ReactRelayNetworkLayer

The ReactRelayNetworkLayer is a Relay Network Layer with query batching and middleware support.

Main purpose to use this NetworkLayer:

• If your app is making enough individual queries to be a performance problem on first page load
• If your app should manipulate request on the fly - log them, change or made some fallbacks if request fails

Available middlewares:

• url - for manipulating fetch url on fly via thunk. Options:
  • url - string or function(req) for single request (default: /graphql)
  • batchUrl - string or function(req) for batch request, server must be prepared for such requests (default: /graphql/batch)
• retry - for request retry if the initial request fails. Options:
  • fetchTimeout - number in milliseconds that defines in how much time will request timeout after it has been sent to the server (default: 15000).
  • retryDelays - array of millisecond that defines the values on which retries are based on (default: [1000, 3000]).
  • statusCodes - array of response status codes which will fire up retryMiddleware (default: status < 200 or status > 300).
  • allowMutations - by default retries disabled for mutations, you may allow process retries for them passing true (default: false)
  • forceRetry - function(cb, delay), when request is delayed for next retry, middleware will call this function and pass to it a callback and delay time. When you call this callback, middleware will proceed request immediately (default: false).
• auth - for adding auth token, and refreshing it if gets 401 response from server. Options:
  • token - string or function(req) which returns token. If function is provided, then it will be called for every request (so you may change tokens on fly).
  • tokenRefreshPromise: - function(req, err) which must return promise with new token, called only if server returns 401 status code and this function is provided.
  • prefix - prefix before token (default: 'Bearer ')
  • If you use auth middleware with retry, retry must be used before auth. Eg. if token expired when retries apply, then retry can call auth middleware again.
• logger - for logging requests and responses. Options:
  • logger - log function (default: console.log.bind(console, '[RELAY-NETWORK]'))
  • If you use Relay@^0.9.0 you may turn on relay's internal extended mutation debugger. For this you should open browser console and type __DEV__=true. With webpack you may use webpack.BannerPlugin('__DEV__=true;', {raw: true}) or webpack.DefinePlugin({__DEV__: true}).
  • If you use Relay@^0.8.0 you may turn on internal Relay requests debugger: import RelayNetworkDebug from 'react-relay/lib/RelayNetworkDebug'; RelayNetworkDebug.init();
• perf - simple time measure for network request. Options:
  • logger - log function (default: console.log.bind(console, '[RELAY-NETWORK]'))
• gqErrors - display errors data to console from graphql response. If you want see stackTrace for errors, you should tune formatError param in graphqlHTTP (see example below). Options:
  • logger - log function (default: console.error.bind(console))
  • prefix - prefix message (dafault: [RELAY-NETWORK] GRAPHQL SERVER ERROR:)
• defer - experimental Right now deferMiddleware() just set defer as supported option for Relay. So this middleware allow to community play with defer() in cases, which was described by @wincent.

CHANGELOG

Installation

npm install react-relay-network-layer

Part 1: Batching several requests into one

Joseph Savona wrote: For legacy reasons, Relay splits "plural" root queries into individual queries. In general we want to diff each root value separately, since different fields may be missing for different root values.

Also if you use react-relay-router and have multiple root queries in one route pass, you may notice that default network layer will produce several http requests.

So for avoiding multiple http-requests, the ReactRelayNetworkLayer is the right way to combine it in single http-request.

Example how to enable batching

...on server

Firstly, you should prepare server to proceed the batch request:

import express from 'express';
import graphqlHTTP from 'express-graphql';
import { graphqlBatchHTTPWrapper } from 'react-relay-network-layer';
import bodyParser from 'body-parser';
import myGraphqlSchema from './graphqlSchema';

// setup standart `graphqlHTTP` express-middleware
const graphQLMiddleware = graphqlHTTP({ 
  schema: myGraphqlSchema,
  formatError: (error) => ({ // better errors for development. `stack` used in `gqErrors` middleware
    message: error.message,
    stack: process.env.NODE_ENV === 'development' ? error.stack.split('\n') : null,
  }),
});

// declare route for batch query
server.use('/graphql/batch',
  bodyParser.json(),
  graphqlBatchHTTPWrapper(graphQLMiddleware)
);

// declare standard graphql route
server.use('/graphql',
  graphQLMiddleware
);

...on client

And right after server side ready to accept batch queries, you may enable batching on the client:

Relay.injectNetworkLayer(new RelayNetworkLayer([
  urlMiddleware({
    url: '/graphql',
    batchUrl: '/graphql/batch', // <--- route for batch queries 
  }),
], { disableBatchQuery: false })); // <--- set to FALSE, or may remove `disableBatchQuery` option at all

How batching works internally

Internally batching in NetworkLayer prepare list of queries [ {id, query, variables}, ...] sends it to server. And server returns list of responces [ {id, payload}, ...], (where id is the same value as client requested for identifying which data goes with which query, and payload is standard response of GraphQL server: { data, error }).

