Bitwise middleware

bitwise.middleware.node.js

function userCan(req,res,next) {                        // `req,res,next` is the standard Express middle argument signature (request, response and next middleware)
  const
    tempKey   = 'userCanTemp',                          // This can be any value
    routeKey  = rk(routePrefix,req.route.path),         // `rk` joins each argument with a colon, req.route.path is the Express route
    user      = req.query.user;                         // In this example, were getting the user from the query string, but you'd get it form another middleware most likely
  let
    userKey;                                          

  if (!user) {                                          // if `user` isn't defined, then we'll reject
    res.status(403).end();
  } else {
    userKey = rk(userPrefix,user);                      // create the user key with `rk`
  }

  client
    .multi()                                            // start the multi transaction
    .bitop('AND',tempKey,userKey,routeKey)              // The result of `userKey` AND'ed with `routeKey` and stored in `tempKey`
    .bitop('XOR',tempKey,tempKey,routeKey)              // The result of `tempKey` XOR'ed with `routeKey` and stored back in `tempKey`
    .bitcount(tempKey)                                  // count the bits in `tempKey`'s value
    .bitfield(rk(routeKey,'level'),'GET','u7','9')      // grabbing a unsigned 7-bit word from routeKey+':level'
    .bitfield(userKey,'GET','u7','9')                   // grabbing a unsigned 7-bit word from `userKey`
    .exec(function(err,responses) { 
      if (err) { next(err); } else {                    // handle errors
        let 
          capMisses = responses[2];                     // capability misses are stored in the 2nd result
        if (
          (capMisses === 0) &&                          // make sure no bits are misses
          (responses[3] >= responses[4])) {             // that the  user level is greater than the route level
          next();                                       // pass it on to the next middleware
        } else {
          res.status(401).end();                        // otherwise reject it.
        } 
      }
    });
}