source: MondoRescue/branches/2.2.5/mindi-busybox/libbb/xreadlink.c

/* 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 {
        buf = xrealloc(buf, bufsize += GROWBY);
        readsize = readlink(path, buf, bufsize);
        if (readsize == -1) {
            free(buf);
            return NULL;
        }
    } while (bufsize < readsize + 1);

    buf[readsize] = '\0';

    return buf;
}

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