Details about UDP communication instances in one of network programming in Linux

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As for the specific communication process, there is a lot of online information.

No explanation. The detailed explanation is included in the code comment.

Client code:

Client. cpp

# Include <stdio. h> # include <sys/types. h> # include <sys/socket. h> # include <netinet/in. h> # include <unistd. h> # include <errno. h> # include <string. h> # include <stdlib. h> # include <sys/IOCTL. h> # include <net/if. h> # include <ARPA/inet. h> # define dest_ip "127.0.0.1" # define serv_port 8000int main () {/* socket file descriptor */INT sock_fd;/* Create UDP socket */sock_fd = socket (af_inet, sock_dgram, 0); If (sock_fd <0) {perror ("socket"); exit (1) ;}/ * defines a connection address structure */struct sockaddr_in addr_serv; int Len; memset (& addr_serv, 0, sizeof (struct sockaddr_in )); // ************* set the protocol family to IPv4 ************ // addr_serv.sin_family = af_inet; // ************** set the connection server port ************ // both the port number and IP address it is stored in network bytes, you need to re-Sort addr_serv.sin_port = htons (serv_port); // convert to the network byte order, small End-> Large End // ************** set the connection server address ************//// 0th writing methods, use inaddr_any to represent the server address/* inaddr_any to indicate that no matter which Nic receives the data, the program will receive the data as long as the port number corresponds * // addr_serv.sin_addr.s_addr = htonl (inaddr_any ); // 1st address conversion methods (Point-to-10 conversion to in_addr_t type) addr_serv.sin_addr.s_addr = inet_addr ("127.0.0.1 "); // error returned inaddr_none // 2nd // inet_aton ("127.0.0.1", & addr_serv.sin_addr ); // ************** set the connection server address ************ // Len = sizeof (addr_serv); // ************* when obtaining the MAC address of the local machine, you can ignore ************ // struct ifreq IFR; IFR. ifr_addr.sa_family = af_inet; strncpy (IFR. ifr_name, "eth0", ifnamsiz-1); IOCTL (sock_fd, siocgifhwaddr, & IFR); printf ("I Am a client, my mac address :"); printf ("%. 2x: %. 2x: %. 2x: %. 2x: %. 2x: %. 2x \ n ", (unsigned char) IFR. ifr_hwaddr.sa_data [0], (unsigned char) IFR. ifr_hwaddr.sa_data [1], (unsigned char) IFR. ifr_hwaddr.sa_data [2], (unsigned char) IFR. ifr_hwaddr.sa_data [3], (unsigned char) IFR. ifr_hwaddr.sa_data [4], (unsigned char) IFR. ifr_hwaddr.sa_data [5]); // the MAC address is obtained, and INT recv_num; int send_num; char send_buf [20] = "Hi, I am the client"; char recv_buf [20]; // receive Cache/**************** send data to the server *************/// /compared with TCP, UDP saves the connect function, namely three handshakes, and can directly send data // int sendto (INT socket, void * buffer. size_t size, int flags, struct sockaddr * ADDR, socklen_t length) send_num = sendto (sock_fd, send_buf, strlen (send_buf), 0 (struct sockaddr *) & addr_serv, Len ); printf ("client: % s \ n", send_buf); If (send_num <0) {perror ("sendto error"); exit (1 );} // *************** receive server data ************** // int recvfrom (int socket, void * buffer, size_t size, int flags, struct sockaddr * ADDR, socklen_t * length-PTR) recv_num = recvfrom (sock_fd, recv_buf, sizeof (recv_buf), 0, (struct sockaddr *) & addr_serv, (socklen_t *) Len); recv_buf [recv_num] = '\ 0'; printf ("received by the Client: % d Bytes: % s \ n ", recv_num, recv_buf); close (sock_fd); Return 0 ;}

Server code:

Server. cpp

# Include <stdio. h> # include <sys/types. h> # include <sys/socket. h> # include <netinet/in. h> # include <unistd. h> # include <errno. h> # include <string. h> # include <stdlib. h> # include <sys/IOCTL. h> # include <net/if. h> # define serv_port 8000int main () {/* socket file descriptor */INT sock_fd;/* Create UDP socket */sock_fd = socket (af_inet, sock_dgram, 0 ); if (sock_fd <0) {perror ("socket"); exit (1) ;}/ * Set address */struct sockaddr_ I N addr_serv; int Len; memset (& addr_serv, 0, sizeof (struct sockaddr_in); addr_serv.sin_family = af_inet; // htons meaning: H: Host N: Network s: short l: long L: longaddr_serv.sin_port = htons (serv_port); // converts it to the network byte sequence. The Small End-> large end/* inaddr_any indicates that no matter which network adapter receives data, as long as the port number corresponds, the program will receive */addr_serv.sin_addr.s_addr = htonl (inaddr_any); Len = sizeof (addr_serv);/* bind socket * // int BIND (INT socket, struct sockaddr * ADDR, socklen_t Length) if (BIND (sock_fd, (struct sockaddr *) & addr_serv, sizeof (addr_serv) <0) {perror ("BIND error:"); exit (1 );} int recv_num; int send_num; char send_buf [20] = "I am server! "; Char recv_buf [20]; // receives the cache struct sockaddr_in addr_client; // gets the local MAC address struct ifreq IFR; IFR. ifr_addr.sa_family = af_inet; strncpy (IFR. ifr_name, "eth0", ifnamsiz-1); IOCTL (sock_fd, siocgifhwaddr, & IFR); printf ("I Am a server, my mac address :"); printf ("%. 2x: %. 2x: %. 2x: %. 2x: %. 2x: %. 2x \ n ", (unsigned char) IFR. ifr_hwaddr.sa_data [0], (unsigned char) IFR. ifr_hwaddr.sa_data [1], (unsigned char) IFR. ifr_hwaddr.sa_data [2], (unsigned Char) IFR. ifr_hwaddr.sa_data [3], (unsigned char) IFR. ifr_hwaddr.sa_data [4], (unsigned char) IFR. ifr_hwaddr.sa_data [5]); // loop wait while (1) {printf ("server wait: \ n");/* recvfrom () receives data from UDP-based APIs, includes the IP address of the sender. Because the data packet may come from any host * flag = 0, regular reading, equivalent to the read () function. Flag = msg_peek, read data but do not refresh the read buffer. MSG--OOB, read out-of-band data, common data ignored */recv_num = recvfrom (sock_fd, recv_buf, sizeof (recv_buf), 0, (struct sockaddr *) & addr_client, (socklen_t *) & Len); If (recv_num <0) {perror ("recvfrom error:"); exit (1) ;} recv_buf [recv_num] = '\ 0 '; printf ("server received: % d Bytes: % s \ n", recv_num, recv_buf); // send data send_num = sendto (sock_fd, send_buf, recv_num, 0, (struct sockaddr *) & addr_client, Len); printf ("server Description: % s \ n", send_buf); If (send_num <0) {perror ("sendto error: "); exit (1) ;}close (sock_fd); Return 0 ;}