fix: add api patch

Signed-off-by: Bence Csati <bence.csati@axoflow.com>

Author: csatib02

lib/fluent/plugin/elasticsearch_api_bugfix.rb

@@ -0,0 +1,43 @@
+# Elasticsearch API 9.x Compatibility Patch
+# 
+# Fixes crashes in elasticsearch-api gem 9.1.2 when connecting to ES 7.x/8.x servers.
+# 
+# Bug: The gem expects ES 9 headers and crashes with NoMethodError when they're nil
+# Fix: Add nil safety checks and skip ES9-specific processing for ES 7/8
+#
+# This patch is only needed if using elasticsearch gem 9.x
+# Not needed if using elasticsearch gem 7.x or 8.x
+
+require 'elasticsearch/api'
+
+module Elasticsearch
+  module API
+    module Utils
+      class << self
+        if method_defined?(:update_ndjson_headers!)
+          alias_method :original_update_ndjson_headers!, :update_ndjson_headers!
+          
+          def update_ndjson_headers!(headers, client_headers)
+            return headers unless client_headers.is_a?(Hash)
+            
+            current_content = client_headers.keys.find { |c| c.to_s.match?(/content[-_]?type/i) }
+            return headers unless current_content
+            
+            content_value = client_headers[current_content]
+            return headers unless content_value
+            
+            # ES 7/8 compatibility: Only process ES9-specific headers
+            # If no "compatible-with" present, this is ES 7/8 format
+            return headers unless content_value.to_s.include?('compatible-with')
+            
+            # ES 9 detected, safe to call original
+            original_update_ndjson_headers!(headers, client_headers)
+          rescue StandardError => e
+            warn "[elasticsearch-api-compat] Failed to update headers: #{e.class} - #{e.message}"
+            headers
+          end
+        end
+      end
+    end
+  end
+end

lib/fluent/plugin/out_elasticsearch.rb

@@ -27,6 +27,7 @@
 require_relative 'elasticsearch_index_lifecycle_management'
 require_relative 'elasticsearch_tls'
 require_relative 'elasticsearch_fallback_selector'
+require_relative 'elasticsearch_api_bugfix'
 begin
   require_relative 'oj_serializer'
 rescue LoadError
@@ -631,6 +632,11 @@ def client(host = nil, compress_connection = false)
 
         ssl_options = { verify: @ssl_verify, ca_file: @ca_file}.merge(@ssl_version_options)
 
+        transport_options_hash = {
+          headers: headers || { 'Content-Type' => 'application/json' },
+          request: { timeout: @request_timeout },
+          ssl: ssl_options,
+        }
         transport = TRANSPORT_CLASS::Transport::HTTP::Faraday.new(connection_options.merge(
                                                                             options: {
                                                                               reload_connections: local_reload_connections,