UDP客户端与服务端执行bind和connect

udp服务器使用connect()函数指明套接字的目的地址/端口号，使服务器只接受特定主机的请求；
udp服务器调用了bind()函数为服务器套接字绑定本地地址/端口，使得客户端知道发数据的目的地址/端口；

udp客户端调用connect()函数指明目的地址/端口后，可使用send()函数向目的地址发送数据；
udp客户端在发送数据之前，用bind()函数绑定本地地址/端口，可避免操作系统该套接字随机分配地址信息和端口号；

上代码

配置参数

#define INET_SERVER_IP_ADDR    "192.168.1.39"
#define INET_CLIENT_IP_ADDR    "192.168.1.102"#define SERVER_UDP_PORT    "9877"
#define CLIENT_UDP_PORT    "9871"#define INET_IP_ADDR_LENGTH    (16U)#define UDP_DGRAM_LEN_MAX    (1024U)
#define MSG_SEND_INTERVAL    (50000)   /* unit: us */

服务器：

void server_init(void)
{pid_t pid;siginfo_t info;int server_sockfd;struct sockaddr_in local_addr, remote_addr;/* print_addrinfo("ftp"); */   /* domain daytime stream http ftp *//*____________________________________________________________________________________________*/server_sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);if(server_sockfd < 0){perror("socket() fail");exit(EXIT_FAILURE);}/* socket_set_reuseaddr(); *//*____________________________________________________________________________________________*/memset(&local_addr, 0, sizeof(local_addr));if(inet_pton(AF_INET, INET_SERVER_IP_ADDR, &(local_addr.sin_addr)) < 0){perror("inet_pton() error");close(server_sockfd);exit(EXIT_FAILURE);}else{local_addr.sin_family = AF_INET;local_addr.sin_port = htons(atol(SERVER_UDP_PORT));}if(-1 == bind(server_sockfd, (struct sockaddr *)(&local_addr), sizeof(local_addr))){perror("bind() fail");close(server_sockfd);exit(EXIT_FAILURE);}/*____________________________________________________________________________________________*/char client_addr[INET_IP_ADDR_LENGTH];int ret;char rcv_buf[UDP_DGRAM_LEN_MAX] = {'\0'};memset(&remote_addr, 0, sizeof(remote_addr));socklen_t addr_len = sizeof(remote_addr);ret = recvfrom(server_sockfd, rcv_buf, UDP_DGRAM_LEN_MAX, 0, (struct sockaddr *)&remote_addr, &addr_len);if(-1 == ret){perror("recvfrom() failure");exit(EXIT_FAILURE);}else{if(NULL == inet_ntop(AF_INET, &remote_addr.sin_addr, client_addr, INET_IP_ADDR_LENGTH)){perror("inet_ntop() error");}else{printf("Received %d Bytes From Client: %s (Port: %u)\n", ret, client_addr, ntohs(remote_addr.sin_port));printf("%s\n", rcv_buf);}}/*____________________________________________________________________________________________*/#if falseif(inet_pton(AF_INET, INET_CLIENT_IP_ADDR, &(remote_addr.sin_addr)) < 0){perror("inet_pton() error");exit(EXIT_FAILURE);}else{remote_addr.sin_family = AF_INET;remote_addr.sin_port = htons(atol(CLIENT_UDP_PORT));}#endif#ifdef SERVER_CONNECT_ENif(-1 == connect(server_sockfd, (struct sockaddr *)(&remote_addr), sizeof(remote_addr))){perror("connect() fail");close(server_sockfd);exit(EXIT_FAILURE);}else{printf("Successfully Connected To Client-Socket!\n");}/*____________________________________________________________________________________________*/char send_buf[] = {"Of course, I still love you!"};if(-1 == send(server_sockfd, send_buf, sizeof(send_buf), 0)){perror("send() fail");}#elsechar send_buf[] = {"Of course, I still love you!"};if(-1 == sendto(server_sockfd, send_buf, sizeof(send_buf), 0, (struct sockaddr *)(&remote_addr), sizeof(remote_addr))){perror("sendto() fail");}#endif/*____________________________________________________________________________________________*/sigaction_config();/*____________________________________________________________________________________________*/pid = fork();if(pid < 0){perror("fork() error");}else if(pid == 0)  /* child */{#ifdef SERVER_CONNECT_ENdgram_send(server_sockfd);#elsedgram_sendto(server_sockfd, (struct sockaddr *)(&remote_addr), sizeof(remote_addr));#endif}else  /* parent */{#ifdef SERVER_CONNECT_ENdgram_recv(server_sockfd);#elsedgram_receive(server_sockfd);#endifif(-1 == waitid(P_PID, 0, &info, WEXITED)){perror("waitid() failure");}close(server_sockfd);exit(EXIT_SUCCESS);}
}

