-1 returned from ZipEntry.ExternalFileAttributes

[emmayspark]

Steps to reproduce

1. Zip a file on Linux using Info-Zip
2. Unzip using the library
3. Try to retrieve the file permissions
   int unixFilePermission = zipEntry.ExternalFileAttributes;

Expected behavior

unixFilePermission returns the right int value

Actual behavior

ExternalFileAttributes returns -1 for all extracted files (zip entry)

Version of SharpZipLib

1.3.3

Obtained from (only keep the relevant lines)

• Package installed using NuGet

[piksel]

Could you provide the code you are using?
For ZipFile it always reads the four bytes from the central headers and assign them to the entry:

SharpZipLib/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs

Line 3629 in 71fe846

ExternalFileAttributes = (int)externalAttributes

So that would mean that the actual value inside the file is actually -1, or perhaps there is something else going on with how you read them...

[emmayspark]

Thanks @piksel

using (var zipInputStream = new ZipInputStream(zipFile))
 {
    while (zipInputStream.GetNextEntry() is ZipEntry zipEntry
       {
                  var entryFileName = zipEntry.Name;
                  int unixFilePermission = zipEntry.ExternalFileAttributes; // return -1 
        }
 }

Here is the code and zipEntry.ExternalFileAttributes alwasy returns -1.

So you are saying it's reading value from central headers which was set to -1 before I zip?
What does it mean the value is -1 - what permission does it stand for?

[piksel]

Ooh, you are using ZipOutputStream... It doesn't support reading the external file attributes, since those are stored in the end of the file, and not along with the header and file data.

[emmayspark]

thanks @piksel, then this case there is no way I can read external file attributes? I'm looking at the code in GetNextEntry() and seems we might be able to add header and file data.?

SharpZipLib/src/ICSharpCode.SharpZipLib/Zip/ZipInputStream.cs

Line 186 in 71fe846

if (header == ZipConstants.CentralHeaderSignature ||

• also I'm using zipInputStream not outputStream :)

[piksel]

also I'm using zipInputStream not outputStream :)

haha, yeah, that was just a typo of mine.

well, the ZipInputStream reads the zipfile as a stream, from the start to the end. the problem is that zipfiles contains one header just before the data for each entry, but also a "index" at the end of the archive. it's in this index that the external attributes are written, meaning that you would have to seek to the end the input to get to it. this would not be feasible for a streaming zip file, where random access might not be possible.

you could instead used ZipFile to read the archive, which uses the "index" at the end of the file:

using (var zipFile = new ZipFile(outStream))
{
    foreach (ZipEntry zipEntry in zipFile)
    {
        var entryFileName = zipEntry.Name;
        int unixFilePermission = zipEntry.ExternalFileAttributes;
    }
}

[emmayspark]

Thanks In my case, I'm trying to extract and parse data immediately without needing to wait for the ZIP file to buffer. because of the structure of zip archive format, I believe zip permission cannot be retrieved in real-time.

Do you think there is a way to check the point to central directory to retrieve permission while I'm streaming a zip archive?

[piksel]

Not anything I tried, but the central directory is at the very end, so you could make a custom stream wrapper that buffers the reads and permits seeking within the last BUFFER_SIZE bytes. That way you could just open the stream with ZipFile after the last entry has been read, iterate over the entries and just update the permissions.

I think that would work. Reading the data wouldn't work of course, but as long as you allow the seeks, the iteration of the entries should work...