my_symlink.c

/* Copyright (c) 2001, 2023, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   Without limiting anything contained in the foregoing, this file,
   which is part of C Driver for MySQL (Connector/C), is also subject to the
   Universal FOSS Exception, version 1.0, a copy of which can be found at
   http://oss.oracle.com/licenses/universal-foss-exception.

   This program 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, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

#include "mysys_priv.h"
#include "my_sys.h"
#include "mysys_err.h"
#include <m_string.h>
#include <errno.h>
#include "my_thread_local.h"
#include "my_dir.h"
#ifdef HAVE_REALPATH
#include <sys/param.h>
#include <sys/stat.h>
#endif

/*
  Reads the content of a symbolic link
  If the file is not a symbolic link, return the original file name in to.

  RETURN
    0  If filename was a symlink,    (to will be set to value of symlink)
    1  If filename was a normal file (to will be set to filename)
   -1  on error.
*/

int my_readlink(char *to, const char *filename, myf MyFlags)
{
#ifndef HAVE_READLINK
  my_stpcpy(to,filename);
  return 1;
#else
  int result=0;
  int length;
  DBUG_ENTER("my_readlink");

  if ((length=readlink(filename, to, FN_REFLEN-1)) < 0)
  {
    /* Don't give an error if this wasn't a symlink */
    set_my_errno(errno);
    if (my_errno() == EINVAL)
    {
      result= 1;
      my_stpcpy(to,filename);
    }
    else
    {
      if (MyFlags & MY_WME)
      {
        char errbuf[MYSYS_STRERROR_SIZE];
        my_error(EE_CANT_READLINK, MYF(0), filename,
                 errno, my_strerror(errbuf, sizeof(errbuf), errno));
      }
      result= -1;
    }
  }
  else
    to[length]=0;
  DBUG_PRINT("exit" ,("result: %d", result));
  DBUG_RETURN(result);
#endif /* HAVE_READLINK */
}


/* Create a symbolic link */

int my_symlink(const char *content, const char *linkname, myf MyFlags)
{
#ifndef HAVE_READLINK
  return 0;
#else
  int result;
  DBUG_ENTER("my_symlink");
  DBUG_PRINT("enter",("content: %s  linkname: %s", content, linkname));

  result= 0;
  if (symlink(content, linkname))
  {
    result= -1;
    set_my_errno(errno);
    if (MyFlags & MY_WME)
    {
      char errbuf[MYSYS_STRERROR_SIZE];
      my_error(EE_CANT_SYMLINK, MYF(0), linkname, content,
               errno, my_strerror(errbuf, sizeof(errbuf), errno));
    }
  }
  else if ((MyFlags & MY_SYNC_DIR) && my_sync_dir_by_file(linkname, MyFlags))
    result= -1;
  DBUG_RETURN(result);
#endif /* HAVE_READLINK */
}

#if defined(MAXPATHLEN)
#define BUFF_LEN MAXPATHLEN
#else
#define BUFF_LEN FN_LEN
#endif


int my_is_symlink(const char *filename MY_ATTRIBUTE((unused)),
                  ST_FILE_ID *file_id)
{
#if defined (HAVE_LSTAT) && defined (S_ISLNK)
  struct stat stat_buff;
  int result= !lstat(filename, &stat_buff) && S_ISLNK(stat_buff.st_mode);
  if (file_id && !result)
  {
    file_id->st_dev= stat_buff.st_dev;
    file_id->st_ino= stat_buff.st_ino;
  }
  return result;
#elif defined (_WIN32)
  DWORD dwAttr = GetFileAttributes(filename);
  return (dwAttr != INVALID_FILE_ATTRIBUTES) &&
    (dwAttr & FILE_ATTRIBUTE_REPARSE_POINT);
#else  /* No symlinks */
  return 0;
#endif
}

/*
  Resolve all symbolic links in path
  'to' may be equal to 'filename'
*/

int my_realpath(char *to, const char *filename, myf MyFlags)
{
#if defined(HAVE_REALPATH)
  int result=0;
  char buff[BUFF_LEN];
  char *ptr;
  DBUG_ENTER("my_realpath");

  DBUG_PRINT("info",("executing realpath"));
  if ((ptr=realpath(filename,buff)))
      strmake(to,ptr,FN_REFLEN-1);
  else
  {
    /*
      Realpath didn't work;  Use my_load_path() which is a poor substitute
      original name but will at least be able to resolve paths that starts
      with '.'.
    */
    DBUG_PRINT("error",("realpath failed with errno: %d", errno));
    set_my_errno(errno);
    if (MyFlags & MY_WME)
    {
      char errbuf[MYSYS_STRERROR_SIZE];
      my_error(EE_REALPATH, MYF(0), filename,
               my_errno(), my_strerror(errbuf, sizeof(errbuf), my_errno()));
    }
    my_load_path(to, filename, NullS);
    result= -1;
  }
  DBUG_RETURN(result);
#elif defined(_WIN32)
  int ret= GetFullPathName(filename,FN_REFLEN, to, NULL);
  if (ret == 0 || ret > FN_REFLEN)
  {
    set_my_errno((ret > FN_REFLEN) ? ENAMETOOLONG : GetLastError());
    if (MyFlags & MY_WME)
    {
      char errbuf[MYSYS_STRERROR_SIZE];
      my_error(EE_REALPATH, MYF(0), filename,
               my_errno(), my_strerror(errbuf, sizeof(errbuf), my_errno()));
    }
    /* 
      GetFullPathName didn't work : use my_load_path() which is a poor 
      substitute original name but will at least be able to resolve 
      paths that starts with '.'.
    */  
    my_load_path(to, filename, NullS);
    return -1;
  }
#else
  my_load_path(to, filename, NullS);
#endif
  return 0;
}


/**
  Return non-zero if the file descriptor and a previously lstat-ed file
  identified by file_id point to the same file
*/
int my_is_same_file(File file, const ST_FILE_ID *file_id)
{
  MY_STAT stat_buf;
  if (my_fstat(file, &stat_buf, MYF(0)) == -1)
  {
    set_my_errno(errno);
    return 0;
  }
  return (stat_buf.st_dev == file_id->st_dev)
    && (stat_buf.st_ino == file_id->st_ino);
}