socket.c

/* basic socket operations, UNIX-native */

 /* pointer arithmetics:
  *
  * push(pointer, v) INDICATES *(pointer++) = v
  * pop(pointer) INDICATES *(--pointer)
  * (*++v)[0] INDICATES (**++v)
  *           INDICATES first char in v
  *           INDICATES name of string/vector v
  * likewise, *v[0] INDICATES **v
  *       and *v[n] INDICATES **(v + n)
  * returntype (*funct)(args) INDICATES a function funct with arguments args which returns...
  * char **argv INDICATES pointer to char pointer
  * int(*v)[len] INDICATES pointer "v" to a vector of "len" int elements
  * int *v[len] INDICATES vector "v" of "len" pointers to int elements
  * void *funct() INDICATES function "funct" that returns a pointer-to-void
  * void (*funct)() INDICATES pointer to a function "funct" that returns void
  *
  */

 /* useful characters: [] # */

 # include <stdio.h>
 # include <stdlib.h> // for exit
 # include <sys/types.h>
 # include <sys/socket.h>
 # include <netinet/in.h>
 # include <netdb.h>
 # include <fcntl.h> // for O_RDWR

 # define BUFFER 256
 # define exception(x) { puts(x); exit(1); }
 # define h_addr h_addr_list[0]

struct socket_in {
   short family; // domain, e.g. AF_INET
   unsigned short port;
   struct in_addr addr; // IP number
   char zero[8]; // unused bytes
 };

 int main(int argc, char * argv[])
    {
     /* creation of a TCP socket */
     int sock;
     struct socket_in mysock;
     sock = socket(AF_INET, SOCK_STREAM, 0); // Internet, TCP, type 0 (default)
     mysock.family = AF_INET;
     mysock.port = 1999;
     mysock.addr.s_addr = INADDR_ANY; // can receive data from any address or socket


     /* binding */
     /* SOCK and MYSOCK will be used without being reinstanced */
     char c;
     bind(sock, &mysock, sizeof(mysock)); // binds sock and mysock
     if(fork() != 0) close(sock); // in parent process: closes socket
     else // in child process: uses socket
    {
     while(read(0, &c, 1) == -1); // waits until there is no more data to read
     close(sock);
    }


     /* accept */
     /* SOCK will be used without being reinstanced */
     int sock_acc;
     struct sockaddr address;
     int addrlen;
     sock_acc = accept(sock, &address, &addrlen); // accepts communication from sock
     close(sock);
     close(sock_acc);


     /* connect */
     /* SOCK and MYSOCK will be used without being reinstanced */
     int length, success;
     struct hostent * hp; // used in gethostbyname() to save the return value
     hp = gethostbyname("conde.dis.uniroma1.it");
     memcpy(&mysock.addr, hp->h_addr, 4); // copying from address to hp.address ???
     success = connect(sock, &mysock, sizeof(mysock)); // attempts connection
     if(success == -1) exception("Connection error\n");
     close(sock);

     return 0;
    }

 // the program segfaults, why?