从 bind 系统调用的参数来看, 一个 socket 只能与一个 socket 地址绑定, 即一个 socket 只能用来监听一个端口. 因此, 服务器如果要同时监听多个端口, 就必须创建多个 socket 并将它们分别绑定到各自端口上. 即使是同一个端口, 如果服务器要同时监听该端口上的 tcp 和 udp 请求, 也必须分别创建流 socket 和数据报 socket 并绑定到该端口上. 对此, 可以使用 i/o 复用技术来管理这些 socket

#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 UPD_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) {
	epoll_event event;
	event.data.fd = fd;
	event.events = EPOLLIN | EPOLLET;

	epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);

	setnonblocking(fd);
}


int main(int argc, char const *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;
	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);

	bzero(&address, sizeof(address));
	address.sin_family = AF_INET;
	inet_pton(AF_INET, ip, &address.sin_addr);
	address.sin_port = htons(port);
	int uppfd = socket(PF_INET, SOCK_DGRAM, 0);
	assert(uppfd >= 0);

	ret = bind(uppfd, (struct sockaddr*)&address, sizeof(address));
	assert(ret != -1);

	epoll_event events[MAX_EVENT_NUMBER];
	int epollfd = epoll_create(5);
	assert(epollfd != -1);

	// 
	addfd(epollfd, listenfd);
	addfd(epollfd, uppfd);

	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;
			
			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);

				addfd(epollfd, connfd);

			} else if(sockfd == uppfd) {
				char buf[UPD_BUFFER_SIZE];
				memset(buf, '\0', UPD_BUFFER_SIZE);
				struct sockaddr_in client_address;
				socklen_t client_addrlength = sizeof(client_address);

				ret = recvfrom(uppfd, buf, UPD_BUFFER_SIZE - 1, 0, (struct sockaddr*)&client_address, &client_addrlength);

				if(ret > 0) {
					sendto(uppfd, buf, UPD_BUFFER_SIZE - 1, 0, (struct sockaddr*)&client_address, client_addrlength);
				}

			} 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) {
						if((errno == EAGAIN) || (errno == EWOULDBLOCK)) {
							break;
						}

						close(sockfd);
						break;

					} else if(ret == 0) {
						close(sockfd);

					} else {
						send(sockfd, buf, ret, 0);
					}
				}

			} else {
				printf("something else happened\n");

			}
		}
	}

	close(listenfd);

	return 0;
}