【发布时间】：2012-11-20 04:33:54
【问题描述】：
下面是一个演示该问题的 C# 程序。
服务器开始监听一个套接字。客户端连接到服务器，发送消息，使用 Shutdown(SocketShutdown.Send) 关闭其发送的一半连接，让服务器知道消息的结尾在哪里，并等待服务器的响应。服务器读取消息，进行一些冗长的计算（此处模拟睡眠调用），向客户端发送消息，然后关闭连接。
在 Windows 上，客户端的 Receive 调用总是在 2 分钟后失败，并显示“连接尝试失败，因为连接方在一段时间后没有正确响应，或者建立连接失败，因为连接的主机没有响应”，即使超时设置为无限。
如果我在 Linux 中使用 Mono 运行程序，即使我将“长时间操作”设置为 10 分钟也不会发生超时，但无论我使用 Mono 还是 .NET 运行它都会在 Windows 中发生。如果我将超时设置为 1 秒，它会在 1 秒后超时。换句话说，它在我设置的超时时间或 2 分钟内超时，以较小者为准。
一个类似的示例程序，其中服务器向客户端发送消息，没有从客户端到服务器的消息，也没有半关闭，按预期工作，没有超时。
我可以通过修改我的协议来解决这个问题，以使用其他方法在消息完成时向服务器指示（可能在消息前面加上消息的长度）。但我想知道这里发生了什么。为什么当超时设置为无限时，Socket.Receive在半关闭连接上超时？
据我了解，仅发送半关闭的连接应该能够无限期地继续接收数据。 Windows 的这样一个基本部分似乎不太可能存在错误。我做错了吗？
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Net.Sockets;
using System.Net;
using System.Threading.Tasks;
using System.Diagnostics;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
// Start server thread
Thread serverThread = new Thread(ServerStart);
serverThread.IsBackground = true;
serverThread.Start();
// Give the server some time to start listening
Thread.Sleep(2000);
ClientStart();
}
static int PortNumber = 8181;
static void ServerStart()
{
TcpListener listener = new TcpListener(new IPEndPoint(IPAddress.Any, PortNumber));
listener.Start();
while (true)
{
TcpClient client = listener.AcceptTcpClient();
Task connectionHandlerTask = new Task(ConnectionEntryPoint, client);
connectionHandlerTask.Start();
}
listener.Stop();
}
static void ConnectionEntryPoint(object clientObj)
{
using (TcpClient client = (TcpClient)clientObj)
using (NetworkStream stream = client.GetStream())
{
// Read from client until client closes its send half.
byte[] requestBytes = new byte[65536];
int bufferPos = 0;
int lastReadSize = -1;
while (lastReadSize != 0)
{
lastReadSize = stream.Read(requestBytes, bufferPos, 65536 - bufferPos);
bufferPos += lastReadSize;
}
client.Client.Shutdown(SocketShutdown.Receive);
string message = Encoding.UTF8.GetString(requestBytes, 0, bufferPos);
// Sleep for 2 minutes, 30 seconds to simulate a long-running calculation, then echo the client's message back
byte[] responseBytes = Encoding.UTF8.GetBytes(message);
Console.WriteLine("Waiting 2 minutes 30 seconds.");
Thread.Sleep(150000);
try
{
stream.Write(responseBytes, 0, responseBytes.Length);
}
catch (SocketException ex)
{
Console.WriteLine("Socket exception in server: {0}", ex.Message);
}
}
}
static void ClientStart()
{
using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
{
// Set receive timeout to infinite.
socket.ReceiveTimeout = -1;
// Connect to server
socket.Connect(IPAddress.Loopback, PortNumber);
// Send a message to the server, then close the send half of the client's connection
// to let the server know it has the entire message.
string requestMessage = "Hello";
byte[] requestBytes = Encoding.UTF8.GetBytes(requestMessage);
socket.Send(requestBytes);
socket.Shutdown(SocketShutdown.Send);
// Read the server's response. The response is done when the server closes the connection.
byte[] responseBytes = new byte[65536];
int bufferPos = 0;
int lastReadSize = -1;
Stopwatch timer = Stopwatch.StartNew();
try
{
while (lastReadSize != 0)
{
lastReadSize = socket.Receive(responseBytes, bufferPos, 65536 - bufferPos, SocketFlags.None);
bufferPos += lastReadSize;
}
string responseMessage = Encoding.UTF8.GetString(responseBytes, 0, bufferPos);
Console.WriteLine(responseMessage);
}
catch (SocketException ex)
{
// Timeout always occurs after 2 minutes. Why?