客户端：

void client_init(void)
{pid_t pid;siginfo_t info;int client_sockfd;struct sockaddr_in local_addr, remote_addr;/*____________________________________________________________________________________________*/client_sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);if(client_sockfd < 0){perror("socket() fail");exit(EXIT_FAILURE);}/*____________________________________________________________________________________________*/memset(&local_addr, 0, sizeof(local_addr));local_addr.sin_family = AF_INET;local_addr.sin_port = htons(atol(CLIENT_UDP_PORT));local_addr.sin_addr.s_addr = htonl(INADDR_ANY);if(-1 == bind(client_sockfd, (struct sockaddr *)(&local_addr), sizeof(local_addr))){perror("bind() fail");close(client_sockfd);exit(EXIT_FAILURE);}/*____________________________________________________________________________________________*/memset(&remote_addr, 0, sizeof(remote_addr));if(inet_pton(AF_INET, INET_SERVER_IP_ADDR, &(remote_addr.sin_addr)) < 0){perror("inet_pton() error");close(client_sockfd);exit(EXIT_FAILURE);}else{remote_addr.sin_family = AF_INET;remote_addr.sin_port = htons(atol(SERVER_UDP_PORT));}/*____________________________________________________________________________________________*/char send_buf[] = {"Hello World!"};int ret;ret = sendto(client_sockfd, send_buf, sizeof(send_buf), 0, (struct sockaddr *)(&remote_addr), sizeof(remote_addr));if(-1 == ret){perror("sendto() failure");close(client_sockfd);exit(EXIT_FAILURE);}else{printf("Say \"Hello\" To Server: %s With Port: %s\n", INET_SERVER_IP_ADDR, SERVER_UDP_PORT);fflush(stdout);}/*____________________________________________________________________________________________*/char server_addr[INET_IP_ADDR_LENGTH];char rcv_buf[UDP_DGRAM_LEN_MAX] = {'\0'};memset(&remote_addr, 0, sizeof(remote_addr));socklen_t addr_len = sizeof(remote_addr);ret = recvfrom(client_sockfd, rcv_buf, UDP_DGRAM_LEN_MAX, 0, (struct sockaddr *)&remote_addr, &addr_len);if(-1 == ret){perror("recvfrom() failure");exit(EXIT_FAILURE);}else{if(NULL == inet_ntop(AF_INET, &remote_addr.sin_addr, server_addr, INET_IP_ADDR_LENGTH)){perror("inet_ntop() error");}else{printf("Received %d Bytes From Server: %s (Port: %u)\n", ret, server_addr, ntohs(remote_addr.sin_port));printf("%s\n", rcv_buf);}}/*____________________________________________________________________________________________*/if(-1 == connect(client_sockfd, (struct sockaddr *)(&remote_addr), sizeof(remote_addr))){perror("connect() fail");close(client_sockfd);exit(EXIT_FAILURE);}else{printf("Successfully Connected To Server-Socket!\n");}/*____________________________________________________________________________________________*/sigaction_config();/*____________________________________________________________________________________________*/pid = fork();if(pid < 0){perror("fork() error");}else if(pid == 0)  /* child */{dgram_send(client_sockfd);}else  /* parent */{dgram_recv(client_sockfd);if(-1 == waitid(P_PID, 0, &info, WEXITED)){perror("waitid() failure");}close(client_sockfd);exit(EXIT_SUCCESS);}
}

测试：

服务端：