Question

我正在尝试使用ZLIB .NET库中的字典，但ZStream成员inflateSetDictionary始终返回Z_STREAM_ERROR。我已将此跟踪到Inflate.inflateSetDictionary的子调用，该调用测试是否（z.istate.mode == DICT0）

有没有人知道如何在这个库中使用字典或知道任何好的例子。我的代码的简化版本如下所示......

public class Form1 : System.Windows.Forms.Form
{
    static private string sDictionary = "VALUE1,VALUE2,VALUE3";

    class GZOutputStream : ZOutputStream
    {
        public GZOutputStream(Stream in_Renamed)
            : base(in_Renamed)
        {

            byte[] dictionary = System.Text.ASCIIEncoding.ASCII.GetBytes(sDictionary);
            z.inflateSetDictionary(dictionary, dictionary.Length);
        }

        public GZOutputStream(Stream in_Renamed, int level)
            : base(in_Renamed, level)
        {

            byte[] dictionary = System.Text.ASCIIEncoding.ASCII.GetBytes(sDictionary);
            z.deflateSetDictionary(dictionary, dictionary.Length);
        }
    }


    class GZInputStream : ZInputStream
    {
        public GZInputStream(Stream in_Renamed)
            : base(in_Renamed)
        {

            byte[] dictionary = System.Text.ASCIIEncoding.ASCII.GetBytes(sDictionary);
            z.inflateSetDictionary(dictionary, dictionary.Length);
        }

        public GZInputStream(Stream in_Renamed, int level)
            : base(in_Renamed, level)
        {

            byte[] dictionary = System.Text.ASCIIEncoding.ASCII.GetBytes(sDictionary);
            z.deflateSetDictionary(dictionary, dictionary.Length);
        }
    }


    public static void CopyStream(System.IO.Stream input, System.IO.Stream output)
    {
        byte[] buffer = new byte[2000];
        int len;
        while ((len = input.Read(buffer, 0, 2000)) > 0)
        {
            output.Write(buffer, 0, len);
        }
        output.Flush();
    }

    private void compressFile(string inFile, string outFile)
    {
        FileStream outFileStream = new System.IO.FileStream(outFile, System.IO.FileMode.Create);
        GZOutputStream outZStream = new GZOutputStream(outFileStream, 1); // zlibConst.Z_DEFAULT_COMPRESSION);
        System.IO.FileStream inFileStream = new System.IO.FileStream(inFile, System.IO.FileMode.Open);          
        try
        {
            CopyStream(inFileStream, outZStream);
        }
        finally
        {
            outZStream.Close();
            outFileStream.Close();
            inFileStream.Close();
        }
    }


    private void decompressFile(string inFile, string outFile)
    {
        FileStream outFileStream = new FileStream(outFile, FileMode.Create);
        GZOutputStream outZStream = new GZOutputStream(outFileStream);
        FileStream inFileStream = new FileStream(inFile, FileMode.Open);            
        try
        {
            CopyStream(inFileStream, outZStream);
        }
        finally
        {
            outZStream.Close();
            outFileStream.Close();
            inFileStream.Close();
        }
    }

}

Answer 1

我设法通过字典使zlib压缩工作基于DotNetZip（nuget，github）。

由于api调用既不需要明显的，也不需要记录，也不需要简短，因此我将包装器放在它自己的nuget包ZlibWithDictionary（nuget，github）中。

用法很简单：

var compressed_byte_array = DeflateCompression.ZlibCompressWithDictionary(
    bytes_array_to_compress, 
    CompressionLevel.Default, 
    null /*use default window size in bits; possible values 9-15*/, 
    CompressionStrategy.Default, 
    byte_array_of_dictionary
);
var decompressed_byte_array = DeflateCompression.ZlibDecompressWithDictionary(
    compressed_byte_array,
    byte_array_of_dictionary
);

如果您希望手动使用相应的zlib apis，则可以仔细阅读the source for the DeflateCompression wrapper。

Answer 2

虽然我没有完成解决我的问题，但我想分享我的进展......

解压缩数据流时，必须等到inflate（..）函数返回Z_NEED_DICT，因此我将以下代码段添加到ZLIB类ZInputStream和ZOutputStream中，以检查从z.inflate返回的错误值...

            if (err == zlibConst.Z_NEED_DICT)
            {
                byte[] dictionary = System.Text.ASCIIEncoding.ASCII.GetBytes(sDictionary);
                z.inflateSetDictionary(dictionary, dictionary.Length);
                err = z.inflate(flush_Renamed_Field);
            }

另外，来自Inflate.inflate函数的以下代码部分似乎有错误...

                    case DICT4: 

                    if (z.avail_in == 0)
                        return r; r = f;

                    z.avail_in--; z.total_in++;
                     z.istate.need = ((z.next_in[z.next_in_index++] & 0xff) << 24) & unchecked((int)0xff000000L);
                    z.istate.mode = DICT3;
                    goto case DICT3;

在此代码中，z.istate.need的值设置为值0xffffffffxx000000，这是不正确的，因为顶部位应为零，例如0x00000000xx0000。

以下更改修复了此问题..

z.istate.need = ((z.next_in[z.next_in_index++] & 0xff) << 24) & 0xff000000L;

如何在ZLIB.NET中使用字典？

2 个答案: