Added Elasticsearch proxy example (#1398)

Co-authored-by: István Zoltán Szabó <istvan.szabo@elastic.co>

docs/examples/proxy/api/autocomplete.js

@@ -0,0 +1,105 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you 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.
+ */
+
+// IMPORTANT: this is not a production ready code & purely for demonstration purposes,
+//            we make no guarantees on it's security and stability
+
+// NOTE: to make this endpoint work, you should create an ApiKey with 'read' permissions
+
+'use strict'
+
+const { Client } = require('@elastic/elasticsearch')
+const authorize = require('../utils/authorize')
+
+const INDEX = '<index-name>'
+const client = new Client({
+  cloud: {
+    id: process.env.ELASTIC_CLOUD_ID
+  }
+})
+
+module.exports = async (req, res) => {
+  const [err, token] = authorize(req)
+  if (err) {
+    res.status(401)
+    res.json(err)
+    return
+  }
+
+  if (typeof req.query.q !== 'string') {
+    res.status(400)
+    res.json({
+      error: 'Bad Request',
+      message: 'Missing parameter "query.q"',
+      statusCode: 400
+    })
+    return
+  }
+
+  if (req.query.q.length < 3) {
+    res.status(400)
+    res.json({
+      error: 'Bad Request',
+      message: 'The length of "query.q" should be at least 3',
+      statusCode: 400
+    })
+    return
+  }
+
+  try {
+    const response = await client.search({
+      index: INDEX,
+      // You could directly send from the browser
+      // the Elasticsearch's query DSL, but it will
+      // expose you to the risk that a malicious user
+      // could overload your cluster by crafting
+      // expensive queries.
+      body: {
+        _source: ['id', 'url', 'name'], // the fields you want to show in the autocompletion
+        size: 0,
+        // https://www.elastic.co/guide/en/elasticsearch/reference/current/search-suggesters-completion.html
+        suggest: {
+          suggestions: {
+            prefix: req.query.q,
+            completion: {
+              field: 'suggest',
+              size: 5
+            }
+          }
+        }
+      }
+    }, {
+      headers: {
+        Authorization: `ApiKey ${token}`
+      }
+    })
+
+    // It might be useful to configure http control caching headers
+    // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
+    // res.setHeader('stale-while-revalidate', '30')
+    res.json(response.body)
+  } catch (err) {
+    res.status(err.statusCode || 500)
+    res.json({
+      error: err.name,
+      message: err.message,
+      statusCode: err.statusCode || 500
+    })
+  }
+}