TCP之简单回传（三）

鉴于TCP之简单回传（一）   中所出现的问题，本博文所要采取的一种方法是：

服务器端和客户端共同遵守如下约定：
接收的字节流中，若遇到'
'，表示一次传送完毕。

具体为：

客户端把每次欲发送的数据的最后一个字符设置为 ' '；

而服务器每次接收时，一个一个字符的从缓冲区中取出一个字符，然后再判断该字符是否为' '，若不是，则继续读取；若是，则退出循环，表示本次接收结束；

实现代码如下：

//按字符读取--->由于每读取一个字符就产生一次系统调用,故效率较低
ssize_t readline_slow(int fd, void *usrbuf, size_t maxlen)
{
    char *bufp = (char*)usrbuf;//偏移位置
    ssize_t nread;
    size_t nleft = maxlen -1 ;//剩余字节数
    char ch;//保存每次读取的字符
    while( nleft > 0)//只要还有没读的，就一直循环
    {
        if(-1 == (nread=read(fd, &ch, 1)))//把从fd中读取的字符存进ch中
        {
            if(errno == EINTR)//被中断信号打断
                continue;
            return -1;//err
        }else if(0 == nread )
            break; //EOF
        
        *bufp = ch;//将读取的字符存进buf
        bufp++;//向前移动
        
        nleft --;//剩余字节数--
        if(ch == '
')//如果该字符为
。本次读取完成
            break;
    }
    *bufp ='';//
    return (maxlen- nleft -1);//最大长度 -剩余的字符 - ''
}

本程序中所用到的函数都可以在 TCP之函数封装 中找到；

server服务器端：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define ERR_EXIT(m) 
    do { 
        perror(m);
        exit(EXIT_FAILURE);
    }while(0)

void do_server(int fd);

int main(int argc, const char *argv[])
{
//socket    
    int listenfd = socket(AF_INET, SOCK_STREAM, 0 );
    if( -1 == listenfd)
        ERR_EXIT("socket");
//地址复用
    int on = 1;
    if(setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof on) < 0)
        ERR_EXIT("setsockopt");
//bind
    struct sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(8888); //主机字节序转化为网络字节序
    addr.sin_addr.s_addr = inet_addr("127.0.0.1");//点分十进制转化成网络字节序
    if( -1 == bind( listenfd, (struct sockaddr*)&addr, sizeof(addr)))
        ERR_EXIT("bind");

//listen
    if( -1 == listen(listenfd,SOMAXCONN ))
        ERR_EXIT("listen");
    
//accept    
    int peerfd = accept(listenfd, NULL, NULL);//对方的IP&PORT

//read&write    
    do_server(peerfd);

//close
    close(peerfd);
    close(listenfd);
    return 0;
}

void do_server(int  fd)
{
    char recvbuf[1024100] = {0};
    int cnt =0;
    while(1)
    {
        int nread = readline_slow(fd, recvbuf, sizeof(recvbuf));
        if(nread == -1)//err
        {
            if(errno == EINTR)
                continue;
            ERR_EXIT("read");
        }else if (nread == 0 )//write close
        {
            printf("close...
");
            exit(EXIT_FAILURE);
        }
        
        // ok 
        printf("count = %d recv size = %d
",++cnt, nread);
        memset(recvbuf, 0, sizeof(recvbuf));
    }
}

client客户端：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define ERR_EXIT(m) 
    do { 
        perror(m);
        exit(EXIT_FAILURE);
    }while(0)
void do_server(int fd);

int main(int argc, const char *argv[])
{
//socket
    int peerfd = socket(AF_INET, SOCK_STREAM,0);
    if( -1 == peerfd)
        ERR_EXIT("socket");
//connect
    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(8888);
    addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    
    if( -1 == connect(peerfd,(struct sockaddr*)&addr, sizeof(addr) ))
        ERR_EXIT("connect");

//read&write
    do_server(peerfd);

    return 0;
}

void do_server(int fd)
{
    #define SIZE 1024
    char sendbuf[SIZE +1]= {0};
    int i ;
    for (i = 0; i < SIZE-1; i++) //attention
    {
        sendbuf[i]= 'a';    
    }
    sendbuf[SIZE-1] = '
';//标志位
    int cnt =0;
    while(1)
    {
        int i;
        for (i = 0; i < 10; i++) 
        {
            int nwrite =writen(fd, sendbuf, SIZE);//发送SIZE个数据中最后一个字符为

            if( nwrite != SIZE)
                ERR_EXIT("writen");
            printf("cout = %d,write %d bytes
",++cnt, SIZE);
        }
        nano_sleep(4.5);
    }
}

测试结果：

./server
count = 1 recv size = 1024
count = 2 recv size = 1024
count = 3 recv size = 1024
count = 4 recv size = 1024
count = 5 recv size = 1024
count = 6 recv size = 1024
count = 7 recv size = 1024
count = 8 recv size = 1024
count = 9 recv size = 1024
count = 10 recv size = 1024
count = 11 recv size = 1024
count = 12 recv size = 1024
count = 13 recv size = 1024
count = 14 recv size = 1024
count = 15 recv size = 1024
count = 16 recv size = 1024
count = 17 recv size = 1024
count = 18 recv size = 1024
count = 19 recv size = 1024
count = 20 recv size = 1024

./client
count = 1 recv size = 1024
count = 2 recv size = 1024
count = 3 recv size = 1024
count = 4 recv size = 1024
count = 5 recv size = 1024
count = 6 recv size = 1024
count = 7 recv size = 1024
count = 8 recv size = 1024
count = 9 recv size = 1024
count = 10 recv size = 1024
count = 11 recv size = 1024
count = 12 recv size = 1024
count = 13 recv size = 1024
count = 14 recv size = 1024
count = 15 recv size = 1024
count = 16 recv size = 1024
count = 17 recv size = 1024
count = 18 recv size = 1024
count = 19 recv size = 1024
count = 20 recv size = 1024

注意：本程序效率比较低下，原因在于：

每次读取一个字符都要系统调用一次read函数。

解决方法：TCP之简单回传（四）