feat: support customize dns lookup function (#723)

Since Redis cluster doesn't support hostname at all (redis/redis#2410),
it's reasonable to resolve the hostnames to IPs before connecting.

lib/cluster/ClusterOptions.ts

@@ -1,4 +1,7 @@
 import {NodeRole} from './util'
+import {lookup} from 'dns'
+
+export type DNSLookupFunction = (hostname: string, callback: (err: NodeJS.ErrnoException, address: string, family: number) => void) => void
 
 /**
  * Options for Cluster constructor
@@ -93,9 +96,26 @@ export interface IClusterOptions {
   redisOptions?: any
 
   /**
+   * By default, When a new Cluster instance is created,
+   * it will connect to the Redis cluster automatically.
+   * If you want to keep the instance disconnected until the first command is called,
+   * set this option to `true`.
+   *
    * @default false
    */
   lazyConnect?: boolean
+
+  /**
+   * Hostnames will be resolved to IP addresses via this function.
+   * This is needed when the addresses of startup nodes are hostnames instead
+   * of IPs.
+   *
+   * You may provide a custom `lookup` function when you want to customize
+   * the cache behavior of the default function.
+   *
+   * @default require('dns').lookup
+   */
+  dnsLookup?: DNSLookupFunction
 }
 
 export const DEFAULT_CLUSTER_OPTIONS: IClusterOptions = {
@@ -108,5 +128,6 @@ export const DEFAULT_CLUSTER_OPTIONS: IClusterOptions = {
   retryDelayOnClusterDown: 100,
   retryDelayOnTryAgain: 100,
   slotsRefreshTimeout: 1000,
-  slotsRefreshInterval: 5000
+  slotsRefreshInterval: 5000,
+  dnsLookup: lookup
 }

lib/cluster/index.ts

@@ -2,16 +2,16 @@ import {EventEmitter} from 'events'
 import ClusterAllFailedError from '../errors/ClusterAllFailedError'
 import {defaults, noop} from '../utils/lodash'
 import ConnectionPool from './ConnectionPool'
-import {NodeKey, IRedisOptions, normalizeNodeOptions, NodeRole} from './util'
+import {NodeKey, IRedisOptions, normalizeNodeOptions, NodeRole, getUniqueHostnamesFromOptions} from './util'
 import ClusterSubscriber from './ClusterSubscriber'
 import DelayQueue from './DelayQueue'
 import ScanStream from '../ScanStream'
-import {AbortError} from 'redis-errors'
+import {AbortError, RedisError} from 'redis-errors'
 import * as asCallback from 'standard-as-callback'
 import * as PromiseContainer from '../promiseContainer'
 import {CallbackFunction} from '../types';
 import {IClusterOptions, DEFAULT_CLUSTER_OPTIONS} from './ClusterOptions'
-import {sample, CONNECTION_CLOSED_ERROR_MSG, shuffle, timeout} from '../utils'
+import {sample, CONNECTION_CLOSED_ERROR_MSG, shuffle, timeout, zipMap} from '../utils'
 import * as commands from 'redis-commands'
 
 const Deque = require('denque')
@@ -30,7 +30,7 @@ type ClusterStatus = 'end' | 'close' | 'wait' | 'connecting' | 'connect' | 'read
  */
 class Cluster extends EventEmitter {
   private options: IClusterOptions
-  private startupNodes: IRedisOptions[]
+  private startupNodes: Array<string | number | object>
   private connectionPool: ConnectionPool
   private slots: Array<NodeKey[]> = []
   private manuallyClosing: boolean
@@ -43,6 +43,18 @@ class Cluster extends EventEmitter {
   private status: ClusterStatus
   private isRefreshing: boolean = false
 
+  /**
+   * Every time Cluster#connect() is called, this value will be
+   * auto-incrementing. The purpose of this value is used for
+   * discarding previous connect attampts when creating a new
+   * connection.
+   *
+   * @private
+   * @type {number}
+   * @memberof Cluster
+   */
+  private connectionEpoch: number = 0
+
   /**
    * Creates an instance of Cluster.
    *
@@ -54,7 +66,7 @@ class Cluster extends EventEmitter {
     super()
     Commander.call(this)
 
-    this.startupNodes = normalizeNodeOptions(startupNodes)
+    this.startupNodes = startupNodes
     this.options = defaults(this.options, options, DEFAULT_CLUSTER_OPTIONS)
 
     // validate options
@@ -117,59 +129,68 @@ class Cluster extends EventEmitter {
         reject(new Error('Redis is already connecting/connected'))
         return
       }
+      const epoch = ++this.connectionEpoch
       this.setStatus('connecting')
 
