1.REUSEADDR（地址重复利用）
1.REUSEADDR解决服务器关闭后重新绑定地址，在day3中知道服务器端必须绑定地址
2.服务器端尽可能使用REUSEADDR
3.在绑定之前尽可能调用setsockopt来设置REUSEADDR套接字选项
4.使用REUSEADDR选项可以使得不必等待TIME_WAIT状态消失就可以重启服务器
man setsockopt

2.处理多客户连接（process-per-conection）
一个连接一个进程来处理并发
服务器处于监听状态，每次连接一个客户端创建一个进程

||---------------------------------------------------------------------
服务器
#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)

void do_service(int conn)
{
char recvbuf[1024];
while(1)
{
memset(recvbuf, 0, sizeof(recvbuf));
int ret = read(conn, recvbuf, sizeof(recvbuf));

if (ret == 0)
{
printf("client close\n");
break;
}
/*捕捉客服端是否关闭*/
else if (ret == 1)
ERR_EXIT("read");//失败也退出来

fputs(recvbuf, stdout);
write(conn, recvbuf,ret);
}
}
close(conn);
}

int main(void)
{
int listenfd;
if((listenfd = 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 = htonl(INADDR_ANY);

int on = 1;
if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
ERR_EXIT("setsockopt");/*实现地址重复利用，这样可以使服务器关闭后不用等待TIME_WAIT消失后在重新启动服务器，而可以直接启动服务器*/

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

if(listen(listenfd, SOMAXCONM) < 0)
ERR_EXIT("listen");

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

pid_t pid;

while(1)
{
if((coon = accept(listen,(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(); //创建一个父进程
if(pid == -1)
ERR_EXIT("fork");
if(pid == 0)
{
close(listenfd);
do_service(conn);
exit(EXIT_SUCCESS);/*一旦捕捉到客户端关闭，这个服务就没有必要保留*/
}
else
close(conn);
return 0;
}
||------------------------------------------------------------

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)

int main(void)
{
int sock;
if((listenfd = 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");
char sendbuf[1024] = {0};
char recvbuf[1024] = {0};
while(fgets(sendbuf,sizeof(sendbuf),stdin) != NULL)
{
write(sock,sendbuf,strlen(sendbuf));
read(sock,recvbuf,sizeof(recvbuf));

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

close(sock);

return 0;
}

||------------------------------------------------------------

3.点对点聊天程序
先开服务器端，在开客户端
当客户端或者服务器端关闭后父进程关闭但是子进程还没有关闭可以通过信号来实现
#include<signal.h>
man 2 kill
||---------------------------------------------------------------------

实现p2p的服务的服务器
||------------------------------------------------------------

#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>

#include<signal.h>
void handler(int sig)
{
printf("recv a sig=%d\n",sig);
exit(EXIT_SUCCESS);
}

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

int main(void)
{
int listenfd;
if((listenfd = 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 = htonl(INADDR_ANY);

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

if(listen(listenfd, SOMAXCONM) < 0)
ERR_EXIT("listen");

struct sockaddr_in peeraddr;
socklen_t peerlen = sizeof(peeraddr);
int coon;
if((coon = accept(listen,(struct sockaddr*)&peeraddr,&peerlen)) < 0)
ERR_EXIT("accept");

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

pid_t pid;
pid = fork();
if(pid == -1)
ERR_EXIT("fork");

if(pid == 0)
{
signal(SIGUSR1, handler);/*借助SIGUSR1信号关联一个kill*/
char sendbuf[1024] = {0};
while (fgets(sendbuf,sizeof(sendbuf),stdin) != NULL)
{
write(conn,sendbuf,strlen(sendbuf));
memset(sendbuf, 0, sizeof(sendbuf)); //清空缓冲区，以便第二次输出不会只覆盖一部分
}
exit(EXIT_SUCCESS);
}
else
{
char recvbuf[1024];
while(1)
{
memset(recvbuf, 0, sizeof(recvbuf));
int ret = read(conn, recvbuf, sizeof(recvbuf));
/*错误处理*/
if (ret == -1)
ERR_EXIT("read");
else if (ret == 0)
{
printf("peer close\n");//对方关闭了
break;
}
fputs(recvbuf, stdout);
}
kill(pid,SIGUSR1);
exit(EXIT_SUCCESS);
}
return 0;
}
||------------------------------------------------------------

实现p2p的服务的客户端

#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>

#include<signal.h>
void handler(int sig)
{
printf("recv a sig=%d\n",sig);
exit(EXIT_SUCCESS);
}

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

int main(void)
{
int sock;
if((listenfd = 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");

pid_t pid;
pid = fork();
if(pid == -1)
ERR_EXIT("fork");
if(pid == 0)
{
//父进程一直接受
char recvbuf[1024];
while(1)
{
memset(recvbuf, 0, sizeof(recvbuf));
int ret = read(sock, recvbuf, sizeof(recvbuf));
if(ret == -1)
ERR_EXIT("read");
else if(ret == 0)
{
printf("peer close\n"); //对等方关闭
break;
}
fputs(recvbuf,stdout); //当大于0，把接收到是数据输出
}
close(sock);
kill(pid, SIGUSR1);
}
else
{
signal(SIGUSR1, handler);
//子进程一直发送
char sendbuf[1024] = {0};
while(fgets(sendbuf,sizeof(sendbuf),stdin) != NULL)
{
write(sock,sendbuf,strlen(sendbuf));
memset(sendbuf,0,sizeof(sendbuf));
}
close(sock);
}

return 0;
}

||---------------------------------------------------------------------