第十六章網絡IPC:套接字

1. 套接字描述符

套接字是通信端點的抽象。

int socket(int domain, int type, int protocol); //創建一個套接字，返回套接字的描述符

//domain確定通信的特性，type確定套接字的類型，protocol代表通信協議

int shutdown(int sockfd, int how); //套接字的通信是雙向的，它用來禁止一個套接字的I/O。

2. 尋址

i. 字節序(大小端)

TCP/IP協議棧使用大端字節序。

ii. 地址格式

const char *inet_ntop(int domain, const void *restrict addr, char *restrict str, socklen_t size);

int inet_pton(int domain, const char* restrict str, void *restrict addr); //將文本字符串轉換成網絡字節序的二進制地址，上面的函數恰恰是相反的操作

iii. 地址查詢

//找到給定計算機系統的主機信息

struct hostent *gethostent(void); //找到給定計算機系統的主機信息

void sethostent(int stayopen);

void endhostent(void);

//獲得網絡名字和網絡編號

struct netent *getnetbyaddr(unit32_t net, int type);

struct netent *getnetbyname(const char* name);

struct netent *getnetent(void);

void setnetent(int stayopen);

void endnetent(void);

//在協議名字和協議編號之間進行映射

struct protoent *getprotobyname(const char *name);

struct protoent *getprotobynumber(int proto);

struct protoent *getprotoent(void);

void setprotoent(int stayopen);

void endprotoent(void);

//服務是由地址的端口號部分表示的。每一個服務由一個唯一的衆所周知的端口號來支持。

struct servent *getservbyname(const char *name, const char *proto);

struct servent *getservbyport(int port, const char *proto); //是不是寫錯了

struct servent *getservent(void);

void setservent(int stayopen);

void endservent(void);

//將一個主機名和服務名映射到一個地址

int getaddrinfo(const char *restrict host, const char *restrict service, const struct addrinfo *restrict hint, struct addrinfo **restrict res); //若出錯返回錯誤碼

const char *gai_strerror(int error); //將返回的錯誤碼轉換成錯誤消息

void freeaddrinfo(struct addrinfo *ai); //釋放

int getnameinfo(const struct sockaddr *restrict addr, socklen_t alen, char *restrict host, socklen_t hostlen, char *restrict service, socklen_t servlen, int flags); //將一個地址名轉換成一個主機名和服務名

iX. 將套接字與地址關聯

int bind(int sockfd, const struct sockaddr *addr, socklen_t len); //使用bind函數關聯地址和套接字

int getsockname(int sockfd, struct sockaddr *restrict addr, socklen_t *restrict alenp); //發現綁定到套接字上的地址

//如果套接字已經和對等方連接，調用getpeername來找到對方的地址

int getpeername(int sockfd, strcut sockaddr *restrict addr, socklen_t *restrict alenp);

3. 建立連接

int connect(int sockfd, const struct sockaddr *addr, socklen_t len); //客戶端與服務器端進行連接

int listen(int sockfd, int backlog); //服務器告知願意接受連接請求

int accept(int sockfd, struct sockaddr *restrict addr, socklen_t *restrict len); //服務器調用了listen沒所用的套接字就能接受連接請求，使用accept獲得連接請求並進行連接。

4. 數據傳輸

ssize_t send(int sockfd, const void *buf, size_t nbytes, int flags); //發送數據，要求套接字必須已經連接

ssize_t sendto(int sockfd, const void *buf, size_t nbytes, int flags, const struct sockaddr *destaddr, socklen_t destlen); //可以在無連接的套接字上面加上一個目標地址

ssize_t sendmsg(int scokfd, const struct msghdr *msg, int flag); //跟writev函數類似

ssize_t recv(int sockfd, void *buf, size_t nbytes, int flags); //跟read相似，但是可以指定標誌來控制如何接收數據

ssize_t recvfrom(int sockfd, void *restrict buf, size_t len, int flags, struct sockaddr *restrict addr, socklen_t *restrict addrlen); //得到數據發送者的源地址

ssize_t recvmsg(int sockfd, struct msghdr *msg, int flags); //類似於readv

//面向連接的客戶端，客戶端從系統的uptime命令獲得輸出

#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <sys/socket.h>

#define BUFLEN 128

extern int connect_retry(int, int, int, const struct sockaddr *, socklen_t);

