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    <p>This is a base class for a component that needs to handle data that is either uncompressed, PKZIP compressed (sharpziplib) or GZip compressed (built in .net). Perhaps a bit more than you need but should get you going. This is an example of using @PhonicUK's suggestion to parse the header of the data stream. The derived classes you see in the little factory mathod handled the specifics of PKZip and GZip decompression.</p> <pre><code>abstract class Expander { private const int ZIP_LEAD_BYTES = 0x04034b50; private const ushort GZIP_LEAD_BYTES = 0x8b1f; public abstract MemoryStream Expand(Stream stream); internal static bool IsPkZipCompressedData(byte[] data) { Debug.Assert(data != null &amp;&amp; data.Length &gt;= 4); // if the first 4 bytes of the array are the ZIP signature then it is compressed data return (BitConverter.ToInt32(data, 0) == ZIP_LEAD_BYTES); } internal static bool IsGZipCompressedData(byte[] data) { Debug.Assert(data != null &amp;&amp; data.Length &gt;= 2); // if the first 2 bytes of the array are theG ZIP signature then it is compressed data; return (BitConverter.ToUInt16(data, 0) == GZIP_LEAD_BYTES); } public static bool IsCompressedData(byte[] data) { return IsPkZipCompressedData(data) || IsGZipCompressedData(data); } public static Expander GetExpander(Stream stream) { Debug.Assert(stream != null); Debug.Assert(stream.CanSeek); stream.Seek(0, 0); try { byte[] bytes = new byte[4]; stream.Read(bytes, 0, 4); if (IsGZipCompressedData(bytes)) return new GZipExpander(); if (IsPkZipCompressedData(bytes)) return new ZipExpander(); return new NullExpander(); } finally { stream.Seek(0, 0); // set the stream back to the begining } } } </code></pre>
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    1. COThis is helpful but from the research I have done the PK file header or magic number is not a reliable way of determining if a file is zip. Thank you though.
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      1. USSean Dunford
    2. COHaven't had trouble with that but this is from a system where the sources of the compressed data are well understood and controlled. Good luck!
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    3. COI am going to have to do an audit on our file system to be sure. I believe the mix of a PK magic number check, file extension, and try catch on unzip will be enough. We originally wanted to avoid using a try catch to determine if the file was a zip but it has to be in there. Even if we assume a zip on magic number we still need to try catch to determine if the zip is corrupted. I wish I could rep you but too noob right now. We also have reworked how we will upload files to remove some of the ambiguity. Thanks again.
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