tmpfile-util: if no path is passed to fopen_temporary() make one up

Let's beef up functionality a bit, and modernize the whole function.

src/basic/tmpfile-util.c

@@ -19,38 +19,48 @@
 #include "tmpfile-util.h"
 #include "umask-util.h"
 
-int fopen_temporary(const char *path, FILE **_f, char **_temp_path) {
-        FILE *f;
-        char *t;
-        int r, fd;
+int fopen_temporary(const char *path, FILE **ret_f, char **ret_temp_path) {
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_free_ char *t = NULL;
+        _cleanup_close_ int fd = -1;
+        int r;
 
-        assert(path);
-        assert(_f);
-        assert(_temp_path);
+        if (path) {
+                r = tempfn_xxxxxx(path, NULL, &t);
+                if (r < 0)
+                        return r;
+        } else {
+                const char *d;
 
-        r = tempfn_xxxxxx(path, NULL, &t);
-        if (r < 0)
-                return r;
+                r = tmp_dir(&d);
+                if (r < 0)
+                        return r;
+
+                t = path_join(d, "XXXXXX");
+                if (!t)
+                        return -ENOMEM;
+        }
 
         fd = mkostemp_safe(t);
-        if (fd < 0) {
-                free(t);
+        if (fd < 0)
                 return -errno;
-        }
 
         /* This assumes that returned FILE object is short-lived and used within the same single-threaded
          * context and never shared externally, hence locking is not necessary. */
 
         r = fdopen_unlocked(fd, "w", &f);
         if (r < 0) {
-                unlink(t);
-                free(t);
-                safe_close(fd);
+                (void) unlink(t);
                 return r;
         }
 
-        *_f = f;
-        *_temp_path = t;
+        TAKE_FD(fd);
+
+        if (ret_f)
+                *ret_f = TAKE_PTR(f);
+
+        if (ret_temp_path)
+                *ret_temp_path = TAKE_PTR(t);
 
         return 0;
 }