input.c

/* input.c -- functions to perform buffered input with synchronization. */

/* Copyright (C) 1992-2021 Free Software Foundation, Inc.

   This file is part of GNU Bash, the Bourne Again SHell.

   Bash is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   Bash 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 General Public License for more details.

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

#include "config.h"

#include "bashtypes.h"
#if !defined (_MINIX) && defined (HAVE_SYS_FILE_H)
#  include <sys/file.h>
#endif
#include "filecntl.h"
#include "posixstat.h"
#include <stdio.h>
#include <errno.h>

#if defined (HAVE_UNISTD_H)
#  include <unistd.h>
#endif

#include "bashansi.h"
#include "bashintl.h"

#include "shell.h"
#include "input.h"
#include "externs.h"
#include "trap.h"

#if !defined (errno)
extern int errno;
#endif /* !errno */

#if defined (EAGAIN)
#  define X_EAGAIN EAGAIN
#else
#  define X_EAGAIN -99
#endif

#if defined (EWOULDBLOCK)
#  define X_EWOULDBLOCK EWOULDBLOCK
#else
#  define X_EWOULDBLOCK -99
#endif

extern void termsig_handler PARAMS((int));

/* Functions to handle reading input on systems that don't restart read(2)
   if a signal is received. */

static char localbuf[1024];
static int local_index = 0, local_bufused = 0;

/* Posix and USG systems do not guarantee to restart read () if it is
   interrupted by a signal.  We do the read ourselves, and restart it
   if it returns EINTR. */
int
getc_with_restart (stream)
     FILE *stream;
{
  unsigned char uc;

  CHECK_TERMSIG;

  /* Try local buffering to reduce the number of read(2) calls. */
  if (local_index == local_bufused || local_bufused == 0)
    {
      while (1)
	{
	  QUIT;
	  run_pending_traps ();

	  local_bufused = read (fileno (stream), localbuf, sizeof(localbuf));
	  if (local_bufused > 0)
	    break;
	  else if (local_bufused == 0)
	    {
	      local_index = 0;
	      return EOF;
	    }
	  else if (errno == X_EAGAIN || errno == X_EWOULDBLOCK)
	    {
	      if (sh_unset_nodelay_mode (fileno (stream)) < 0)
		{
		  sys_error (_("cannot reset nodelay mode for fd %d"), fileno (stream));
		  local_index = local_bufused = 0;
		  return EOF;
		}
	      continue;
	    }
	  else if (errno != EINTR)
	    {
	      local_index = local_bufused = 0;
	      return EOF;
	    }
	  else if (interrupt_state || terminating_signal)	/* QUIT; */
	    local_index = local_bufused = 0;
	}
      local_index = 0;
    }
  uc = localbuf[local_index++];
  return uc;
}

int
ungetc_with_restart (c, stream)
     int c;
     FILE *stream;
{
  if (local_index == 0 || c == EOF)
    return EOF;
  localbuf[--local_index] = c;
  return c;
}

#if defined (BUFFERED_INPUT)

/* A facility similar to stdio, but input-only. */

#if defined (USING_BASH_MALLOC)
#  define MAX_INPUT_BUFFER_SIZE	8172
#else
#  define MAX_INPUT_BUFFER_SIZE	8192
#endif

#if !defined (SEEK_CUR)
#  define SEEK_CUR 1
#endif /* !SEEK_CUR */

#ifdef max
#  undef max
#endif
#define max(a, b)	(((a) > (b)) ? (a) : (b))
#ifdef min
#  undef min
#endif
#define min(a, b)	((a) > (b) ? (b) : (a))

int bash_input_fd_changed;

/* This provides a way to map from a file descriptor to the buffer
   associated with that file descriptor, rather than just the other
   way around.  This is needed so that buffers are managed properly
   in constructs like 3<&4.  buffers[x]->b_fd == x -- that is how the
   correspondence is maintained. */
static BUFFERED_STREAM **buffers = (BUFFERED_STREAM **)NULL;
static int nbuffers;

