tzfile.c

Linux下头文件time.h的实现源码

/* Copyright (C) 1991-1993,1995-2001,2003,2004,2006, 2007
   Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library 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.

   The GNU C Library 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 the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <assert.h>
#include <limits.h>
#include <stdio.h>
#include <stdio_ext.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/stat.h>

#define	NOID
#include <timezone/tzfile.h>

int __use_tzfile;
static dev_t tzfile_dev;
static ino64_t tzfile_ino;
static time_t tzfile_mtime;

struct ttinfo
  {
    long int offset;		/* Seconds east of GMT.  */
    unsigned char isdst;	/* Used to set tm_isdst.  */
    unsigned char idx;		/* Index into `zone_names'.  */
    unsigned char isstd;	/* Transition times are in standard time.  */
    unsigned char isgmt;	/* Transition times are in GMT.  */
  };

struct leap
  {
    time_t transition;		/* Time the transition takes effect.  */
    long int change;		/* Seconds of correction to apply.  */
  };

static void compute_tzname_max (size_t) internal_function;

static size_t num_transitions;
libc_freeres_ptr (static time_t *transitions);
static unsigned char *type_idxs;
static size_t num_types;
static struct ttinfo *types;
static char *zone_names;
static long int rule_stdoff;
static long int rule_dstoff;
static size_t num_leaps;
static struct leap *leaps;
static char *tzspec;

#include <endian.h>
#include <byteswap.h>

/* Decode the four bytes at PTR as a signed integer in network byte order.  */
static inline int
__attribute ((always_inline))
decode (const void *ptr)
{
  if (BYTE_ORDER == BIG_ENDIAN && sizeof (int) == 4)
    return *(const int *) ptr;
  if (sizeof (int) == 4)
    return bswap_32 (*(const int *) ptr);

  const unsigned char *p = ptr;
  int result = *p & (1 << (CHAR_BIT - 1)) ? ~0 : 0;

  result = (result << 8) | *p++;
  result = (result << 8) | *p++;
  result = (result << 8) | *p++;
  result = (result << 8) | *p++;

  return result;
}


static inline int64_t
__attribute ((always_inline))
decode64 (const void *ptr)
{
  if ((BYTE_ORDER == BIG_ENDIAN))
    return *(const int64_t *) ptr;

  return bswap_64 (*(const int64_t *) ptr);
}


void
__tzfile_read (const char *file, size_t extra, char **extrap)
{
  static const char default_tzdir[] = TZDIR;
  size_t num_isstd, num_isgmt;
  register FILE *f;
  struct tzhead tzhead;
  size_t chars;
  register size_t i;
  size_t total_size;
  size_t types_idx;
  size_t leaps_idx;
  int was_using_tzfile = __use_tzfile;
  int trans_width = 4;
  size_t tzspec_len;

  if (sizeof (time_t) != 4 && sizeof (time_t) != 8)
    abort ();

  __use_tzfile = 0;

  if (file == NULL)
    /* No user specification; use the site-wide default.  */
    file = TZDEFAULT;
  else if (*file == '\0')
    /* User specified the empty string; use UTC with no leap seconds.  */
    goto ret_free_transitions;
  else
    {
      /* We must not allow to read an arbitrary file in a setuid
	 program.  So we fail for any file which is not in the
	 directory hierachy starting at TZDIR
	 and which is not the system wide default TZDEFAULT.  */
      if (__libc_enable_secure
	  && ((*file == '/'
	       && memcmp (file, TZDEFAULT, sizeof TZDEFAULT)
	       && memcmp (file, default_tzdir, sizeof (default_tzdir) - 1))
	      || strstr (file, "../") != NULL))
	/* This test is certainly a bit too restrictive but it should
	   catch all critical cases.  */
	goto ret_free_transitions;
    }

  if (*file != '/')
    {
      const char *tzdir;
      unsigned int len, tzdir_len;
      char *new, *tmp;

      tzdir = getenv ("TZDIR");
      if (tzdir == NULL || *tzdir == '\0')
	{
	  tzdir = default_tzdir;
	  tzdir_len = sizeof (default_tzdir) - 1;
	}
      else
	tzdir_len = strlen (tzdir);
      len = strlen (file) + 1;
      new = (char *) __alloca (tzdir_len + 1 + len);
      tmp = __mempcpy (new, tzdir, tzdir_len);
      *tmp++ = '/';
      memcpy (tmp, file, len);
      file = new;
    }

