10socket编程

这一节主要关注的还是粘包问题，我们利用recv实现一个recv_peek函数，它的目的是偷窥目的，它是利用recv的一个msg_peek参数与read的区别，read读取后

会擦除缓冲区的内容，而recv结合msg_peek会读取的时候并不擦除缓冲区的内容，起到一个可以偷窥的目的，利用这个特性可以用recv实现一个readline函数

进而利用readline来给出另一个解决回射服务器的粘包问题：

客户端：

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

ssize_t readn(int fd, void *buf, size_t count)
{
        size_t nleft = count;
        ssize_t nread;
        char *bufp = (char*)buf;

        while (nleft > 0)
        {
                if ((nread = read(fd, bufp, nleft)) < 0)
                {
                        if (errno == EINTR)
                                continue;
                        return -1;
                }
                else if (nread == 0)
                        return count - nleft;

                bufp += nread;
                nleft -= nread;
        }

        return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
        size_t nleft = count;
        ssize_t nwritten;
        char *bufp = (char*)buf;

        while (nleft > 0)
        {
                if ((nwritten = write(fd, bufp, nleft)) < 0)
                {
                        if (errno == EINTR)
                                continue;
                        return -1;
                }
                else if (nwritten == 0)
                        continue;

                bufp += nwritten;
                nleft -= nwritten;
        }

        return count;
}
// recv_peek的实现
ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
        while (1)
        {
                int ret = recv(sockfd, buf, len, MSG_PEEK);
                if (ret == -1 && errno == EINTR)
                        continue;
                return ret;
        }
}

// readline的实现
ssize_t readline(int sockfd, void *buf, size_t maxline)
{
        int ret;
        int nread;
        char *bufp = buf;
        int nleft = maxline;
        while (1)
        {
                ret = recv_peek(sockfd, bufp, nleft);
                if (ret < 0)   //失败
                        return ret;
                else if (ret == 0)  //对等方关闭
                        return ret;

                nread = ret;
                int i;
                for (i=0; i<nread; i++)   //开始偷窥\n
                {
                        if (bufp[i] == '\n')
                        {
                                ret = readn(sockfd, bufp, i+1);
                                if (ret != i+1)
                                        exit(EXIT_FAILURE);

                                return ret;
                        }
                }

                if (nread > nleft)
                        exit(EXIT_FAILURE);
                //如果已偷窥的没有\n读取后继续读继续偷窥
                nleft -= nread;
                ret = readn(sockfd, bufp, nread);
                if (ret != nread)
                        exit(EXIT_FAILURE);

                bufp += nread;
        }

        return -1;
}

int main(void)
{
	int sock;
	if ((sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
		ERR_EXIT("socket");

	struct sockaddr_in servaddr;
	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(5188);
	servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");

	if (connect(sock, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
		ERR_EXIT("connect");
        //这里假如了一个getsockname函数的使用，获取自己的ip和端口号
	struct sockaddr_in localaddr;
	socklen_t addrlen = sizeof(localaddr);  //要初始化
	if (getsockname(sock, (struct sockaddr*)&localaddr, &addrlen) < 0)
		ERR_EXIT("getsockname");

	printf("ip=%s port=%d\n", inet_ntoa(localaddr.sin_addr), ntohs(localaddr.sin_port));

	char sendbuf[1024] = {0};
	char recvbuf[1024] = {0};
	while (fgets(sendbuf, sizeof(sendbuf), stdin) != NULL)
	{
		writen(sock, sendbuf, strlen(sendbuf));

		int ret = readline(sock, recvbuf, sizeof(recvbuf));
                if (ret == -1)
                        ERR_EXIT("readline");
                else if (ret == 0)
                {
                        printf("client close\n");
                        break;
                }

		fputs(recvbuf, stdout);
		memset(sendbuf, 0, sizeof(sendbuf));
		memset(recvbuf, 0, sizeof(recvbuf));
	}

	close(sock);

	return 0;
}

服务器端：

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

ssize_t readn(int fd, void *buf, size_t count)
{
	size_t nleft = count;
	ssize_t nread;
	char *bufp = (char*)buf;

	while (nleft > 0)
	{
		if ((nread = read(fd, bufp, nleft)) < 0)
		{
			if (errno == EINTR)
				continue;
			return -1;
		}
		else if (nread == 0)
			return count - nleft;

		bufp += nread;
		nleft -= nread;
	}

	return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
	size_t nleft = count;
	ssize_t nwritten;
	char *bufp = (char*)buf;

