gofer

gofer

A gofer, go-fer or gopher /ˈɡoʊfər/ is an employee who specializes in delivery of special items to their superior(s). The special items may be anything from a cup of coffee to a tailored suit or a car.

— Wikipedia: Gofer

npm install --save gofer

A base class for HTTP clients. Usable in node, browsers, and react-native. The design is meant to enforce a certain level of consistency in how the clients are configured and instrumented.

Use in browsers might require a fetch polyfill.

If you used gofer 2.x before, you might want to read about all the changes in 3.x.

API docs • Walkthrough

Features

Options mappers

Option mappers are called in the order they are registered in and can potentially do anything they want. This can range from applying defaults over resolving custom api options to injecting access tokens.

Defaults merging

All configuration is just defaults which is one of the things making option mappers so powerful. The precedence rules are (first wins):

1. Explicit configuration in the API call
2. Scoped overrides using client.with(options)
3. Endpoint-level defaults
4. Service-level defaults
5. Global defaults

See the walkthrough below for how these are configured.

Copy with defaults / scoped overrides

You can create a copy of the API with hard defaults using with. This enables a nice pattern:

// We'll assume MyApiClient has an option mapper than knows how to
// properly send an accessToken, e.g. using an Authentication header
var client = new MyApiClient(config);

// After retrieving an access token
var authenticatedClient = client.with({ accessToken: 'some-token' });

// This one will now send an access token
// ~> `curl -H 'Authentication: Bearer some-token' \
//          http://api.example.com/personal/some-id`
authenticatedClient.protectedResource('some-id');

// This one was not changed, so it will not send one
// ~> `curl http://api.example.com/personal/some-id`
client.protectedResource('some-id');

This sounds great, but...

Why not use service specific client libraries?

Well, in a way that's what gofer encourages. The difference is that by basing all client libraries on this one, you gain consistency and unified configuration. Creating a client for a new service often takes just a couple of lines.

Why not use request?

request is a great swiss army knive for making API calls. This makes it an awesome first pick if you're looking for a quick way to talk to a wide variety of 3rd party services. But it's lacking in a few areas we care a lot about:

• Good, predictable error handling
• Flexible configuration
• Instrumentation friendly

Walkthrough

Let's say we need a client for the Github API. The first step is to generate a Github client class:

var Gofer = require('gofer');

var pkg = require('./package.json')

function Github(config) {
  Gofer.call(this, config, 'github', pkg.version, pkg.name);
}
Github.prototype = Object.create(Gofer.prototype);
Github.prototype.constructor = Github;

The name you choose here ("github") determines which section of the configuration it will accept. It's also part of the instrumentation as serviceName.

Let's define a simple endpoint to get the emojis from Github:

Github.prototype.registerEndpoints({
  // Every instance of Github will get an `emojis` property. On
  // access it will be initialized with an instrumented version of the
  // `fetch` function. The `fetch` function works similar to WHATWG/fetch.
  emojis: function(fetch) {
    // the value returned here will be what users see in `new Github().emojis`
    return function(cb) {
      // fetch(uri: string, options: object?, callback: function?)
      return fetch('/emojis', {}, cb);
    };
  },
});

To create an instance, we need to provide configuration. Configuration exists on three levels: global, per-service, and per-endpoint.

var config = {
  globalDefaults: {
    // these apply to all gofers
    connectTimeout: 30,
    timeout: 100,
  },
  github: {
    // these apply for every call made with Github
    clientId: '<VALID CLIENT ID HERE>',
    endpointDefaults: {
      // these only apply for calls to the emojis endpoint
      emojis: {
        connectTimeout: 100,
        timeout: 2000,
      },
    },
  },
};

To make our client a little nicer to use we'll add an option mapper that defaults baseUrl to the public Github API. The options we return will be passed on to fetch.

var assign = require('lodash/assign');
Github.prototype.addOptionMapper(function(opts) {
  // opts contains the already merged options, including global-, service-,
  // and endpoint-defaults. In our example opts.timeout will be 2000, etc.
  return assign({ baseUrl: 'https://api.github.com' }, opts);
});

Finally we can instantiate and make the call:

var github = new Github(config);

// The `fetch`-style:
github.emojis()
  .then(function (res) {
    return res.json();
  })
  .done(function (emojiList) {
    console.log('Returned %d emojis', Object.keys(emojiList).length);
  });

// Using the added convenience of req.json()
github.emojis().json()
  .done(function (emojiList) {
    console.log('Returned %d emojis', Object.keys(emojiList).length);
  });

// Or, using the callback interface:
github.emojis(function (error, emojiList, response) {
  if (error) throw error;
  console.log('Returned %d emojis', Object.keys(emojiList).length);
  console.log('Response status %d', response.statusCode);
});

You can check examples/github.js for a richer example.