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Because System.IO.Compression.ZipArchive.CreateEntry completely discards the CompressionLevel argument, one cannot properly add zero-byte archive entries.
CompressionLevel.NoCompression should be translated to SharpZipLib's CompressionMethod.Stored to ensure the entry is stored but not compressed.
Without translating NoCompression to Stored, invalid archives are created:
$ unzip foo.zip
error: invalid compressed data to inflate
The corefx System.IO.Compression (NuGet) correctly handles CompressionLevel.NoCompression:
$ unzip foo.zip
It further does the right thing when the argument is omitted (defaulting to CompressionLevel.Optimal) by presumably setting the entry to stored instead of compressed if _no data was written to the archive stream_.
We will be using the NuGet from corefx from now on, since it also eliminates the SharpZipLib dependency, but I wanted to file this regardless.
mono master now uses CoreFX implementation which should resolved this issue as well.