为什么？重构后的 C# 错误：'The stream is invalid or no corresponding signature was found.'

Question

这是这里的后续问题：使用SevenZipSharp将流解压缩为字符串。

以下代码的工作原理是它获取字符串并成功压缩和解压缩它。

using System;
using System.IO;
using SevenZip;
namespace _7ZipWrapper
{
public class ProgramOriginal
{
public static void Main()
// This should be broken into separate methods
{
// Setup Input String
var strToCompress = "This String"; // will pass as parameter
var memStreamToCompress = new MemoryStream();
var StringToStream = new StreamWriter(memStreamToCompress);
StringToStream.Write(strToCompress);
StringToStream.Flush();
// Confirm the Input Stream is As-Expected
memStreamToCompress.Position = 0;
var MemoryAsString = new StreamReader(memStreamToCompress);
Console.WriteLine("Stream in memory: " + MemoryAsString.ReadToEnd());
Console.ReadKey();
// Setup the SevenZip Dll
SevenZipCompressor.SetLibraryPath(@"C:Temp7za64.dll");
// Set up a compressor...
SevenZipCompressor SevenZipC = new SevenZipCompressor();
SevenZipC.CompressionMethod = CompressionMethod.Ppmd;
SevenZipC.CompressionLevel = global::SevenZip.CompressionLevel.Ultra;
SevenZipC.ScanOnlyWritable = true;
// Compress PassedStream -> CompressedStream
var compressedMemoryStream = new MemoryStream();
SevenZipC.CompressStream(memStreamToCompress, compressedMemoryStream, "Optional Password Field");
compressedMemoryStream.Position = 0;
StreamReader compressedMemoryAsString = new StreamReader(compressedMemoryStream);
// Show that we have a compressed String
compressedMemoryStream.Position = 0;
Console.WriteLine(compressedMemoryAsString.ReadToEnd());
Console.ReadKey();
// Set up a decompressor... (only needs to know what to decompress)
compressedMemoryStream.Position = 0;
var SevenZipE = new SevenZip.SevenZipExtractor(compressedMemoryStream, "Optional Password Field");
// Decompress CompressedStream
var DecompressedMemoryStream = new MemoryStream();
SevenZipE.ExtractFile(0, DecompressedMemoryStream);
// Show that DecompressedMemoryStream is valid
DecompressedMemoryStream.Position = 0;
StreamReader decompressedStreamAsText = new StreamReader(DecompressedMemoryStream);
Console.WriteLine("Decompressed String: " + decompressedStreamAsText.ReadToEnd());
Console.ReadKey();
}
}
}

但是，上面的代码显然在当前形式下没有什么好处(这注定要成为COM DLL(。

我以为我在家里很忙，重构将是轻而易举的，但是，我试图将代码重新排列成有用的东西让我不知所措，为什么下面的代码会抛出 System.ArgumentException("流无效或找不到相应的签名"(，但上面的代码运行没有问题。

从根本上说，一定存在某种差异，但我不知道是什么原因造成的，以及如何解决。附有简要解释的解决方案将不胜感激。

using System;
using System.IO;
using SevenZip;
namespace _7ZipWrapper
{
public class Program
{
public static void Main()
{
// Setup Input String
var strToCompress = "This String"; // will eventually pass as parameter

// Convert input string to memory stream
var memStreamToCompress = StringToStream(strToCompress);

// Confirm the Input Stream is As-Expected
memStreamToCompress.Position = 0;
var MemoryAsString = new StreamReader(memStreamToCompress);
Console.WriteLine("Stream in memory: " + MemoryAsString.ReadToEnd());
Console.ReadKey();
// Compress the Stream
memStreamToCompress.Position = 0;
var compressedString = StreamCompress(memStreamToCompress, "password");
// Decompress the String
var memStreamToRestore = StringToStream(compressedString);
memStreamToRestore.Position = 0;
var decompressedString = StreamDecompress(memStreamToRestore, "password");
Console.WriteLine(decompressedString);
Console.ReadKey();
}
private static MemoryStream StringToStream(string strToMemoryStream)
{
var memoryStream = new MemoryStream();
var writer = new StreamWriter(memoryStream);
writer.Write(strToMemoryStream);
writer.Flush();
return memoryStream;
}
private static MemoryStream StringToStream1(string strToMemoryStream)
{
var memoryStream = new MemoryStream();
var writer = new StreamWriter(memoryStream);
writer.Write(strToMemoryStream);
writer.Flush();
return memoryStream;
}

private static string StreamCompress(MemoryStream memStreamToCompress, string optionalPassword)
{
// Setup the SevenZip Dll
SevenZipCompressor.SetLibraryPath(@"C:Temp7za64.dll");
// Set up a compressor...
SevenZipCompressor SevenZip = new SevenZipCompressor();
SevenZip.CompressionMethod = CompressionMethod.Ppmd;
SevenZip.CompressionLevel = global::SevenZip.CompressionLevel.Ultra;
SevenZip.ScanOnlyWritable = true;
// Compress PassedStream -> CompressedStream
var compressedMemoryStream = new MemoryStream();
SevenZip.CompressStream(memStreamToCompress, compressedMemoryStream, optionalPassword); // "Optional Password Field"
compressedMemoryStream.Position = 0;
StreamReader compressedMemoryAsString = new StreamReader(compressedMemoryStream);
return compressedMemoryAsString.ReadToEnd();
}
private static string StreamDecompress(MemoryStream compressedMemoryStream, string optionalPassword)
{
// Setup the SevenZip Dll
SevenZipExtractor.SetLibraryPath(@"C:Temp7za64.dll");
// Set up a decompressor... (only needs to know what to decompress)
compressedMemoryStream.Position = 0;
// CRASHES Next Line: System.ArgumentException: 'The stream is invalid or no corresponding signature was found.'
var SevenZip = new SevenZip.SevenZipExtractor(compressedMemoryStream, optionalPassword);  
// Decompress CompressedStream
var DecompressedMemoryStream = new MemoryStream();
SevenZip.ExtractFile(0, DecompressedMemoryStream);
// Show that DecompressedMemoryStream is valid
DecompressedMemoryStream.Position = 0;
StreamReader decompressedStreamAsText = new StreamReader(DecompressedMemoryStream);
return decompressedStreamAsText.ReadToEnd();
}
}
}

