Add a new GET script languages API endpoint

To provide additional language options for scripted fields, Kibana needs
to know what languages are available for inline scripting in
Elasticsearch. This new Kibana API grabs up to date information from
Elasticsearch and provides it in an easy to digest format for the UI.

The response body from the API is a simple JSON array with a list of
languages that are enabled for inline scripting. The API also filters
out languages that don't make sense in scripted fields, like 'mustache'.

An example request might look like this:

`GET /api/kibana/scripts/languages`

200 OK
`['expression', 'painless']`

src/core_plugins/kibana/index.js

@@ -1,6 +1,7 @@
 import ingest from './server/routes/api/ingest';
 import search from './server/routes/api/search';
 import settings from './server/routes/api/settings';
+import scripts from './server/routes/api/scripts';
 
 module.exports = function (kibana) {
   return new kibana.Plugin({
@@ -84,6 +85,7 @@ module.exports = function (kibana) {
       ingest(server);
       search(server);
       settings(server);
+      scripts(server);
     }
   });
 

src/core_plugins/kibana/server/routes/api/scripts/index.js

@@ -0,0 +1,5 @@
+import { registerLanguages } from './register_languages';
+
+export default function (server) {
+  registerLanguages(server);
+}

src/core_plugins/kibana/server/routes/api/scripts/register_languages.js

@@ -0,0 +1,27 @@
+import _ from 'lodash';
+import handleESError from '../../../lib/handle_es_error';
+
+export function registerLanguages(server) {
+  server.route({
+    path: '/api/kibana/scripts/languages',
+    method: 'GET',
+    handler: function (request, reply) {
+      const callWithRequest = server.plugins.elasticsearch.callWithRequest;
+
+      return callWithRequest(request, 'cluster.getSettings', {
+        include_defaults: true,
+        filter_path: '**.script.engine.*.inline'
+      })
+      .then((esResponse) => {
+        const langs = _.get(esResponse, 'defaults.script.engine', {});
+        const inlineLangs = _.pick(langs, (lang) => lang.inline === 'true');
+        const supportedLangs = _.omit(inlineLangs, 'mustache');
+        return _.keys(supportedLangs);
+      })
+      .then(reply)
+      .catch((error) => {
+        reply(handleESError(error));
+      });
+    }
+  });
+}

test/intern_api.js

@@ -1,7 +1,8 @@
 define({
   suites: [
     'test/unit/api/ingest/index',
-    'test/unit/api/search/index'
+    'test/unit/api/search/index',
+    'test/unit/api/scripts/index'
   ],
   excludeInstrumentation: /(fixtures|node_modules)\//,
   loaderOptions: {

test/unit/api/scripts/_languages.js

@@ -0,0 +1,27 @@
+define(function (require) {
+  var expect = require('intern/dojo/node!expect.js');
+
+  return function (bdd, request) {
+    bdd.describe('Languages API', function getLanguages() {
+
+      bdd.it('should return 200 with an array of languages', function () {
+        return request.get('/kibana/scripts/languages')
+        .expect(200)
+        .then(function (response) {
+          expect(response.body).to.be.an('array');
+        });
+      });
+
+      bdd.it('should only return langs enabled for inline scripting', function () {
+        return request.get('/kibana/scripts/languages')
+        .expect(200)
+        .then(function (response) {
+          expect(response.body).to.contain('expression');
+          expect(response.body).to.contain('painless');
+
+          expect(response.body).to.not.contain('groovy');
+        });
+      });
+    });
+  };
+});

test/unit/api/scripts/index.js

@@ -0,0 +1,13 @@
+define(function (require) {
+  var bdd = require('intern!bdd');
+  var serverConfig = require('intern/dojo/node!../../../server_config');
+  var request = require('intern/dojo/node!supertest-as-promised');
+  var url = require('intern/dojo/node!url');
+  var languages = require('./_languages');
+
+  bdd.describe('scripts API', function () {
+    request = request(url.format(serverConfig.servers.kibana) + '/api');
+
+    languages(bdd, request);
+  });
+});