	while (nleft > 0)
	{
		if ((nwritten = write(fd, bufp, nleft)) < 0)
		{
			if (errno == EINTR)
				continue;
			return -1;
		}
		else if (nwritten == 0)
			continue;

		bufp += nwritten;
		nleft -= nwritten;
	}

	return count;
}

ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
	while (1)
	{
		int ret = recv(sockfd, buf, len, MSG_PEEK);
		if (ret == -1 && errno == EINTR)
			continue;
		return ret;
	}
}

ssize_t readline(int sockfd, void *buf, size_t maxline)
{
	int ret;
	int nread;
	char *bufp = buf;
	int nleft = maxline;
	while (1)
	{
		ret = recv_peek(sockfd, bufp, nleft);
		if (ret < 0)
			return ret;
		else if (ret == 0)
			return ret;

		nread = ret;
		int i;
		for (i=0; i<nread; i++)
		{
			if (bufp[i] == '\n')
			{
				ret = readn(sockfd, bufp, i+1);
				if (ret != i+1)
					exit(EXIT_FAILURE);

				return ret;
			}
		}

		if (nread > nleft)
			exit(EXIT_FAILURE);

		nleft -= nread;
		ret = readn(sockfd, bufp, nread);
		if (ret != nread)
			exit(EXIT_FAILURE);

		bufp += nread;
	}

	return -1;
}

void do_service(int conn)
{
	char recvbuf[1024];
        while (1)
        {
                memset(recvbuf, 0, sizeof(recvbuf));
                int ret = readline(conn, recvbuf, 1024);
		if (ret == -1)
			ERR_EXIT("readline");
		if (ret == 0)
		{
			printf("client close\n");
			break;
		}

                fputs(recvbuf, stdout);
                writen(conn, recvbuf, strlen(recvbuf));
        }
}

int main(void)
{
	int listenfd;
	if ((listenfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
/*	if ((listenfd = socket(PF_INET, SOCK_STREAM, 0)) < 0)*/
		ERR_EXIT("socket");

	struct sockaddr_in servaddr;
	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(5188);
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	/*servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");*/
	/*inet_aton("127.0.0.1", &servaddr.sin_addr);*/

	int on = 1;
	if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
		ERR_EXIT("setsockopt");

	if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
		ERR_EXIT("bind");
	if (listen(listenfd, SOMAXCONN) < 0)
		ERR_EXIT("listen");

	struct sockaddr_in peeraddr;
	socklen_t peerlen = sizeof(peeraddr);
	int conn;

	pid_t pid;
	while (1)
	{
		if ((conn = accept(listenfd, (struct sockaddr*)&peeraddr, &peerlen)) < 0)
			ERR_EXIT("accept");

		printf("ip=%s port=%d\n", inet_ntoa(peeraddr.sin_addr), ntohs(peeraddr.sin_port));

		pid = fork();
		if (pid == -1)
			ERR_EXIT("fork");
		if (pid == 0)
		{
			close(listenfd);
			do_service(conn);
			exit(EXIT_SUCCESS);
		}
		else
			close(conn);
	}

	return 0;
}

这里的程序都是和先前的关系密切，有一些知识淡忘了可以回顾。

下面介绍两个函数：

gethostname:获取主机名

gethostbyname:利用主机名获取主机地址。

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

int main(void)
{
	char host[100] = {0};
	if (gethostname(host, sizeof(host)) < 0)
		ERR_EXIT("gethostname");

	struct hostent *hp;  //查看一下gethostbyname的返回值
	if ((hp = gethostbyname(host)) == NULL)
		ERR_EXIT("gethostbyname");

	int i = 0;  //这里务必要初始化
	while (hp->h_addr_list[i] != NULL)
	{
		printf("%s\n", inet_ntoa(*(struct in_addr*)hp->h_addr_list[i]));
		i++;
	}

	char ip[16] = {0};
	getlocalip(ip);
	printf("localip=%s\n", ip);
	return 0;
}

会有好几个ip都是本机的ip。

下面我们在写一个获取本机默认ip的工具函数：

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

int getlocalip(char *ip)
{
	char host[100] = {0};
        if (gethostname(host, sizeof(host)) < 0)
		return -1;
	struct hostent *hp;
        if ((hp = gethostbyname(host)) == NULL)
		return -1;

	strcpy(ip, inet_ntoa(*(struct in_addr*)hp->h_addr));
	return 0;

}

int main(void)
{
	char ip[16] = {0};
	getlocalip(ip);
	printf("localip=%s\n", ip);
	return 0;
}

写的比较简单，不会的随时度娘。。。。。睡觉了。。。。