ExcelReaderFactory.CreateReader throwing exception for End of Central Directory mismatch when called with a MemoryStream

Given the following:

private static void diffZipArchiveEntry(ZipArchiveEntry zipArchiveEntry1, ZipArchiveEntry zipArchiveEntry2)
{
    using (var stream1 = zipArchiveEntry1.Open())
    using (var stream2 = zipArchiveEntry2.Open())
    using (var xlsxReader1 = ExcelReaderFactory.CreateReader(stream1))
    using (var xlsxReader2 = ExcelReaderFactory.CreateReader(stream2))
    {
        // compare the two streams
    }
}

A System.NotSupportedException is thrown on the factory method. Just wanted to see if this intentional or not and whether I have to hit the disk and extract these .zip files before comparing the .xlsx inside them or whether it’s another issue entirely.

[andersnm]

Hi,

ExcelDataReader requires a seekable stream as input, and after verifying with a little program, it appears ZipArchiveEntry.Open() does not return a seekable stream.

To avoid the disk, there’s also an option to extract into a MemoryStream and pass that to the ExcelReaderFactory, if appropriate for your use case.

            var zip = System.IO.Compression.ZipFile.OpenRead("..\\..\\test.zip");
            var entry = zip.Entries[0];
            var stream = entry.Open();
            Console.WriteLine("Can seek: " + stream.CanSeek.ToString());

            // Output:
            // Can seek: False

[atecce]

Rofl. Looks like I tried to load the same stream into a memory stream twice. Thanks for all your help!