#define ALLOCATE_BUFFERS(n) \
	do { if ((n) >= nbuffers) allocate_buffers (n); } while (0)

/* Make sure `buffers' has at least N elements. */
static void
allocate_buffers (n)
     int n;
{
  register int i, orig_nbuffers;

  orig_nbuffers = nbuffers;
  nbuffers = n + 20;
  buffers = (BUFFERED_STREAM **)xrealloc
    (buffers, nbuffers * sizeof (BUFFERED_STREAM *));

  /* Zero out the new buffers. */
  for (i = orig_nbuffers; i < nbuffers; i++)
    buffers[i] = (BUFFERED_STREAM *)NULL;
}

/* Construct and return a BUFFERED_STREAM corresponding to file descriptor
   FD, using BUFFER. */
static BUFFERED_STREAM *
make_buffered_stream (fd, buffer, bufsize)
     int fd;
     char *buffer;
     size_t bufsize;
{
  BUFFERED_STREAM *bp;

  bp = (BUFFERED_STREAM *)xmalloc (sizeof (BUFFERED_STREAM));
  ALLOCATE_BUFFERS (fd);
  buffers[fd] = bp;
  bp->b_fd = fd;
  bp->b_buffer = buffer;
  bp->b_size = bufsize;
  bp->b_used = bp->b_inputp = bp->b_flag = 0;
  if (bufsize == 1)
    bp->b_flag |= B_UNBUFF;
  if (O_TEXT && (fcntl (fd, F_GETFL) & O_TEXT) != 0)
    bp->b_flag |= B_TEXT;
  return (bp);
}

/* Allocate a new BUFFERED_STREAM, copy BP to it, and return the new copy. */
static BUFFERED_STREAM *
copy_buffered_stream (bp)
     BUFFERED_STREAM *bp;
{
  BUFFERED_STREAM *nbp;

  if (!bp)
    return ((BUFFERED_STREAM *)NULL);

  nbp = (BUFFERED_STREAM *)xmalloc (sizeof (BUFFERED_STREAM));
  xbcopy ((char *)bp, (char *)nbp, sizeof (BUFFERED_STREAM));
  return (nbp);
}

int
set_bash_input_fd (fd)
     int fd;
{
  if (bash_input.type == st_bstream)
    bash_input.location.buffered_fd = fd;
  else if (interactive_shell == 0)
    default_buffered_input = fd;
  return 0;
}

int
fd_is_bash_input (fd)
     int fd;
{
  if (bash_input.type == st_bstream && bash_input.location.buffered_fd == fd)
    return 1;
  else if (interactive_shell == 0 && default_buffered_input == fd)
    return 1;
  return 0;
}

/* Save the buffered stream corresponding to file descriptor FD (which bash
   is using to read input) to a buffered stream associated with NEW_FD.  If
   NEW_FD is -1, a new file descriptor is allocated with fcntl.  The new
   file descriptor is returned on success, -1 on error. */
int
save_bash_input (fd, new_fd)
     int fd, new_fd;
{
  int nfd;

  /* Sync the stream so we can re-read from the new file descriptor.  We
     might be able to avoid this by copying the buffered stream verbatim
     to the new file descriptor. */
  if (buffers[fd])
    sync_buffered_stream (fd);

  /* Now take care of duplicating the file descriptor that bash is
     using for input, so we can reinitialize it later. */
  nfd = (new_fd == -1) ? fcntl (fd, F_DUPFD, 10) : new_fd;
  if (nfd == -1)
    {
      if (fcntl (fd, F_GETFD, 0) == 0)
	sys_error (_("cannot allocate new file descriptor for bash input from fd %d"), fd);
      return -1;
    }

  if (nfd < nbuffers && buffers[nfd])
    {
      /* What's this?  A stray buffer without an associated open file
	 descriptor?  Free up the buffer and report the error. */
      internal_error (_("save_bash_input: buffer already exists for new fd %d"), nfd);
      if (buffers[nfd]->b_flag & B_SHAREDBUF)
	buffers[nfd]->b_buffer = (char *)NULL;
      free_buffered_stream (buffers[nfd]);
    }

