重温WIN32 API ------ 一个简单的UDP服务器类

最近一个项目需要使用简单的UDP进行通信，为方便调用，使用C++类封装了一个简单的UDP服务器类。

1 基本思路

网络通信程序设计中最难的部分就是IO的处理，不同操作系统平台提供不同的IO处理机制，Windows平台有select模型、完成端口等，Linux平台则是poll和epoll。由于本项目要求简单，通信量也不大，所以没有采用这些与平台相关的IO模型，而是采用简单的专用线程来负责侦听。当收到数据包时，自动调用用户指定的回调函数，算是设计模式中”订阅模式“的简单实现，也是来自于模仿C#中的event机制。

 

多线程程序必须要考虑同步的问题。主线程通过线程安全地设置一个变量来通知UDP侦听线程退出，为防止侦听线程中的recvfrom()一直阻塞而无法退出线程，主线程采用closesocket()来强制侦听线程的recvfrom()返回。（其他让recvfrom退出的方法包括发送专用udp数据包）

 

另外类使用者需要注意的是，回调函数是在侦听线程中执行，所以要避免非UI线程直接更新UI的问题。回调函数如果涉及到窗口UI操作，需要处理数据后通过SendMessage()的方式通知UI线程，然后由UI线程来实际执行UI更新操作。

2 代码实现

就一个UDPServer类，头文件UDPServer.h，实现文件UDPServer.cpp。

 

#pragma once#include <WinSock2.h>#include <Ws2tcpip.h>#include <iphlpapi.h>#pragma comment(lib, "IPHLPAPI.lib")#pragma comment(lib, "WS2_32")#include <vector>using namespace std;typedef void(*UDPRecvFun)(void* sender, BYTE*, int);   // 收到UDP数据包后的回调函数原型/*                            UDP服务器类功能描述：建立UDP侦听，建立一个专用线程负责接收UDP数据包。该类采用类似于C#的事件驱动设计模式。使用样例：void AfterRecv(void* sender, BYTE* data, int len)  // 回调函数实现{   ......}UDPServer pServer = new UDPServer("127.0.0.1", 8888);pServer.AddCallback(AfterRecv);    // 增加一个回调， 收到UDP包后会自动调用此函数pServer->StartUDPServer(); // 开始侦听pServer->StopUDPServer(); // 可选，因为析构函数会自动调用此方法delete pServer;*/class UDPServer{public:UDPServer(unsigned int ip, unsigned short port);UDPServer(char* ip, unsigned short port);~UDPServer();protected:static DWORD WINAPI UDPServerThreadFunc(void* state);void StartUDPServer(unsigned int ip, unsigned short port);void StartUDPServer(char* ip, unsigned short port);void OnRecv(BYTE*, int);private:unsigned long IP;unsigned short port;SOCKET sock; // socketHANDLE tid;  // 侦听线程IDCRITICAL_SECTION cs; // 线程同步用int isEnd; // 是否终止侦听vector<UDPRecvFun> listOnRecv;  // 收到UDP包后的回调函数列表public:SOCKET GetSocket(){ return this->sock; }protected:int GetIsEnd();void SetIsEnd(int n);public:void StartUDPServer();void StopUDPServer();void AddCallback(UDPRecvFun cb); // 增加一个回调函数};

 

