Merge pull request #327 from alphagov/enable-adding-more-custom-logst…

…asher-fields

Enable adding custom LogStasher fields from apps

CHANGELOG.md

@@ -1,3 +1,7 @@
+# 9.7.0
+
+* Enable adding custom LogStasher fields from apps ([#327](https://github.com/alphagov/govuk_app_config/pull/327))
+
 # 9.6.0
 
 * Allow YouTube thumbnails from https://i.ytimg.com in the global Content Security Policy ([#328](https://github.com/alphagov/govuk_app_config/pull/328))

README.md

@@ -149,6 +149,20 @@ allow JSON format logs and `Govuk-Request-Id` to be visible.
 For development logs, in order to see the production style logs, developers should
 set `GOVUK_RAILS_JSON_LOGGING`in `govuk-docker` -> `docker-compose` files.
 
+### Logger configuration
+
+To include additional custom fields in your Rails logs, you can declare them
+within a `GovukJsonLogging.configure` block in a `config/initializers/` file.
+
+Example of adding a key/value to log entries based on a request header:
+
+```ruby
+GovukJsonLogging.configure do
+  add_custom_fields do |fields|
+    fields[:govuk_custom_field] = request.headers["GOVUK-Custom-Header"]
+  end
+end
+```
 
 ## Content Security Policy generation
 

lib/govuk_app_config/govuk_json_logging.rb

@@ -3,7 +3,23 @@
 require "action_controller"
 
 module GovukJsonLogging
-  def self.configure
+  class Configuration
+    def initialize
+      @custom_fields_block = proc {}
+    end
+
+    attr_reader :custom_fields_block
+
+    def add_custom_fields(&block)
+      @custom_fields_block = block if block_given?
+    end
+  end
+
+  def self.configure(&block)
+    configuration = Configuration.new
+
+    configuration.instance_eval(&block) if block_given?
+
     # We disable buffering, so that logs aren't lost on crash or delayed
     # indefinitely while troubleshooting.
     $stdout.sync = true
@@ -31,6 +47,8 @@ def self.configure
       fields[:govuk_request_id] = request.headers["GOVUK-Request-Id"]
       fields[:varnish_id] = request.headers["X-Varnish"]
       fields[:govuk_app_config] = GovukAppConfig::VERSION
+
+      instance_exec(fields, &configuration.custom_fields_block) if block_given?
     end
 
     Rails.application.config.logstasher.enabled = true

lib/govuk_app_config/version.rb

@@ -1,3 +1,3 @@
 module GovukAppConfig
-  VERSION = "9.6.0".freeze
+  VERSION = "9.7.0".freeze
 end

spec/lib/govuk_json_logging_spec.rb

@@ -3,6 +3,11 @@
 require "govuk_app_config/govuk_json_logging"
 require "rack/test"
 
+class TestController < ActionController::Base
+  include LogStasher::ActionController::Instrumentation
+  def index; end
+end
+
 RSpec.describe GovukJsonLogging do
   let(:govuk_headers_class) do
     Class.new do
@@ -78,6 +83,66 @@ def self.headers
       expect(fake_stdout.read).to match(/test default log entry/)
     end
 
+    context "given a block" do
+      it "evals the block" do
+        done = false
+        expect {
+          GovukJsonLogging.configure do
+            done = true
+          end
+        }.to change { done }.to(true)
+      end
+
+      context "and the block configures custom fields" do
+        describe "any subsequently-created ActionController" do
+          let(:headers) { { "REMOTE_ADDR" => "10.10.10.10" } }
+          let(:mock_request) { ActionDispatch::TestRequest.new(Rack::MockRequest.env_for("http://example.com:8080/", headers)) }
+          let(:mock_response) { ActionDispatch::TestResponse.new }
+
+          before do
+            GovukJsonLogging.configure do
+              add_custom_fields do |fields|
+                fields[:govuk_custom_field] = request.headers["GOVUK-Custom-Header"]
+              end
+            end
+
+            @controller = TestController.new
+            allow(@controller).to receive(:request).and_return(mock_request)
+            allow(@controller).to receive(:response).and_return(mock_response)
+          end
+
+          it "has a logstasher_add_custom_fields_to_payload method" do
+            expect(@controller.methods).to include(:logstasher_add_custom_fields_to_payload)
+          end
+
+          describe "calling the logstasher_add_custom_fields_to_payload" do
+            let(:payload) { {} }
+
+            it "executes the block" do
+              expect(@controller).to receive(:logstasher_add_custom_fields_to_payload)
+              @controller.send(:append_info_to_payload, payload)
+            end
+
+            it "adds the custom fields to the payload" do
+              @controller.send(:append_info_to_payload, payload)
+              expect(payload.keys).to include(:govuk_custom_field)
+            end
+
+            context "when the custom field has a value" do
+              before do
+                mock_request.headers["GOVUK-Custom-header"] = "My header value"
+              end
+
+              it "sets the custom field value in the payload" do
+                @controller.send(:append_info_to_payload, payload)
+                expect(payload[:govuk_custom_field]).to eq("My header value")
+              end
+            end
+          end
+        end
+      end
+    end
+
     describe "when making requests to the application" do
       include Rack::Test::Methods