c#流读取和反序列化

Question

我有这样的代码:

public static List<ReplicableObject> ParseStreamForObjects(Stream stream) 
{
   List<ReplicableObject> result = new List<ReplicableObject>();
   while (true) 
   {
      // HERE I want to check that there's at least four bytes left in the stream
      BinaryReader br = new BinaryReader(stream);
      int length = br.ReadInt32();
      // HERE I want to check that there's enough bytes left in the stream
      byte[] bytes = br.ReadBytes(length);
      MemoryStream ms = new MemoryStream(bytes);
      ms.Position = 0;
      result.Add((ReplicableObject) Formatter.Deserialize(ms));
      ms.Close();
      br.Close();
   }
   return result;
}

不幸的是，流对象总是一个TCP流，这意味着没有查找操作。那么，我如何检查以确保我没有超出我放置//HERE注释的流呢?

Answer 1

我认为没有任何方法可以查询NetworkStream以找到您正在寻找的数据。你可能需要做的是将流提供的任何数据缓冲到另一个数据结构中，然后一旦你知道它有足够的字节，就从该结构中解析对象。

NetworkStream类提供了一个DataAvailable属性，它告诉您是否有任何数据可以读取，Read()方法返回一个值，表明它实际检索了多少字节。您应该能够使用这些值来执行所需的缓冲。

Answer 2

见Skeets先生页面

有时候，你事先不知道流的长度(例如网络流)，只是想把整个流读入缓冲区。这里有一个方法可以做到这一点:

/// <summary>
/// Reads data from a stream until the end is reached. The
/// data is returned as a byte array. An IOException is
/// thrown if any of the underlying IO calls fail.
/// </summary>
/// <param name="stream">The stream to read data from</param>
public static byte[] ReadFully (Stream stream)
{
    byte[] buffer = new byte[32768];
    using (MemoryStream ms = new MemoryStream())
    {
        while (true)
        {
            int read = stream.Read (buffer, 0, buffer.Length);
            if (read <= 0)
                return ms.ToArray();
            ms.Write (buffer, 0, read);
        }
    }
}

这应该给你一些想法。一旦有了字节数组，检查Length就很容易了。

在您的示例中，它看起来像这样:

int bytes_to_read = 4;
byte[] length_bytes = new byte[bytes_to_read];
int bytes_read = stream.Read(length_bytes, 0, length_bytes.Length);
// Check that there's at least four bytes left in the stream
if(bytes_read != bytes_to_read) break;
int bytes_in_msg = BitConverter.ToInt32(length_bytes);
byte[] msg_bytes = new byte[bytes_in_msg];
bytes_read = stream.Read(msg_bytes, 0, msg_bytes.Length);
// Check that there's enough bytes left in the stream
if(bytes_read != bytes_in_msg ) break;
...