skip a .DS_Store file but it isn't working. I've reproduced it. The dummy stream stuff you mentioned doesn't have anything to do with it.
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Reference: starred/sharpcompress#210
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