  /* If we were already using tzfile, check whether the file changed.  */
  struct stat64 st;
  if (was_using_tzfile
      && stat64 (file, &st) == 0
      && tzfile_ino == st.st_ino && tzfile_dev == st.st_dev
      && tzfile_mtime == st.st_mtime)
    {
      /* Nothing to do.  */
      __use_tzfile = 1;
      return;
    }

  /* Note the file is opened with cancellation in the I/O functions
     disabled.  */
  f = fopen (file, "rc");
  if (f == NULL)
    goto ret_free_transitions;

  /* Get information about the file we are actually using.  */
  if (fstat64 (fileno (f), &st) != 0)
    {
      fclose (f);
      goto ret_free_transitions;
    }

  free ((void *) transitions);
  transitions = NULL;

  /* Remember the inode and device number and modification time.  */
  tzfile_dev = st.st_dev;
  tzfile_ino = st.st_ino;
  tzfile_mtime = st.st_mtime;

  /* No threads reading this stream.  */
  __fsetlocking (f, FSETLOCKING_BYCALLER);

 read_again:
  if (__builtin_expect (fread_unlocked ((void *) &tzhead, sizeof (tzhead),
					1, f) != 1, 0)
      || memcmp (tzhead.tzh_magic, TZ_MAGIC, sizeof (tzhead.tzh_magic)) != 0)
    goto lose;

  num_transitions = (size_t) decode (tzhead.tzh_timecnt);
  num_types = (size_t) decode (tzhead.tzh_typecnt);
  chars = (size_t) decode (tzhead.tzh_charcnt);
  num_leaps = (size_t) decode (tzhead.tzh_leapcnt);
  num_isstd = (size_t) decode (tzhead.tzh_ttisstdcnt);
  num_isgmt = (size_t) decode (tzhead.tzh_ttisgmtcnt);

  /* For platforms with 64-bit time_t we use the new format if available.  */
  if (sizeof (time_t) == 8 && trans_width == 4
      && tzhead.tzh_version[0] != '\0')
    {
      /* We use the 8-byte format.  */
      trans_width = 8;

      /* Position the stream before the second header.  */
      size_t to_skip = (num_transitions * (4 + 1)
			+ num_types * 6
			+ chars
			+ num_leaps * 8
			+ num_isstd
			+ num_isgmt);
      if (fseek (f, to_skip, SEEK_CUR) != 0)
	goto lose;

      goto read_again;
    }

  total_size = num_transitions * (sizeof (time_t) + 1);
  total_size = ((total_size + __alignof__ (struct ttinfo) - 1)
		& ~(__alignof__ (struct ttinfo) - 1));
  types_idx = total_size;
  total_size += num_types * sizeof (struct ttinfo) + chars;
  total_size = ((total_size + __alignof__ (struct leap) - 1)
		& ~(__alignof__ (struct leap) - 1));
  leaps_idx = total_size;
  total_size += num_leaps * sizeof (struct leap);
  tzspec_len = (sizeof (time_t) == 8 && trans_width == 8
		? st.st_size - (ftello (f)
				+ num_transitions * (8 + 1)
				+ num_types * 6
				+ chars
				+ num_leaps * 8
				+ num_isstd
				+ num_isgmt) - 1 : 0);

  /* Allocate enough memory including the extra block requested by the
     caller.  */
  transitions = (time_t *) malloc (total_size + tzspec_len + extra);
  if (transitions == NULL)
    goto lose;

  type_idxs = (unsigned char *) transitions + (num_transitions
					       * sizeof (time_t));
  types = (struct ttinfo *) ((char *) transitions + types_idx);
  zone_names = (char *) types + num_types * sizeof (struct ttinfo);
  leaps = (struct leap *) ((char *) transitions + leaps_idx);
  if (sizeof (time_t) == 8 && trans_width == 8)
    tzspec = (char *) leaps + num_leaps * sizeof (struct leap) + extra;
  else
    tzspec = NULL;
  if (extra > 0)
    *extrap = (char *) &leaps[num_leaps];

  if (sizeof (time_t) == 4 || __builtin_expect (trans_width == 8, 1))
    {
      if (__builtin_expect (fread_unlocked (transitions, trans_width + 1,
					    num_transitions, f)
			    != num_transitions, 0))
	goto lose;
    }
  else
    {
      if (__builtin_expect (fread_unlocked (transitions, 4, num_transitions, f)
			    != num_transitions, 0)
	  || __builtin_expect (fread_unlocked (type_idxs, 1, num_transitions,
					       f) != num_transitions, 0))
	goto lose;
    }

