5
下面是一个展示问题的C＃程序。为什么Socket.Receive超时就当超时时间设置为无限半关闭的连接？
服务器启动，监听套接字。客户端连接到服务器，发送消息时，使用关机（SocketShutdown.Send）关闭其连接的发送一半让服务器知道该消息的结尾是，并等待来自服务器的响应。服务器读取消息，做一些冗长的计算（在这里模拟一个睡眠呼叫），向客户端发送消息并关闭连接。
在Windows上，客户端的接收呼叫在2分钟后总是失败，“连接尝试失败，因为连接方在一段时间后没有正确响应，或者建立的连接失败，因为连接的主机未能响应”，甚至尽管超时设置为无限。
如果我使用Mono在Linux中运行程序，即使将“冗长操作”设置为10分钟，也不会发生超时，但是它发生在Windows中是否使用Mono或.NET运行。如果我将超时设置为1秒，则在1秒后超时。换句话说，它在我设定的超时时间内超时，或者2分钟，以较少者为准。
其中服务器发送消息到客户端，没有消息从客户端到服务器和没有半关闭，工作与无超时预期类似的示例程序。
我可以通过修改我的协议来解决这个问题，使用一些其他方法向服务器指示消息何时完成（可能是消息的长度为消息的前缀）。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？
据我所知，只有其发送半闭的连接应能继续无限期地接收数据。在Windows的这样一个基本部分中似乎不太可能存在缺陷。难道我做错了什么？
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);
}
}
}
}
}
下面的程序添加前缀4个字节的消息长度的消息，而不是使用socket.Shutdown（SocketShutdown.Send）以表示邮件的末尾。超时不不发生此计划。
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);
}
}
}
}
}
什么是赏金？你回答自己的问题不是吗？ – jeremy
是的，发布赏金后几天没有得到真正的答案。 –