timer.Stop();
Console.WriteLine("Socket exception in client after {0}: {1}", timer.Elapsed, ex.Message);
}
}
}
}
}
以下程序使用 4 字节消息长度作为消息前缀，而不是使用 socket.Shutdown(SocketShutdown.Send) 来表示消息结束。此程序中不会发生超时。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Sockets;
using System.Net;
using System.Threading.Tasks;
using System.Diagnostics;
using System.Threading;
namespace WithoutShutdown
{
class Program
{
static void Main(string[] args)
{
// Start server thread
Thread serverThread = new Thread(ServerStart);
serverThread.IsBackground = true;
serverThread.Start();
// Give the server some time to start listening
Thread.Sleep(2000);
ClientStart();
}
static int PortNumber = 8181;
static void ServerStart()
{
TcpListener listener = new TcpListener(new IPEndPoint(IPAddress.Any, PortNumber));
listener.Start();
while (true)
{
TcpClient client = listener.AcceptTcpClient();
Task connectionHandlerTask = new Task(ConnectionEntryPoint, client);
connectionHandlerTask.Start();
}
listener.Stop();
}
static void SendMessage(Socket socket, byte[] message)
{
// Send a 4-byte message length followed by the message itself
int messageLength = message.Length;
byte[] messageLengthBytes = BitConverter.GetBytes(messageLength);
socket.Send(messageLengthBytes);
socket.Send(message);
}
static byte[] ReceiveMessage(Socket socket)
{
// Read 4-byte message length from the client
byte[] messageLengthBytes = new byte[4];
int bufferPos = 0;
int lastReadSize = -1;
while (bufferPos < 4)
{
lastReadSize = socket.Receive(messageLengthBytes, bufferPos, 4 - bufferPos, SocketFlags.None);
bufferPos += lastReadSize;
}
int messageLength = BitConverter.ToInt32(messageLengthBytes, 0);
// Read the message
byte[] messageBytes = new byte[messageLength];
bufferPos = 0;
lastReadSize = -1;
while (bufferPos < messageLength)
{
lastReadSize = socket.Receive(messageBytes, bufferPos, messageLength - bufferPos, SocketFlags.None);
bufferPos += lastReadSize;
}
return messageBytes;
}
static void ConnectionEntryPoint(object clientObj)
{
using (TcpClient client = (TcpClient)clientObj)
{
byte[] requestBytes = ReceiveMessage(client.Client);
string message = Encoding.UTF8.GetString(requestBytes);
// Sleep for 2 minutes, 30 seconds to simulate a long-running calculation, then echo the client's message back
byte[] responseBytes = Encoding.UTF8.GetBytes(message);
Console.WriteLine("Waiting 2 minutes 30 seconds.");
Thread.Sleep(150000);
try
{
SendMessage(client.Client, responseBytes);
}
catch (SocketException ex)
{
Console.WriteLine("Socket exception in server: {0}", ex.Message);
}
}
}
static void ClientStart()
{
using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
{
// Set receive timeout to infinite.
socket.ReceiveTimeout = -1;
// Connect to server
socket.Connect(IPAddress.Loopback, PortNumber);
// Send a message to the server
string requestMessage = "Hello";
byte[] requestBytes = Encoding.UTF8.GetBytes(requestMessage);
SendMessage(socket, requestBytes);
// Read the server's response.
Stopwatch timer = Stopwatch.StartNew();
try
{
byte[] responseBytes = ReceiveMessage(socket);
string responseMessage = Encoding.UTF8.GetString(responseBytes);
Console.WriteLine(responseMessage);
}
catch (SocketException ex)
{
// Timeout does not occur in this program because it does not call socket.Shutdown(SocketShutdown.Send)
timer.Stop();
Console.WriteLine("Socket exception in client after {0}: {1}", timer.Elapsed, ex.Message);
}
}
}
}
}
【问题讨论】：
-
赏金有什么用？你回答了你自己的问题不是吗？
-
是的，在发布赏金几天后并没有得到任何真正的答案。