  /* Check for bogus indices in the data file, so we can hereafter
     safely use type_idxs[T] as indices into `types' and never crash.  */
  for (i = 0; i < num_transitions; ++i)
    if (__builtin_expect (type_idxs[i] >= num_types, 0))
      goto lose;

  if ((BYTE_ORDER != BIG_ENDIAN && (sizeof (time_t) == 4 || trans_width == 4))
      || (BYTE_ORDER == BIG_ENDIAN && sizeof (time_t) == 8
	  && trans_width == 4))
    {
      /* Decode the transition times, stored as 4-byte integers in
	 network (big-endian) byte order.  We work from the end of
	 the array so as not to clobber the next element to be
	 processed when sizeof (time_t) > 4.  */
      i = num_transitions;
      while (i-- > 0)
	transitions[i] = decode ((char *) transitions + i * 4);
    }
  else if (BYTE_ORDER != BIG_ENDIAN && sizeof (time_t) == 8)
    {
      /* Decode the transition times, stored as 8-byte integers in
	 network (big-endian) byte order.  */
      for (i = 0; i < num_transitions; ++i)
	transitions[i] = decode64 ((char *) transitions + i * 8);
    }

  for (i = 0; i < num_types; ++i)
    {
      unsigned char x[4];
      int c;
      if (__builtin_expect (fread_unlocked (x, 1, sizeof (x), f) != sizeof (x),
			    0))
	goto lose;
      c = getc_unlocked (f);
      if (__builtin_expect ((unsigned int) c > 1u, 0))
	goto lose;
      types[i].isdst = c;
      c = getc_unlocked (f);
      if (__builtin_expect ((size_t) c > chars, 0))
	/* Bogus index in data file.  */
	goto lose;
      types[i].idx = c;
      types[i].offset = (long int) decode (x);
    }

  if (__builtin_expect (fread_unlocked (zone_names, 1, chars, f) != chars, 0))
    goto lose;

  for (i = 0; i < num_leaps; ++i)
    {
      unsigned char x[8];
      if (__builtin_expect (fread_unlocked (x, 1, trans_width, f)
			    != trans_width, 0))
	goto lose;
      if (sizeof (time_t) == 4 || trans_width == 4)
	leaps[i].transition = (time_t) decode (x);
      else
	leaps[i].transition = (time_t) decode64 (x);

      if (__builtin_expect (fread_unlocked (x, 1, 4, f) != 4, 0))
	goto lose;
      leaps[i].change = (long int) decode (x);
    }

  for (i = 0; i < num_isstd; ++i)
    {
      int c = getc_unlocked (f);
      if (__builtin_expect (c == EOF, 0))
	goto lose;
      types[i].isstd = c != 0;
    }
  while (i < num_types)
    types[i++].isstd = 0;

  for (i = 0; i < num_isgmt; ++i)
    {
      int c = getc_unlocked (f);
      if (__builtin_expect (c == EOF, 0))
	goto lose;
      types[i].isgmt = c != 0;
    }
  while (i < num_types)
    types[i++].isgmt = 0;

  /* Read the POSIX TZ-style information if possible.  */
  if (sizeof (time_t) == 8 && tzspec != NULL)
    {
      /* Skip over the newline first.  */
      if (getc_unlocked (f) != '\n'
	  || (fread_unlocked (tzspec, 1, tzspec_len - 1, f)
	      != tzspec_len - 1))
	tzspec = NULL;
      else
	tzspec[tzspec_len - 1] = '\0';
    }
  else if (sizeof (time_t) == 4 && tzhead.tzh_version != '\0')
    {
      /* Get the TZ string.  */
      if (__builtin_expect (fread_unlocked ((void *) &tzhead, sizeof (tzhead),
					    1, f) != 1, 0)
	  || (memcmp (tzhead.tzh_magic, TZ_MAGIC, sizeof (tzhead.tzh_magic))
	      != 0))
	goto lose;

      size_t num_transitions2 = (size_t) decode (tzhead.tzh_timecnt);
      size_t num_types2 = (size_t) decode (tzhead.tzh_typecnt);
      size_t chars2 = (size_t) decode (tzhead.tzh_charcnt);
      size_t num_leaps2 = (size_t) decode (tzhead.tzh_leapcnt);
      size_t num_isstd2 = (size_t) decode (tzhead.tzh_ttisstdcnt);
      size_t num_isgmt2 = (size_t) decode (tzhead.tzh_ttisgmtcnt);

      /* Position the stream before the second header.  */
      size_t to_skip = (num_transitions2 * (8 + 1)
			+ num_types2 * 6
			+ chars2
			+ num_leaps2 * 12
			+ num_isstd2