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Berkeley Socket

Network Programming

TCP Socket : Server Server

socket()

bind()

listen()

accept()

TCP Socket : Server socket()

bind()

listenfd = socket(AF_INET, SOCK_STREAM, 0);// AF_INET: IPv4, AF_INET6: IPv6// SOCK_STREAM: TCP, SOCK_DGRAM: UDP

bzero(&serv_addr, sizeof(serv_addr));serv_addr.sin_family = AF_INET;serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);serv_addr.sin_port = htons(23);// htonl: host to network (long)// htons: host to network (short)bind(listenfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));

TCP Socket : Server listen()

accept()

listen(listenfd, LISTENQ);// LISTENQ: the maximum length the queue of pending// connections

connfd = accept(listenfd, (struct sockaddr *) NULL, NULL);

// or

cli_len = sizeof(cli_addr);connfd = accept(listenfd, (struct sockaddr *) &cli_addr, cli_len);

TCP Socket : Client Client

socket()

connect()

TCP Socket : Client socket()

connect()

sockfd = socket(AF_INET, SOCK_STREAM, 0);// AF_INET: IPv4, AF_INET6: IPv6// SOCK_STREAM: TCP, SOCK_DGRAM: UDP

char *server_ip = “140.113.210.143”;bzero(&serv_addr, sizeof(serv_addr));serv_addr.sin_family = AF_INET;serv_addr.sin_addr.s_addr = inet_addr(server_ip);serv_addr.sin_port = htons(23);// inet_addr: ascii dotted-decimal addr to network addr// htons: host to network (short)connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));

TCP Socket : functions convert values between host and network

Internet address manipulation routines

#include <netinet/in.h>uint32_t htonl(uint32_t hostlong);uint16_t htons(uint16_t hostshort);uint32_t ntohl(uint32_t netlong);uint16_t ntohs(uint16_t netshort);

#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>in_addr_t inet_addr(const char *cp);char * inet_ntoa(struct in_addr in);int inet_pton(int af, const char * restrict src, void * restrict dst);

TCP Socket : functions inet_ntoa()

inet_pton()

inet_ntoa(cli_addr.sin_addr);// return ascii ip address of client

char *server_ip = “140.113.210.143”;inet_pton(AF_INET, server_ip, &serv_addr.sin_addr);// return 1: address valid// return 0: address not parseable// return -1: error occurred// inet_pton is valid for AF_INET and AF_INET6

Socket Options SO_REUSEADDR

bind to the ip/port already in use bind to the same port at different ip

SO_REUSEPORT bind to the same port at the same ip

int opt = 1;setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

int opt = 1;setsockopt(sockfd, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt));

Socket Options

#include <sys/types.h>#include <sys/socket.h>

sockfd = socket(. . . .);

int opt = 1;setsockopt(sockfd, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt));

bind(sockfd, . . . .);

TCP : TIME_WAIT

Client Server

close

Active Close FIN_WAIT_1 Passive Close

CLOSE_WAIT

FIN M

ACK M+1

FIN N

ACK N+1

FIN_WAIT_2

TIME_WAIT

close

LAST_ACK

CLOSED

TCP : TIME_WAIT TIME_WAIT

Wait 2MSL (Maximum Segment Lifetime) For 2 Reasons:

If last ACK (ACK N+1) lost ... Let lost duplicate packets timeout