【C++】网络编程
<h2 id="前言">前言</h2><p>围绕Socket 的基础概念、I/O 模型，逐步实现阻塞 I/O 客户端 - 服务器、多进程 / 多线程服务端处理，以及基于 select、poll、epoll 的 I/O 多路复用服务端，侧重与如何实现。</p>
<h2 id="什么是socket">什么是socket</h2>
<p>在C++中，Socket编程是一种用于在网络上进行通信的技术，它允许不同主机上的应用程序通过TCP/IP协议族进行数据交换。Socket作为应用层与TCP/IP协议族通信的中间软件抽象层，提供了一组接口，隐藏了协议的复杂性，使得开发者只需要关注简单的接口即可实现网络通信。</p>
<h3 id="io">I/O</h3>
<p>I/O (Input/Output) - 输入输出：泛指计算机与外部世界的数据交换，socket是网络I/O；</p>
<p>进行I/O时分为两步：一是检测是否符合条件，二是进行操作。阻塞条件下不满足条件就会一直检测直到符合条件；非阻塞检测一次就会返回。</p>
<p>I/O多路复用就是只检测，找到符合条件的文件描述符，然后只处理这些文件描述符。现在常见的I/O多路复用有三种select、poll、epoll，在检测时select、poll是通过轮询进行检测，epoll是通过回调进行实现。还有就是select需要每次把关注的fd集合拷贝到内核，而epoll只需要第一次把fd拷贝到红黑树中；</p>
<p>阻塞 I/O（Blocking I/O）：满足发送/接收条件才输入输出</p>
<ul>
<li>当进程执行I/O操作时，如果条件不满足，进程会被操作系统挂起（睡眠），直到条件满足才被唤醒继续执行。</li>
</ul>
<pre><code class="language-bat">应用程序 内核 网络
| | |
| send() | |
|--------------->| |
| | wait buffer space |
| |<----------------> |
| | copy data |
| | start send |
| |------------------>|
| return size | |
|<---------------| |
应用程序 内核 网络
| | |
| recv() | |
|--------------->| |
| |check recv buffer|
| | if null->wait |
| |<--------------->|
| | else recv |
| |<----------------|
| | copy data to |
| return size |user space |
|<---------------| |
</code></pre>
<p>非阻塞 I/O（Non-blocking I/O）：</p>
<ul>
<li>当进程执行I/O操作时，如果条件不满足，系统调用立即返回一个错误，而不是让进程进入睡眠状态。进程可以继续执行其他任务，稍后再重试。</li>
</ul>
<ul>
<li>非阻塞 I/O 的关键特征
<ul>
<li>立即返回：无论I/O是否完成，立即返回控制权</li>
<li>错误码指示：用特殊错误码表示"需要等待"</li>
<li>主动轮询：需要程序主动检查I/O状态</li>
<li>并行处理：可以在等待I/O时做其他事情</li>
</ul>
</li>
</ul>
<table>
<thead>
<tr>
<th style="text-align: left">模型</th>
<th style="text-align: center">特点</th>
<th style="text-align: center">适用场景</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align: left"><strong>阻塞 I/O</strong></td>
<td style="text-align: center">条件不满足时进程挂起</td>
<td style="text-align: center">简单应用，连接数少</td>
</tr>
<tr>
<td style="text-align: left"><strong>非阻塞 I/O</strong></td>
<td style="text-align: center">立即返回，需要轮询</td>
<td style="text-align: center">需要实时响应的应用</td>
</tr>
<tr>
<td style="text-align: left"><strong>I/O 多路复用</strong></td>
<td style="text-align: center">一个线程管理多个 I/O</td>
<td style="text-align: center">高并发服务器</td>
</tr>
</tbody>
</table>
<h3 id="tcp-udp">TCP-UDP</h3>
<table>
<thead>
<tr>
<th style="text-align: center">特性</th>
<th style="text-align: center">TCP</th>
<th style="text-align: center">UDP</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align: center"><strong>连接</strong></td>
<td style="text-align: center">面向连接</td>
<td style="text-align: center">无连接</td>
</tr>
<tr>
<td style="text-align: center"><strong>可靠性</strong></td>
<td style="text-align: center">可靠，自动重传</td>
<td style="text-align: center">不可靠，可能丢包</td>
</tr>
<tr>
<td style="text-align: center"><strong>顺序性</strong></td>
<td style="text-align: center">保证数据顺序</td>
<td style="text-align: center">不保证顺序</td>
</tr>
<tr>
<td style="text-align: center"><strong>流量控制</strong></td>
<td style="text-align: center">有滑动窗口</td>
<td style="text-align: center">无</td>
</tr>
<tr>
<td style="text-align: center"><strong>头部开销</strong></td>
<td style="text-align: center">20-60字节</td>
<td style="text-align: center">8字节</td>
</tr>
</tbody>
</table>
<p>连接：tcp三次握手，四次挥手</p>
<ul>
<li><strong>SYN</strong> (Synchronize)：同步序号，用于建立连接</li>
<li><strong>ACK</strong> (Acknowledgment)：确认标志</li>
<li><strong>FIN</strong> (Finish)：结束标志，用于关闭连接</li>
<li><strong>RST</strong> (Reset)：重置连接</li>
<li><strong>PSH</strong> (Push)：推送数据</li>
<li><strong>URG</strong> (Urgent)：紧急指针有效</li>
</ul>
<pre><code class="language-bat">连接-三次握手
Client Server
| |
| 1. SYN (seq=x) |
|--------------------------------------->|
| |
| 2. SYN-ACK (seq=y, ack=x+1) |
|<---------------------------------------|
| |
| 3. ACK (ack=y+1) |
|--------------------------------------->|
| |
| 连接建立，开始数据传输 |
|<======================================>|
断开连接-四次挥手
Client Server
| |
| 1. FIN (seq=u) |
|--------------------------------------->|
| |
| 2. ACK (ack=u+1) |
|<---------------------------------------|
| |
| 服务器处理剩余数据 |
|<======================================>|
| |
| 3. FIN (seq=v, ack=u+1) |
|<---------------------------------------|
| |
| 4. ACK (ack=v+1) |
|--------------------------------------->|
| 双方关闭连接 |
</code></pre>
<h3 id="send-recv">send-recv</h3>
<p>tcp使用send-recv收发消息；</p>
<ul>
<li>发送消息-send</li>
</ul>
<pre><code class="language-C++">ssize_t send(int sockfd, // 目标socket文件描述符
const void *buf, // 要发送的数据缓冲区
size_t len, // 要发送的数据长度
int flags); // 发送标志（通常为0）
// 0 - 默认行为，阻塞发送
send(sockfd, buf, len, 0);
// MSG_DONTWAIT - 非阻塞发送
send(sockfd, buf, len, MSG_DONTWAIT);
// MSG_NOSIGNAL - 不生成SIGPIPE信号
send(sockfd, buf, len, MSG_NOSIGNAL);
// MSG_OOB - 发送带外数据（紧急数据）
send(sockfd, buf, len, MSG_OOB);
// MSG_MORE - 提示有更多数据要发送（用于UDP）
send(sockfd, buf, len, MSG_MORE);
// 可以组合使用
send(sockfd, buf, len, MSG_DONTWAIT | MSG_NOSIGNAL);
</code></pre>
<ul>
<li>接收消息- recv</li>
</ul>
<pre><code class="language-C++">ssize_t recv(int sockfd, // socket文件描述符
void *buf, // 接收数据缓冲区
size_t len, // 缓冲区长度
int flags); // 接收标志（通常为0）
// 常用的flags值：
// 0 - 默认行为，阻塞接收
recv(sockfd, buf, len, 0);
// MSG_DONTWAIT - 非阻塞接收
recv(sockfd, buf, len, MSG_DONTWAIT);