void print_uptime(int sockfd)
{
	int n;
	char buf[BUFLEN];

	while((n = recv(sockfd, buf, BUFLEN, 0)) > 0)
		write(STDOUT_FILENO, buf, n);
	if(n < 0)
		err_sys("recv error");
}

int main(int argc, char *argv[])
{
	struct addrinfo *alist, *aip;
 	struct addrinfo hint;
  	int sockfd, err;

	if(argc != 2)
		err_quit("usage: ruptime hostname");
	memset(&hint, 0, sizeof(hint));
  	hint.ai_socktype = SOCK_STREAM;
  	hint.ai_canonname = NULL;
  	hint.ai_addr = NULL;
	hint.ai_next = NULL;
  	if((err = getaddrinfo(argv[1], "ruptime", &hint, &alist)) != 0)
		err_quit("getaddrinfo error: %s", gai_strerror(err));
	for(aip = alist; aip != NULL; aip = aip->ai_next) {
		if((sockfd = connect_retry(aip->ai_family, SOCK_STREAM, 0, aip->ai_addr, aip->ai_addrlen)) < 0) {
			err = errno;
		} else{
			print_uptime(sockfd);
			exit(0);
		}
	}
	err_exit(err, "can't connect to %s", argv[1]);
}

//面向連接的服務器

#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <syslog.h>
#include <sys/socket.h>

#define BUFLEN 128
#define QLEN 10

#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 256
#endif

extern int initserver(int, const struct sockaddr *, socklen_t, int);

void serve(int sockfd)
{
	int clfd;
	FILE *fp;
	char buf[BUFLEN];
	
	set_cloexec(sockfd); //???
	for(;;) {
		if((clfd = accept(sockfd, NULL, NULL)) < 0){
			syslog(LOG_ERR, "ruptime: accept error: %s", strerror(errno));
			exit(1);
		}
		set_cloexec(clfd);
		if((fp = popen("/usr/bin/uptime", "r")) == NULL) {
			sprintf(buf, "error: %s\n", strerror(errno));
			send(clfd, buf, strlen(buf), 0);
		} else {
			while(fgets(buf, BUFLEN, fp) != NULL)
				send(clfd, buf, strlen(buf), 0);
			pclose(fp);
		}
		close(clfd);
	}
}

int main(int argc, char *argv[])
{
	struct addrinfo *alist, *aip;
	struct addrinfo hint;
	int sockfd, err, n;
	char *host;
	
	if(argc != 1)
		err_quit("usage: ruptimed");
	if((n = sysconf(_SC_HOST_NAME_MAX)) < 0)
		n = HOST_NAME_MAX;
	if((host = malloc(n)) == NULL)
		err_sys("malloc error");
	if(gethostname(host, n) < 0)
		err_sys("gethostname error");
	daemonize("ruptimed");
	memset(&hint, 0, sizeof(hint));
	hint.ai_flags = AI_CANONNAME;
	hint.ai_socktype = SOCK_STREAM;
	hint.ai_canonname = NULL;
	hint.ai_addr = NULL;
	hint.ai_next = NULL;
	if((err = getaddrinfo(host, "ruptime", &hint, &alist)) != 0) {
		syslog(LOG_ERR, "ruptimed: getaddrinfo error: %s", gai_strerror(err));
		exit(1);
	}
	for(aip = alist; aip != NULL; aip = aip->ai_next) {
		if((sockfd = initserver(SOCK_STREAM, aip->ai_addr, aip->ai_addrlen, QLEN)) >= 0) {
		serve(sockfd);
		exit(0);
		}
	}
	exit(1);
}

//無連接的客戶端

#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <sys/socket.h>

#define BUFLEN 128
#define TIMEOUT 20

void sigalrm(int signo)
{
}

void print_uptime(int sockfd, struct addrinfo *aip)
{
	int n;
	char buf[BUFLEN];

	buf[0] = 0;
	if(sendto(sockfd, buf, 1, 0, aip->ai_addr, aip->ai_addrlen) < 0)
		err_sys("sendto error");
	alarm(TIMEOUT);
	if((n = recvfrom(sockfd, buf, BUFLEN, 0, NULL, NULL)) < 0) {
		if(errno != EINTR)
			alarm(0);
		err_sys("recv error");
	}
	alarm(0);
	write(STDOUT_FILENO, buf, n);
}