-      if (!Array.isArray(this.startupNodes) || this.startupNodes.length === 0) {
-        throw new Error('`startupNodes` should contain at least one node.')
-      }
-
-      this.connectionPool.reset(this.startupNodes)
-
-      function readyHandler() {
-        this.setStatus('ready')
-        this.retryAttempts = 0
-        this.executeOfflineCommands()
-        this.resetNodesRefreshInterval()
-        resolve()
-      }
+      this.resolveStartupNodeHostnames().then((nodes) => {
+        if (this.connectionEpoch !== epoch) {
+          debug('discard connecting after resolving startup nodes because epoch not match: %d != %d', epoch, this.connectionEpoch)
+          reject(new RedisError('Connection is discarded because a new connection is made'))
+          return
+        }
+        if (this.status !== 'connecting') {
+          debug('discard connecting after resolving startup nodes because the status changed to %s', this.status)
+          reject(new RedisError('Connection is aborted'))
+          return
+        }
+        this.connectionPool.reset(nodes)
+
+        function readyHandler() {
+          this.setStatus('ready')
+          this.retryAttempts = 0
+          this.executeOfflineCommands()
+          this.resetNodesRefreshInterval()
+          resolve()
+        }
 
-      let closeListener: () => void
-      const refreshListener = () => {
-        this.removeListener('close', closeListener)
-        this.manuallyClosing = false
-        this.setStatus('connect')
-        if (this.options.enableReadyCheck) {
-          this.readyCheck((err, fail) => {
-            if (err || fail) {
-              debug('Ready check failed (%s). Reconnecting...', err || fail)
-              if (this.status === 'connect') {
-                this.disconnect(true)
+        let closeListener: () => void
+        const refreshListener = () => {
+          this.removeListener('close', closeListener)
+          this.manuallyClosing = false
+          this.setStatus('connect')
+          if (this.options.enableReadyCheck) {
+            this.readyCheck((err, fail) => {
+              if (err || fail) {
+                debug('Ready check failed (%s). Reconnecting...', err || fail)
+                if (this.status === 'connect') {
+                  this.disconnect(true)
+                }
+              } else {
+                readyHandler.call(this)
               }
-            } else {
-              readyHandler.call(this)
-            }
-          })
-        } else {
-          readyHandler.call(this)
+            })
+          } else {
+            readyHandler.call(this)
+          }
         }
-      }
 
-      closeListener = function () {
-        this.removeListener('refresh', refreshListener)
-        reject(new Error('None of startup nodes is available'))
-      }
+        closeListener = function () {
+          this.removeListener('refresh', refreshListener)
+          reject(new Error('None of startup nodes is available'))
+        }
 
-      this.once('refresh', refreshListener)
-      this.once('close', closeListener)
-      this.once('close', this.handleCloseEvent.bind(this))
+        this.once('refresh', refreshListener)
+        this.once('close', closeListener)
+        this.once('close', this.handleCloseEvent.bind(this))
 
-      this.refreshSlotsCache(function (err) {
-        if (err && err.message === 'Failed to refresh slots cache.') {
-          Redis.prototype.silentEmit.call(this, 'error', err)
-          this.connectionPool.reset([])
-        }
-      }.bind(this))
-      this.subscriber.start()
+        this.refreshSlotsCache(function (err) {
+          if (err && err.message === 'Failed to refresh slots cache.') {
+            Redis.prototype.silentEmit.call(this, 'error', err)
+            this.connectionPool.reset([])
+          }
+        }.bind(this))
+        this.subscriber.start()
+      }).catch(reject)
     })
   }
 
@@ -639,6 +660,51 @@ class Cluster extends EventEmitter {
       }
     })
   }
+
+  private dnsLookup (hostname: string): Promise<string> {
+    return new Promise((resolve, reject) => {
+      this.options.dnsLookup(hostname, (err, address) => {
+        if (err) {
+          debug('failed to resolve hostname %s to IP: %s', hostname, err.message)
+          reject(err)
+        } else {
+          debug('resolved hostname %s to IP %s', hostname, address)
+          resolve(address)
+        }
+      })
+    });
+  }
+
+  /**
+   * Normalize startup nodes, and resolving hostnames to IPs.
+   *
+   * This process happens every time when #connect() is called since
+   * #startupNodes and DNS records may chanage.
+   *
+   * @private
+   * @returns {Promise<IRedisOptions[]>}
+   */
+  private resolveStartupNodeHostnames(): Promise<IRedisOptions[]> {
+    if (!Array.isArray(this.startupNodes) || this.startupNodes.length === 0) {
+      return Promise.reject(new Error('`startupNodes` should contain at least one node.'))
+    }
+    const startupNodes = normalizeNodeOptions(this.startupNodes)
+
+    const hostnames = getUniqueHostnamesFromOptions(startupNodes)
+    if (hostnames.length === 0) {
+      return Promise.resolve(startupNodes)
+    }
+
+    return Promise.all(hostnames.map((hostname) => this.dnsLookup(hostname))).then((ips) => {
+      const hostnameToIP = zipMap(hostnames, ips)
+
+      return startupNodes.map((node) => (
+        hostnameToIP.has(node.host)
+          ? Object.assign({}, node, {host: hostnameToIP.get(node.host)})
+          : node
+      ))
+    })
+  }
 }
 
