Add api compatibility header support (#1478)

docs/advanced-config.asciidoc

@@ -84,3 +84,17 @@ const client = new Client({
   Serializer: MySerializer
 })
 ----
+
+[discrete]
+==== Migrate to v8
+
+The Node.js client can be configured to emit an HTTP header
+``Accept: application/vnd.elasticsearch+json; compatible-with=7``
+which signals to Elasticsearch that the client is requesting
+``7.x`` version of request and response bodies. This allows for
+upgrading from 7.x to 8.x version of Elasticsearch without upgrading
+everything at once. Elasticsearch should be upgraded first after
+the compatibility header is configured and clients should be upgraded
+second.
+To enable to setting, configure the environment variable
+``ELASTIC_CLIENT_APIVERSIONING`` to ``true``.

index.js

@@ -116,6 +116,10 @@ class Client extends ESAPI {
         disablePrototypePoisoningProtection: false
       }, opts)
 
+    if (process.env.ELASTIC_CLIENT_APIVERSIONING === 'true') {
+      options.headers = Object.assign({ accept: 'application/vnd.elasticsearch+json; compatible-with=7' }, options.headers)
+    }
+
     this[kInitialOptions] = options
     this[kExtensions] = []
     this.name = options.name

lib/Transport.js

@@ -38,6 +38,7 @@ const clientVersion = require('../package.json').version
 const userAgent = `elasticsearch-js/${clientVersion} (${os.platform()} ${os.release()}-${os.arch()}; Node.js ${process.version})`
 const MAX_BUFFER_LENGTH = buffer.constants.MAX_LENGTH
 const MAX_STRING_LENGTH = buffer.constants.MAX_STRING_LENGTH
+const kApiVersioning = Symbol('api versioning')
 
 class Transport {
   constructor (opts) {
@@ -64,6 +65,7 @@ class Transport {
     this.generateRequestId = opts.generateRequestId || generateRequestId()
     this.name = opts.name
     this.opaqueIdPrefix = opts.opaqueIdPrefix
+    this[kApiVersioning] = process.env.ELASTIC_CLIENT_APIVERSIONING === 'true'
 
     this.nodeFilter = opts.nodeFilter || defaultNodeFilter
     if (typeof opts.nodeSelector === 'function') {
@@ -295,7 +297,8 @@ class Transport {
       //    - the request is not a HEAD request
       //    - the payload is not an empty string
       if (result.headers['content-type'] !== undefined &&
-          result.headers['content-type'].indexOf('application/json') > -1 &&
+          (result.headers['content-type'].indexOf('application/json') > -1 ||
+          result.headers['content-type'].indexOf('application/vnd.elasticsearch+json') > -1) &&
           isHead === false &&
           payload !== ''
       ) {
@@ -369,7 +372,7 @@ class Transport {
       }
 
       if (params.body !== '') {
-        headers['content-type'] = headers['content-type'] || 'application/json'
+        headers['content-type'] = headers['content-type'] || (this[kApiVersioning] ? 'application/vnd.elasticsearch+json; compatible-with=7' : 'application/json')
       }
 
     // handle ndjson body
@@ -386,7 +389,7 @@ class Transport {
         params.body = params.bulkBody
       }
       if (params.body !== '') {
-        headers['content-type'] = headers['content-type'] || 'application/x-ndjson'
+        headers['content-type'] = headers['content-type'] || (this[kApiVersioning] ? 'application/vnd.elasticsearch+x-ndjson; compatible-with=7' : 'application/x-ndjson')
       }
     }
 

test/unit/client.test.js

@@ -1422,6 +1422,56 @@ test('Disable prototype poisoning protection', t => {
   })
 })
 
+test('API compatibility header (json)', t => {
+  t.plan(4)
+
+  function handler (req, res) {
+    t.equal(req.headers.accept, 'application/vnd.elasticsearch+json; compatible-with=7')
+    t.equal(req.headers['content-type'], 'application/vnd.elasticsearch+json; compatible-with=7')
+    res.setHeader('Content-Type', 'application/vnd.elasticsearch+json; compatible-with=7')
+    res.end(JSON.stringify({ hello: 'world' }))
+  }
+
+  buildServer(handler, ({ port }, server) => {
+    process.env.ELASTIC_CLIENT_APIVERSIONING = 'true'
+    const client = new Client({
+      node: `http://localhost:${port}`
+    })
+
+    client.index({ index: 'foo', body: {} }, (err, { body }) => {
+      t.error(err)
+      t.same(body, { hello: 'world' })
+      server.stop()
+      delete process.env.ELASTIC_CLIENT_APIVERSIONING
+    })
+  })
+})
+
+test('API compatibility header (x-ndjson)', t => {
+  t.plan(4)
+
+  function handler (req, res) {
+    t.equal(req.headers.accept, 'application/vnd.elasticsearch+json; compatible-with=7')
+    t.equal(req.headers['content-type'], 'application/vnd.elasticsearch+x-ndjson; compatible-with=7')
+    res.setHeader('Content-Type', 'application/vnd.elasticsearch+json; compatible-with=7')
+    res.end(JSON.stringify({ hello: 'world' }))
+  }
+
+  buildServer(handler, ({ port }, server) => {
+    process.env.ELASTIC_CLIENT_APIVERSIONING = 'true'
+    const client = new Client({
+      node: `http://localhost:${port}`
+    })
+
+    client.bulk({ index: 'foo', body: [{}, {}] }, (err, { body }) => {
+      t.error(err)
+      t.same(body, { hello: 'world' })
+      server.stop()
+      delete process.env.ELASTIC_CLIENT_APIVERSIONING
+    })
+  })
+})
+
 test('Bearer auth', t => {
   t.plan(3)