Fix OpenTelemetry span processing when using logstasher

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+* Fix OpenTelemetry errors when using with Logstasher gem ([#372](https://github.com/alphagov/govuk_app_config/pull/372))
+
 # 9.11.0
 
 * Add GDS::SSO::PermissionDeniedError to excluded exceptions list ([#366](https://github.com/alphagov/govuk_app_config/pull/366))

lib/govuk_app_config/govuk_json_logging.rb

@@ -16,6 +16,12 @@ def add_custom_fields(&block)
   end
 
   def self.configure(&block)
+    # Fixes the monkey patch from the logstasher gem to support Rails 7
+    config = Rails.application.config.logstasher
+    if (!config.controller_monkey_patch && config.controller_monkey_patch != false) || config.controller_monkey_patch == true
+      require_relative "./govuk_json_logging/rails_ext/action_controller/metal/instrumentation"
+    end
+
     configuration = Configuration.new
 
     configuration.instance_eval(&block) if block_given?

lib/govuk_app_config/govuk_json_logging/rails_ext/action_controller/metal/instrumentation.rb

@@ -0,0 +1,65 @@
+# This is copied from
+# https://github.com/shadabahmed/logstasher/blob/main/lib/logstasher/rails_ext/action_controller/metal/instrumentation.rb
+# Changes have been highlight in comments, otherwise the code is the same.
+
+module ActionController
+  module Instrumentation
+    alias_method "orig_process_action", "process_action"
+
+    def process_action(*args)
+      # The raw payload has been updated to reflect the payload structure used
+      # in Rails 7.1, primarily the addition of the `headers`, `request` keys
+      # and using `request.filtered_path` instead of `request.fullpath`.
+      # https://github.com/rails/rails/blame/d39db5d1891f7509cde2efc425c9d69bbb77e670/actionpack/lib/action_controller/metal/instrumentation.rb#L60
+      raw_payload = {
+        controller: self.class.name,
+        action: action_name,
+        request:,
+        params: request.filtered_parameters,
+        headers: request.headers,
+        format: request.format.ref,
+        method: request.request_method,
+        path: begin
+          request.filtered_path
+        rescue StandardError
+          "unknown"
+        end,
+      }
+
+      LogStasher.add_default_fields_to_payload(raw_payload, request)
+
+      LogStasher.clear_request_context
+      LogStasher.add_default_fields_to_request_context(request)
+
+      ActiveSupport::Notifications.instrument("start_processing.action_controller", raw_payload.dup)
+
+      ActiveSupport::Notifications.instrument("process_action.action_controller", raw_payload) do |payload|
+        if respond_to?(:logstasher_add_custom_fields_to_request_context)
+          logstasher_add_custom_fields_to_request_context(LogStasher.request_context)
+        end
+
+        if respond_to?(:logstasher_add_custom_fields_to_payload)
+          before_keys = raw_payload.keys.clone
+          logstasher_add_custom_fields_to_payload(raw_payload)
+          after_keys = raw_payload.keys
+          # Store all extra keys added to payload hash in payload itself. This is a thread safe way
+          LogStasher::CustomFields.add(*(after_keys - before_keys))
+        end
+
+        result = super
+
+        payload[:status] = response.status
+        append_info_to_payload(payload)
+        LogStasher.store.each do |key, value|
+          payload[key] = value
+        end
+
+        LogStasher.request_context.each do |key, value|
+          payload[key] = value
+        end
+        result
+      end
+    end
+    alias_method "logstasher_process_action", "process_action"
+  end
+end

spec/lib/govuk_json_logging_spec.rb

@@ -16,6 +16,7 @@ def self.headers
       end
     end
   end
+
   before do
     stub_const("DummyLoggingRailsApp", Class.new(Rails::Application) do
       config.hosts.clear