// MSG_PEEK - 查看数据但不从缓冲区移除
recv(sockfd, buf, len, MSG_PEEK);
// MSG_OOB - 接收带外数据（紧急数据）
recv(sockfd, buf, len, MSG_OOB);
// MSG_WAITALL - 等待接收所有请求的字节
recv(sockfd, buf, len, MSG_WAITALL);
// MSG_TRUNC - 即使数据被截断也返回数据包长度（原始长度）
recv(sockfd, buf, len, MSG_TRUNC);
// 可以组合使用（某些组合可能无效）
recv(sockfd, buf, len, MSG_DONTWAIT | MSG_PEEK);
</code></pre>
<h2 id="tcp实例">TCP实例</h2>
<h3 id="简单实例">简单实例</h3>
<p>实现一个简单的单线程、单个连接的阻塞I/O的客户端-服务器程序</p>
<h4 id="server">server</h4>
<pre><code class="language-c++">#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define PORT 8080
#define BUFFER_SIZE 1024
int main() {
int server_fd, client_fd;
struct sockaddr_in address, client_addr;
socklen_t client_len = sizeof(client_addr);
char buffer;
// 创建socket
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd == 0) {
perror("socket failed");
return 1;
}
int opt = 1;
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0) {
perror("setsockopt failed");
close(server_fd);
return 1;
}
// 设置地址
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(PORT);
// 绑定
if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
perror("bind failed");
return 1;
}
// 监听
if (listen(server_fd, 3) < 0) {
perror("listen");
return 1;
}
printf("Server started on port %d\n", PORT);
// 接受连接
client_fd = accept(server_fd, (struct sockaddr*)&client_addr, &client_len);
if (client_fd < 0) {
perror("accept");
return 1;
}
printf("Client connected\n");
while (1) {
// 读取数据
int bytes_read = read(client_fd, buffer, BUFFER_SIZE - 1);
if (bytes_read > 0) {
buffer = '\0';
printf("Received: %s\n", buffer);
// 发送响应
const char* response = "Hello from server!\n";
write(client_fd, response, strlen(response));
}
else if (bytes_read == 0) {
printf("Client disconnected\n");
break;
}
else {
perror("Read failed");
break;
}
}
// 关闭连接
close(client_fd);
return 0;
}
</code></pre>
<ul>
<li>CMakeLists.txt</li>
</ul>
<pre><code class="language-bash">cmake_minimum_required(VERSION 3.0)
project(socketServer)
# include_directories(${CMAKE_SOURCE_DIR}/CMAKE_SOURCE_DIRinclude)
include_directories(include)
add_compile_options(-g -std=c++11 -o2 -Wall)
set(CMAKE_BUILD_TYPE Debug)
# 设置可执行文件输出目录（在 build/bin/）
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_SOURCE_DIR}/lib)
# 设置库文件输出目录（在 build/lib/）
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_SOURCE_DIR}/lib)
add_executable(server./src/server.cpp)
target_link_libraries(server PRIVATE pthread)
</code></pre>
<h4 id="client">client</h4>
<pre><code> #include <iostream>
#include <string>
#include <cstring>
#include <cerrno>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define SERVER_IP "127.0.0.1"
#define PORT 8080
#define BUFFER_SIZE 1024
int main() {
int sock = 0;
struct sockaddr_in serv_addr;
char buffer = {0};
// 创建socket
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
std::cerr << "Socket creation error: " << strerror(errno) << std::endl;
return EXIT_FAILURE;
}
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(PORT);
// 转换IP地址
if (inet_pton(AF_INET, SERVER_IP, &serv_addr.sin_addr) <= 0) {
std::cerr << "Invalid address/Address not supported: " << strerror(errno) << std::endl;
return EXIT_FAILURE;
}
// 连接服务器
if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
std::cerr << "Connection failed: " << strerror(errno) << std::endl;
return EXIT_FAILURE;
}
std::cout << "Connected to server at " << SERVER_IP << ":" << PORT << std::endl;
std::cout << "Type your messages (type 'exit' to quit):" << std::endl;
while (true) {
// 获取用户输入
std::string input;
//不使用do-while 如果直接按enter，程序会向下走，send发送为空，但是服务端接收不到，就会在read中等待
//客户端也会在read中等待
do{
std::cout << "> ";
std::getline(std::cin, input);
}while(input.empty());
// 检查退出命令
if (input == "exit") {
break;
}
// 发送消息到服务器
if (send(sock, input.c_str(), input.length(), 0) < 0) {
std::cerr << "Send failed: " << strerror(errno) << std::endl;
break;
}
std::cout << "Message sent to server" << std::endl;
// 接收服务器响应
memset(buffer, 0, BUFFER_SIZE);
int valread = read(sock, buffer, BUFFER_SIZE - 1);
if (valread < 0) {
std::cerr << "Read error: " << strerror(errno) << std::endl;
break;
} else if (valread == 0) {
std::cout << "Server closed the connection" << std::endl;
break;
} else {
buffer = '\0';
std::cout << "Server response:\n" << buffer << std::endl;
}
}
close(sock);
std::cout << "Connection closed" << std::endl;
return 1;
}
</code></pre>
<h4 id="非阻塞方式">非阻塞方式</h4>
<pre><code class="language-C++"> // 获取当前文件状态标志
int flags = fcntl(fd, F_GETFL, 0);
if (flags < 0) {
perror("fcntl F_GETFL");
return -1;
}
// 添加非阻塞标志
if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) < 0) {
perror("fcntl F_SETFL");
return -1;
}
</code></pre>
<pre><code class="language-C++"> int on = 1;// 1表示启用非阻塞
if (ioctl(fd, FIONBIO, &on) < 0) {
perror("ioctl FIONBIO");
return -1;
}
</code></pre>
<h3 id="服务端接收多个客户端">服务端接收多个客户端</h3>
<ul>
<li>多进程、多线程、select、poll、epoll
<ul>
<li><strong>少量连接</strong>：多进程/多线程</li>
<li><strong>中等并发</strong>：select/poll</li>
<li><strong>高并发</strong>：epoll</li>
</ul>
</li>
</ul>
<h4 id="多进程-fork">多进程 fork()</h4>
<pre><code class="language-C++">#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <signal.h>
