net.c

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/* net.c: TCP/IP client code.

   To build a test-stub, compile with

   gcc -DTEST net.c

   Add a -DSTRERROR_NOT_DEFINED if strerror() doesn't exist on your machine.

   Once the program is compiled, try stuff like "./a.out xcf.berkeley.edu 79"
   and then enter "ali" followed by RETURN. Port 79 is the WHOIS or finger
   port.

   Or do "./a.out stanford.edu 25" and start forging mail. Port 25 is the
   sendmail port.

   The a.out produced behaves like a poor man's version of line-buffered
   telnet.
*/


#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <sys/ioctl.h>
#include <string.h>
#include <errno.h>
#include "net.h"


static NetErrnoType net_errno = E_NET_OK;
static int saved_errno = 0;

/* Translations between ``net_errno'' values and human readable strings.
*/
static char *net_syserrlist[] = {
        "All was chill"
};




#ifdef STRERROR_NOT_DEFINED
const char *strerror(int errno) { return sys_errlist[errno]; }
#endif

static void NetSetErrno(NetErrnoType e)
{
  if(e == E_NET_ERRNO)saved_errno = errno;
  net_errno = e;
}



/* NetErrStr()
 *--------------------------------------------------------------------
 * Returns a diagnostic message for the last failure.
 */
const char *NetErrStr()
{
  return net_errno==E_NET_ERRNO ? strerror(saved_errno) :
    net_syserrlist[net_errno];
}

/* NetErrNo()
 *--------------------------------------------------------------------
 * Returns a diagnostic number for the last failure.
 */
NetErrnoType NetErrNo()
{
  return net_errno;
}

/* NetMakeContact()
 *--------------------------------------------------------------------
 * Makes a tcp connection to a host:port pair.
 *--------------------------------------------------------------------
 * ``Hostname'' can either be in the form of a hostname or an IP address
 * represented as a string. If the hostname is not found as it is,
 * ``hostname'' is assumed to be an IP address, and it is treated as such.
 *
 * If the lookup succeeds, a TCP connection is established with the
 * specified ``port'' number on the remote host and a stream socket is
 * returned.
 *
 * On any sort of error, an error code can be obtained with @NetErrNo()
 * and a message with @NetErrStr().
 */
SOCKET
NetMakeContact(const char *hname, int port)
{
  int fd;
  struct sockaddr_in addr;
  struct hostent *hent;

  fd = socket(AF_INET, SOCK_STREAM, 0);
  if(fd == -1)
    {
      NetSetErrno(E_NET_ERRNO);
      return -1;
    }


  hent = gethostbyname(hname);
  if(hent == NULL)
    addr.sin_addr.s_addr = inet_addr(hname);
  else
    memcpy(&addr.sin_addr, hent->h_addr, hent->h_length);
  addr.sin_family = AF_INET;
  addr.sin_port = htons(port);

  if(connect(fd, (struct sockaddr *)&addr, sizeof(addr)))
    {
      NetSetErrno(E_NET_ERRNO);
      return -1;
    }

  NetSetErrno(E_NET_OK);
  return fd;
}



#ifdef TEST

int xmit(int fd1, int fd2)
{
  int l;
  char iobuf[1024];

  l = read(fd1, iobuf, sizeof(iobuf));
  if(l<=0)return -1;

  l = write(fd2, iobuf, l);
  if(l<=0)return -1;

  return 0;
}

main(int argc, char **argv)
{
  SOCKET s;
  fd_set readfds;

  if(argc != 3) {
    fprintf(stderr, "usage: %s hostname port\n", argv[0]); exit(-1);
  }

  s = NetMakeContact(argv[1], atoi(argv[2]));
  if(s==-1) {
    fprintf(stderr, "Network error: %s\n", NetErrStr()); exit(-1);
  }

  /* Make the socket non-blocking */
  ioctl(s, FIONBIO, 1);


  FD_ZERO(&readfds);

  for(;;)
    {
      FD_SET(0, &readfds);
      FD_SET(s, &readfds);

      if(select(s+1, &readfds, NULL, NULL, NULL) == -1) break;

      if(FD_ISSET(s, &readfds))
        if(xmit(s, 1)) break;
      if(FD_ISSET(0, &readfds))
        if(xmit(0, s)) break;
    }
}


#endif