Merge pull request #220 from lutovich/1.2-seed-uri-resolution

Remember seed uri and DNS-lookup during rediscovery

Author: Zhen Li

src/v1/internal/connection-providers.js

@@ -23,18 +23,20 @@ import Session from '../session';
 import RoundRobinArray from './round-robin-array';
 import RoutingTable from './routing-table';
 import Rediscovery from './rediscovery';
+import hasFeature from './features';
+import {DnsHostNameResolver, DummyHostNameResolver} from './host-name-resolvers';
 
 class ConnectionProvider {
 
   acquireConnection(mode) {
-    throw new Error('Abstract method');
+    throw new Error('Abstract function');
   }
 
   _withAdditionalOnErrorCallback(connectionPromise, driverOnErrorCallback) {
     // install error handler from the driver on the connection promise; this callback is installed separately
     // so that it does not handle errors, instead it is just an additional error reporting facility.
     connectionPromise.catch(error => {
-      driverOnErrorCallback(error)
+      driverOnErrorCallback(error);
     });
     // return the original connection promise
     return connectionPromise;
@@ -61,10 +63,12 @@ export class LoadBalancer extends ConnectionProvider {
 
   constructor(address, connectionPool, driverOnErrorCallback) {
     super();
-    this._routingTable = new RoutingTable(new RoundRobinArray([address]));
+    this._seedRouter = address;
+    this._routingTable = new RoutingTable(new RoundRobinArray([this._seedRouter]));
     this._rediscovery = new Rediscovery();
     this._connectionPool = connectionPool;
     this._driverOnErrorCallback = driverOnErrorCallback;
+    this._hostNameResolver = LoadBalancer._createHostNameResolver();
   }
 
   acquireConnection(mode) {
@@ -109,7 +113,42 @@ export class LoadBalancer extends ConnectionProvider {
   _refreshRoutingTable(currentRoutingTable) {
     const knownRouters = currentRoutingTable.routers.toArray();
 
-    const refreshedTablePromise = knownRouters.reduce((refreshedTablePromise, currentRouter, currentIndex) => {
+    return this._fetchNewRoutingTable(knownRouters, currentRoutingTable).then(newRoutingTable => {
+      if (LoadBalancer._isValidRoutingTable(newRoutingTable)) {
+        // one of the known routers returned a valid routing table - use it
+        return newRoutingTable;
+      }
+
+      if (!newRoutingTable) {
+        // returned routing table was undefined, this means a connection error happened and the last known
+        // router did not return a valid routing table, so we need to forget it
+        const lastRouterIndex = knownRouters.length - 1;
+        LoadBalancer._forgetRouter(currentRoutingTable, knownRouters, lastRouterIndex);
+      }
+
+      // none of the known routers returned a valid routing table - try to use seed router address for rediscovery
+      return this._fetchNewRoutingTableUsingSeedRouterAddress(knownRouters, this._seedRouter);
+    }).then(newRoutingTable => {
+      if (LoadBalancer._isValidRoutingTable(newRoutingTable)) {
+        this._updateRoutingTable(newRoutingTable);
+        return newRoutingTable;
+      }
+
+      // none of the existing routers returned valid routing table, throw exception
+      throw newError('Could not perform discovery. No routing servers available.', SERVICE_UNAVAILABLE);
+    });
+  }
+
+  _fetchNewRoutingTableUsingSeedRouterAddress(knownRouters, seedRouter) {
+    return this._hostNameResolver.resolve(seedRouter).then(resolvedRouterAddresses => {
+      // filter out all addresses that we've already tried
+      const newAddresses = resolvedRouterAddresses.filter(address => knownRouters.indexOf(address) < 0);
+      return this._fetchNewRoutingTable(newAddresses, null);
+    });
+  }
+
+  _fetchNewRoutingTable(routerAddresses, routingTable) {
+    return routerAddresses.reduce((refreshedTablePromise, currentRouter, currentIndex) => {
       return refreshedTablePromise.then(newRoutingTable => {
         if (newRoutingTable) {
           if (!newRoutingTable.writers.isEmpty()) {
@@ -120,28 +159,14 @@ export class LoadBalancer extends ConnectionProvider {
           // returned routing table was undefined, this means a connection error happened and we need to forget the
           // previous router and try the next one
           const previousRouterIndex = currentIndex - 1;
-          this._forgetRouter(currentRoutingTable, knownRouters, previousRouterIndex);
+          LoadBalancer._forgetRouter(routingTable, routerAddresses, previousRouterIndex);
         }
 