#define PORT 8080
#define BUFFER_SIZE 1024
int main() {
int server_fd, client_fd;
struct sockaddr_in address, client_addr;
socklen_t client_len = sizeof(client_addr);
char buffer;
// 创建socket
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd == 0) {
perror("socket failed");
return 1;
}
int opt = 1;
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0) {
perror("setsockopt failed");
close(server_fd);
return 1;
}
// 设置地址
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(PORT);
// 绑定
if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
perror("bind failed");
return 1;
}
// 监听
if (listen(server_fd, 3) < 0) {
perror("listen");
return 1;
}
signal(SIGCHLD, SIG_IGN);
printf("Server started on port %d\n", PORT);
// 只需要修改主循环部分
while (true) {
// 接受连接
client_fd = accept(server_fd, (struct sockaddr*)&client_addr, &client_len);
if (client_fd < 0) {
perror("accept faild!");
continue;// 继续等待下一个连接
}
printf("Client connected\n");
// 创建子进程处理客户端
pid_t pid = fork();
if (pid < 0) {
perror("fork failed");
close(client_fd);
continue;
}
if (pid == 0) {// 子进程
close(server_fd);// 子进程不需要监听socket
// 处理客户端连接（使用你现有的while循环）
while (true) {
int bytes_read = read(client_fd, buffer, BUFFER_SIZE - 1);
if (bytes_read > 0) {
buffer = '\0';
printf("PID %d Received: %s\n", getpid(), buffer);
const char* response = "server received!\n";
write(client_fd, response, strlen(response));
}
else if (bytes_read == 0) {
printf("PID %d Client disconnected\n", getpid());
break;
}
else {
perror("Read failed");
break;
}
}
close(client_fd);
exit(0);// 子进程退出
}
else {// 父进程
close(client_fd);// 父进程关闭客户端socket，继续监听
}
}
// 关闭连接
close(client_fd);
return 0;
}
</code></pre>
<h4 id="多线程-stdthread">多线程 std::thread</h4>
<pre><code class="language-C++">#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <thread>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <signal.h>
#include <iostream>
#define PORT 8080
#define BUFFER_SIZE 1024
// 客户端处理线程函数
void handle_client(int client_fd) {
char buffer;
std::cout << "Thread " << std::this_thread::get_id() << ": Client connected" << std::endl;
while (1) {
memset(buffer, 0, BUFFER_SIZE);
int bytes_read = read(client_fd, buffer, BUFFER_SIZE - 1);
if (bytes_read > 0) {
buffer = '\0';
const char * response = "receive over!";
std::cout<< "received:" << buffer << std::endl;
write(client_fd, response, strlen(response));
}
else if (bytes_read == 0) {
printf("Thread %lu: Client disconnected\n", pthread_self());
break;
}
else {
perror("Read failed");
break;
}
}
close(client_fd);
return;
}
int main() {
int server_fd, client_fd;
struct sockaddr_in address, client_addr;
socklen_t client_len = sizeof(client_addr);
// 创建socket
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd == 0) {
perror("socket failed");
return 1;
}
int opt = 1;
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0) {
perror("setsockopt failed");
close(server_fd);
return 1;
}
// 设置地址
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(PORT);
// 绑定
if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
perror("bind failed");
return 1;
}
// 监听
if (listen(server_fd, 3) < 0) {
perror("listen");
return 1;
}
signal(SIGCHLD, SIG_IGN);
printf("Server started on port %d\n", PORT);
while (true) {
// 接受连接
client_fd = accept(server_fd, (struct sockaddr*)&client_addr, &client_len);
if (client_fd < 0) {
perror("accept faild!");
continue;// 继续等待下一个连接
}
char client_ip;
inet_ntop(AF_INET, &client_addr.sin_addr, client_ip, sizeof(client_ip));
int client_port = ntohs(client_addr.sin_port);
std::cout << "New client connected from " << client_ip << ":" << client_port << std::endl;
try {
std::thread client_thread(handle_client, client_fd);
client_thread.detach();// 分离线程，让它在后台运行
}
catch (const std::exception& e) {
std::cerr << "Failed to create thread: " << e.what() << std::endl;
close(client_fd);
}
}
close(client_fd);
std::cout << "Server stopped" << std::endl;
return 0;
}
</code></pre>
<h4 id="select多路复用">select多路复用</h4>
<p>使用select 实现，并做简单的封装。</p>
<p>虽然使用多线程和多进程都可以实现对多个客户端监听，每一个进程/线程都会在send/recv处阻塞，等待发送/接收；</p>
<p>select、poll、epoll可以对文件描述符进行监控，当有事件触发时才会去调用。</p>
<p>select实现I/O多路复用就是对fd_set（位图）的操作，如果要监控可读操作，就声明一个read的位图，把已经连接到服务器的clientfd记录下来（不如clientfd=10，就是把位图中第十个值置为1）；通过select对位图进行监控，当有满足read的文件描述符时值不变，不满足的清空，所以要把连接的客户端存起来避免丢失。所以返回的fd_set就是满足可读的已连接客户端，对这些客户端进行操作就行了。</p>
<p>这里面存在的问题就是系统默认fd_set大小为1024，所以最多连接1020个客户端（0-标准输入流、1-标准输出流、2-标准错误流、3-服务端文件描述符），当客户端连接过多时会丢失或者出现错误。</p>
<p>还有就是fd_set会从用户态拷贝到内核，再拷贝出来，性能上不是很好。</p>
<hr>
<p><code>select</code> 是一种 I/O 多路复用技术，允许程序同时监视多个文件描述符（file descriptors），等待一个或多个描述符变为"就绪"状态（可读、可写或发生异常）</p>
<p>I/O多路复用就是使用一个线程管理多个io是否就绪。</p>
<hr>
<ul>
<li>
<p>先了解一下几个概念</p>
</li>
<li>
<p>fd_set是什么</p>
</li>
</ul>
<p>fd_set是一个存放文件描述符的<strong>数组</strong>，大小为1024位； 结构体实际上就是定义一个 长整型的数组 long int fds_bits;</p>
<p>1024 = int * 数组个数 * 8 位，能够储存1024个文件描述符；也就是实际能够储存1024个socket的文件描述符。</p>
<p>每个进程默认打开3个文件描述符，0-标准输入流、1-标准输出流、2-标准错误流</p>
<pre><code class="language-C++">/* The fd_set member is required to be an array of longs.*/
typedef long int __fd_mask;
/* Some versions of <linux/posix_types.h> define this macros.*/
#undef __NFDBITS
