GZipStream and decompression

问题:

I have code that should do the compression:

FileStream fs = new FileStream("g:\\gj.txt", FileMode.Open);
FileStream fd = new FileStream("g:\\gj.zip", FileMode.Create);
GZipStream csStream = new GZipStream(fd, CompressionMode.Compress);

byte[] compressedBuffer = new byte[500];
int offset = 0;
int nRead;

nRead = fs.Read(compressedBuffer, offset, compressedBuffer.Length);
while (nRead > 0)
{
    csStream.Write(compressedBuffer, offset, nRead);
    offset = offset + nRead;
    nRead = fs.Read(compressedBuffer, offset, compressedBuffer.Length);
}

fd.Close();
fs.Close();

and I think it does, but I want to decompress what was compressed the way above. I do somethink like that:

FileStream fd = new FileStream("g:\\gj.new", FileMode.Create);
FileStream fs = new FileStream("g:\\gj.zip", FileMode.Open);
GZipStream csStream = new GZipStream(fs, CompressionMode.Decompress);

byte[] decompressedBuffer = new byte[500];
int offset = 0;
int nRead;

nRead=csStream.Read(decompressedBuffer, offset, decompressedBuffer.Length);
while (nRead > 0)
{
    fd.Write(decompressedBuffer, offset, nRead);
    offset = offset + nRead;
    nRead = csStream.Read(decompressedBuffer, offset, decompressedBuffer.Length);
}

fd.Close();
fs.Close();

and here it doesn't... I've got nRead = 0 befeore entering the loop... What I do wrong?? The test file I use is the simpliest TEXT file (size: 104 bytes)...

回答1:

My first thought is that you haven't closed csStream. If you use using this happens automatically. Since gzip buffers data, you could be missing some.

Secondly; don't increment offset; that is the offset in the buffer (not the stream). Leave at 0:

using (Stream fs = File.OpenRead("gj.txt"))
using (Stream fd = File.Create("gj.zip"))
using (Stream csStream = new GZipStream(fd, CompressionMode.Compress))
{
    byte[] buffer = new byte[1024];
    int nRead;
    while ((nRead = fs.Read(buffer, 0, buffer.Length))> 0)
    {
        csStream.Write(buffer, 0, nRead);
    }
}

using (Stream fd = File.Create("gj.new.txt"))
using (Stream fs = File.OpenRead("gj.zip"))
using (Stream csStream = new GZipStream(fs, CompressionMode.Decompress))
{
    byte[] buffer = new byte[1024];
    int nRead;
    while ((nRead = csStream.Read(buffer, 0, buffer.Length)) > 0)
    {
        fd.Write(buffer, 0, nRead);
    }
}

回答2:

The two methods I have are like James Roland mentioned.

private static byte[] Compress(HttpPostedFileBase file)
{
    var to = new MemoryStream();
    var from = new GZipStream(to, CompressionMode.Compress);
    file.InputStream.CopyTo(from);
    from.Close();
    return to.ToArray();
}

private byte[] Decompress(byte [] img)
{
    var to = new MemoryStream();
    var from = new MemoryStream(img);
    var compress = new GZipStream(from, CompressionMode.Decompress);
    compress.CopyTo(to);
    from.Close();
    return to.ToArray();
}

However, I'm using an upload with

Request.Files[0] 

then compress and save in the db. Then I pull the img out, decompress and set a src with

$"data:image/gif;base64,{ToBase64String(Decompress(img))}";

回答3:

Code below demonstrates compression and decompression using GZipStream:

using System;
using System.IO;
using System.IO.Compression;

// ...
    static void Main(string[] args)
    {
        string folder = @"c:\temp";
        string dataPath = Path.Combine(folder, "data.dat");
        string compressedPath = Path.Combine(folder, "compressed.gz");
        string decompressedPath = Path.Combine(folder, "decompressed.dat");

        using (FileStream fileReader = File.OpenRead(dataPath))
        using (FileStream fileWriter = File.Create(compressedPath))
        using (GZipStream compressionStream = new GZipStream(fileWriter, CompressionMode.Compress))
        {
            // Compresses and writes byte array contents to file

            int readlength = 0;
            byte[] buffer = new byte[1024];

            do
            {
                readlength = fileReader.Read(buffer, 0, buffer.Length);
                compressionStream.Write(buffer, 0, readlength);

            } while (readlength > 0);
        }

        using (FileStream fileReader = File.OpenRead(compressedPath))
        using (FileStream fileWriter = File.OpenWrite(decompressedPath))
        using (GZipStream compressionStream = new GZipStream(fileReader, CompressionMode.Decompress))
        {
            // Decompresses and reads data from stream to file

            int readlength = 0;
            byte[] buffer = new byte[1024];

            do
            {
                readlength = compressionStream.Read(buffer, 0, buffer.Length);
                fileWriter.Write(buffer, 0, readlength);

            } while (readlength > 0);
        }

        FileInfo dataFile = new FileInfo(dataPath);
        FileInfo compressedFile = new FileInfo(compressedPath);
        FileInfo decompressedFile = new FileInfo(decompressedPath);
        Console.WriteLine($"Uncompressed file size: {dataFile.Length} bytes");
        Console.WriteLine($"Compressed file size: {compressedFile.Length} bytes");
        Console.WriteLine($"Decompressed file size: {decompressedFile.Length} bytes");

        Console.Write("Press any key to quit . . . ");
        Console.ReadKey(true);
    }