Network client/server

<Beginning Linux Programming_4th>  chapter 15 Sockets

1  A simple local client/server

1)  client.c

// 1) header files
// int socket(int domain, int type, int protocol);
#include <sys/types.h>
// int connect(int socket, const struct sockaddr*address,size_t address_len);
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
/* struct sockaddr_in{
    short int sin_family; // AF_INET
    unsigned short int sin_port; // Port number
    struct in_addr sin_addr; //Internet address
}; */
#include <netinet/in.h>
#include <arpa/inet.h>
// size_t write(int fildes, const void *buf, size_t nbytes);
// size_t read(int fildes, const void *buf, size_t nbytes);
#include <unistd.h>

// 2) socket
int main ()
{
// 127.0.0.1    loopback network
// 192.168.1.1  local area network via an Ethernet adaptor
// 158.152.x.x  modem link to an Internet service provider
    int  sockfd;
    int  len;
    struct  sockaddr_in  address;
    int  result;
    char  ch = 'A';

/* struct in_addr{
    unsigned long int s_addr;
}; */
    sockfd = socket(AF_INET, SOCK_STREAM, );
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = inet_addr("127.0.0.1");
    address.sin_port = htons();
    len = sizeof(address);
/* sizeof(变量/数据类型); // 结果是一个整数
   变量或此种数据类型的变量所占的内存空间字节数
   printf("the size of char is %d bytes\n", sizeof(char)); */
// 3)  connect
    result = connect(sockfd, (struct sockaddr*) &address, len);
    if(result == -)
    {
        perror("oops: client");
        exit();
    }

// 4)  write, read and close
    write(sockfd, &ch, );
    read(sockfd, &ch, );
    printf("char from server = %c\n", ch);

    close(sockfd);
    exit();
}

/* convert 16-bit/32-bit integers between host and network ordering
<netinet/in.h>
unsigned long int htol(unsigned long int hostlong);
unsigned short int htos(unsigned short int hostshort);
unsigned long int ntohl(unsigned long int netlong);
unsigned short int ntohs(unsigned short int netshort);

2)  server.c

// 1)  header files
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

// 2)  socket
int main()
{
  int server_sockfd, client_sockfd;
  int server_len, client_len;

  struct  sockaddr_in  server_address;
  struct  sockaddr_in  client_address;
  unlink("server_socket");

  server_sockfd = socket(AF_INET, SOCK_STREAM, );
  server_address.sin_family = AF_INET;
  server_address.sin_addr.s_addr = htonl(INADDR_ANY);
  server_address.sin_port = htons();
  server_len = sizeof(server_address);

// 3)  bind, listen
  bind(server_sockfd, (struct sockaddr*)&server_address, server_len);
  listen(server_sockfd, );

// 4) while loop: accept - read/write - close
  while()
  {
    char ch;
    printf("server waiting\n");
    client_len = sizeof(client_address);
    client_sockfd = accept(server_sockfd, (struct sockaddr*)&client_address, &client_len);

    read(client_sockfd, &ch, );
    ch++;
    write(client_sockfd, &ch,);

    close(client_sockfd);
  }
}
// int bind(int socket, const struct sockaddr* address, size_t address_len);
// int listen(int socket, int backlog);
// int accept(int socket, struct sockaddr* address, size_t* address_len);

2  A server for multiple clients

server2.c

// 1)  header files
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <signal.h>
#include <unistd.h>

// 2)  socket
int main()
{
  int server_sockfd, client_sockfd;
  int server_len, client_len;

  struct  sockaddr_in  server_address;
  struct  sockaddr_in  client_address;

  server_sockfd = socket(AF_INET, SOCK_STREAM, );
  server_address.sin_family = AF_INET;
  server_address.sin_addr.s_addr = htonl(INADDR_ANY);
  server_address.sin_port = htons();
  server_len = sizeof(server_address);

// 3)  bind, listen, signal
  bind(server_sockfd, (struct sockaddr*)&server_address, server_len);
  listen(server_sockfd, );
  signal(SIGCHLD, SIG_IGN);

// 4) while loop: accept - fork
  while()
  {
    char ch;
    printf("server waiting\n");
    client_len = sizeof(client_address);
    client_sockfd = accept(server_sockfd, (struct sockaddr*)&client_address, &client_len);

    if(fork() == )
    {
      read(client_sockfd, &ch, );
      sleep();
      ch++;
      write(client_sockfd, &ch,);
      close(client_sockfd);
      exit();
    }
    else
    {
      close(client_sockfd);
    }
  }
}

3  An improved server for multiple clients

server3.c

// header files
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <unistd.h>

// 1) socket
int main()
{
  int server_sockfd, client_sockfd;
  int server_len, client_len;

  struct  sockaddr_in  server_address;
  struct  sockaddr_in  client_address;

  int result;
  fd_set readfds, testfds;

  server_sockfd = socket(AF_INET, SOCK_STREAM, );
  server_address.sin_family = AF_INET;
  server_address.sin_addr.s_addr = htonl(INADDR_ANY);
  server_address.sin_port = htons();
  server_len = sizeof(server_address);

// 2) bind, listen
  bind(server_sockfd, (struct sockaddr*)&server_address, server_len);
  listen(server_sockfd, );
  FD_ZERO(&readfds);
  FD_SET(server_sockfd, &readfds);

// 3) while loop: server activity, client activity
  while()
  {
    char ch;
    int fd;
    int nread;
    testfds = readfds;
    printf("server waiting\n");
    result = select(FD_SETSIZE, &testfds, (fd_set*), (fd_set*), (struct timeval*));

    if(result<){
      perror("server");
      exit();
    }

    for(fd=; fd<FD_SETSIZE; fd++)
    {
      if(FD_ISSET(fd, &testfds))
      {
        if(fd==server_sockfd)
        {
            client_len = sizeof(client_address);
            client_sockfd = accept(server_sockfd, (struct sockaddr*)&client_address, &client_len);
            FD_SET(client_sockfd, &readfds);
            printf("adding client an fd %d\n", client_sockfd);
        }
        else
        {
            ioctl(fd, FIONREAD, &nread);

            if(nread==)
            {
              close(fd);
              FD_CLR(fd, &readfds);
              printf("removing client on fd %d\n", fd);
            }
            else
            {
              read(fd, &ch, );
              sleep();
              printf("serving client on fd %d\n", fd);
              ch++;
              write(fd, &ch, );
             }
          } // 1st if
       } // 2nd if
     } //for
  } // while
} // main

小结：

client: socket -- connect --r/w -- close

server: socket -- bind -- listen -- accept -- r/w -- close

while(1)

server2: socket -- bind -- listen -- signal -- accept -- fork

while(1)