/* It's easier to assume 8-bit bytes than to get CHAR_BIT.*/
#define __NFDBITS (8 * (int) sizeof (__fd_mask))
#define __FD_ELT(d) ((d) / __NFDBITS)
#define __FD_MASK(d) ((__fd_mask) (1UL << ((d) % __NFDBITS)))
/* fd_set for select and pselect.*/
typedef struct
{
/* XPG4.2 requires this member name.Otherwise avoid the name
from the global namespace.*/
#ifdef __USE_XOPEN
__fd_mask fds_bits;
# define __FDS_BITS(set) ((set)->fds_bits)
#else
__fd_mask __fds_bits;
# define __FDS_BITS(set) ((set)->__fds_bits)
#endif
} fd_set;
</code></pre>
<ul>
<li>文件描述符的分配规则</li>
</ul>
<p>寻找最小的未使用的文件描述符，所以连接数较少时可以使用select进行实现。</p>
<ul>
<li>文件描述符如何映射到socket</li>
</ul>
<p>好像是：进程控制块-进程描述表->文件描述符表->文件对象；具体怎么映射的没了解</p>
<pre><code class="language-C++">int select(int maxfdp, //最大文件描述符值加1
fd_set *readfds, //指向可读文件描述符集合的指针可读时接收
fd_set *writefds, //指向可写文件描述符集合的指针可写时发送
fd_set *exceptfds, //指向异常文件描述符集合的指针 常见：带外数据到达（TCP紧急数据）
struct timeval *timeout); //超时时间结构体指针
</code></pre>
<hr>
<ul>
<li>实现</li>
</ul>
<pre><code class="language-C++"> #include <iostream>
#include <sys/select.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <cstring>
#include <vector>
#include <algorithm>
#define PORT 8080
#define BUFFER_SIZE 1024
#define MAX_CLIENTS 10
class TCPServer {
private:
int server_socket;
fd_set readfds;
int client_socket;
int max_sd;
public:
TCPServer() {
server_socket = -1;
// 初始化客户端socket数组
for (int i = 0; i < MAX_CLIENTS; i++) {
client_socket = 0;
}
}
void init() {
int opt = 1;
struct sockaddr_in address;
// 创建主socket
if ((server_socket = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
perror("socket failed");
exit(EXIT_FAILURE);
}
// 设置socket选项，允许地址重用
if (setsockopt(server_socket, SOL_
perror("setsockopt");
exit(EXIT_FAILURE);
}
// 配置地址
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(PORT);
// 绑定socket
if (bind(server_socket, (struct sockaddr *)&address, sizeof(address)) < 0) {
perror("bind failed");
exit(EXIT_FAILURE);
}
std::cout << "Listener on port " << PORT << std::endl;
// 开始监听
if (listen(server_socket, MAX_CLIENTS) < 0) {
perror("listen");
exit(EXIT_FAILURE);
}
}
void run() {
int activity, new_socket, sd;
int max_sd;
struct sockaddr_in address;
socklen_t addrlen = sizeof(address);
char buffer;
std::cout << "Waiting for connections..." << std::endl;
while (true) {
// 清空文件描述符集合
FD_ZERO(&readfds);
// 添加主socket到集合
FD_SET(server_socket, &readfds);
max_sd = server_socket;
// 添加客户端socket到集合
for (int i = 0; i < MAX_CLIENTS; ++i) {
sd = client_socket;
if (sd > 0) {
FD_SET(sd, &readfds);
}
max_sd = max_sd > sd ? max_sd : sd;
}
// 等待活动
struct timeval timeout;
timeout.tv_sec = 0;// 秒
timeout.tv_usec = 500;
activity = select(max_sd + 1, &readfds, NULL, NULL, &timeout);
if (activity < 0 && errno != EINTR) {
std::cerr << "select error" << std::endl;
continue;
}else if (activity == 0) {
// 超时处理
continue;
}
// 如果有新连接
if (FD_ISSET(server_socket, &readfds)) {
if ((new_socket = accept(server_socket,
(struct sockaddr *)&address,
&addrlen)) < 0) {
perror("accept");
exit(EXIT_FAILURE);
}
std::cout << "New connection, socket fd: " << new_socket
<< ", IP: " << inet_ntoa(address.sin_addr)
<< ", Port: " << ntohs(address.sin_port) << std::endl;
// 添加到客户端数组
for (int i = 0; i < MAX_CLIENTS; i++) {
if (client_socket == 0) {
client_socket = new_socket;
std::cout << "Adding to list of sockets as " << i <<" client id: " << new_sock et << std::endl;
break;
}
}
}
// 检查客户端socket的IO操作
for (int i = 0; i < MAX_CLIENTS; i++) {
sd = client_socket;
memset(buffer,0,BUFFER_SIZE);
if (FD_ISSET(sd, &readfds)) {
// 检查是否断开连接
int valread = read(sd, buffer, BUFFER_SIZE);
if (valread == 0) {
// 客户端断开连接
getpeername(sd, (struct sockaddr*)&address, &addrlen);
std::cout << "Host disconnected, IP: " << inet_ntoa(address.sin_addr)
<< ", Port: " << ntohs(address.sin_port) << std::endl;
close(sd);
client_socket = 0;
} else {
// 处理接收到的数据
buffer = '\0';
std::cout << "Received: " << buffer << std::endl;
// 回声给客户端
send(sd, buffer, strlen(buffer), 0);
}
}
}
}
}
~TCPServer() {
close(server_socket);
for (int i = 0; i < MAX_CLIENTS; ++i) {
if (client_socket > 0) {
std::cout << "close client :"<< client_socket << std::endl;
close(client_socket);
}
}
}
};
int main() {
TCPServer server;
server.init();
server.run();
return 0;
}
</code></pre>
<h4 id="poll多路复用">poll多路复用</h4>
<p>poll不再使用位图对文件描述符存储，而是通过pollfd进行控制，可以声明pollfd的数组（所以就没有了1024的限制）。</p>
<ul>
<li>poll改进</li>
</ul>
<p><strong>没有最大文件描述符限制</strong>：<code>poll</code> 使用数组，可以处理任意数量的文件描述符</p>
<p><strong>更高效</strong>：不需要每次调用都重新设置文件描述符集合</p>
<p><strong>更清晰的事件分离</strong>：每个文件描述符都有独立的事件输入和输出字段</p>
<hr>
<ul>
<li>poll事件常量</li>
</ul>
<table>
<thead>
<tr>
<th style="text-align: center">事件常量</th>
<th style="text-align: center">值（通常）</th>
<th style="text-align: center">说明</th>
<th style="text-align: center">对象</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align: center"><strong><code>POLLIN</code></strong></td>
<td style="text-align: center">0x001</td>
<td style="text-align: center">数据可读（普通数据）</td>
<td style="text-align: center">events/revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLPRI</code></strong></td>
<td style="text-align: center">0x002</td>
