Zlib-compatible compression streams?

Question

Are System.IO.Compression.GZipStream or System.IO.Compression.Deflate compatible with zlib compression?

Answer 1

DotNetZip includes a DeflateStream, a ZlibStream, and a GZipStream, to handle RFC 1950, 1951, and 1952. The all use the DEFLATE Algorithm but the framing and header bytes are different for each one.

As an advantage, the streams in DotNetZip do not exhibit the anomaly of expanding data size under compression, reported against the built-in streams. Also, there is no built-in ZlibStream, whereas DotNetZip gives you that, for good interop with zlib.

Answer 2

They just compressing the data using zlib or deflate algorithms , but does not provide the output for some specific file format. This means that if you store the stream as-is to the hard drive most probably you will not be able to open it using some application (gzip or winrar) because file headers (magic number, etc ) are not included in stream an you should write them yourself.

Answer 3

gzip is deflate + some header/footer data, like a checksum and length, etc. So they're not compatible in the sense that one method can use a stream from the other, but they employ the same compression algorithm.

Answer 4

I agree with andreas. You probably won't be able to open the file in an external tool, but if that tool expects a stream you might be able to use it. You would also be able to deflate the file back using the same compression class.

Answer 5

From MSDN about System.IO.Compression.GZipStream:

This class represents the gzip data format, which uses an industry standard algorithm for lossless file compression and decompression.

From the zlib FAQ:

The gz* functions in zlib on the other hand use the gzip format.

So zlib and GZipStream should be interoperable, but only if you use the zlib functions for handling the gzip-format.

System.IO.Compression.Deflate and zlib are reportedly not interoperable.

If you need to handle zip files (you probably don't, but someone else might need this) you need to use SharpZipLib or another third-party library.

Answer 6

Starting from .NET Framework 4.5 the System.IO.Compression.DeflateStream class uses the zlib library.

From the class's MSDN article:

This class represents the Deflate algorithm, which is an industry-standard algorithm for lossless file compression and decompression. Starting with the .NET Framework 4.5, the DeflateStream class uses the zlib library. As a result, it provides a better compression algorithm and, in most cases, a smaller compressed file than it provides in earlier versions of the .NET Framework.