TCP通信机制：三次握手、四次挥手、滑动窗口

/************************************************************
  >File Name  : server.c
  >Author     : Mindtechnist
  >Company    : Mindtechnist
  >Create Time: 2022年08月14日 星期日 19时53分24秒
************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <arpa/inet.h>
#include <ctype.h>

int main(int argc, char* argv[])
{
  //创建用于监听的套接字
  int lfd = socket(AF_INET, SOCK_STREAM, 0);
  if(lfd == -1)
  {
    perror("socket err");
    exit(1);
  }  

  //bind
  struct sockaddr_in server_addr;
  //init
  memset(&server_addr, 0, sizeof(server_addr));  
  //bzero(&server_addr, sizeof(serve_addr));
  server_addr.sin_family = AF_INET; //IPv4
  server_addr.sin_port = htons(8765);
  server_addr.sin_addr.s_addr = htonl(INADDR_ANY); //使用本机任意IP

  int ret = bind(lfd, (struct sockaddr*)&server_addr, sizeof(server_addr));
  if(ret == -1)
  {
    perror("bind err");
    exit(1);
  }

  //设置监听
  ret = listen(lfd, 128);
  if(ret == -1)
  {
    perror("listen err");
    exit(1);
  }
  
  //等待并接受连接请求
  struct sockaddr_in client_addr;
  socklen_t client_len = sizeof(client_addr);
  int cfd = accept(lfd, (struct sockaddr*)&client_addr, &client_len);
  if(cfd == -1)
  {
    perror("accept err");
    exit(1);
  }
   
  char ipbuf[64];
  printf("client ip: %s, port: %d\n",
      inet_ntop(AF_INET, &client_addr.sin_addr.s_addr, ipbuf, sizeof(ipbuf)),
      ntohs(client_addr.sin_port));

  //通信
  while(1)
  {
    //接收数据
    char buf[1024] = {0};
    int len = read(cfd, buf, sizeof(buf));
    if(len < 0)
    {
      perror("read err");
      break;
    }
    else if(len == 0)
    {
      printf("client disconnect ...\n");
      break;
    }  
    else 
    {
      //读到数据
      printf("read buf : %s\n", buf);
      for(int i = 0; i < len; i++)
      {
        buf[i] = toupper(buf[i]);
      }
      printf("toupper read buf: %s\n", buf);
      //发送数据
      write(cfd, buf, strlen(buf) + 1);
    }
  }

  close(lfd);
  close(cfd);
  
  return 0;
}

/************************************************************
  >File Name  : client.c
  >Author     : Mindtechnist
  >Company    : Mindtechnist
  >Create Time: 2022年08月15日 星期一 11时13分29秒
 ************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <arpa/inet.h>
#include <fcntl.h>

int main(int argc, char* argv[])
{
  if(argc < 2)
  {
    printf("err:./exe port\n");
    return -1;
  }
  int port = atoi(argv[1]);

  //创建套接字
  int fd = socket(AF_INET, SOCK_STREAM, 0);
  if(fd == -1)
  {
    perror("socket err");
    exit(1);
  }

  //连接服务器
  struct sockaddr_in server_addr;
  memset(&server_addr, 0, sizeof(server_addr));
  server_addr.sin_family = AF_INET;
  inet_pton(AF_INET, "127.0.0.1", &server_addr.sin_addr.s_addr);
  int ret = connect(fd, (struct sockaddr*)&server_addr, sizeof(server_addr));
  if(ret == -1)
  {
    perror("connect err");
    exit(1);
  }

  //通信
  while(1)
  {
    //接收键盘输入
    char buf[512];
    printf("please input string: \n");
    fgets(buf, sizeof(buf), stdin);
    //发送给服务器
    write(fd, buf, strlen(buf));

    //接收服务端数据
    int len = read(fd, buf, sizeof(buf));
    if(len < 0)
    {
      perror("read err");
      exit(1);
    }
    else if(len == 0)
    {
      printf("server close connect ...\n");
      break;
    }
    else
    {
      printf("read buf: %s, buflen: %d\n", buf, len);
    }
  }  

  close(fd);

  return 0;
}