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readn.c

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/************************************************************************
* File: readn.c
* Purpose: Provides a C file for the readn function from
* the book Advanced Programming in the UNIX Environment  by Richard Stevens.
* The readn function calls the read function repeatedly until n bytes
* have been read from the file descriptor.
*************************************************************************/

/* This is neccessary to avoid muliple definitions of fd_set, etc when both
* PCNFS and Windows Sockets are to be available. */
#ifdef USE_PCNFS
#undef USE_PCNFS
#endif

#include "rcs_defs.hh"          /* _Windows */

#include "readn.h"              /* readn(int, void *, int, double) */
#if !defined(_Windows) && !defined(MSDOS) || defined(gnuwin32)
#include <unistd.h>             /* read(), select() */
#include <sys/types.h>          /* typedef fd_set, FD_ZERO, FD_SET */
#ifdef VXWORKS
#include <sys/times.h>          /* struct timeval */
#else
#include <sys/time.h>           /* struct timeval */
#endif
#else
#ifdef _Windows
#ifndef UNDER_CE
#include <io.h>                 /* read() */
#endif
#ifdef USE_OLD_WINSOCK
#include <winsock.h>            /* select(), typedef fd_set, FD_ZERO, FD_SET, struct */
#else
#include <winsock2.h>
#endif

#else
#include <tklib.h>
#endif /* struct timeval */
#endif
#include <stddef.h>             /* size_t */
#include <errno.h>              /* errno */
#include <string.h>             /* strerror() */
#include <math.h>               /* modf() */
#include "rcs_prnt.hh"          /* rcs_print_error() */
#include "sokintrf.h"           /* dl_select() */

/* Read "n" bytes from a descriptor. */
int
readn (int fd, void *vptr, int n, double _timeout)
{
  int nleft, nread;
  char *ptr;
  double int_part;
  struct timeval timeout_tv;
  fd_set read_fd_set;
  timeout_tv.tv_sec = (long) _timeout;
  timeout_tv.tv_usec = (long) (_timeout * 1000000.0);
  if (timeout_tv.tv_usec >= 1000000)
    {
      timeout_tv.tv_usec = timeout_tv.tv_usec % 1000000;
    }
  FD_ZERO (&read_fd_set);
  RCS_FD_SET (fd, &read_fd_set);


  ptr = (char *) vptr;
  nleft = n;
  while (nleft > 0)
    {
      if (_timeout > 0.0)
        {
          switch (dl_select
                  (fd + 1, &read_fd_set, (fd_set *) NULL, (fd_set *) NULL,
                   &timeout_tv))
            {
            case -1:
              rcs_print_error ("Error in select: %d -> %s\n", errno,
                               strerror (errno));
              return -1;

            case 0:
              rcs_print_error ("Read timed out.\n");
              return -1;

            default:
              break;
            }
        }
      if ((nread = read (fd, ptr, nleft)) == -1)
        {
          rcs_print_error ("Read error: %d = %s\n", errno, strerror (errno));
          return (-1);          /* error, return < 0 */
        }
      else if (nread == 0)
        {
          rcs_print_error ("readn: Premature EOF recieved.\n");
          return (-1);
        }

      nleft -= nread;
      ptr += nread;
    }
  return (n - nleft);           /* return >= 0 */
}

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