udp --- 用户数据报协议，是一个无连接的简单的面向数据报的运输层协议。
udp不提供可靠性，它只是把应用程序传给IP层的数据报发送出去，但是并不能保证它们能到达目的地。
udp在传输数据报前不用在客户和服务器之间建立一个连接，且没有超时重发等机制，故而传输速度很快。
udp是一种面向无连接的协议，每个数据报都是一个独立的信息，包括完整的源地址或目的地址，它在网络上以任何可能的路径传往目的地，因此能否到达目的地，到达目的地的时间以及内容的正确性都是不能被保证的。
udp通讯流程很简单，具体步骤如下：
微信图片_20230908105059.png
udp服务端代码
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdbool.h>
#include <pthread.h>
#define BUFFER_SIZE 1024 // buf size
struct CONNECT_INFO {
struct sockaddr_in client_addr;
};
static int sock_fd;
static volatile bool is_connect = false;
bool udp_server_init(short port) {
struct sockaddr_in server_addr;
sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (sock_fd == -1) {
perror("socket");
return false;
}
// initialize address.
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
// bind the local port.
if ((bind(sock_fd, (struct sockaddr *)&server_addr,
sizeof(struct sockaddr_in))) == -1) {
perror("bind");
return false;
}
return true;
}
void *send_thread(void *arg) {
struct CONNECT_INFO *info = (struct CONNECT_INFO *)arg;
if (info == NULL) {
printf("error connect info");
return (void*)-1;
}
while (1) {
char send_buf[BUFFER_SIZE];
bzero(send_buf, sizeof(send_buf));
// input from keyboard.
char *str = fgets(send_buf, sizeof(send_buf), stdin);
if (str == NULL) {
perror("fgets");
continue;
}
if (strlen(str) <= 1) {
continue;
}
if(is_connect == false) {
printf("No client are available!\n");
continue;
}
// send data.
if ((sendto(sock_fd, send_buf, strlen(str) - 1, 0,
(struct sockaddr *)&info->client_addr,
sizeof(struct sockaddr_in))) < 0) {
perror("sendto");
continue;
}
}
return (void*)0;
}
int main(int argc, char *argv[]) {
// check your input.
if (argc != 2) {
printf("Usage:\n");
printf(" %s <port number>\n", argv[0]);
return -1;
}
short port = atoi(argv[1]);
bool ret = udp_server_init(port);
if (ret == false) {
goto err;
}
pthread_t t_id;
struct CONNECT_INFO info;
socklen_t addr_len = sizeof(struct sockaddr_in);
memset(&info, 0, sizeof(info));
pthread_create(&t_id, NULL, send_thread, (void *)&info);
pthread_detach(t_id);
printf("Waiting for client connectionn\n");
while (1) {
// recive from client.
char recv_buf[BUFFER_SIZE];
bzero(recv_buf, sizeof(recv_buf));
if ((recvfrom(sock_fd, recv_buf, sizeof(recv_buf), 0,
(struct sockaddr *)&info.client_addr, &addr_len)) <= 0) {
perror("recvfrom");
goto err;
}
printf("[Recv from client %s:%d] : %s\n",
inet_ntoa(info.client_addr.sin_addr),
htons(info.client_addr.sin_port),
recv_buf);
is_connect = true;
}
close(sock_fd);
return 0;
err:
close(sock_fd);
return -1;
}
udp客户端代码：
#include <stdio.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>
#define BUFFER_SIZE 1024 // buf size
int main(int argc, char *argv[]) {
// check the arguments.
if (argc != 3) {
printf("Usage:\n");
printf(" %s <server_addr> <portnumber>\n", argv[0]);
return -1;
}
int sock_fd;
char send_buf[BUFFER_SIZE];
char recv_buf[BUFFER_SIZE];
struct sockaddr_in server_addr;
char *addr = argv[1];
short port = atoi(argv[2]);
// initialize address.
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = inet_addr(addr);
server_addr.sin_port = htons(port);
// create udp socket.
sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (sock_fd == -1) {
perror("socket");
return -1;
}
pid_t pid = fork();
if (pid > 0) {
// The parent process is responsible for sending messages.
while (1) {
bzero(send_buf, sizeof(send_buf));
// read from stdin.
char *str = fgets(send_buf, sizeof(send_buf), stdin);
if (str == NULL) {
perror("fgets");
goto err;
}
if (strlen(str) <= 1) {
continue;
}
// send data.
if ((sendto(sock_fd, send_buf, strlen(str) - 1, 0,
(struct sockaddr *)&server_addr,
sizeof(struct sockaddr_in))) < 0) {
perror("sendto");
goto err;
}
}
}
else if (pid == 0) {
// The child process is responsible for receiving messages.
while (1) {
bzero(recv_buf, sizeof(recv_buf));
socklen_t addr_len = sizeof(struct sockaddr_in);
if ((recvfrom(sock_fd, recv_buf, sizeof(recv_buf), 0,
(struct sockaddr *)&server_addr,
&addr_len)) <= 0) {
perror("recvfrom");
goto err;
}
printf("[Recv from server %s:%d] : %s\n",
inet_ntoa(server_addr.sin_addr),
htons(server_addr.sin_port),
recv_buf);
}
}
close(sock_fd);
return 0;
err:
close(sock_fd);
return -1;
}
编译后运行结果：
160406w8j9cocly2a3ncsl.png.thumb.jpg
160442vfuv6gvfuq518fuf.png.thumb.jpg
