ネットワーク・プログラミング（C言語）
Network Programming in C

第3回 10月23日 Lecture 4, October 23:
Basic socket programming 1

Outline of This Lecture

• What's a Socket?
• Socket Operation
• Server Example Code
• Tools
• Homework

What's a Socket? aka Internet Protocol addressing (v4/v6)

• Local Address (IPv4 or IPv6)
• Local Port number (if ULP is TCP or UDP)
• Remote Address (IPv4 or IPv6)
• Remote Port number (if ULP is TCP or UDP)
• Upper-Layer Protocol identifier (e.g., TCP or UDP)

For Internet services using TCP or UDP, your service name is your port number. Important services use well-known port numbers, assigned by the IANA.

Socket Operation

• Create the socket by calling socket()
• Call bind() to create an address (especially the port number)
• Use listen() to control the number of connections that the socket will support
• accept() a new connection (this creates a new socket for you!)
• Use read() and write() to receive and send data
• shutdown() the connection socket when you're done
• close() the connection socket
• Return to accept() and wait for the next incoming connection

Server Example Code

// Server code in C
// adapted from http://en.wikipedia.org/wiki/Berkeley_sockets
 
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <unistd.h>

int main()
{
  struct addrinfo hint;
  struct sockaddr_storage bindaddr_storage;
  struct sockaddr_in6 *bindaddr6 = 
    (struct sockaddr_in6 *)&bindaddr_storage;
  struct sockaddr_in *bindaddr = 
    (struct sockaddr_in *)&bindaddr_storage;
  struct addrinfo *result;
  struct sockaddr_storage peer;
  int peersize;
  char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
  int retval;

  int i32SocketFD = socket(PF_INET6, SOCK_STREAM, 0);
 
  char msg[] = "Success!\n";

  if(-1 == i32SocketFD)
    {
      perror("can not create socket");
      exit(-1);
    }
  
  bzero(&bindaddr_storage, sizeof(bindaddr_storage));
  bindaddr6->sin6_family = AF_INET6;
  bindaddr6->sin6_addr = in6addr_any;	/* struct assignment */
  bindaddr6->sin6_port = htons(12345);
 
  if(-1 == bind(i32SocketFD,(struct sockaddr*) bindaddr6,
                sizeof(struct addrinfo)))
    {
      printf("error bind failed");
      perror("main");
      exit(-1);
    }
 
  if(-1 == listen(i32SocketFD, 10))
    {
      printf("error listen failed");
      exit(-1);
    }

  // Here, you should print out your local address using
  // getsockname() and getnameinfo() (and gai_strerror on error)

  for(; ;)
    {
      int i32ConnectFD = accept(i32SocketFD, NULL, NULL);
 
      if(0 > i32ConnectFD)
	{
          // improve error reporting here, using perror()
	  printf("error accept failed");
	  exit(-1);
	}


      // Here, you should print out your local address 
      // and the peer address using
      // getsockname(), getpeername(), and getnameinfo()
      // (and gai_strerror on error)

      // perform read write operations ...
      // add error checking and reporting here
      write(i32ConnectFD, msg, sizeof(msg));
      // wait one minute; this lets us see the connection in place, and
      // even see the behavior as we try to start a second connection
      // at the same time
      sleep(60);

      // add error checking and reporting here
      shutdown(i32ConnectFD, 2);
 
      // add error checking and reporting here
      close(i32ConnectFD);
    }
  // add error checking and reporting here
  close(i32SocketFD);
  return 0;
}

Tools

• tcpdump (the original network monitor, perhaps)
• Wireshark
• netstat
• (if you don't know about ifconfig, you should)

宿題
Homework

1. Take the above program, and edit where the comments are to print out information about the connections, using getnameinfo(), getpeerinfo(), and gai_strerror().
2. Test for errors from the system calls in the above code. Use perror() where appropriate.
3. Modify the above server so that it calls fork() and creates a second process after accepting the connection. The parent should close() the connection socket and return to waiting for a new connection, while the child should close the initial socket, process the connection, then exit.
4. Learn to use a wire monitoring tool, such as Wireshark or tcpdump. Capture the packets of two connections to your server to show that both connections are being processed at the same time.