Compress and decompress a Stream with Compression.

问题:

I am trying to compress and decompress a Stream using Compression.DeflateStream. Compressing seems to work correctly since the code below compresses my Stream to a 110 bytes long array. However, reading the decompressed Stream results in an empty string.

class Program
{
    static void Main(string[] args)
    {
        // Compress a random string value
        string value = Path.GetRandomFileName();
        byte[] compressedBytes;

        using (var writer = new StreamWriter(new MemoryStream()))
        {
            writer.Write(value);
            writer.Flush();
            writer.BaseStream.Position = 0;

            compressedBytes = Compress(writer.BaseStream);
        }

        // Decompress compressed bytes
        Stream decompressedStream = Decompress(compressedBytes);
        // here already applies: decompressedStream.Length == 0

        using (var reader = new StreamReader(decompressedStream))
        {
            string decompressedValue = reader.ReadToEnd();

            if (value == decompressedValue)
                Console.WriteLine("Success");
            else
                Console.WriteLine("Failed");
        }
    }

    private static byte[] Compress(Stream input)
    {
        using (var compressStream = new MemoryStream())
        using (var compressor = new DeflateStream(compressStream, CompressionMode.Compress))
        {
            input.CopyTo(compressor);
            return compressStream.ToArray();
        }
    }

    private static Stream Decompress(byte[] input)
    {
        var output = new MemoryStream();

        using (var compressStream = new MemoryStream(input))
        using (var decompressor = new DeflateStream(compressStream, CompressionMode.Decompress))
            decompressor.CopyTo(output);

        output.Position = 0;
        return output;
    }
}

Can anyone help me on this one? Many thanks.

回答1:

Fix your Compress function:

private static byte[] Compress(Stream input)
{
    using(var compressStream = new MemoryStream())
    using(var compressor = new DeflateStream(compressStream, CompressionMode.Compress))
    {
        input.CopyTo(compressor);
        compressor.Close();
        return compressStream.ToArray();
    }
}

compressed stream was not flushed before returning the resulting byte array.

回答2:

Try closing the streams:

class Program
{
    static void Main(string[] args)
    {
        // Compress a random string value
        string value = DateTime.Now.ToLongTimeString();
        byte[] compressedBytes;

        using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(value)))
        {
            compressedBytes = Compress(stream);
        }


        // Decompress compressed bytes
        using (var decompressedStream = Decompress(compressedBytes))
        using (var reader = new StreamReader(decompressedStream))
        {
            string decompressedValue = reader.ReadToEnd();

            if (value == decompressedValue)
                Console.WriteLine("Success");
            else
                Console.WriteLine("Failed");
        }
    }

    public static byte[] Compress(Stream input)
    {
        using (var compressedStream = new MemoryStream())
        using (var zipStream = new GZipStream(compressedStream, CompressionMode.Compress))
        {
            input.CopyTo(zipStream);
            zipStream.Close();
            return compressedStream.ToArray();
        }
    }

    public static Stream Decompress(byte[] data)
    {
        var output = new MemoryStream();
        using(var compressedStream = new MemoryStream(data))
        using(var zipStream = new GZipStream(compressedStream, CompressionMode.Decompress))
        {
            zipStream.CopyTo(output);
            zipStream.Close();
            output.Position = 0;
            return output;
        }
    }
}

回答3:

All those answers are far away from ideal form because all of you forgot that "using" disposing and closing streams its means that additional Close() is not needed. I think that ideal code will be like this:

public static class CompressionHelper
{
    public static byte[] Compress(byte[] data)
    {
        byte[] compressArray = null;
        try
        {
            using (MemoryStream memoryStream = new MemoryStream())
            {
                using (DeflateStream deflateStream = new DeflateStream(memoryStream, CompressionMode.Compress))
                {
                    deflateStream.Write(data, 0, data.Length);
                }
                compressArray = memoryStream.ToArray();
            }
        }
        catch (Exception exception)
        {
            // do something !
        }
        return compressArray;
    }

    public static byte[] Decompress(byte[] data)
    {
        byte[] decompressedArray = null;
        try
        {
            using (MemoryStream decompressedStream = new MemoryStream())
            {
                using (MemoryStream compressStream = new MemoryStream(data))
                {
                    using (DeflateStream deflateStream = new DeflateStream(compressStream, CompressionMode.Decompress))
                    {
                        deflateStream.CopyTo(decompressedStream);
                    }
                }
                decompressedArray = decompressedStream.ToArray();
            }
        }
        catch (Exception exception)
        {
            // do something !
        }

        return decompressedArray;
    }
}