/**
 * Copyright (c) Members of the EGEE Collaboration. 2010.
 * See http://www.eu-egee.org/partners/ for details on the copyright
 * holders.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Authors: Oscar Koeroo, Mischa Sall\'e, Aram Verstegen
 *      NIKHEF Amsterdam, the Netherlands
 *      <grid-mw-security@nikhef.nl>
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>

/* Make sure at least internally we have a PATH_MAX */
#ifndef PATH_MAX
#define PATH_MAX    1024
#endif

/* Make sure at least internally we have a SYMLOOP_MAX */
#ifndef SYMLOOP_MAX
#define SYMLOOP_MAX _POSIX_SYMLOOP_MAX
#endif

/*!
 * Returns the fully canonicalized and absolute path for a diretory or NULL on
 * error. Memory for the return string is malloced and should be freed by the
 * caller. Any path cannot be longer than PATH_MAX. Note that it is necessary
 * that we can chdir to dir.
 * NOTE: This function is not thread-safe
 * \param dir non-absolute and/or non-canonical directory
 * \return canonical absolute directory
 */
char *cgul_realdir(const char *dir) {
    int olddir;
    char buf[PATH_MAX],*path;

    /* Safe old dir and then go to the new one */
    if ( (olddir=open(".",O_RDONLY))==-1 ||
	 chdir(dir)==-1 )
	return NULL;
    /* Get the location, don't exit yet when failed: need to go back */
    path=getcwd(buf,PATH_MAX);
    /* Go back, note that it's really bad if this fails! */
    if ( fchdir(olddir) ||
	 close(olddir) )
	return NULL;
    /* Make a copy */
    if (path)
	path=strdup(buf);
    
    return path;
}

/*!
 * Returns the fully canonicalized and absolute path for any path or NULL on
 * error. Note that this function substitutes the unsafe realpath() or the
 * GNU-only canonicalize_file_name().
 * Memory for the return string is malloced and should be freed by the
 * caller. Any path cannot be longer than PATH_MAX. Any directory has to be
 * accessible, including if it's the last element.
 * NOTE: This function is not thread-safe
 * \param inpath non-absolute and/or non-canonical path
 * \param instat optional stat information on the input (for performance, if
 *               already available). When NULL it will be determined locally
 *               when needed.
 * \return canonical absolute path
 */
char *cgul_realpath(const char *inpath, struct stat *instat)	{
    char buf[PATH_MAX], path[PATH_MAX];
    char *pos,*canonicdir;
    int pathlen,filelen,linklen, linkcount=0;
    struct stat st;

    /* Check and store the length of the input (incl \0) */
    if ( (pathlen=1+strlen(inpath)) > PATH_MAX)	{
	errno=ENAMETOOLONG;
	return NULL;
    }
    /* Check last compo is dir: then just return realdir() */
    if (instat==NULL)	{
	if (stat(inpath, &st)==-1) /* Error */
	    return NULL;
	instat=&st;
    }
    if (S_ISDIR(instat->st_mode))
	return cgul_realdir(inpath);

    /* Make path absolute */
    if (inpath[0]!='/')	{ /* relative */
	/* get and add cwd */
	if (!getcwd(buf,PATH_MAX))  {
	    if (errno==ERANGE) errno=ENAMETOOLONG;
	    return NULL;
	}
	if ( (pathlen=snprintf(path,PATH_MAX,"%s/%s",buf,inpath))>PATH_MAX ) {
	    errno=ENAMETOOLONG;
	    return NULL;
	}
    } else /* absolute */
	strcpy(path,inpath);

    /* Now loop over symlink, if any */
    /* readlink wants buffersize without \0: PATH_MAX-1 */
    while ( (linklen=readlink(path,buf,PATH_MAX-1)) != -1 )   {
	if (++linkcount > SYMLOOP_MAX)	{ /* Too many symlinks */
	    errno=ELOOP;
	    return NULL;
	}
	buf[linklen]='\0';
	/* Check the symlink */
	if (buf[0]=='/')    /* absolute: replaces entire path */
	    strcpy(path,buf);
	else {	/* relative: replaces last component */
	    pos=strrchr(path,'/'); /* Has to exist, we made it absolute */
	    filelen=strlen(pos+1); /* length of remainder without \0 */
	    /* Note: pathlen is with \0, filelen and linklen without, hence
	     * combined as follows is with \0 and should be <= PATH_MAX */
	    if (pathlen-filelen+linklen>PATH_MAX)  {
		errno=ENAMETOOLONG;
		return NULL;
	    }
	    strcpy(pos+1,buf); /* It fits, so use strcpy */
	}
    }
    /* Alway end due to realink: check it's due to non-symlink */
    if (errno!=EINVAL) /* i.e. other error */
	return NULL;

    /* Now path is not a symlink */

    /* Find dir part */
    pos=strrchr(path,'/'); /* Has to exist, we made it absolute */
    /* dir: up to pos, file: pos+1 till end */
    pos[0]='\0';
    canonicdir=cgul_realdir(path);
    pos[0]='/'; /* Clean but unnecessary */
    /* Put them together, canonicdir doesn't end with a / */
    pathlen=snprintf(buf,PATH_MAX,"%s/%s",canonicdir,pos+1);
    free(canonicdir); /* Done with canonicdir */
    if (pathlen>PATH_MAX)   {
	errno=ENAMETOOLONG;
	return NULL;
    }

    /* Return duplicate, or NULL when fails */
    return strdup(buf);
}