Connection configuration provider - without changes to drivers

lib/client.js

@@ -55,7 +55,13 @@ function Client(config = {}) {
     this.version = config.version;
   }
 
-  this.connectionSettings = cloneDeep(config.connection || {});
+  if (config.connection && config.connection instanceof Function) {
+    this.connectionConfigProvider = config.connection;
+    this.connectionConfigExpirationChecker = () => true; // causes the provider to be called on first use
+  } else {
+    this.connectionSettings = cloneDeep(config.connection || {});
+    this.connectionConfigExpirationChecker = null;
+  }
   if (this.driverName && config.connection) {
     this.initializeDriver();
     if (!config.pool || (config.pool && config.pool.max !== 0)) {
@@ -254,16 +260,36 @@ Object.assign(Client.prototype, {
     // choose the smallest, positive timeout setting and set on poolConfig
     poolConfig.acquireTimeoutMillis = Math.min(...timeouts);
 
-    return Object.assign(poolConfig, {
-      create: () => {
-        return this.acquireRawConnection().then(async (connection) => {
-          connection.__knexUid = uniqueId('__knexUid');
+    const updatePoolConnectionSettingsFromProvider = async () => {
+      if (!this.connectionConfigProvider) {
+        return; // static configuration, nothing to update
+      }
+      if (
+        !this.connectionConfigExpirationChecker ||
+        !this.connectionConfigExpirationChecker()
+      ) {
+        return; // not expired, reuse existing connection
+      }
+      const providerResult = await this.connectionConfigProvider();
+      if (providerResult.expirationChecker) {
+        this.connectionConfigExpirationChecker =
+          providerResult.expirationChecker;
+        delete providerResult.expirationChecker; // MySQL2 driver warns on receiving extra properties
+      } else {
+        this.connectionConfigExpirationChecker = null;
+      }
+      this.connectionSettings = providerResult;
+    };
 
-          if (poolConfig.afterCreate) {
-            await promisify(poolConfig.afterCreate)(connection);
-          }
-          return connection;
-        });
+    return Object.assign(poolConfig, {
+      create: async () => {
+        await updatePoolConnectionSettingsFromProvider();
+        const connection = await this.acquireRawConnection();
+        connection.__knexUid = uniqueId('__knexUid');
+        if (poolConfig.afterCreate) {
+          await promisify(poolConfig.afterCreate)(connection);
+        }
+        return connection;
       },
 
       destroy: (connection) => {

test/integration/connection-config-provider.js

@@ -0,0 +1,71 @@
+/*global expect*/
+
+'use strict';
+
+const _ = require('lodash');
+const makeKnex = require('../../knex');
+
+module.exports = function(config) {
+  describe('Connection configuration provider', function() {
+    let configWorkingCopy;
+    let providerInvocationCount;
+    let connectionConfigWorkingCopy;
+
+    this.beforeEach(() => {
+      configWorkingCopy = _.cloneDeep(config);
+      configWorkingCopy.pool.min = 1;
+      configWorkingCopy.pool.max = 2;
+      providerInvocationCount = 0;
+      connectionConfigWorkingCopy = configWorkingCopy.connection;
+    });
+
+    it('is not used when configuration is static', async function() {
+      return runTwoConcurrentTransactions(0);
+    });
+
+    it('can return a promise for a config object, which is reused when not given given an expiry checker', async () => {
+      configWorkingCopy.connection = () => {
+        ++providerInvocationCount;
+        return Promise.resolve(connectionConfigWorkingCopy);
+      };
+      return runTwoConcurrentTransactions(1);
+    });
+
+    it('can return a config object, which is reused when not given given an expiry checker', async () => {
+      configWorkingCopy.connection = () => {
+        ++providerInvocationCount;
+        return connectionConfigWorkingCopy;
+      };
+      return runTwoConcurrentTransactions(1);
+    });
+
+    it('reuses the same resolved config when not yet expired', async () => {
+      configWorkingCopy.connection = () => {
+        ++providerInvocationCount;
+        return Object.assign(connectionConfigWorkingCopy, {
+          expirationChecker: () => false,
+        });
+      };
+      return runTwoConcurrentTransactions(1);
+    });
+
+    it('replaces the resolved config when expired', async () => {
+      configWorkingCopy.connection = () => {
+        ++providerInvocationCount;
+        return Object.assign(connectionConfigWorkingCopy, {
+          expirationChecker: () => true,
+        });
+      };
+      return runTwoConcurrentTransactions(2);
+    });
+
+    async function runTwoConcurrentTransactions(expectedInvocationCount) {
+      const knex = makeKnex(configWorkingCopy);
+      await knex.transaction(async (trx) => {
+        await knex.transaction(async (trx2) => {});
+      });
+      await knex.destroy();
+      expect(providerInvocationCount).equals(expectedInvocationCount);
+    }
+  });
+};

