Add BaseGraphqlService, support [github] V4 API (#3763)

* add base class for Graphql APIs
* add GithubAuthV4Service + updates to GH token pool
* update github forks to use GithubAuthV4Service
* rename GithubAuthService to GithubAuthV3Service

services/github/github-auth-service.js

@@ -1,20 +1,23 @@
 'use strict'
 
+const gql = require('graphql-tag')
+const { mergeQueries } = require('../../core/base-service/graphql')
 const { staticAuthConfigured } = require('./github-helpers')
 const { BaseJsonService } = require('..')
+const { BaseGraphqlService } = require('..')
 
 function createRequestFetcher(context, config) {
   const { sendAndCacheRequestWithCallbacks, githubApiProvider } = context
 
-  return async (url, { qs }) =>
+  return async (url, options) =>
     githubApiProvider.requestAsPromise(
       sendAndCacheRequestWithCallbacks,
       url,
-      qs
+      options
     )
 }
 
-class GithubAuthService extends BaseJsonService {
+class GithubAuthV3Service extends BaseJsonService {
   constructor(context, config) {
     super(context, config)
     this._requestFetcher = createRequestFetcher(context, config)
@@ -23,11 +26,11 @@ class GithubAuthService extends BaseJsonService {
 }
 
 // Use Github auth, but only when static auth is configured. By using this
-// class, in production it will behave like GithubAuthService, and in self-
+// class, in production it will behave like GithubAuthV3Service, and in self-
 // hosting (i.e. with a configured token) like BaseJsonService. This is
 // useful when consuming GitHub endpoints which are not rate-limited: it
 // avoids wasting API quota on them in production.
-class ConditionalGithubAuthService extends BaseJsonService {
+class ConditionalGithubAuthV3Service extends BaseJsonService {
   constructor(context, config) {
     super(context, config)
     if (staticAuthConfigured()) {
@@ -39,7 +42,57 @@ class ConditionalGithubAuthService extends BaseJsonService {
   }
 }
 
-module.exports = {
-  GithubAuthService,
-  ConditionalGithubAuthService,
+class GithubAuthV4Service extends BaseGraphqlService {
+  constructor(context, config) {
+    super(context, config)
+    this._requestFetcher = createRequestFetcher(context, config)
+    this.staticAuthConfigured = true
+  }
+
+  async _requestGraphql(attrs) {
+    const url = `/graphql`
+
+    /*
+    The Github v4 API requires us to query the rateLimit object to return
+    rate limit info in the query body instead of the headers:
+    https://developer.github.com/v4/guides/resource-limitations/#returning-a-calls-rate-limit-status
+    This appends the relevant rateLimit query clause to each
+    call to the GH v4 API so we can keep track of token usage.
+    */
+    const query = mergeQueries(
+      attrs.query,
+      gql`
+        query {
+          rateLimit {
+            limit
+            cost
+            remaining
+            resetAt
+          }
+        }
+      `
+    )
+
+    return super._requestGraphql({ ...attrs, ...{ url, query } })
+  }
+}
+
+/*
+Choosing between the Github V3 and V4 APIs when creating a new badge:
+
+With the V3 API, one request = one point off the usage limit.
+With the V4 API one request may be many points off the usage limit depending
+on the query (but will be a minimum of one).
+https://developer.github.com/v4/guides/resource-limitations/#calculating-nodes-in-a-call
+
+If we can save ourselves some usage limit it may be worth going with a
+REST (V3) call over a graphql query.
+All other things being equal, a graphql query will almost always be a smaller
+number of bytes over the wire and a smaller/simpler object to parse.
+*/
+
+module.exports = {
+  GithubAuthV3Service,
+  ConditionalGithubAuthV3Service,
+  GithubAuthV4Service,
 }