[CLIENT] Adds API compatibility header

Author: picandocodigo

elasticsearch-transport/lib/elasticsearch/transport/client.rb

@@ -145,14 +145,15 @@ def initialize(arguments={}, &block)
         @options[:http]                 ||= {}
 
         set_api_key if (@api_key = @arguments[:api_key])
+        set_compatibility_header if ENV['ELASTIC_CLIENT_APIVERSIONING']
 
         @seeds = extract_cloud_creds(@arguments)
         @seeds ||= __extract_hosts(@arguments[:hosts] ||
-                                     @arguments[:host] ||
-                                     @arguments[:url] ||
-                                     @arguments[:urls] ||
-                                     ENV['ELASTICSEARCH_URL'] ||
-                                     DEFAULT_HOST)
+                                   @arguments[:host] ||
+                                   @arguments[:url] ||
+                                   @arguments[:urls] ||
+                                   ENV['ELASTICSEARCH_URL'] ||
+                                   DEFAULT_HOST)
 
         @send_get_body_as = @arguments[:send_get_body_as] || 'GET'
         @opaque_id_prefix = @arguments[:opaque_id_prefix] || nil
@@ -200,6 +201,17 @@ def set_api_key
         @arguments.delete(:password)
       end
 
+      def set_compatibility_header
+        return unless ['1', 'true'].include?(ENV['ELASTIC_CLIENT_APIVERSIONING'])
+
+        add_header(
+          {
+            'Accept' => 'application/vnd.elasticsearch+json;compatible-with=7',
+            'Content-Type' => 'application/vnd.elasticsearch+json; compatible-with=7'
+          }
+        )
+      end
+
       def add_header(header)
         headers = @arguments[:transport_options]&.[](:headers) || {}
         headers.merge!(header)

elasticsearch-transport/spec/elasticsearch/transport/client_spec.rb

@@ -1428,6 +1428,46 @@
       end
     end
 
+    context 'when using the API Compatibility Header' do
+      it 'sets the API compatibility headers' do
+        ENV['ELASTIC_CLIENT_APIVERSIONING'] = 'true'
+        client = described_class.new(host: hosts)
+        headers = client.transport.connections.first.connection.headers
+
+        expect(headers['Content-Type']).to eq('application/vnd.elasticsearch+json; compatible-with=7')
+        expect(headers['Accept']).to eq('application/vnd.elasticsearch+json;compatible-with=7')
+
+        response = client.perform_request('GET', '/')
+        expect(response.headers['content-type']).to eq('application/json; charset=UTF-8')
+
+        ENV.delete('ELASTIC_CLIENT_APIVERSIONING')
+      end
+
+      it 'does not use API compatibility headers' do
+        val = ENV.delete('ELASTIC_CLIENT_APIVERSIONING')
+        client = described_class.new(host: hosts)
+        expect(client.transport.connections.first.connection.headers['Content-Type']).to eq('application/json')
+        ENV['ELASTIC_CLIENT_APIVERSIONING'] = val
+      end
+
+      it 'does not use API compatibility headers when it is set to unsupported values' do
+        val = ENV.delete('ELASTIC_CLIENT_APIVERSIONING')
+
+        ENV['ELASTIC_CLIENT_APIVERSIONING'] = 'test'
+        client = described_class.new(host: hosts)
+        expect(client.transport.connections.first.connection.headers['Content-Type']).to eq('application/json')
+
+        ENV['ELASTIC_CLIENT_APIVERSIONING'] = 'false'
+        client = described_class.new(host: hosts)
+        expect(client.transport.connections.first.connection.headers['Content-Type']).to eq('application/json')
+
+        ENV['ELASTIC_CLIENT_APIVERSIONING'] = '3'
+        client = described_class.new(host: hosts)
+        expect(client.transport.connections.first.connection.headers['Content-Type']).to eq('application/json')
+        ENV['ELASTIC_CLIENT_APIVERSIONING'] = val
+      end
+    end
+
     context 'when Elasticsearch response includes a warning header' do
       let(:client) do
         Elasticsearch::Transport::Client.new(hosts: hosts)