Implement lfs.realpath()

src/lfs.c

@@ -12,6 +12,7 @@
 **   lfs.lock (fh, mode)
 **   lfs.lock_dir (path)
 **   lfs.mkdir (path)
+**   lfs.realpath (path)
 **   lfs.rmdir (path)
 **   lfs.setmode (filepath, mode)
 **   lfs.symlinkattributes (filepath [, attributename])
@@ -909,6 +910,35 @@ static int link_info (lua_State *L) {
         return ret;
 }
 
+/*
+** Retrieve canonicalized absolute pathname using realpath()
+** Upon success the function returns the resolved path, otherwise the return
+** values are `nil`, an error message (string) and the error number.
+**
+** Note that the Windows implementation differs from the POSIX function,
+** for example it doesn't test if the resolved path is actually reachable.
+** E.g. "C:\foo\..\bar" will happily resolve to "C:\bar",
+** even if neither C:\foo nor C:\bar exist.
+*/
+static int get_realpath (lua_State *L) {
+        const char *path = luaL_checkstring (L, 1);
+        char *resolved;
+#ifdef _WIN32
+        resolved = _fullpath(NULL, path, 0);
+#else
+        resolved = realpath(path, NULL);
+#endif
+        if (resolved) {
+                lua_pushstring(L, resolved);
+                free(resolved);
+                return 1;
+        }
+        /* an error occured */
+        lua_pushnil(L);
+        lua_pushfstring(L, "lfs.realpath('%s') failed: %s", path, strerror(errno));
+        lua_pushinteger(L, errno);
+        return 3;
+}
 
 /*
 ** Assumes the table is on top of the stack.
@@ -931,6 +961,7 @@ static const struct luaL_Reg fslib[] = {
         {"link", make_link},
         {"lock", file_lock},
         {"mkdir", make_dir},
+        {"realpath", get_realpath},
         {"rmdir", remove_dir},
         {"symlinkattributes", link_info},
         {"setmode", lfs_f_setmode},

tests/test.lua

@@ -65,6 +65,20 @@ f:close()
 io.write(".")
 io.flush()
 
+-- Check that realpath can resolve the parent of tmpdir (= "current")
+assert(lfs.realpath(tmpdir..sep.."..") == current)
+
+-- Non-existent paths will error on POSIX (errno 2), but not on Windows!
+local ok, err = lfs.realpath("C:\\foo\\..\\bar")
+if not ok then
+        assert(err:match("No such file or directory"))
+else
+        assert(ok == "C:\\bar")
+end
+
+io.write(".")
+io.flush()
+
 -- Change access time
 local testdate = os.time({ year = 2007, day = 10, month = 2, hour=0})
 assert (lfs.touch (tmpfile, testdate))
@@ -95,6 +109,7 @@ if lfs.link (tmpfile, "_a_link_for_test_", true) then
   assert (lfs.symlinkattributes("_a_link_for_test_", "target") == tmpfile)
   assert (lfs.link (tmpfile, "_a_hard_link_for_test_"))
   assert (lfs.attributes (tmpfile, "nlink") == 2)
+  assert (lfs.realpath"_a_link_for_test_" == tmpfile)
   assert (os.remove"_a_link_for_test_")
   assert (os.remove"_a_hard_link_for_test_")
 end