Part 2: Middlewares

Example of injecting NetworkLayer with middlewares on the client side.

import Relay from 'react-relay';
import {
  RelayNetworkLayer, retryMiddleware, urlMiddleware, authMiddleware, loggerMiddleware, 
  perfMiddleware, gqErrorsMiddleware
} from 'react-relay-network-layer';

Relay.injectNetworkLayer(new RelayNetworkLayer([
  urlMiddleware({
    url: (req) => '/graphql',
  }),
  loggerMiddleware(),
  gqErrorsMiddleware(),
  perfMiddleware(),
  retryMiddleware({
    fetchTimeout: 15000,
    retryDelays: (attempt) => Math.pow(2, attempt + 4) * 100, // or simple array [3200, 6400, 12800, 25600, 51200, 102400, 204800, 409600],
    forceRetry: (cb, delay) => { window.forceRelayRetry = cb; console.log('call `forceRelayRetry()` for immediately retry! Or wait ' + delay + ' ms.'); },
    statusCodes: [500, 503, 504]
  }),
  authMiddleware({
    token: () => store.get('jwt'),
    tokenRefreshPromise: (req) => {
      console.log('[client.js] resolve token refresh', req);
      return fetch('/jwt/refresh')
        .then(res => res.json())
        .then(json => {
          const token = json.token;
          store.set('jwt', token);
          return token;
        })
        .catch(err => console.log('[client.js] ERROR can not refresh token', err));
    },
  }),
  
  // example of the custom inline middleware (add `X-Request-ID` to request headers)
  next => req => {
    req.headers['X-Request-ID'] = uuid.v4();
    return next(req);
  }
], { disableBatchQuery: true }));

How middlewares work internally

Middlewares on bottom layer use fetch method. So req is compliant with a fetch() options. And res can be obtained via resPromise.then(res => ...), which returned by fetch().

Middlewares have 3 phases:

• setup phase, which runs only once, when middleware added to the NetworkLayer
• capturing phase, when you may change request object, and pass it down via next(req)
• bubbling phase, when you may change response promise, made re-request or pass it up unchanged

Basic skeleton of middleware:

export default function skeletonMiddleware(opts = {}) {
  // [SETUP PHASE]: here you can process `opts`, when you create Middleware
  
  return next => req => {
    // [CAPTURING PHASE]: here you can change `req` object, before it will pass to following middlewares.
    // ...some code which modify `req`
    
    const resPromise = next(req); // pass request to following middleware and get response promise from it
    
    // [BUBBLING PHASE]: here you may change response of underlying middlewares, via promise syntax 
    // ...some code, which may add `then()` or `catch()` to response promise
    //    resPromise.then(res => { console.log(res); return res; })
    
    return resPromise; // return response promise to upper middleware 
  };
}

Middlewares use LIFO (last in, first out) stack. Or simply put - use compose function. So if you pass such middlewares [M1(opts), M2(opts)] to NetworkLayer it will be work such way:

• call setup phase of M1 with its opts
• call setup phase of M2 with its opts
• for each request
• call capture phase of M1
• call capture phase of M2
• call fetch method
• call bubbling phase of M2
• call bubbling phase of M1
• chain to resPromise.then(res => res.json()) and pass this promise for resolving/rejecting Relay requests.

TODO

• Support defer, see relay/issues/288
• Rewrite batching as middleware, keep in mind principles of how works DataLoader via eventLoop (process.nextTick())
• [*] Improve performance of graphqlBatchHTTPWrapper, by removing JSON.parse (need find proper way how to get result from express-graphql in json, not stringified)
• Write server side middleware for express-graphql.
• Find brave peoples
• who made fixes and remove misspelling and missunderstanding in readme.MD
• may be write tests (I haven't enough experience in it)

Contribute

I actively welcome pull requests with code and doc fixes. Also if you made great middleware and want share it within this module, please feel free to open PR.

License

MIT