lib/ttyname_r.c

/* Determine name of a terminal.

   Copyright (C) 2010-2026 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* Written by Bruno Haible <bruno@clisp.org>, 2010.  */

#include <config.h>

#include <unistd.h>

#include <errno.h>
#include <limits.h>
#include <string.h>
#if defined __ANDROID__
# include <stdio.h>
#endif

int
ttyname_r (int fd, char *buf, size_t buflen)
#undef ttyname_r
{
#if defined __ANDROID__
  /* On Android, read the result from the /proc file system.  */
  if (!isatty (fd))
    /* We rely on isatty to set errno properly (i.e. EBADF or ENOTTY).  */
    return errno;
  else if (buflen == 0)
    return ERANGE;
  else
    {
      char procfile[14+11+1];
      char largerbuf[512];
      sprintf (procfile, "/proc/self/fd/%d", fd);
      ssize_t ret =
        (buflen < sizeof (largerbuf)
         ? readlink (procfile, largerbuf, sizeof (largerbuf))
         : readlink (procfile, buf, buflen <= INT_MAX ? buflen : INT_MAX));
      if (ret < 0)
        return errno;
      if ((size_t) ret >= buflen)
        return ERANGE;
      if (buflen < sizeof (largerbuf))
        memcpy (buf, largerbuf, (size_t) ret);
      buf[(size_t) ret] = '\0';
      return 0;
    }
#elif HAVE_TTYNAME_R
  /* When ttyname_r exists, use it.  */
  /* This code is multithread-safe.  */
  /* On Solaris, ttyname_r always fails if buflen < 128.
     So provide a buffer that is large enough.  */
  char largerbuf[512];
# if HAVE_POSIXDECL_TTYNAME_R
  int err =
    (buflen < sizeof (largerbuf)
     ? ttyname_r (fd, largerbuf, sizeof (largerbuf))
     : ttyname_r (fd, buf, buflen <= INT_MAX ? buflen : INT_MAX));
  if (err != 0)
    return err;
  if (buflen < sizeof (largerbuf))
    {
      size_t namelen = strlen (largerbuf) + 1;
      if (namelen > buflen)
        return ERANGE;
      memcpy (buf, largerbuf, namelen);
    }
# else
  char *name =
    (buflen < sizeof (largerbuf)
     ? ttyname_r (fd, largerbuf, sizeof (largerbuf))
     : ttyname_r (fd, buf, buflen <= INT_MAX ? buflen : INT_MAX));
  if (name == NULL)
    return errno;
  if (name != buf)
    {
      size_t namelen = strlen (name) + 1;
      if (namelen > buflen)
        return ERANGE;
      memmove (buf, name, namelen);
    }
# endif
  return 0;
#elif HAVE_TTYNAME
  /* Note: This is not multithread-safe.  */
  char *name = ttyname (fd);
  if (name == NULL)
    return errno;
  size_t namelen = strlen (name) + 1;
  if (namelen > buflen)
    return ERANGE;
  memcpy (buf, name, namelen);
  return 0;
#else
  /* Platforms like mingw: no ttys exist at all.  */
  return ENOTTY;
#endif
}