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

第6回 11月4日 Lecture 6, November 4:
Basic socket programming 1

Outline of This Lecture

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

First, the PowerPoint slides.

• 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.

• 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 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);
 
  // *** attention: on MacOS, this has to be
  // sizeof(struct sockaddr_in6)!!! ***
  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;
}

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

1. Take the above program, and edit where the comments are to print out information about the connections, using getnameinfo() 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.