#include "stdafx.h"#include "UDPServer.h"#include "LogWriter.h"UDPServer::UDPServer(unsigned int ip, unsigned short port){this->sock = NULL;this->tid = NULL;this->listOnRecv.clear();this->IP = ip;this->port = port;::InitializeCriticalSection(&this->cs);isEnd = 0;}UDPServer::UDPServer(char* ip, unsigned short port){this->sock = NULL;this->tid = NULL;this->listOnRecv.clear();this->IP = ::inet_addr(ip);this->port = port;::InitializeCriticalSection(&this->cs);isEnd = 0;}UDPServer::~UDPServer(){if (this->tid != NULL){StopUDPServer();}::DeleteCriticalSection(&this->cs);}/*功能：线程安全地设置isEnd*/void UDPServer::SetIsEnd(int n){::EnterCriticalSection(&this->cs);this->isEnd = n;::LeaveCriticalSection(&this->cs);}/*功能: 线程安全地读取isEnd*/int UDPServer::GetIsEnd(){::EnterCriticalSection(&this->cs);int r = this->isEnd;::LeaveCriticalSection(&this->cs);return r;}/*功能：停止UDP服务器（线程）*/void UDPServer::StopUDPServer(){if (this->tid != NULL){this->SetIsEnd(1);  // 设置停止标记::closesocket(this->sock);// 唤醒recvfrom() //::shutdown(this->sock, SD_BOTH); 不好用this->sock = NULL;::WaitForSingleObject(this->tid, INFINITE);// 等待UDP专用线程结束this->tid = NULL;}}/*功能：调用回调列表里的所有函数*/void UDPServer::OnRecv(BYTE* data, int len){vector<UDPRecvFun>::iterator it;for (it = this->listOnRecv.begin(); it != this->listOnRecv.end(); it++){if (*it != NULL){(*it)(this, data, len);}}}/*功能:启动UDP侦听服务器参数:ip-侦听IP字符串; port-侦听端口*/void UDPServer::StartUDPServer(char* ip, unsigned short port){unsigned long nIP = ::inet_addr(ip);if (nIP == INADDR_NONE){LOG(L"IP 地址%s 错误");return;}this->StartUDPServer(nIP, port);}/*线程函数传参结构，用于安全地向子线程传参*/class UDPThreadState{public:UDPServer* obj;SOCKET scok;};/*功能：开启UDP侦听线程， 本函数不阻塞参数：ip - 侦听IP，port-侦听端口*/void UDPServer::StartUDPServer(unsigned int ip, unsigned short port){if (this->sock != NULL) return;this->sock = ::socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);if (sock == INVALID_SOCKET){this->sock = NULL;LOG(L"UDP服务器创建socket失败");return;}sockaddr_in sin;sin.sin_family = AF_INET;sin.sin_port = htons(port);sin.sin_addr.S_un.S_addr = ip;if (::bind(sock, (sockaddr*)&sin, sizeof(sin)) == SOCKET_ERROR){LOG(L"bind() failed");return;}wchar_t log[1024];swprintf_s(log, L"UDP服务器绑定到了 %S:%d",::inet_ntoa(sin.sin_addr), ::ntohs(sin.sin_port)); // 注意%S与%sLOG(log);UDPThreadState* state = new UDPThreadState();state->obj = this;state->scok = sock;this->tid = ::CreateThread(NULL, 0, UDPServerThreadFunc, (void*)state, NULL, NULL);if (tid == NULL){delete state;}}/*功能：UDP 侦听线程函数，静态函数参数：符合ThreadProc规范要求*/DWORD UDPServer::UDPServerThreadFunc(void* state){// 解析线程函数参数UDPThreadState* pstate = (UDPThreadState*)state;UDPServer* obj = pstate->obj;SOCKET sockServer = pstate->scok;delete pstate; pstate = NULL;wchar_t log[100];swprintf_s(log, L"UDP侦听线程 %d 已经启动", ::GetCurrentThreadId());LOG(log);char buff[1024];sockaddr_in remoteAddr;int nLen = sizeof(remoteAddr);while (1){if (1 == obj->GetIsEnd()){break;}int n = ::recvfrom(sockServer, buff, 1024, 0, (sockaddr*)&remoteAddr, &nLen);if (n == SOCKET_ERROR){wchar_t log[128];swprintf_s(log, L"recvfrom返回错误号:%d", ::WSAGetLastError());LOG(log);}else if (n == 0){LOG(L"socket关闭,recvfrom() 退出");}else{wchar_t log[128];swprintf_s(log, L"接收到UDP包, 大小%d字节，来自%S:%d",n, ::inet_ntoa(remoteAddr.sin_addr), ::ntohs(remoteAddr.sin_port)); // 注意%S与%sLOG(log);obj->OnRecv((BYTE*)buff, n);}}swprintf_s(log, L"UDP侦听线程 %d 退出", ::GetCurrentThreadId());LOG(log);return 0;}/*功能：启动侦听*/void UDPServer::StartUDPServer(){this->StartUDPServer(this->IP, this->port);}/*功能：向回调函数链表中增加一个回调函数参数：cb-用户定义的回调函数名*/void UDPServer::AddCallback(UDPRecvFun cb){this->listOnRecv.push_back(cb);}

测试代码：

Radar::Radar(){// 建立服务器1this->pUDPServer = new UDPServer(”172.16.35.144", 8888);this->pUDPServer->AddCallback(Radar::AfterRecvUDP);// 建立服务器2pUDPServer2 = new UDPServer("172.16.35.144", 9999);pUDPServer2->AddCallback(Radar::AfterRecvUDP);}

// 回调函数

void Radar::AfterRecvUDP(void* sender, BYTE* data, int len){data[len] = 0;::MessageBoxA(::AfxGetApp()->GetMainWnd()->m_hWnd, (char*)data, "C", MB_OK);}