feat: caching installation tokens

index.js

@@ -1,12 +1,14 @@
 module.exports = App
 
-const getSignedJsonWebToken = require('./lib/get-signed-json-web-token')
+const getCache = require('./lib/get-cache')
 const getInstallationAccesToken = require('./lib/get-installation-access-token')
+const getSignedJsonWebToken = require('./lib/get-signed-json-web-token')
 
-function App ({ id, privateKey }) {
+function App ({ id, privateKey, cache }) {
   const state = {
     id,
-    privateKey
+    privateKey,
+    cache: cache || getCache()
   }
   const api = {
     getSignedJsonWebToken: getSignedJsonWebToken.bind(null, state),

lib/get-cache.js

@@ -0,0 +1,13 @@
+module.exports = getCache
+
+// https://github.com/isaacs/node-lru-cache#readme
+const LRU = require('lru-cache')
+
+function getCache () {
+  return new LRU({
+    // cache max. 15000 tokens, that will use less than 10mb memory
+    max: 15000,
+    // Cache for 1 minute less than GitHub expiry
+    maxAge: 1000 * 60 * 59
+  })
+}

lib/get-installation-access-token.js

@@ -6,13 +6,22 @@ const getSignedJsonWebToken = require('./get-signed-json-web-token')
 
 // https://developer.github.com/v3/apps/#create-a-new-installation-token
 function getInstallationAccesToken (state, { installationId }) {
-  return request('POST /app/installations/:installation_id/access_tokens', {
+  const token = state.cache.get(installationId)
+  if (token) {
+    return Promise.resolve(token)
+  }
+
+  return request({
+    method: 'POST',
+    url: '/app/installations/:installation_id/access_tokens',
     installation_id: installationId,
     headers: {
       accept: 'application/vnd.github.machine-man-preview+json',
       // TODO: cache the installation token if it's been less than 60 minutes
       authorization: `bearer ${getSignedJsonWebToken(state)}`
     }
+  }).then(response => {
+    state.cache.set(installationId, response.data.token)
+    return response.data.token
   })
-    .then(response => response.data.token)
 }