我正在编写一个 .NET XMPP 库是为了好玩，正如其他地方所讨论的那样，.NET 4.5 之前的版本中的XmlReader实现不适合从 a 解析 XML，NetworkStream因为它在填充内部 4KB 缓冲区或达到 EOF 之前不会开始解析.
其他图书馆根本不使用来解决这个问题XmlReader。正如前面链接的问题中提到的，jabber-net 使用 Java XML 解析器的一个端口。我在搜索时发现的一个实现 Babel IM 使用它自己的简单 XML 解析器。我不确定 agsXMPP 是做什么的。
但是，随着 .NET 4.5 的发布，新的异步功能XmlReader显然得到了升级，现在可以进行真正的异步解析。因此，我使用它来构建一个相当简单的 XMPP 客户端，该客户端可以连接到服务器并发送和接收消息。
然而，症结实际上似乎在于与服务器断开连接。在断开连接时，我通常只想Dispose()使用我的XmlReader实例和底层流。但是，Dispose()实际上会抛出一个InvalidOperationException带有消息“异步操作已经在进行中”的消息。如果您在异步时调用它...以及消息中的内容。然而，由于 XMPP 的性质，我XmlReader基本上一直在执行异步操作，因为它等待来自服务器的 XML 节从管道中下来。
似乎没有任何方法可以用来告诉它取消任何挂起的XmlReader异步操作，以便我可以Dispose()干净地处理它。有没有比简单地不尝试处理这种情况更好的方法来处理这种情况XmlReader？XMPP规范声明服务器应该</stream:stream>在断开连接时发送结束标记。我可以将其用作不尝试执行另一次异步读取的信号，因为管道中不应有任何其他内容，但不能保证这一点。
这是一些示例代码。LongLivedTextStream基本上模拟一个打开NetworkStream，因为它永远不会到达 EOF，并且会阻塞直到可以读取至少 1 个字节。您可以将 XML 文本“注入”到其中，它XmlReader会很乐意解析，但尝试处置阅读器将触发上述异常。
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml;
namespace Example
{
class LongLivedTextStream : Stream
{
ManualResetEvent moarDatas = new ManualResetEvent(false);
List<byte> data = new List<byte>();
int pos = 0;
public void Inject(string text)
{
data.AddRange(new UTF8Encoding(false).GetBytes(text));
moarDatas.Set();
}
public override int Read(byte[] buffer, int offset, int count)
{
var bytes = GetBytes(count).ToArray();
for (int i = 0; offset + i < buffer.Length && i < bytes.Length; i++)
{
buffer[offset + i] = bytes[i];
}
return bytes.Length;
}
private IEnumerable<byte> GetBytes(int count)
{
int returned = 0;
while (returned == 0)
{
if (pos < data.Count)
{
while (pos < data.Count && returned < count)
{
yield return data[pos];
pos += 1; returned += 1;
}
}
else
{
moarDatas.Reset();
moarDatas.WaitOne();
}
}
}
#region Other Stream Members
public override bool CanRead
{
get { return true; }
}
public override bool CanSeek
{
get { return false; }
}
public override bool CanWrite
{
get { return false; }
}
public override void Flush() { }
public override long Length
{
get { throw new NotSupportedException(); }
}
public override long Position
{
get { throw new NotSupportedException(); }
set { throw new NotSupportedException(); }
}
public override long Seek(long offset, SeekOrigin origin)
{
throw new NotSupportedException();
}
public override void SetLength(long value)
{
throw new NotSupportedException();
}
public override void Write(byte[] buffer, int offset, int count)
{
throw new NotSupportedException();
}
#endregion
}
public class Program
{
public static void Main(string[] args)
{
Test();
Console.ReadLine();
}
public static async void Test()
{
var stream = new LongLivedTextStream();
var reader = XmlReader.Create(stream, new XmlReaderSettings() { Async = true });
var t = Task.Run(() =>
{
stream.Inject("<root>");
Thread.Sleep(2000);
stream.Inject("value");
Thread.Sleep(2000);
stream.Inject("</root>");
Thread.Sleep(2000);
reader.Dispose(); // InvalidOperationException: "An asynchronous operation is already in progress."
Console.WriteLine("Disposed");
});
while (await reader.ReadAsync())
{
bool kill = false;
switch (reader.NodeType)
{
case XmlNodeType.Element:
Console.WriteLine("Start: " + reader.LocalName);
break;
case XmlNodeType.EndElement:
Console.WriteLine("End: " + reader.LocalName);
//kill = true; // I could use a particular EndElement as a signal to not try another read
break;
case XmlNodeType.Text:
Console.WriteLine("Text: " + await reader.GetValueAsync());
break;
}
if (kill) { break; }
}
}
}
}
编辑
此示例使用实际NetworkStream并显示如果 IClose()或Dispose()基础流的ReadAsync()调用XmlReader不会像希望的那样返回 false，而是继续阻塞。
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml;
namespace Example
{
public class Program
{
public static void Main(string[] args)
{
NetworkStream stream = null;
var endpoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 50000);
var serverIsUp = new ManualResetEvent(false);
var doneWriting = new ManualResetEvent(false);
var t1 = Task.Run(() =>
{
var server = new TcpListener(endpoint);
server.Start();
serverIsUp.Set();
var client = server.AcceptTcpClient();
var writer = new StreamWriter(client.GetStream());
writer.Write("<root>"); writer.Flush();
Thread.Sleep(2000);
writer.Write("value"); writer.Flush();
Thread.Sleep(2000);
writer.Write("</root>"); writer.Flush();
Thread.Sleep(2000);
doneWriting.Set();
});
var t2 = Task.Run(() =>
{
doneWriting.WaitOne();
stream.Dispose();
Console.WriteLine("Disposed of Stream");
});
var t3 = Task.Run(async () =>
{
serverIsUp.WaitOne();
var socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
socket.Connect(endpoint);
stream = new NetworkStream(socket, true);
var reader = XmlReader.Create(stream, new XmlReaderSettings() { Async = true });
bool val;
while (val = await reader.ReadAsync())
{
bool kill = false;
switch (reader.NodeType)
{
case XmlNodeType.Element:
Console.WriteLine("Start: " + reader.LocalName);
break;
case XmlNodeType.EndElement:
Console.WriteLine("End: " + reader.LocalName);
//kill = true; // I could use a particular EndElement as a signal to not try another read
break;
case XmlNodeType.Text:
Console.WriteLine("Text: " + await reader.GetValueAsync());
break;
}
if (kill) { break; }
}
// Ideally once the underlying stream is closed, ReadAsync() would return false
// we would get here and could safely dispose the reader, but that's not the case
// ReadAsync() continues to block
reader.Dispose();
Console.WriteLine("Disposed of Reader");
});
Console.ReadLine();
}
}
}