如何使用蓝鸟来保证节点休息客户端

Question

I'm trying to promisify the node-rest-client library (tried restler but seems not to be re-entrant and caused problems with parallel POSTs to same endpoint).

I've tried to use a similar approach to the provided filter/promisifer shown in the bluebird docs for restler, however can't seem to get it working.

node-rest-client uses a combination of callback function with two arguments for successful response whilst also providing an event emitter for timeouts and errors.

var Promise = require("bluebird");
var methodNamesToPromisify = "get post put del patch".split(" ");

function EventEmitterPromisifier(originalMethod) {
    // return a function
    return function promisified() {
        var args = [].slice.call(arguments);
        var self = this;
        return new Promise(function(resolve, reject) {
            var emitter = originalMethod.apply(self, args, function(data, response){
              resolve([data, response]);
            });

            emitter
                .on("error", function(err) {
                    reject(err);
                })
                .on("requestTimeout", function() {
                    reject(new Promise.TimeoutError());
                })
                .on("responseTimeout", function() {
                    reject(new Promise.TimeoutError());
                });
        });
    };
};

exports.promisifyClient = function(restClient){

  Promise.promisifyAll(restClient, {
      filter: function(name) {
          return methodNamesToPromisify.indexOf(name) > -1;
      },
      promisifier: EventEmitterPromisifier
  });
}

and elsewhere in the code:

var Client = require('node-rest-client').Client;

var constants = require('../../config/local.env');

var restClient = new Client();
promisifyClient(restClient);

which successfully adds promisified functions to restClient

However, when I call postAsync(url, options).then(...) the node-rest-client library throws an error saying the callback is undefined.

As far s I can see this should work, but it seems the callback function provided in the promisifier isn't making it through to the library.

I'm hoping someone with more experience in Bluebird might be able to see what I'm doing wrong.

Answer 1

The .apply method does only take two arguments - the this context and an arguments array - but you are passing three.

You'll need to put the callback onto the array to get it passed as the last argument to originalmethod :

function EventEmitterPromisifier(originalMethod) {
    return function promisified() {
        var args = [].slice.call(arguments),
            self = this;
        return new Promise(function(resolve, reject) {
            function timeout() {
                reject(new Promise.TimeoutError());
            }
            args.push(function(data, response){
                resolve([data, response]);
            });
            originalMethod.apply(self, args)
//                                     ^^^^
            .on("error", reject)
            .on("requestTimeout", timeout)
            .on("responseTimeout", timeout);
        });
    };
}