minix/lib/other/realpath.c

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2009-12-04 08:52:22 +01:00
/* realpath() - resolve absolute path Author: Erik van der Kouwe
* 4 December 2009
*
* Based on this specification:
* http://www.opengroup.org/onlinepubs/000095399/functions/realpath.html
*/
#include <errno.h>
#include <limits.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
static char *append_path_component(char *path, const char *component,
size_t component_length);
static char *process_path_component(const char *component,
size_t component_length, char *resolved_name, int last_part, int max_depth);
static char *realpath_recurse(const char *file_name, char *resolved_name,
int max_depth);
static char *remove_last_path_component(char *path);
static char *append_path_component(char *path, const char *component,
size_t component_length)
{
size_t path_length, slash_length;
/* insert or remove a slash? */
path_length = strlen(path);
slash_length =
((path[path_length - 1] == '/') ? 0 : 1) +
((component[0] == '/') ? 0 : 1) - 1;
/* check whether this fits */
if (path_length + slash_length + component_length >= PATH_MAX)
{
errno = ENAMETOOLONG;
return NULL;
}
/* insert slash if needed */
if (slash_length > 0)
path[path_length] = '/';
/* copy the bytes */
memcpy(path + path_length + slash_length, component, component_length);
path[path_length + slash_length + component_length] = 0;
return path;
}
static char *process_path_component(const char *component,
size_t component_length, char *resolved_name, int last_part, int max_depth)
{
char readlink_buffer[PATH_MAX + 1];
ssize_t readlink_buffer_length;
struct stat stat_buffer;
/* handle zero-length components */
if (!component_length)
{
if (last_part)
return resolved_name;
else
{
errno = ENOENT;
return NULL;
}
}
/* ignore current directory components */
if (component_length == 1 && component[0] == '.')
return resolved_name;
/* process parent directory components */
if (component_length == 2 && component[0] == '.' && component[1] == '.')
return remove_last_path_component(resolved_name);
/* not a special case, so just add the component */
if (!append_path_component(resolved_name, component, component_length))
return NULL;
/* stat partially resolved file */
if (lstat(resolved_name, &stat_buffer) < 0)
{
if (last_part && errno == ENOENT)
return resolved_name;
else
return NULL;
}
if (S_ISLNK(stat_buffer.st_mode))
{
/* resolve symbolic link */
readlink_buffer_length = readlink(resolved_name, readlink_buffer,
sizeof(readlink_buffer) - 1);
if (readlink_buffer_length < 0)
return NULL;
readlink_buffer[readlink_buffer_length] = 0;
/* recurse to resolve path in link */
remove_last_path_component(resolved_name);
if (!realpath_recurse(readlink_buffer, resolved_name, max_depth - 1))
return NULL;
/* stat symlink target */
if (lstat(resolved_name, &stat_buffer) < 0)
{
if (last_part && errno == ENOENT)
return resolved_name;
else
return NULL;
}
}
/* non-directories may appear only as the last component */
if (!last_part && !S_ISDIR(stat_buffer.st_mode))
{
errno = ENOTDIR;
return NULL;
}
return resolved_name;
}
static char *realpath_recurse(const char *file_name, char *resolved_name,
int max_depth)
{
const char *file_name_component;
/* avoid infinite recursion */
if (max_depth <= 0)
{
errno = ELOOP;
return NULL;
}
/* relative to root or to current? */
if (file_name[0] == '/')
{
/* relative to root */
resolved_name[0] = '/';
resolved_name[1] = '\0';
file_name++;
}
/* process the path component by component */
while (*file_name)
{
/* extract a slash-delimited component */
file_name_component = file_name;
while (*file_name && *file_name != '/')
file_name++;
/* check length of component */
if (file_name - file_name_component > PATH_MAX)
{
errno = ENAMETOOLONG;
return NULL;
}
/* add the component to the current result */
if (!process_path_component(
file_name_component,
file_name - file_name_component,
resolved_name,
!*file_name,
max_depth))
return NULL;
/* skip the slash */
if (*file_name == '/')
file_name++;
}
return resolved_name;
}
static char *remove_last_path_component(char *path)
{
char *current, *slash;
/* find the last slash */
slash = NULL;
for (current = path; *current; current++)
if (*current == '/')
slash = current;
/* truncate after the last slash, but do not remove the root */
if (slash > path)
*slash = 0;
else if (slash == path)
slash[1] = 0;
return path;
}
char *realpath(const char *file_name, char *resolved_name)
{
/* check parameters */
if (!file_name || !resolved_name)
{
errno = EINVAL;
return NULL;
}
if (strlen(file_name) > PATH_MAX)
{
errno = ENAMETOOLONG;
return NULL;
}
/* basis to resolve against: root or CWD */
if (file_name[0] == '/')
*resolved_name = 0;
else if (!getcwd(resolved_name, PATH_MAX))
return NULL;
/* do the actual work */
return realpath_recurse(file_name, resolved_name, SYMLOOP_MAX);
}