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/* vi: set sw=4 ts=4: */
/*
* xreadlink.c - safe implementation of readlink.
* Returns a NULL on failure...
*/
#include "libbb.h"
/*
* NOTE: This function returns a malloced char* that you will have to free
* yourself. You have been warned.
*/
char *xmalloc_readlink(const char *path)
{
enum { GROWBY = 80 }; /* how large we will grow strings by */
char *buf = NULL;
int bufsize = 0, readsize = 0;
do {
bufsize += GROWBY;
buf = xrealloc(buf, bufsize);
readsize = readlink(path, buf, bufsize);
if (readsize == -1) {
free(buf);
return NULL;
}
} while (bufsize < readsize + 1);
buf[readsize] = '\0';
return buf;
}
/*
* this routine is not the same as realpath(), which
* canonicalizes the given path completely. this routine only
* follows trailing symlinks until a real file is reached, and
* returns its name. if the path ends in a dangling link, or if
* the target doesn't exist, the path is returned in any case.
* intermediate symlinks in the path are not expanded -- only
* those at the tail.
* a malloced char* is returned, which must be freed by the caller.
*/
char *xmalloc_follow_symlinks(const char *path)
{
char *buf;
char *lpc;
char *linkpath;
int bufsize;
int looping = MAXSYMLINKS + 1;
buf = xstrdup(path);
goto jump_in;
while (1) {
linkpath = xmalloc_readlink(buf);
if (!linkpath) {
/* not a symlink, or doesn't exist */
if (errno == EINVAL || errno == ENOENT)
return buf;
free(buf);
return NULL;
}
if (!--looping) {
free(linkpath);
free(buf);
return NULL;
}
if (*linkpath != '/') {
bufsize += strlen(linkpath);
buf = xrealloc(buf, bufsize);
lpc = bb_get_last_path_component_strip(buf);
strcpy(lpc, linkpath);
free(linkpath);
} else {
free(buf);
buf = linkpath;
jump_in:
bufsize = strlen(buf) + 1;
}
}
}
char *xmalloc_readlink_or_warn(const char *path)
{
char *buf = xmalloc_readlink(path);
if (!buf) {
/* EINVAL => "file: Invalid argument" => puzzled user */
bb_error_msg("%s: cannot read link (not a symlink?)", path);
}
return buf;
}
/* UNUSED */
#if 0
char *xmalloc_realpath(const char *path)
{
#if defined(__GLIBC__) && !defined(__UCLIBC__)
/* glibc provides a non-standard extension */
return realpath(path, NULL);
#else
char buf[PATH_MAX+1];
/* on error returns NULL (xstrdup(NULL) ==NULL) */
return xstrdup(realpath(path, buf));
#endif
}
#endif
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