Detecting password protected files

[kemsky]

NPOI Version Used

2.7.5

File Type

• XLSX
• XLS
• DOCX
• XLSM
• OTHER

Use Case

Sometimes files are password protected and we get an exception trying to open it:

ICSharpCode.SharpZipLib.Zip.ZipException: EOF in header
   at ICSharpCode.SharpZipLib.Zip.Compression.Streams.InflaterInputBuffer.ReadLeByte()
   at ICSharpCode.SharpZipLib.Zip.ZipInputStream.SkipUntilNextEntry()
   at ICSharpCode.SharpZipLib.Zip.ZipInputStream.GetNextEntry()
   at NPOI.OpenXml4Net.Util.ZipInputStreamZipEntrySource..ctor(ZipInputStream inp)
   at NPOI.OpenXml4Net.OPC.ZipPackage..ctor(Stream in1, PackageAccess access)
   at NPOI.OpenXml4Net.OPC.OPCPackage.Open(Stream stream, Boolean readOnly)
   at NPOI.Util.PackageHelper.Open(Stream stream, Boolean readOnly)
   at NPOI.XWPF.UserModel.XWPFDocument..ctor(Stream is1)

Description

It would be nice to have at least a meaningful exception thrown or a way to check that file is protected.