<td style="text-align: center">紧急数据可读（带外数据）</td>
<td style="text-align: center">events/revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLOUT</code></strong></td>
<td style="text-align: center">0x004</td>
<td style="text-align: center">数据可写，不阻塞</td>
<td style="text-align: center">events/revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLRDNORM</code></strong></td>
<td style="text-align: center">0x040</td>
<td style="text-align: center">普通数据可读</td>
<td style="text-align: center">events/revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLRDBAND</code></strong></td>
<td style="text-align: center">0x080</td>
<td style="text-align: center">优先级带数据可读</td>
<td style="text-align: center">events/revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLWRNORM</code></strong></td>
<td style="text-align: center">0x100</td>
<td style="text-align: center">普通数据可写</td>
<td style="text-align: center">events/revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLWRBAND</code></strong></td>
<td style="text-align: center">0x200</td>
<td style="text-align: center">优先级带数据可写</td>
<td style="text-align: center">events/revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLERR </code></strong></td>
<td style="text-align: center">0x008</td>
<td style="text-align: center">错误情况</td>
<td style="text-align: center">revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLHUP </code></strong></td>
<td style="text-align: center">0x010</td>
<td style="text-align: center">已挂起</td>
<td style="text-align: center">revents</td>
</tr>
<tr>
<td style="text-align: center"><strong><code>POLLNVAL</code></strong></td>
<td style="text-align: center">0x020</td>
<td style="text-align: center">无效轮询请求</td>
<td style="text-align: center">revents</td>
</tr>
</tbody>
</table>
<hr>
<pre><code class="language-C++">#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <iostream>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <poll.h>
#define PORT 8080
#define MAX_CLIENTS 1000
#define BUFFER_SIZE 1024
#define TIMEOUT -1// 无限等待
class TCPServer{
private:
int server_fd;
char buffer;
struct pollfd fds;// +1 给服务器套接字
int nfds;
public:
TCPServer(){
server_fd = -1;
nfds = 0;
// 初始化所有 pollfd 结构
for (int i = 0; i < MAX_CLIENTS + 1; i++) {
fds.fd = -1;// 表示未使用
fds.events = 0;
fds.revents = 0;
}
};
void init(){
// 创建监听套接字
if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
perror("socket failed");
exit(EXIT_FAILURE);
}
// 设置 SO_REUSEADDR 选项
int opt = 1;
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) {
perror("setsockopt failed");
exit(EXIT_FAILURE);
}
struct sockaddr_in address;
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(PORT);
// 绑定地址
if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
perror("bind failed");
exit(EXIT_FAILURE);
}
// 开始监听listen(server_fd, 10) 等待连接的最大个数
if (listen(server_fd, 10) < 0) {
perror("listen failed");
exit(EXIT_FAILURE);
}
printf("Server listening on port %d\n", PORT);
// 添加服务器套接字到 pollfd 数组
fds.fd = server_fd;
fds.events = POLLIN;// 监视可读事件（新连接）
nfds = 1;// 当前监视的文件描述符数量
};
void run(){
int current_size = 0;
while (1) {
// 调用 poll，等待事件发生
int ret = poll(fds, nfds, TIMEOUT);
if (ret < 0) {
perror("poll failed");
break;
} else if (ret == 0) {
// 超时（本例中不会发生，因为TIMEOUT=-1）
continue;
}
current_size = nfds;// 保存当前大小，因为 nfds 可能在循环中改变
// 检查所有文件描述符
for (int i = 0; i < current_size; i++) {
if (fds.fd < 0) continue;// 跳过未使用的文件描述符
// 检查是否有事件发生
if (fds.revents == 0) continue;
// 检查是否是错误事件
if (fds.revents & (POLLERR | POLLHUP | POLLNVAL)) {
printf("Error on fd %d, closing connection\n", fds.fd);
close(fds.fd);
fds.fd = -1;
fds.revents = 0;
continue;
}
// 如果是服务器套接字，处理新连接
if (fds.fd == server_fd) {
if (fds.revents & POLLIN)
handle_client_connect();
}
// 处理客户端套接字
else {
handle_client_event(i);
}
}
}
};
void handle_client_connect(){
// 接受新连接
struct sockaddr_in address;
socklen_t addrlen = sizeof(address);
int new_socket = accept(server_fd, (struct sockaddr *)&address, &addrlen);
if (new_socket < 0) {
perror("accept failed");
return ;
}
printf("New connection, socket fd is %d, IP: %s, port: %d\n",new_socket,
inet_ntoa(address.sin_addr), ntohs(address.sin_port));
// 查找空位添加新客户端
int added = 0 ;
for (int j = 1; j < MAX_CLIENTS + 1; ++j) {
if (fds.fd == -1) {
fds.fd = new_socket;
fds.events = POLLIN | POLLRDHUP;// 监视可读和连接关闭
fds.revents = 0;
added = 1;
nfds = j >= nfds ? j+1 : nfds;
break;
}
}
if (!added) {
printf("Too many clients, rejecting connection\n");
close(new_socket);
}
};
void handle_client_event(int fd_index){
// 检查连接是否关闭
if (fds.revents & POLLRDHUP) {
printf("Client %d disconnected\n", fds.fd);
close(fds.fd);
fds.fd = -1;
fds.revents = 0;
return;
}
// 检查是否有数据可读
if (fds.revents & POLLIN) {
memset(buffer,0,BUFFER_SIZE);
int valread = read(fds.fd, buffer, BUFFER_SIZE);
if (valread == 0) {
// 客户端正常关闭连接
printf("Client %d closed connection\n", fds.fd);
close(fds.fd);
fds.fd = -1;
} else if (valread < 0) {
// 读取错误
perror("read failed");
close(fds.fd);
fds.fd = -1;
} else {
// 回显数据
buffer = '\0';
std::cout << "Received from client : " << fds.fd <<" " << buffer << std: :endl;
send(fds.fd,buffer,strlen(buffer),0);
}
}
}
~TCPServer(){