test/integration/index.js

@@ -6,6 +6,7 @@ const config = require('../knexfile');
 const fs = require('fs');
 
 Object.keys(config).forEach((dialectName) => {
+  require('./connection-config-provider')(config[dialectName]);
   return require('./suite')(logger(knex(config[dialectName])));
 });
 

types/index.d.ts

@@ -1609,17 +1609,7 @@ declare namespace Knex {
     client?: string | typeof Client;
     dialect?: string;
     version?: string;
-    connection?:
-      | string
-      | ConnectionConfig
-      | MariaSqlConnectionConfig
-      | MySqlConnectionConfig
-      | MsSqlConnectionConfig
-      | OracleDbConnectionConfig
-      | PgConnectionConfig
-      | RedshiftConnectionConfig
-      | Sqlite3ConnectionConfig
-      | SocketConnectionConfig;
+    connection?: string | StaticConnectionConfig | ConnectionConfigProvider;
     pool?: PoolConfig;
     migrations?: MigratorConfig;
     postProcessResponse?: (result: any, queryContext: any) => any;
@@ -1636,6 +1626,21 @@ declare namespace Knex {
     log?: Logger;
   }
 
+  type StaticConnectionConfig =
+    | ConnectionConfig
+    | MariaSqlConnectionConfig
+    | MySqlConnectionConfig
+    | MsSqlConnectionConfig
+    | OracleDbConnectionConfig
+    | PgConnectionConfig
+    | RedshiftConnectionConfig
+    | Sqlite3ConnectionConfig
+    | SocketConnectionConfig;
+
+  type ConnectionConfigProvider  = SyncConnectionConfigProvider | AsyncConnectionConfigProvider;
+  type SyncConnectionConfigProvider  = () => StaticConnectionConfig;
+  type AsyncConnectionConfigProvider  = () => Promise<StaticConnectionConfig>;
+
   interface ConnectionConfig {
     host: string;
     user: string;
@@ -1660,6 +1665,7 @@ declare namespace Knex {
     requestTimeout?: number;
     stream?: boolean;
     parseJSON?: boolean;
+    expirationChecker?(): boolean;
     options?: {
       encrypt?: boolean;
       instanceName?: string;
@@ -1707,6 +1713,7 @@ declare namespace Knex {
     read_default_group?: string;
     charset?: string;
     streamHWM?: number;
+    expirationChecker?(): boolean;
   }
 
   interface MariaSslConfiguration {
@@ -1716,6 +1723,7 @@ declare namespace Knex {
     capath?: string;
     cipher?: string;
     rejectUnauthorized?: boolean;
+    expirationChecker?(): boolean;
   }
 
   // Config object for mysql: https://github.com/mysqljs/mysql#connection-options
@@ -1743,6 +1751,7 @@ declare namespace Knex {
     flags?: string;
     ssl?: string | MariaSslConfiguration;
     decimalNumbers?: boolean;
+    expirationChecker?(): boolean;
   }
 
   interface OracleDbConnectionConfig {
@@ -1755,6 +1764,7 @@ declare namespace Knex {
     debug?: boolean;
     requestTimeout?: number;
     connectString?: string;
+    expirationChecker?(): boolean;
   }
 
   // Config object for pg: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/pg/index.d.ts
@@ -1778,6 +1788,7 @@ declare namespace Knex {
   interface Sqlite3ConnectionConfig {
     filename: string;
     debug?: boolean;
+    expirationChecker?(): boolean;
   }
 
   interface SocketConnectionConfig {
@@ -1786,6 +1797,7 @@ declare namespace Knex {
     password: string;
     database: string;
     debug?: boolean;
+    expirationChecker?(): boolean;
   }
 
   interface PoolConfig {