  /* Reinitialize bash_input.location. */
  if (bash_input.type == st_bstream)
    {
      bash_input.location.buffered_fd = nfd;
      fd_to_buffered_stream (nfd);
      close_buffered_fd (fd);	/* XXX */
    }
  else
    /* If the current input type is not a buffered stream, but the shell
       is not interactive and therefore using a buffered stream to read
       input (e.g. with an `eval exec 3>output' inside a script), note
       that the input fd has been changed.  pop_stream() looks at this
       value and adjusts the input fd to the new value of
       default_buffered_input accordingly. */
    bash_input_fd_changed++;

  if (default_buffered_input == fd)
    default_buffered_input = nfd;

  SET_CLOSE_ON_EXEC (nfd);
  return nfd;
}

/* Check that file descriptor FD is not the one that bash is currently
   using to read input from a script.  FD is about to be duplicated onto,
   which means that the kernel will close it for us.  If FD is the bash
   input file descriptor, we need to seek backwards in the script (if
   possible and necessary -- scripts read from stdin are still unbuffered),
   allocate a new file descriptor to use for bash input, and re-initialize
   the buffered stream.  Make sure the file descriptor used to save bash
   input is set close-on-exec. Returns 0 on success, -1 on failure.  This
   works only if fd is > 0 -- if fd == 0 and bash is reading input from
   fd 0, sync_buffered_stream is used instead, to cooperate with input
   redirection (look at redir.c:add_undo_redirect()). */
int
check_bash_input (fd)
     int fd;
{
  if (fd_is_bash_input (fd))
    {
      if (fd > 0)
	return ((save_bash_input (fd, -1) == -1) ? -1 : 0);
      else if (fd == 0)
        return ((sync_buffered_stream (fd) == -1) ? -1 : 0);
    }
  return 0;
}
      
/* This is the buffered stream analogue of dup2(fd1, fd2).  The
   BUFFERED_STREAM corresponding to fd2 is deallocated, if one exists.
   BUFFERS[fd1] is copied to BUFFERS[fd2].  This is called by the
   redirect code for constructs like 4<&0 and 3</etc/rc.local. */
int
duplicate_buffered_stream (fd1, fd2)
     int fd1, fd2;
{
  int is_bash_input, m;

  if (fd1 == fd2)
    return 0;

  m = max (fd1, fd2);
  ALLOCATE_BUFFERS (m);

  /* If FD2 is the file descriptor bash is currently using for shell input,
     we need to do some extra work to make sure that the buffered stream
     actually exists (it might not if fd1 was not active, and the copy
     didn't actually do anything). */
  is_bash_input = (bash_input.type == st_bstream) &&
		  (bash_input.location.buffered_fd == fd2);

  if (buffers[fd2])
    {
      /* If the two objects share the same b_buffer, don't free it. */
      if (buffers[fd1] && buffers[fd1]->b_buffer && buffers[fd1]->b_buffer == buffers[fd2]->b_buffer)
	buffers[fd2] = (BUFFERED_STREAM *)NULL;
      /* If this buffer is shared with another fd, don't free the buffer */
      else if (buffers[fd2]->b_flag & B_SHAREDBUF)
	{
	  buffers[fd2]->b_buffer = (char *)NULL;
	  free_buffered_stream (buffers[fd2]);
	}
      else
	free_buffered_stream (buffers[fd2]);
    }
  buffers[fd2] = copy_buffered_stream (buffers[fd1]);
  if (buffers[fd2])
    buffers[fd2]->b_fd = fd2;

  if (is_bash_input)
    {
      if (!buffers[fd2])
	fd_to_buffered_stream (fd2);
      buffers[fd2]->b_flag |= B_WASBASHINPUT;
    }

  if (fd_is_bash_input (fd1) || (buffers[fd1] && (buffers[fd1]->b_flag & B_SHAREDBUF)))
    buffers[fd2]->b_flag |= B_SHAREDBUF;

  return (fd2);
}

/* Return 1 if a seek on FD will succeed. */
#define fd_is_seekable(fd) (lseek ((fd), 0L, SEEK_CUR) >= 0)