// 关闭所有连接
for (int i = 0; i < nfds; i++) {
if (fds.fd >= 0) {
close(fds.fd);
}
}
if (server_fd >= 0) {
close(server_fd);
}
printf("Server shutdown complete\n");
};
};
int main() {
TCPServer server;
server.init();
server.run();
return 0;
}
</code></pre>
<ul>
<li>事件</li>
</ul>
<pre><code class="language-C++">#define POLLIN 0x001 /* There is data to read.*/
#define POLLPRI 0x002 /* There is urgent data to read.*/
#define POLLOUT 0x004 /* Writing now will not block.*/
#if defined __USE_XOPEN || defined __USE_XOPEN2K8
/* These values are defined in XPG4.2.*/
# define POLLRDNORM 0x040 /* Normal data may be read.*/
# define POLLRDBAND 0x080 /* Priority data may be read.*/
# define POLLWRNORM 0x100 /* Writing now will not block.*/
# define POLLWRBAND 0x200 /* Priority data may be written.*/
#endif
#ifdef __USE_GNU
/* These are extensions for Linux.*/
# define POLLMSG 0x400
# define POLLREMOVE 0x1000
# define POLLRDHUP 0x2000
#endif
/* Event types always implicitly polled for.These bits need not be set in
`events', but they will appear in `revents' to indicate the status of
the file descriptor.*/
#define POLLERR 0x008 /* Error condition.*/
#define POLLHUP 0x010 /* Hung up.*/
#define POLLNVAL 0x020 /* Invalid polling request.*/
</code></pre>
<h5 id="selectpoll-缺点">select/poll 缺点</h5>
<ol>
<li>每次调用时要重复地从用户态读入参数。</li>
<li>每次调用时要重复地扫描文件描述符。</li>
<li>每次在调用开始时，要把当前进程放入各个文件描述符的等待队列。在调用结束后，又把进程从各个等待队列中删除。</li>
</ol>
<p>poll核心时间可分为可读、可写、异常事件。</p>
<h4 id="epoll多路复用">epoll()多路复用</h4>
<ul>
<li>
<p>水平触发 ：fd事件没有被处理或者没有处理全部，下次还会报告这个fd</p>
</li>
<li>
<p>边缘触发：程序在处理文件描述符的就绪事件时，必须确保将其处理完毕，否则 epoll_wait 将不会重复通知该文件描述符的就绪状态。</p>
</li>
<li>
<p>基于红黑树+链表+回调函数</p>
</li>
</ul>
<pre><code class="language-bat">用户空间 内核空间
│ │
│ epoll_create() │
├───────────────────────────────> │ 创建eventpoll结构
│ │ • 初始化红黑树(rbr)
│ │ • 初始化就绪链表(rdllist)
│ │
│ epoll_ctl(EPOLL_CTL_ADD, fd) │
├───────────────────────────────> │ • 分配epitem结构
│ │ • 插入红黑树(O(log n))
│ │ • 设置文件回调函数
│ │
│ epoll_wait() │
├───────────────────────────────> │ • 检查rdllist是否为空
│ │ • 空则阻塞进程
│ │
│ 数据到达 │ • 网卡中断/定时器触发
│ │ • 调用ep_poll_callback()
│ │ • 将epitem加入rdllist
│ │ • 唤醒等待进程
│ │
│ <───────────────────────────────┤ • 复制events到用户空间
│ │ • 清空rdllist(LT模式)
│ │
│ 处理事件 │
│───────────────────────────────> │
│ │
</code></pre>
<hr>
<pre><code class="language-C++">#include <iostream>
#include <cstring>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <vector>
#include <cerrno>
#include <arpa/inet.h>
#define MAX_EVENTS 64
#define BUFFER_SIZE 1024
class EpollServer {
private:
int server_fd;
int epoll_fd;
struct sockaddr_in server_addr;
public:
EpollServer(int port) {
// 创建socketSOCK_STREAM (TCP)SOCK_DERAM (UDP)
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
// 设置socket选项
int opt = 1;
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
&opt, sizeof(opt))) {
perror("setsockopt failed");
exit(EXIT_FAILURE);
}
// 绑定地址
memset(&server_addr, 0, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = INADDR_ANY;
server_addr.sin_port = htons(port);
if (bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0) {
perror("bind failed");
exit(EXIT_FAILURE);
}
// 创建epoll实例
epoll_fd = epoll_create1(0);
if (epoll_fd < 0) {
perror("epoll_create1 failed");
exit(EXIT_FAILURE);
}
// 添加server_fd到epoll
struct epoll_event event;
event.data.fd = server_fd;
event.events = EPOLLIN | EPOLLET;// 边缘触发模式
epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_fd, &event);
// 监听socket
if (listen(server_fd, SOMAXCONN) < 0) {
perror("listen failed");
return;
}
std::cout << "Server listening on port "
<< ntohs(server_addr.sin_port) << std::endl;
}
~EpollServer() {
close(server_fd);
close(epoll_fd);
}
// 设置非阻塞模式
void set_nonblocking(int fd) {
int flags = fcntl(fd, F_GETFL, 0);
fcntl(fd, F_SETFL, flags | O_NONBLOCK);
}
void run() {
// 事件循环
struct epoll_event events;
while (true) {
int nfds = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);
if (nfds < 0) {
perror("epoll_wait failed");
break;
}
for (int i = 0; i < nfds; i++) {
if (events.data.fd == server_fd) {
// 处理新连接
handle_new_connection();
} else {
// 处理客户端数据
if (events.events & EPOLLIN) {
handle_client_data(events.data.fd);
}
if (events.events & (EPOLLRDHUP | EPOLLHUP | EPOLLERR)) {
// 处理连接关闭或错误
close_client(events.data.fd);
}
}
}
}
}
private:
void handle_new_connection() {
struct sockaddr_in client_addr;
socklen_t addr_len = sizeof(client_addr);
// 接受所有待处理的连接
do {
int client_fd = accept(server_fd, (struct sockaddr*)&client_addr, &addr_len);
if (client_fd < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK) {
// 没有更多连接
break;
} else {
perror("accept failed");
break;
}
}
else{
std::cout << "New connection from "
<< inet_ntoa(client_addr.sin_addr)
<< ":" << ntohs(client_addr.sin_port)
<< std::endl;
// 设置非阻塞
set_nonblocking(client_fd);
// 添加到epoll
struct epoll_event event;
event.data.fd = client_fd;
event.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_fd, &event) < 0) {
perror("epoll_ctl add client failed");
close(client_fd);
}else{
std::cout << "Successfully added client fd " << client_fd << " to epoll" << std::endl;
}
break;
}
}while (true);
}
