UNP——TCP分析

tcpserver.c

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <time.h>
#include <arpa/inet.h>
#include "proto.h"

#define bakc_log 50
#define praddr_size 50
#define buffer_size 1024
static void server_job(int sockfd)
{
    int len;
    char buffer[buffer_size];
    len = sprintf(buffer,FMT_STAMP, (long long)time(NULL));

    if(send(sockfd, buffer, len, 0)<0)
    {
        perror("send");
        exit(1);
    }
}

int main()
{
    int sd,std;
    int flag;
    pid_t pid;
    char p_raddr[praddr_size];
    struct sockaddr_in laddr,raddr;
    laddr.sin_family = AF_INET;
    laddr.sin_port = htons(LOCALPORT);
    inet_pton(AF_INET,"0.0.0.0",&laddr.sin_addr);

    socklen_t laddrsize = sizeof(laddr);
    socklen_t raddrsize = sizeof(raddr);
    sd = socket(AF_INET,SOCK_STREAM,0);
    if(sd<0)
    {
        perror("socket");
        exit(1);
    }

    if(setsockopt(sd,SOL_SOCKET,SO_REUSEADDR,&flag,sizeof(flag))<0)
    {
        perror("setsocket");
        exit(1);
    }

    if(bind(sd, (void*)&laddr, laddrsize)<0)
    {
        perror("bind");
        exit(1);
    }

    if(listen(sd,bakc_log)<0)
    {
        perror("listen");
        exit(1);
    }

    while(1)
    {
            //accept返回三个值，std即可能是已连接套接字或错误信息，对端地址，对端地址大小
        std = accept(sd, (void*)&raddr,&raddrsize);  //返回值为全新文件描述符，代表与tcp对端连接，已连接描述符
        if(std < 0)
        {
            perror("accept");
            exit(1);
        }
        pid = fork();  //并发的时候，应该注意：fork之后，子进程和父进程均有已连接描述符和监听描述符，父进程中需close已连接描述符
                        //，将引用计数减为0
        if(pid == 0)
        {
            close(sd);
            inet_ntop(AF_INET,&raddr.sin_addr,p_raddr,praddr_size);
            fprintf(stderr,"Client addr is %s , port is %d\n",p_raddr,ntohs(raddr.sin_port));

            server_job(std);
            close(std);
            exit(0); //子进程结束必须exit0，否则会继续执行
        }
        close(std); //此处必须有，计数减为0，然后才会发送FIN，四次分手
    }

    close(sd);
    exit(0);
}

tcpclient.c

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include "proto.h"
#define raddr_size 40
int main(int argc, char* argv[])
{

    FILE* fp;
    long long stamp;
    struct sockaddr_in laddr,raddr;
    char raddr_ip[raddr_size];
    if(argc < 2)
    {
        fprintf(stderr,"argc");
        exit(1);
    }

    int sd = socket(AF_INET,SOCK_STREAM,0);
    if(sd<0)
    {
        perror("socket");
        exit(1);
    }
    raddr.sin_family = AF_INET;
    raddr.sin_port = htons(LOCALPORT);
    inet_pton(AF_INET,argv[1],&raddr.sin_addr);
    fprintf(stderr,"let's go");
    if(connect(sd,(void*)&raddr,sizeof(raddr))<0)  //conncet开始三次握手，可能出现三种情况1、FIN无ACK，75s后ETIMEOUT
    {
        perror("connect");
        exit(1);
    }

    //一切皆文件
    fp = fdopen(sd,"r+"); //将文件描述符转换成FILE指针打开,这里不能用w，w+，因无需创建fd

    if(fp==NULL)
    {
        perror("fdopen");
        exit(1);
    }

    if(fscanf(fp,FMT_STAMP,&stamp)<1) //返回成功读取的个数，这里只有一个item，正确为1
    {

        fprintf(stderr,"error FMT_STAMP");
    }
    else
    {
        fprintf(stderr,"stamp = %lld\n",stamp);
    }

    fclose(fp); //这里需要关闭fp，因为fdopen已经转成fp

    exit(0);
}

proto.h

#ifndef PROTO_H__
#define PROTO_H__

#define LOCALPORT 1990
#define FMT_STAMP "%lld\r\n"


#endif