/* Take FD, a file descriptor, and create and return a buffered stream
   corresponding to it.  If something is wrong and the file descriptor
   is invalid, return a NULL stream. */
BUFFERED_STREAM *
fd_to_buffered_stream (fd)
     int fd;
{
  char *buffer;
  size_t size;
  struct stat sb;

  if (fstat (fd, &sb) < 0)
    {
      close (fd);
      return ((BUFFERED_STREAM *)NULL);
    }

  size = (fd_is_seekable (fd)) ? min (sb.st_size, MAX_INPUT_BUFFER_SIZE) : 1;
  if (size == 0)
    size = 1;
  buffer = (char *)xmalloc (size);

  return (make_buffered_stream (fd, buffer, size));
}

/* Return a buffered stream corresponding to FILE, a file name. */
BUFFERED_STREAM *
open_buffered_stream (file)
     char *file;
{
  int fd;

  fd = open (file, O_RDONLY);
  return ((fd >= 0) ? fd_to_buffered_stream (fd) : (BUFFERED_STREAM *)NULL);
}

/* Deallocate a buffered stream and free up its resources.  Make sure we
   zero out the slot in BUFFERS that points to BP. */
void
free_buffered_stream (bp)
     BUFFERED_STREAM *bp;
{
  int n;

  if (!bp)
    return;

  n = bp->b_fd;
  if (bp->b_buffer)
    free (bp->b_buffer);
  free (bp);
  buffers[n] = (BUFFERED_STREAM *)NULL;
}

/* Close the file descriptor associated with BP, a buffered stream, and free
   up the stream.  Return the status of closing BP's file descriptor. */
int
close_buffered_stream (bp)
     BUFFERED_STREAM *bp;
{
  int fd;

  if (!bp)
    return (0);
  fd = bp->b_fd;
  if (bp->b_flag & B_SHAREDBUF)
    bp->b_buffer = (char *)NULL;
  free_buffered_stream (bp);
  return (close (fd));
}

/* Deallocate the buffered stream associated with file descriptor FD, and
   close FD.  Return the status of the close on FD. */
int
close_buffered_fd (fd)
     int fd;
{
  if (fd < 0)
    {
      errno = EBADF;
      return -1;
    }
  if (fd >= nbuffers || !buffers || !buffers[fd])
    return (close (fd));
  return (close_buffered_stream (buffers[fd]));
}

/* Make the BUFFERED_STREAM associated with buffers[FD] be BP, and return
   the old BUFFERED_STREAM. */
BUFFERED_STREAM *
set_buffered_stream (fd, bp)
     int fd;
     BUFFERED_STREAM *bp;
{
  BUFFERED_STREAM *ret;

  ret = buffers[fd];
  buffers[fd] = bp;
  return ret;
}

/* Read a buffer full of characters from BP, a buffered stream. */
static int
b_fill_buffer (bp)
     BUFFERED_STREAM *bp;
{
  ssize_t nr;
  off_t o;

  CHECK_TERMSIG;
  /* In an environment where text and binary files are treated differently,
     compensate for lseek() on text files returning an offset different from
     the count of characters read() returns.  Text-mode streams have to be
     treated as unbuffered. */
  if ((bp->b_flag & (B_TEXT | B_UNBUFF)) == B_TEXT)
    {
      o = lseek (bp->b_fd, 0, SEEK_CUR);
      nr = zread (bp->b_fd, bp->b_buffer, bp->b_size);
      if (nr > 0 && nr < lseek (bp->b_fd, 0, SEEK_CUR) - o)
	{
	  lseek (bp->b_fd, o, SEEK_SET);
	  bp->b_flag |= B_UNBUFF;
	  bp->b_size = 1;
	  nr = zread (bp->b_fd, bp->b_buffer, bp->b_size);
	}
    }
  else
    nr = zread (bp->b_fd, bp->b_buffer, bp->b_size);
  if (nr <= 0)
    {
      bp->b_used = bp->b_inputp = 0;
      bp->b_buffer[0] = 0;
      if (nr == 0)
	bp->b_flag |= B_EOF;
      else
	bp->b_flag |= B_ERROR;
      return (EOF);
    }

  bp->b_used = nr;
  bp->b_inputp = 0;
  return (bp->b_buffer[bp->b_inputp++] & 0xFF);
}