注意：虽然我很欣赏这段代码可能存在多个问题，但我正在学习，并打算在 CodeReview 上进行下一次迭代。也就是说，请随时提供建议，但现在这对我来说是一个学习练习。蒂亚

Answer 1

您的工作代码解压缩compressedMemoryStream.损坏的代码解压缩了从compressedMemoryStream创建的字符串。

正如我在你之前的问题中所说，压缩的结果不是文本。如果必须将其表示为文本，则应使用 Base64 或十六进制。但是，仅仅从中读取它，就好像它是 UTF-8 编码的文本(这就是你现在正在做的事情(根本行不通。

您的StreamCompress方法的结果可能应该是byte[]。这很容易实现：

// Note: changed input type to just Stream to make it more general
private static byte[] StreamCompress(Stream input, string optionalPassword)
{
SevenZipCompressor.SetLibraryPath(@"C:Temp7za64.dll");
SevenZipCompressor SevenZip = new SevenZipCompressor();
SevenZip.CompressionMethod = CompressionMethod.Ppmd;
SevenZip.CompressionLevel = global::SevenZip.CompressionLevel.Ultra;
SevenZip.ScanOnlyWritable = true;
var output = new MemoryStream();
SevenZip.CompressStream(input, output, optionalPassword);
// You don't even need to rewind when you call ToArray
return output.ToArray();
}

当您想要解压缩时，只需创建一个MemoryStream来包装该字节数组，作为众多选项之一。

如果你真的需要结果作为字符串，你可以调用Convert.ToBase64String，然后调用Convert.FromBase64String来取回原始字节。与您当前的方法不同，这不会丢失信息。

我还应该指出，除非你想要 7zip 特定的压缩，否则也有很多纯粹管理的压缩库可用。

Answer 2

C# 使用 SevenZipSharp 压缩和解压缩字符串

基本问题是我没有正确使用字符串，将内存流转换为字符串不起作用。解决方案使用 base64 编码使压缩字符串可移植;这使它能够存储在适合我需求的XML/JSON文件中。谢谢希普顿@Daisy(见：这个答案(。

来自 VBA 的构造函数的使用(在更新时传递参数(并不是很明显，但这很有帮助。这是关键：

// Create a memory stream from the input: base64 --> bytes --> memStream
Byte[] compBytes = Convert.FromBase64String(input);
MemoryStream compStreamIn = new MemoryStream(compBytes);

希望这对其他人有所帮助：

using System;
using System.IO;
using System.Text;
using SevenZip;
namespace _7ZipWrapper
{
public class ProgramToModify
{
public static void Main()
{
var input = "Some string"; // Input String will pass as parameter
var compressed = MyEncode(input);
Console.WriteLine("Compressed String: " + compressed);
var decodedString = myDecode(compressed);
Console.WriteLine("Decompressed String: " + decodedString);
Console.ReadKey();
}
// Returns compressed and encoded base64 string from input 
private static String MyEncode(string input) 
{
// Setup the SevenZip Dll
SevenZipCompressor.SetLibraryPath(@"C:Temp7za64.dll");
SevenZipCompressor SevenZipC = new SevenZipCompressor();
SevenZipC.CompressionMethod = CompressionMethod.Ppmd;
SevenZipC.CompressionLevel = global::SevenZip.CompressionLevel.Ultra;
SevenZipC.ScanOnlyWritable = true;
var memoryStream = new MemoryStream(); // Create Memory Stream
var streamWriter = new StreamWriter(memoryStream);
streamWriter.Write(input); // streamWriter writes input to memoryStream
streamWriter.Flush();
// Compress: memoryStream -> cmpdMemoryStream
var cmpdMemoryStream = new MemoryStream();
SevenZipC.CompressStream(memoryStream, cmpdMemoryStream, "Optional Password Field");
Byte[] bytes = cmpdMemoryStream.ToArray();
return Convert.ToBase64String(bytes);
}

// Returns plain string from compressed and encoded input
private static String myDecode(string input) 
{
// Create a memory stream from the input: base64 --> bytes --> memStream
Byte[] compBytes = Convert.FromBase64String(input);
MemoryStream compStreamIn = new MemoryStream(compBytes);
SevenZipExtractor.SetLibraryPath(@"C:Temp7za64.dll");
var SevenZipE = new SevenZip.SevenZipExtractor(compStreamIn, "Optional Password Field");
var OutputStream = new MemoryStream();
SevenZipE.ExtractFile(0, OutputStream);
var OutputBase64 = Convert.ToBase64String(OutputStream.ToArray());
Byte[] OutputBytes = Convert.FromBase64String(OutputBase64);
string output = Encoding.UTF8.GetString(OutputBytes);
return output;
}
}
}