void handle_client_data(int client_fd) {
char buffer;
// 边缘触发模式需要读取所有可用数据
while (true) {
memset(buffer,0,BUFFER_SIZE);
ssize_t bytes_read = read(client_fd, buffer, BUFFER_SIZE - 1);
if (bytes_read > 0) {
buffer = '\0';
std::cout << "Received from client " << client_fd << ": " << buffer;
// 回显数据
send(client_fd, buffer, bytes_read, 0);
// 如果读取的数据少于缓冲区大小，说明数据已读完
if (bytes_read < BUFFER_SIZE - 1) {
break;
}
} else if (bytes_read == 0) {
// 客户端关闭连接
close_client(client_fd);
break;
} else {
if (errno == EAGAIN || errno == EWOULDBLOCK) {
// 数据已读完
break;
} else {
perror("read failed");
close_client(client_fd);
break;
}
}
}
}
void close_client(int client_fd) {
std::cout << "Client " << client_fd << " disconnected" << std::endl;
epoll_ctl(epoll_fd, EPOLL_CTL_DEL, client_fd, nullptr);
close(client_fd);
}
};
int main() {
EpollServer server(8080);
server.run();
return 0;
}
</code></pre>
<h2 id="udp实例">UDP实例</h2>
<p>udp使用sendto-recvfrom收发消息；</p>
<ul>
<li>server</li>
</ul>
<pre><code class="language-C++">#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#define BUFFER_SIZE 1024
class UDPServer {
private:
int server_fd;
struct sockaddr_in server_addr;
public:
UDPServer(int port) {
// 创建UDP socket
server_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (server_fd < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
// 设置地址重用
int opt = 1;
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) {
perror("setsockopt failed");
close(server_fd);
exit(EXIT_FAILURE);
}
// 绑定地址
memset(&server_addr, 0, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = INADDR_ANY;// 监听所有接口
server_addr.sin_port = htons(port);
if (bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0) {
perror("bind failed");
close(server_fd);
exit(EXIT_FAILURE);
}
std::cout << "UDP Server listening on port " << port << std::endl;
}
~UDPServer() {
if (server_fd >= 0) {
close(server_fd);
}
}
void run() {
char buffer;
struct sockaddr_in client_addr;
socklen_t addr_len = sizeof(client_addr);
while (true) {
// 清空缓冲区
memset(buffer, 0, BUFFER_SIZE);
memset(&client_addr, 0, sizeof(client_addr));
// 接收数据
ssize_t recv_len = recvfrom(server_fd, buffer, BUFFER_SIZE - 1, 0,
(struct sockaddr*)&client_addr, &addr_len);
if (recv_len < 0) {
perror("recvfrom failed");
continue;
}
// 获取客户端信息
char client_ip;
inet_ntop(AF_INET, &client_addr.sin_addr,
client_ip, INET_ADDRSTRLEN);
std::cout << "Received from " << client_ip << ":"
<< ntohs(client_addr.sin_port)
<< " (" << recv_len << " bytes): "
<< buffer << std::endl;
// 准备回显消息
std::string echo_msg = "Echo: ";
echo_msg += buffer;
// 发送回显（发送到刚才接收的地址）
sendto(server_fd, echo_msg.c_str(), echo_msg.length(), 0,
(struct sockaddr*)&client_addr, addr_len);
}
}
void run_with_select() {
fd_set read_fds;
struct timeval timeout;
char buffer;
std::cout << "UDP Server with select() running..." << std::endl;
while (true) {
// 设置文件描述符集合
FD_ZERO(&read_fds);
FD_SET(server_fd, &read_fds);
// 设置超时（5秒）
timeout.tv_sec = 5;
timeout.tv_usec = 0;
// 使用select等待数据
int ready = select(server_fd + 1, &read_fds, NULL, NULL, &timeout);
if (ready < 0) {
perror("select failed");
break;
} else if (ready == 0) {
// 超时
std::cout << "Timeout, waiting for data..." << std::endl;
continue;
}
// 有数据可读
if (FD_ISSET(server_fd, &read_fds)) {
struct sockaddr_in client_addr;
socklen_t addr_len = sizeof(client_addr);
ssize_t recv_len = recvfrom(server_fd, buffer, BUFFER_SIZE - 1, 0,
(struct sockaddr*)&client_addr, &addr_len);
if (recv_len > 0) {
buffer = '\0';
std::cout << "Received: " << buffer << std::endl;
// 回显
sendto(server_fd, buffer, recv_len, 0,
(struct sockaddr*)&client_addr, addr_len);
}
}
}
}
};
int main() {
UDPServer server(8080);
server.run();// 或 server.run_with_select();
return 0;
}
</code></pre>
<ul>
<li>client</li>
</ul>
<pre><code class="language-C++">#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string>
class UDPClient {
private:
int client_fd;
struct sockaddr_in server_addr;
public:
UDPClient(const std::string& server_ip, int port) {
// 创建UDP socket
client_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (client_fd < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
// 设置服务器地址
memset(&server_addr, 0, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
// 转换IP地址
if (inet_pton(AF_INET, server_ip.c_str(), &server_addr.sin_addr) <= 0) {
std::cerr << "Invalid address: " << server_ip << std::endl;
close(client_fd);
exit(EXIT_FAILURE);
}
std::cout << "UDP Client ready to send to "
<< server_ip << ":" << port << std::endl;
}
~UDPClient() {
if (client_fd >= 0) {
close(client_fd);
}
}
// 发送单条消息
bool send_message(const std::string& message) {
ssize_t sent = sendto(client_fd, message.c_str(), message.length(), 0,
(struct sockaddr*)&server_addr, sizeof(server_addr));
if (sent < 0) {
perror("sendto failed");
return false;
}
std::cout << "Sent " << sent << " bytes: " << message << std::endl;
return true;
}
// 发送并接收回复（阻塞）
bool send_and_receive(const std::string& message, int timeout_sec = 5) {
// 发送消息
if (!send_message(message)) {
return false;
}
// 设置接收超时
struct timeval timeout;
timeout.tv_sec = timeout_sec;
timeout.tv_usec = 0;
if (setsockopt(client_fd, SOL_SOCKET, SO_RCVTIMEO,