/* Get a character from buffered stream BP. */
#define bufstream_getc(bp) \
  (bp->b_inputp == bp->b_used || !bp->b_used) \
  		? b_fill_buffer (bp) \
		: bp->b_buffer[bp->b_inputp++] & 0xFF

/* Push C back onto buffered stream BP. */
static int
bufstream_ungetc(c, bp)
     int c;
     BUFFERED_STREAM *bp;
{
  if (c == EOF || bp == 0 || bp->b_inputp == 0)
    return (EOF);

  bp->b_buffer[--bp->b_inputp] = c;
  return (c);
}

/* Seek backwards on file BFD to synchronize what we've read so far
   with the underlying file pointer. */
int
sync_buffered_stream (bfd)
     int bfd;
{
  BUFFERED_STREAM *bp;
  off_t chars_left;

  if (buffers == 0 || (bp = buffers[bfd]) == 0)
    return (-1);

  chars_left = bp->b_used - bp->b_inputp;
  if (chars_left)
    lseek (bp->b_fd, -chars_left, SEEK_CUR);
  bp->b_used = bp->b_inputp = 0;
  return (0);
}

int
buffered_getchar ()
{
  CHECK_TERMSIG;

  if (bash_input.location.buffered_fd < 0 || buffers[bash_input.location.buffered_fd] == 0)
    return EOF;

#if !defined (DJGPP)
  return (bufstream_getc (buffers[bash_input.location.buffered_fd]));
#else
  /* On DJGPP, ignore \r. */
  int ch;
  while ((ch = bufstream_getc (buffers[bash_input.location.buffered_fd])) == '\r')
    ;
  return ch;
#endif
}

int
buffered_ungetchar (c)
     int c;
{
  return (bufstream_ungetc (c, buffers[bash_input.location.buffered_fd]));
}

/* Make input come from file descriptor BFD through a buffered stream. */
void
with_input_from_buffered_stream (bfd, name)
     int bfd;
     char *name;
{
  INPUT_STREAM location;
  BUFFERED_STREAM *bp;

  location.buffered_fd = bfd;
  /* Make sure the buffered stream exists. */
  bp = fd_to_buffered_stream (bfd);
  init_yy_io (bp == 0 ? return_EOF : buffered_getchar,
	      buffered_ungetchar, st_bstream, name, location);
}

#if defined (TEST)
void *
xmalloc(s)
int s;
{
	return (malloc (s));
}

void *
xrealloc(s, size)
char	*s;
int	size;
{
	if (!s)
		return(malloc (size));
	else
		return(realloc (s, size));
}

void
init_yy_io ()
{
}

process(bp)
BUFFERED_STREAM *bp;
{
	int c;

	while ((c = bufstream_getc(bp)) != EOF)
		putchar(c);
}

BASH_INPUT bash_input;

struct stat dsb;		/* can be used from gdb */

/* imitate /bin/cat */
main(argc, argv)
int	argc;
char	**argv;
{
	register int i;
	BUFFERED_STREAM *bp;

	if (argc == 1) {
		bp = fd_to_buffered_stream (0);
		process(bp);
		exit(0);
	}
	for (i = 1; i < argc; i++) {
		if (argv[i][0] == '-' && argv[i][1] == '\0') {
			bp = fd_to_buffered_stream (0);
			if (!bp)
				continue;
			process(bp);
			free_buffered_stream (bp);
		} else {
			bp = open_buffered_stream (argv[i]);
			if (!bp)
				continue;
			process(bp);
			close_buffered_stream (bp);
		}
	}
	exit(0);
}
#endif /* TEST */
#endif /* BUFFERED_INPUT */