         // try next router
         const session = this._createSessionForRediscovery(currentRouter);
         return this._rediscovery.lookupRoutingTableOnRouter(session, currentRouter);
       });
     }, Promise.resolve(null));
-
-    return refreshedTablePromise.then(newRoutingTable => {
-      if (newRoutingTable && !newRoutingTable.writers.isEmpty()) {
-        this._updateRoutingTable(newRoutingTable);
-        return newRoutingTable;
-      }
-
-      // forget the last known router because it did not return a valid routing table
-      const lastRouterIndex = knownRouters.length - 1;
-      this._forgetRouter(currentRoutingTable, knownRouters, lastRouterIndex);
-
-      // none of the existing routers returned valid routing table, throw exception
-      throw newError('Could not perform discovery. No routing servers available.', SERVICE_UNAVAILABLE);
-    });
   }
 
   _createSessionForRediscovery(routerAddress) {
@@ -162,12 +187,23 @@ export class LoadBalancer extends ConnectionProvider {
     this._routingTable = newRoutingTable;
   }
 
-  _forgetRouter(routingTable, routersArray, routerIndex) {
+  static _isValidRoutingTable(routingTable) {
+    return routingTable && !routingTable.writers.isEmpty();
+  }
+
+  static _forgetRouter(routingTable, routersArray, routerIndex) {
     const address = routersArray[routerIndex];
-    if (address) {
+    if (routingTable && address) {
       routingTable.forgetRouter(address);
     }
   }
+
+  static _createHostNameResolver() {
+    if (hasFeature('dns_lookup')) {
+      return new DnsHostNameResolver();
+    }
+    return new DummyHostNameResolver();
+  }
 }
 
 export class SingleConnectionProvider extends ConnectionProvider {

src/v1/internal/connector.js

@@ -500,5 +500,7 @@ export {
     connect,
     parseScheme,
     parseUrl,
+    parseHost,
+    parsePort,
     Connection
 }

src/v1/internal/features.js

@@ -40,6 +40,17 @@ const FEATURES = {
     } catch (e) {
       return false;
     }
+  },
+  dns_lookup: () => {
+    try {
+      const lookupFunction = require('dns').lookup;
+      if (lookupFunction && typeof lookupFunction === 'function') {
+        return true;
+      }
+      return false;
+    } catch (e) {
+      return false;
+    }
   }
 };
 

src/v1/internal/host-name-resolvers.js

@@ -0,0 +1,70 @@
+/**
+ * Copyright (c) 2002-2017 "Neo Technology,","
+ * Network Engine for Objects in Lund AB [http://neotechnology.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {parseHost, parsePort} from './connector';
+
+class HostNameResolver {
+
+  resolve() {
+    throw new Error('Abstract function');
+  }
+}
+
+export class DummyHostNameResolver extends HostNameResolver {
+
+  resolve(seedRouter) {
+    return resolveToItself(seedRouter);
+  }
+}
+
+export class DnsHostNameResolver extends HostNameResolver {
+
+  constructor() {
+    super();
+    this._dns = require('dns');
+  }
+
+  resolve(seedRouter) {
+    const seedRouterHost = parseHost(seedRouter);
+    const seedRouterPort = parsePort(seedRouter);
+
+    return new Promise((resolve) => {
+      this._dns.lookup(seedRouterHost, {all: true}, (error, addresses) => {
+        if (error) {
+          resolve(resolveToItself(seedRouter));
+        } else {
+          const addressesWithPorts = addresses.map(address => addressWithPort(address, seedRouterPort));
+          resolve(addressesWithPorts);
+        }
+      });
+    });
+  }
+}
+
+function resolveToItself(address) {
+  return Promise.resolve([address]);
+}
+
+function addressWithPort(addressObject, port) {
+  const address = addressObject.address;
+  if (port) {
+    return address + ':' + port;
+  }
+  return address;
+}