readn writen 函数回射客户端，服务器

/*解决粘包问题*/
#include<stdio.h>
#include<sys/types.h>
#include<string.h>
#include<sys/socket.h>
#include<unistd.h>
#include<stdlib.h>
#include<errno.h>
#include<netinet/in.h>
#include<arpa/inet.h>
void die(char *s)
{perror(s);
exit(0);
}
struct packet
{
    int len;
    char buf[1024];
};

/*readn*/
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;

}
/*writen*/
ssize_t writen(int fd,void* buf,size_t count)
{
    size_t nleft=count;
    ssize_t nwrite;
    char *bufp=(char*)buf;
    while(nleft>0)
    {
        if((nwrite=write(fd,bufp,nleft))<0)
        {
            if(errno==EINTR)
                continue;
            return -1;
        }
        else if(nwrite==0)
            continue;
        bufp+=nwrite;
        nleft-=nwrite;
    }
    return count;
}
void do_service(int conn)
{
    struct packet recvbuf;
    int n;
    while(1)
    {    memset(&recvbuf,0,sizeof(recvbuf));
        int ret=readn(conn,&recvbuf.len,4);
        if(ret==-1)
                die("read");
        else if(ret<4)
        {
            printf("client close\n");
            break;
        }
        n=ntohl(recvbuf.len);
        ret=readn(conn,recvbuf.buf,n);
        if(ret==-1)
                die("read");
        else if(ret<n)
        {
            printf("client close\n");
            break;
        }
            fputs(recvbuf.buf,stdout);
            writen(conn,&recvbuf,4+n);
    }
}
int main(void)
{
    /*socket*/
    int listenfd;
    if((listenfd=socket(AF_INET,SOCK_STREAM,0))<0)
        die("socket");
    /*bind*/
    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"");*/
    /* if(bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr))<0) */
    int yes=1;
        if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1)
            die("reuseaddr");
    if(bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr))<0)
        die("bind");
    /*listen*/
    if(listen(listenfd,SOMAXCONN)<0)
        die("listen");
    /*accept*/
    struct sockaddr_in peeraddr;
    socklen_t peerlen=sizeof(peeraddr);
    int conn;
    /*fork 创建多个进程*/
    pid_t pid;
    while(1){
    if((conn=accept(listenfd,(struct sockaddr*)&peeraddr, &peerlen))<0)
        die("accept");
    printf("ip=%s port=%d\n",inet_ntoa(peeraddr.sin_addr),ntohs(peeraddr.sin_port));
    /*echo function*/
    pid=fork();
    if(pid==-1)
        die("fork");
if(pid==0)
{
close(listenfd);
do_service(conn);
exit(0);
}
else
close(conn);
}
/*close socket*/
return 0;
}

/*echo_client.c*/
#include<stdio.h>
#include<sys/types.h>
#include<string.h>
#include<sys/socket.h>
#include<unistd.h>
#include<stdlib.h>
#include<errno.h>
#include<netinet/in.h>
#include<arpa/inet.h>
void die(char *s)
{perror(s);
exit(0);
}
struct packet
{
    int len;
    char buf[1024];
};

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;

}
/*writen*/
ssize_t writen(int fd,void* buf,size_t count)
{
    size_t nleft=count;
    ssize_t nwrite;
    char *bufp=(char*)buf;
    while(nleft>0)
    {
        if((nwrite=write(fd,bufp,nleft))<0)
        {
            if(errno==EINTR)
                continue;
            return -1;
        }
        else if(nwrite==0)
            continue;
        bufp+=nwrite;
        nleft-=nwrite;
    }
    return count;
}
int main(void)
{
    /*socket*/
    int sock;
    if((sock=socket(AF_INET,SOCK_STREAM,0))<0)
        die("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");
    /*connect*/
    if(connect(sock,(struct sockaddr*)&servaddr,sizeof(servaddr))<0)
        die("connect");
    struct packet sendbuf;
    struct packet recvbuf;
    memset(&sendbuf,0,sizeof(sendbuf));
    memset(&recvbuf,0,sizeof(recvbuf));
    while(fgets(sendbuf.buf,sizeof(sendbuf.buf),stdin)!=NULL)
    {
        int n=strlen(sendbuf.buf);
        sendbuf.len=htonl(n);
        writen(sock,&sendbuf,4+n);
        int ret=readn(sock,&recvbuf.len,4);
        if(ret==-1)
                die("read");
        else if(ret<4)
        {
            printf("client close\n");
            break;
        }
            n=ntohl(recvbuf.len);
            ret=readn(sock,recvbuf.buf,n);
            if(ret==-1)
                die("read");
        else if(ret<n)
        {
            printf("client close\n");
            break;
        }
        fputs(recvbuf.buf,stdout);
        memset(&sendbuf,0,sizeof(sendbuf));
        memset(&recvbuf,0,sizeof(recvbuf));
    }
    close(sock);
    return 0;
}