原文地址: https://blog.csdn.net/hnlyyk/article/details/50955053

在实际工作中，服务器需要同时监听和处理tcp和udp的套接字，同时监听N多的端口。根据bind系统调用来讲，一个socket只能监听一个端口，因此要创建多个socket并绑定到各个端口上。当然同一个端口可以同时绑定tcp和udp的socket，但是要创建两个socket，一个是tcp的一个是udp的。

下面我们就写一个可以同时处理tcp和udp服务的回射服务器。

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <pthread.h>
#define MAX_EVENT_NUMBER 1024
#define TCP_BUFFER_SIZE 512
#define UDP_BUFFER_SIZE 1024
int setnonblocking( int fd )
    int old_option = fcntl( fd, F_GETFL );
    int new_option = old_option | O_NONBLOCK;
    fcntl( fd, F_SETFL, new_option );
    return old_option;
void addfd( int epollfd, int fd )
    struct epoll_event event;
    event.data.fd = fd;
    //event.events = EPOLLIN | EPOLLET;
    event.events = EPOLLIN;//可读事件，默认为LT模式，事件一般被触发多次
    epoll_ctl( epollfd, EPOLL_CTL_ADD, fd, &event );
    setnonblocking( fd );
int main( int argc, char* argv[] )
    if( argc <= 2 )
        printf( "usage: %s ip_address port_number\n", basename( argv[0] ) );
        return 1;
    const char* ip = argv[1];
    int port = atoi( argv[2] );
    int ret = 0;
    //创建tcp套接字，并绑定 、监听
    struct sockaddr_in address;
    bzero( &address, sizeof( address ) );
    address.sin_family = AF_INET;
    inet_pton( AF_INET, ip, &address.sin_addr );
    address.sin_port = htons( port );
    int listenfd = socket( PF_INET, SOCK_STREAM, 0 );
    assert( listenfd >= 0 );
    ret = bind( listenfd, ( struct sockaddr* )&address, sizeof( address ) );
    assert( ret != -1 );
    ret = listen( listenfd, 5 );
    assert( ret != -1 );
    //创建udp套接字，并绑定
    bzero( &address, sizeof( address ) );
    address.sin_family = AF_INET;
    inet_pton( AF_INET, ip, &address.sin_addr );
    address.sin_port = htons( port );
    int udpfd = socket( PF_INET, SOCK_DGRAM, 0 );
    assert( udpfd >= 0 );
    ret = bind( udpfd, ( struct sockaddr* )&address, sizeof( address ) );
    assert( ret != -1 );
    struct epoll_event events[ MAX_EVENT_NUMBER ];
    int epollfd = epoll_create( 5 );
    assert( epollfd != -1 );
    //注册tcp和udp套接字的可读事件
    addfd( epollfd, listenfd );
    addfd( epollfd, udpfd );
    while( 1 )
        int number = epoll_wait( epollfd, events, MAX_EVENT_NUMBER, -1 );
        if ( number < 0 )
            printf( "epoll failure\n" );
            break;
        for ( int i = 0; i < number; i++ )
            int sockfd = events[i].data.fd;
            //tcp有新的可读事件，也即接受到了新的连接
            if ( sockfd == listenfd )
                struct sockaddr_in client_address;
                socklen_t client_addrlength = sizeof( client_address );
                int connfd = accept( listenfd, ( struct sockaddr* )&client_address, &client_addrlength );
                //将新的连接套接字也注册可读事件
                addfd( epollfd, connfd );
            //udp套接字事件处理
            else if ( sockfd == udpfd )
                char buf[ UDP_BUFFER_SIZE ];
                memset( buf, '\0', UDP_BUFFER_SIZE );
                struct sockaddr_in client_address;
                socklen_t client_addrlength = sizeof( client_address );
                ret = recvfrom( udpfd, buf, UDP_BUFFER_SIZE-1, 0, ( struct sockaddr* )&client_address, &client_addrlength );
                if( ret > 0 )
                    sendto( udpfd, buf, UDP_BUFFER_SIZE-1, 0, ( struct sockaddr* )&client_address, client_addrlength );
            //注册的socket发生可读事件
            else if ( events[i].events & EPOLLIN )
                char buf[ TCP_BUFFER_SIZE ];
                while( 1 )
                    memset( buf, '\0', TCP_BUFFER_SIZE );
                    ret = recv( sockfd, buf, TCP_BUFFER_SIZE-1, 0 );
                    if( ret < 0 )
                        //数据接受完毕之后进入下一次可读事件
                        if( ( errno == EAGAIN ) || ( errno == EWOULDBLOCK ) )
                            break;
                        close( sockfd );
                        break;
                    //服务端已经断开连接，所以断开客户端连接
                    else if( ret == 0 )
                        close( sockfd );
                        send( sockfd, buf, ret, 0 );
                printf( "something else happened \n" );