code: function scan(sp, cb) {
      cb = u.onceMaybe(cb);
      var timer = u.timer();
      sp.route = sp.route || '/';
  
      var src = sp.src;
  
      // only construct src, defaults, sendOpts etc. once
      if (!src) {
        sp.name = sp.name || 'staticPath:' + sp.path;
        sp.depth = sp.depth || opts.staticDepth || 5;
        sp.maxAge = 'maxAge' in sp ? sp.maxAge : '10m';
        sp.includeBinaries = true;
        src = sp.src = fsbase(sp);
        if (src.isfile()) { sp.depth = 1; }
        sp.sendOpts = u.assign(
          u.pick(sp, 'maxAge', 'lastModified', 'etag'),
          { dotfiles:'ignore',
            index:false,      // handled at this level
            extensions:false, // ditto
            root:src.path } );
      }
  
      src.listfiles(function(err, files) {
        if (err) return cb(log(err));
        sp.files = files;
        self.scanCnt++;
        mapAllFiles();
        debug('static scan %s-deep %sms %s', sp.depth, timer(), sp.path.replace(/.*\/node_modules\//g, ''));
        debug(files.length > 10 ? '[' + files.length + ' files]' : u.pluck(files, 'filepath'));
        cb();
      });
    }
docs: repeatable scan for single staticPath