int main(int argc, char *argv[])
{
	struct addrinfo *alist, *aip;
	struct addrinfo hint;
	struct sigaction sa;
	int sockfd, err;
	
	if(argc != 2)
		err_quit("usage: ruptime hostname");
	sa.sa_handler = sigalrm;
	sa.sa_flags = 0;
	sigemptyset(&sa.sa_mask);
	if(sigaction(SIGALRM, &sa, NULL) < 0)
		err_sys("sigaction error");
	memset(&hint, 0, sizeof(hint));
	hint.ai_socktype = SOCK_DGRAM;
	hint.ai_canonname = NULL;
	hint.ai_addr = NULL;
	hint.ai_next = NULL;
	if((err = getaddrinfo(argv[1], "ruptime", &hint, &alist)) != 0)
		err_quit("getaddrinfo error %s", gai_strerror(err));
	
	for(aip = alist; aip != NULL; aip = aip->ai_next) {
		if((sockfd = socket(aip->ai_family, SOCK_DGRAM, 0)) < 0) {
			err = errno;
		} else {
			print_uptime(sockfd, aip);
			exit(0);
		}
	}
	fprintf(stderr, "can't contact %s: %s\n", argv[1], strerror(err));
	exit(1);
}

//無連接的服務器

#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <syslog.h>
#include <sys/socket.h>

#define BUFLEN 128
#define MAXADDRLEN 256

#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 256
#endif

extern int initserver(int, const struct sockaddr *, socklen_t, int);

void serve(int sockfd)
{
	int n;
	socklen_t alen;
	FILE *fp;
	char buf[BUFLEN], abuf[MAXADDRLEN];
	struct sockaddr *addr = (struct sockaddr *)abuf;
	
	set_cloexec(sockfd);
	for(;;) {
		alen = MAXADDRLEN;
		if((n = recvfrom(sockfd, buf, BUFLEN, 0, addr, &alen)) < 0) {
			syslog(LOG_ERR, "ruptimed: recvfrom error: %s", strerror(errno));
		exit(1);
		}
		if((fp = popen("/usr/bin/uptime", "r")) == NULL) {
			sprintf(buf, "error: %s\n", strerror(errno));
			sendto(sockfd, buf, strlen(buf), 0, addr, alen);
		} else {
			if(fgets(buf, BUFLEN, fp) != NULL)
				sendto(sockfd, buf, strlen(buf), 0, addr, alen);pclose(fp);
		}
	}
}

int main(int argc, char *argv[])
{
	struct addrinfo *alist, *aip;
	struct addrinfo hint;
	int sockfd, err, n;
	char *host;

	if(argc != 1)
		err_quit("usage: ruptimed");
	if((n = sysconf(_SC_HOST_NAME_MAX)) < 0)
		n = HOST_NAME_MAX;
	if((host = malloc(n)) == NULL)
		err_sys("malloc error");
	if(gethostname(host, n) < 0)
		err_sys("gethostname error");
	daemonize("ruptimed");
	memset(&hint, 0, sizeof(hint));
	hint.ai_flags = AI_CANONNAME;
	hint.ai_socktype = SOCK_DGRAM;
	hint.ai_canonname = NULL;
	hint.ai_addr = NULL;
	hint.ai_next = NULL;
	if((err = getaddrinfo(host, "ruptime", &hint, &alist)) != 0) {
		syslog(LOG_ERR, "ruptimed: getaddrinfo error: %s", gai_strerror(err));
		exit(1);
	}
	for(aip = alist; aip != NULL; aip = aip->ai_next) {
		if((sockfd = initserver(SOCK_DGRAM, aip->ai_addr, aip->ai_addrlen, 0)) >= 0) {
			serve(sockfd);
			exit(0);	
		}
	}
	exit(1);
}

5. 套接字選項

int setsockopt(int sockfd, int level, int option, const void *val, socklen_t len); //設置套接字選項

int getsockopt(int sockfd, int level, int option, void *restrict val, socklen_t *restrict lenp); //查看選項的當前值

6. 帶外數據

int sockatmark(int sockfd); //判斷是否已經到達晉級標記；在標記處，返回1；不在標記處返回0；出錯返回-1。

7. 非阻塞和異步I/O

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第十六章 網絡IPC:套接字

第十六章網絡IPC:套接字