&timeout, sizeof(timeout)) < 0) {
perror("setsockopt timeout failed");
}
// 接收回复
char buffer;
struct sockaddr_in from_addr;
socklen_t addr_len = sizeof(from_addr);
ssize_t recv_len = recvfrom(client_fd, buffer, sizeof(buffer) - 1, 0,
(struct sockaddr*)&from_addr, &addr_len);
if (recv_len < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK) {
std::cout << "Timeout: No response received" << std::endl;
} else {
perror("recvfrom failed");
}
return false;
}
buffer = '\0';
char from_ip;
inet_ntop(AF_INET, &from_addr.sin_addr, from_ip, INET_ADDRSTRLEN);
std::cout << "Received from " << from_ip << ":"
<< ntohs(from_addr.sin_port)
<< " (" << recv_len << " bytes): "
<< buffer << std::endl;
return true;
}
// 广播消息
bool broadcast(const std::string& message, int port) {
// 开启广播选项
int broadcast_enable = 1;
if (setsockopt(client_fd, SOL_SOCKET, SO_BROADCAST,
&broadcast_enable, sizeof(broadcast_enable)) < 0) {
perror("setsockopt broadcast failed");
return false;
}
// 设置广播地址
struct sockaddr_in broadcast_addr;
memset(&broadcast_addr, 0, sizeof(broadcast_addr));
broadcast_addr.sin_family = AF_INET;
broadcast_addr.sin_port = htons(port);
broadcast_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);// 255.255.255.255
// 发送广播
ssize_t sent = sendto(client_fd, message.c_str(), message.length(), 0,
(struct sockaddr*)&broadcast_addr, sizeof(broadcast_addr));
if (sent < 0) {
perror("broadcast sendto failed");
return false;
}
std::cout << "Broadcast " << sent << " bytes" << std::endl;
return true;
}
};
int main() {
UDPClient client("127.0.0.1", 8080);
// 发送测试消息
client.send_and_receive("Hello UDP Server!");
client.send_and_receive("Another message");
// 发送多条消息
for (int i = 0; i < 5; i++) {
std::string msg = "Message " + std::to_string(i);
client.send_and_receive(msg);
}
return 0;
}
</code></pre>
<h3 id="组播">组播</h3>
<p><strong>组播地址范围</strong>：224.0.0.0 - 239.255.255.255</p>
<ul>
<li>224.0.0.0 - 224.0.0.255：本地网络控制块</li>
<li>224.0.1.0 - 238.255.255.255：全球范围组播地址</li>
<li>239.0.0.0 - 239.255.255.255：本地管理组播地址</li>
</ul>
<pre><code class="language-C++">#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
class MulticastServer {
private:
int sock_fd;
struct sockaddr_in multicast_addr;
public:
MulticastServer(const std::string& multicast_ip, int port) {
// 创建UDP socket
sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (sock_fd < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
// 设置组播地址
memset(&multicast_addr, 0, sizeof(multicast_addr));
multicast_addr.sin_family = AF_INET;
multicast_addr.sin_port = htons(port);
if (inet_pton(AF_INET, multicast_ip.c_str(),
&multicast_addr.sin_addr) <= 0) {
std::cerr << "Invalid multicast address" << std::endl;
close(sock_fd);
exit(EXIT_FAILURE);
}
// 设置TTL（生存时间）
unsigned char ttl = 1;// 只在本地网络
if (setsockopt(sock_fd, IPPROTO_IP, IP_MULTICAST_TTL,
&ttl, sizeof(ttl)) < 0) {
perror("setsockopt TTL failed");
}
std::cout << "Multicast Server ready for "
<< multicast_ip << ":" << port << std::endl;
}
void send_message(const std::string& message) {
ssize_t sent = sendto(sock_fd, message.c_str(), message.length(), 0,
(struct sockaddr*)&multicast_addr,
sizeof(multicast_addr));
if (sent < 0) {
perror("multicast sendto failed");
} else {
std::cout << "Multicast sent " << sent << " bytes" << std::endl;
}
}
};
</code></pre>
<pre><code class="language-C++">#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
class MulticastClient {
private:
int sock_fd;
struct sockaddr_in local_addr;
struct ip_mreq mreq;
public:
MulticastClient(const std::string& multicast_ip, int port) {
// 创建UDP socket
sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (sock_fd < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
// 允许地址重用
int reuse = 1;
if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR,
&reuse, sizeof(reuse)) < 0) {
perror("setsockopt reuseaddr failed");
}
// 绑定到任意地址和指定端口
memset(&local_addr, 0, sizeof(local_addr));
local_addr.sin_family = AF_INET;
local_addr.sin_addr.s_addr = htonl(INADDR_ANY);
local_addr.sin_port = htons(port);
if (bind(sock_fd, (struct sockaddr*)&local_addr,
sizeof(local_addr)) < 0) {
perror("bind failed");
close(sock_fd);
exit(EXIT_FAILURE);
}
// 加入多播组
mreq.imr_multiaddr.s_addr = inet_addr(multicast_ip.c_str());
mreq.imr_interface.s_addr = htonl(INADDR_ANY);
if (setsockopt(sock_fd, IPPROTO_IP, IP_ADD_MEMBERSHIP,
&mreq, sizeof(mreq)) < 0) {
perror("setsockopt add membership failed");
close(sock_fd);
exit(EXIT_FAILURE);
}
std::cout << "Joined multicast group " << multicast_ip
<< " on port " << port << std::endl;
}
void receive_messages() {
char buffer;
std::cout << "Listening for multicast messages..." << std::endl;
while (true) {
struct sockaddr_in from_addr;
socklen_t addr_len = sizeof(from_addr);
ssize_t recv_len = recvfrom(sock_fd, buffer, sizeof(buffer) - 1, 0,
(struct sockaddr*)&from_addr, &addr_len);
if (recv_len > 0) {
buffer = '\0';
char from_ip;
inet_ntop(AF_INET, &from_addr.sin_addr,
from_ip, INET_ADDRSTRLEN);
std::cout << "Multicast from " << from_ip << ": "
<< buffer << std::endl;
}
}
}
};
</code></pre><br><br>
来源：https://www.cnblogs.com/hjk-airl/p/19513934
頁:
[1]