.NET GZipStream 压缩和解压缩

Question

下面这段代码有什么问题。我总是得到 FALSE，这意味着压缩后，解压后的数据与原始值不匹配。

public static bool Test()
        {
            string sample = "This is a compression test of microsoft .net gzip compression method and decompression methods";
            System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
            byte[] data = encoding.GetBytes(sample);
            bool result = false;

            //Compress
            MemoryStream cmpStream;
            cmpStream = new MemoryStream();
            GZipStream hgs = new GZipStream(cmpStream, CompressionMode.Compress);
            hgs.Write(data, 0, data.Length);
            byte[] cmpData = cmpStream.ToArray();

            MemoryStream decomStream;
            decomStream = new MemoryStream(cmpData);
            hgs = new GZipStream(decomStream, CompressionMode.Decompress);
            hgs.Read(data, 0, data.Length);

            string sampleOut = System.BitConverter.ToString(data);

            result = String.Equals(sample, sampleOut) ;
            return result;
        }

如果您能指出我在哪里犯了错误，我将不胜感激。

Answer 1

在 Write 调用后关闭 GZipStream。

如果不调用Close，某些数据可能会被缓冲但尚未写入底层流。

Answer 2

试试这个代码：

public static bool Test()
        {
            string sample = "This is a compression test of microsoft .net gzip compression method and decompression methods";

            System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();

            byte[] data = encoding.GetBytes(sample);
            bool result = false;

            // Compress
            MemoryStream cmpStream = new MemoryStream();

            GZipStream hgs = new GZipStream(cmpStream, CompressionMode.Compress);

            hgs.Write(data, 0, data.Length);

            byte[] cmpData = cmpStream.ToArray();

            MemoryStream decomStream = new MemoryStream(cmpData);

            hgs = new GZipStream(decomStream, CompressionMode.Decompress);
            hgs.Read(data, 0, data.Length);

            string sampleOut = encoding.GetString(data);

            result = String.Equals(sample, sampleOut);
            return result;
        }

问题是您没有使用 ASCIIEncoder 来获取样本数据的字符串。

编辑：这是代码的清理版本，以帮助关闭/处置：

public static bool Test()
        {
            string sample = "This is a compression test of microsoft .net gzip compression method and decompression methods";

            System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();

            byte[] data = encoding.GetBytes(sample);

            // Compress.
            GZipStream hgs;
            byte[] cmpData;

            using(MemoryStream cmpStream = new MemoryStream())
            using(hgs = new GZipStream(cmpStream, CompressionMode.Compress))
            {
                hgs.Write(data, 0, data.Length);
                hgs.Close()

                // Do this AFTER the stream is closed which sounds counter intuitive 
                // but if you do it before the stream will not be flushed
                // (even if you call flush which has a null implementation).
                cmpData = cmpStream.ToArray();
            }  

            using(MemoryStream decomStream = new MemoryStream(cmpData))
            using(hgs = new GZipStream(decomStream, CompressionMode.Decompress))
            {
                hgs.Read(data, 0, data.Length);
            }

            string sampleOut = encoding.GetString(data);

            bool result = String.Equals(sample, sampleOut);
            return result;
        }

Answer 3

解决这个问题需要三个问题。
1. WRITE GZipStream 需要关闭后 :: hgs.Close();

2. GZipStream 读取需要使用 WHILE 循环，并将未压缩数据的较小缓冲区写入 MemoryStream :: outStream.Write( ... );

3. 解压后的byte[]数组的转换需要使用编码转换:: string sampleOut = encoding.GetString(data);

这是最终的代码：-

public static bool Test()
        {
            string sample = "This is a compression test of microsoft .net gzip compression method and decompression methods";
            System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
            byte[] data = encoding.GetBytes(sample);
            bool result = false;

            // Compress 
            MemoryStream cmpStream = new MemoryStream();
            GZipStream hgs = new GZipStream(cmpStream, CompressionMode.Compress, true);

            hgs.Write(data, 0, data.Length);
            hgs.Close();


            //DeCompress
            byte[] cmpData = cmpStream.ToArray();
            MemoryStream decomStream = new MemoryStream(cmpData);

            data = new byte[data.Length];
            hgs = new GZipStream(decomStream, CompressionMode.Decompress, true);

            byte[] step = new byte[16]; //Instead of 16 can put any 2^x
            MemoryStream outStream = new MemoryStream();
            int readCount;

            do
            {
                readCount = hgs.Read(step, 0, step.Length);
                outStream.Write(step, 0, readCount);
            } while (readCount > 0);
            hgs.Close();

            string sampleOut = encoding.GetString(outStream.ToArray());
            result = String.Equals(sample, sampleOut);
            return result; 
        }

我在使用 Microsoft .NET GZipStream 对象进行压缩/解压缩工作时遇到了很大的麻烦。最后，我认为我以正确的方式得到了它。非常感谢大家，因为解决方案来自你们所有人。

Answer 4

这是我的最终解决方案的清理版本：

  [Test]
  public void Test_zipping_with_memorystream()
  {
   const string sample = "This is a compression test of microsoft .net gzip compression method and decompression methods";
   var encoding = new ASCIIEncoding();
   var data = encoding.GetBytes(sample);
   string sampleOut;
   byte[] cmpData;

   // Compress 
   using (var cmpStream = new MemoryStream())
   {
    using (var hgs = new GZipStream(cmpStream, CompressionMode.Compress))
    {
     hgs.Write(data, 0, data.Length);
    }
    cmpData = cmpStream.ToArray();
   }

   using (var decomStream = new MemoryStream(cmpData))
   {
    using (var hgs = new GZipStream(decomStream, CompressionMode.Decompress))
    {
     using (var reader = new StreamReader(hgs))
     {
      sampleOut = reader.ReadToEnd();
     }
    }
   }

   Assert.IsNotNullOrEmpty(sampleOut);
   Assert.AreEqual(sample, sampleOut);
  }