 Object.getOwnPropertyNames(Commander.prototype).forEach(name => {

lib/cluster/util.ts

@@ -1,11 +1,15 @@
 import {parseURL} from '../utils'
+import {isIP} from 'net'
+import {DNSLookupFunction} from './ClusterOptions';
 
 export type NodeKey = string
 export type NodeRole = 'master' | 'slave' | 'all'
 
 export interface IRedisOptions {
   port: number,
-  host: string
+  host: string,
+  password?: string,
+  [key: string]: any
 }
 
 export function getNodeKey(node: IRedisOptions): NodeKey {
@@ -43,3 +47,12 @@ export function normalizeNodeOptions(nodes: Array<string | number | object>): IR
     return options
   })
 }
+
+export function getUniqueHostnamesFromOptions (nodes: IRedisOptions[]): string[] {
+  const uniqueHostsMap = {}
+  nodes.forEach((node) => {
+    uniqueHostsMap[node.host] = true
+  })
+
+  return Object.keys(uniqueHostsMap).filter(host => !isIP(host))
+}

lib/types.ts

@@ -1 +1 @@
-export type CallbackFunction<T = void> = (err?: Error | null, result?: T) => void
+export type CallbackFunction<T = void> = (err?: NodeJS.ErrnoException | null, result?: T) => void

lib/utils/index.ts

@@ -325,3 +325,11 @@ export function shuffle<T> (array: T[]): T[] {
  * Error message for connection being disconnected
  */
 export const CONNECTION_CLOSED_ERROR_MSG = 'Connection is closed.'
+
+export function zipMap<K, V> (keys: K[], values: V[]): Map<K, V> {
+  const map = new Map<K, V>()
+  keys.forEach((key, index) => {
+    map.set(key, values[index])
+  })
+  return map
+}

test/functional/cluster/connect.js

@@ -353,4 +353,13 @@ describe('cluster:connect', function () {
       { host: '127.0.0.1', port: '30001' }
     ], { slotsRefreshInterval: 100, redisOptions: { lazyConnect: false } });
   });
+
+  it('throws when startupNodes is empty', (done) => {
+    const cluster = new Redis.Cluster(null, {lazyConnect: true})
+    cluster.connect().catch(err => {
+      expect(err.message).to.eql('`startupNodes` should contain at least one node.')
+      cluster.disconnect()
+      done()
+    })
+  })
 });

test/functional/cluster/dnsLookup.js

@@ -0,0 +1,58 @@
+describe('cluster:dnsLookup', () => {
+  it('resolve hostnames to IPs', (done) => {
+    const slotTable = [
+      [0, 1000, ['127.0.0.1', 30001]],
+      [1001, 16383, ['127.0.0.1', 30002]]
+    ]
+    new MockServer(30001, (argv, c) => {
+    }, slotTable)
+    new MockServer(30002, (argv, c) => {
+    }, slotTable)
+
+    const cluster = new Redis.Cluster([
+      { host: 'localhost', port: '30001' }
+    ])
+    cluster.on('ready', () => {
+      const nodes = cluster.nodes('master')
+      expect(nodes.length).to.eql(2)
+      expect(nodes[0].options.host).to.eql('127.0.0.1')
+      expect(nodes[1].options.host).to.eql('127.0.0.1')
+      cluster.disconnect()
+      done()
+    })
+  })
+
+  it('support customize dnsLookup function', (done) => {
+    let dnsLookupCalledCount = 0
+    const slotTable = [
+      [0, 1000, ['127.0.0.1', 30001]],
+      [1001, 16383, ['127.0.0.1', 30002]]
+    ]
+    new MockServer(30001, (argv, c) => {
+    }, slotTable)
+    new MockServer(30002, (argv, c) => {
+    }, slotTable)
+
+    const cluster = new Redis.Cluster([
+      { host: 'a.com', port: '30001' }
+    ], {
+      dnsLookup (hostname, callback) {
+        dnsLookupCalledCount += 1
+        if (hostname === 'a.com') {
+          callback(null, '127.0.0.1')
+        } else {
+          callback(new Error('Unknown hostname'))
+        }
+      }
+    })
+    cluster.on('ready', () => {
+      const nodes = cluster.nodes('master')
+      expect(nodes.length).to.eql(2)
+      expect(nodes[0].options.host).to.eql('127.0.0.1')
+      expect(nodes[1].options.host).to.eql('127.0.0.1')
+      expect(dnsLookupCalledCount).to.eql(1)
+      cluster.disconnect()
+      done()
+    })
+  })
+})

test/functional/cluster/quit.js

@@ -23,6 +23,7 @@ describe('cluster:quit', () => {
       cluster.quit((err, res) => {
         expect(err).to.eql(null)
         expect(res).to.eql('OK')
+        cluster.disconnect()
         done()
       })
     })
@@ -51,6 +52,7 @@ describe('cluster:quit', () => {
     cluster.on('ready', () => {
       cluster.quit((err) => {
         expect(err.message).to.eql(ERROR_MESSAGE)
+        cluster.disconnect()
         done()
       })
     })