C#压缩和解压缩字节（GZip）

标题：C#压缩和解压缩字节（GZip的使用）

作用：此类在 .NET Framework 2.0 版中是新增的。提供用于压缩和解压缩流的方法和属性。
定义：表示 GZip 数据格式，它使用无损压缩和解压缩文件的行业标准算法。这种格式包括一个检测数据损坏的循环冗余校验值。GZip 数据格式使用的算法与 DeflateStream 类的算法相同，但它可以扩展以使用其他压缩格式。这种格式可以通过不涉及专利使用权的方式轻松实现。gzip 的格式可以从 RFC 1952“GZIP file format specification 4.3（GZIP 文件格式规范 4.3）GZIP file format specification 4.3（GZIP 文件格式规范 4.3）”中获得。此类不能用于压缩大于 4 GB 的文件。

下面给出两个具体Demo:
实例1

//压缩字节
//1.创建压缩的数据流 
//2.设定compressStream为存放被压缩的文件流,并设定为压缩模式
//3.将需要压缩的字节写到被压缩的文件流
public static byte[] CompressBytes(byte[] bytes)
{
    using(MemoryStream compressStream = new MemoryStream())
    {
        using(var zipStream = new GZipStream(compressStream, CompressMode.ComPress))
            zipStream.Write(bytes, 0, bytes.Length);
        return compressStream.ToArray();
    }
}
//解压缩字节
//1.创建被压缩的数据流
//2.创建zipStream对象，并传入解压的文件流
//3.创建目标流
//4.zipStream拷贝到目标流
//5.返回目标流输出字节
public static byte[] Decompress(byte[] bytes)
{
    using(var compressStream = new MemoryStream(bytes))
    {
        using(var zipStream = new GZipStream(compressStream, CompressMode.DeCompress))
        {
            using(var resultStream = new MemoryStream())
            {
                zipStream.CopyTo(resultStream);
                return resultStream.ToArray();
            }
        }
    }
}

实例2(摘自MSDN)：

class Program
    {
        public static int ReadAllBytesFromStream(Stream stream, byte[] buffer)
        {
            int offset = 0;
            int totalCount = 0;
            while (true)
            {
                int bytesRead = stream.Read(buffer, offset, 100);
                if (bytesRead == 0)
                {
                    break;
                }
                offset += bytesRead;
                totalCount += bytesRead;
            }
            return totalCount;
        }

        public static bool CompareData(byte[] buf1, int len1, byte[] buf2, int len2)
        {
            if (len1 != len2)
            {
                Console.WriteLine("Number of bytes in two buffer are diffreent {0}：{1}", len1, len2);
                return false;
            }
            for (int i = 0; i < len1; i++)
            {
                if (buf1[i] != buf2[i])
                {
                    Console.WriteLine("byte {0} is different {1}{2}", i, buf1[i], buf2[i]);
                    return false;
                }
            }
            Console.WriteLine("All byte compare true");
            return true;
        }

        public static void GZipCompressDecompress(string fileName)
        {
            Console.WriteLine("Test compresssion and decompression on file {0}", fileName);
            FileStream infile;
            try
            {
                //Comopress
                infile = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read);
                byte[] buffer = new byte[infile.Length];
                int count = infile.Read(buffer, 0, buffer.Length);
                if (count != buffer.Length)
                {
                    infile.Close();
                    infile.Dispose();
                    Console.WriteLine("Test Failed: Unable to read data from file");
                    return;
                }
                infile.Close();
                MemoryStream ms = new MemoryStream();
                GZipStream compressGZipStream = new GZipStream(ms, CompressionMode.Compress, true);
                Console.WriteLine("Compression");
                compressGZipStream.Write(buffer, 0, buffer.Length);    //从指定字节数组中将压缩的字节写入基础流
                compressGZipStream.Close();
                Console.WriteLine("Original size:{0}, Compressed size:{1}", buffer.Length, ms.ToArray().Length);

                //DeCompress
                ms.Position = 0;
                GZipStream deCompressGZipStream = new GZipStream(ms, CompressionMode.Decompress);
                Console.WriteLine("Decompression");
                byte[] decompressedBuffer = new byte[buffer.Length + 100];

                int totalCount = ReadAllBytesFromStream(deCompressGZipStream, decompressedBuffer);
                Console.WriteLine("Decompressed {0} bytes", totalCount);

                if (!CompareData(buffer, buffer.Length, decompressedBuffer, decompressedBuffer.Length))
                {
                    Console.WriteLine("Error. The two buffers did not compare.");
                }
                deCompressGZipStream.Dispose();
            }
            catch (ArgumentNullException)
            {
                Console.WriteLine("ArgumentNullException:{0}", "Error: The path is null.");
            }
            catch (ArgumentException)
            {
                Console.WriteLine("ArgumentException:{0}", "Error: path is a zero-length string, contains an empty string or one more invlaid characters");
            }
            catch (NotSupportedException)
            {
                Console.WriteLine("NotSupportedException:{0}", "Cite no file, such as 'con:'、'com1'、'lpt1' in NTFS");
            }
            catch (FileNotFoundException)
            {
                Console.WriteLine("FileNotFoundException:{0]", "Find no file");
            }
            catch (IOException)
            {
                Console.WriteLine("IOException:{0}", "Occur I/O error");
            }
            catch (System.Security.SecurityException)
            {
                Console.WriteLine("System.Security.SecurityException{0}:", "The calls has no permission");
            }
            catch (UnauthorizedAccessException)
            {
                Console.WriteLine("UnauthorizedAccessException：{0}", "path specified a file that is read-only, the path is a directory, " +
                    "or caller does not have the required permissions");
            }
        }

        static void Main(string[] args)
        {
            GZipCompressDecompress(@"D:\config.ini");
        }
    }