From 8c37afc8889fb8bad80e8498f0ba7c73267abc0d Mon Sep 17 00:00:00 2001
From: Emanuele Palazzetti <emanuele.palazzetti@datadoghq.com>
Date: Thu, 30 Mar 2017 13:08:38 +0200
Subject: [PATCH] [rails] provide tags setting to include global tags from
 Rails settings

---
 docs/GettingStarted.md                 |  4 +++-
 lib/ddtrace/contrib/rails/framework.rb |  9 ++++++---
 test/contrib/rails/tracer_test.rb      | 10 ++++++++++
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/docs/GettingStarted.md b/docs/GettingStarted.md
index 657d1f056ba..fcf614aa2ea 100644
--- a/docs/GettingStarted.md
+++ b/docs/GettingStarted.md
@@ -65,7 +65,8 @@ of the Datadog tracer, you can override the following defaults:
       debug: false,
       trace_agent_hostname: 'localhost',
       trace_agent_port: 8126,
-      env: Rails.env
+      env: Rails.env,
+      tags: {}
     }
 
 Available settings are:
@@ -88,6 +89,7 @@ Available settings are:
 * ``trace_agent_hostname``: set the hostname of the trace agent.
 * ``trace_agent_port``: set the port the trace agent is listening on.
 * ``env``: set the environment. Defaults to the Rails environment
+* ``tags``: set global tags that should be applied to all spans. Defaults to an empty hash
 
 ### Sinatra
 
diff --git a/lib/ddtrace/contrib/rails/framework.rb b/lib/ddtrace/contrib/rails/framework.rb
index 1e510d577e3..099de932bd6 100644
--- a/lib/ddtrace/contrib/rails/framework.rb
+++ b/lib/ddtrace/contrib/rails/framework.rb
@@ -27,7 +27,8 @@ module Framework
           debug: false,
           trace_agent_hostname: Datadog::Writer::HOSTNAME,
           trace_agent_port: Datadog::Writer::PORT,
-          env: ::Rails.env
+          env: ::Rails.env,
+          tags: {}
         }.freeze
 
         # configure Datadog settings
@@ -47,6 +48,10 @@ def self.configure(config)
             port: datadog_config[:trace_agent_port]
           )
 
+          # set default tracer tags
+          datadog_config[:tracer].set_tags('env' => datadog_config[:env])
+          datadog_config[:tracer].set_tags(datadog_config[:tags])
+
           # set default service details
           datadog_config[:tracer].set_service_info(
             datadog_config[:default_service],
@@ -60,8 +65,6 @@ def self.configure(config)
             Datadog::Ext::AppTypes::CACHE
           )
 
-          datadog_config[:tracer].set_tags('env' => datadog_config[:env])
-
           if defined?(::ActiveRecord)
             begin
               # set default database service details and store it in the configuration
diff --git a/test/contrib/rails/tracer_test.rb b/test/contrib/rails/tracer_test.rb
index 6fc83f02eee..fafd323bea5 100644
--- a/test/contrib/rails/tracer_test.rb
+++ b/test/contrib/rails/tracer_test.rb
@@ -23,6 +23,7 @@ class TracerTest < ActionController::TestCase
     assert_equal(Rails.configuration.datadog_trace[:trace_agent_hostname], Datadog::Writer::HOSTNAME)
     assert_equal(Rails.configuration.datadog_trace[:trace_agent_port], Datadog::Writer::PORT)
     assert_equal(Rails.configuration.datadog_trace[:env], 'test')
+    assert_equal(Rails.configuration.datadog_trace[:tags], {})
   end
 
   test 'a default service and database should be properly set' do
@@ -122,4 +123,13 @@ class TracerTest < ActionController::TestCase
 
     assert_equal(tracer.tags['env'], 'dev')
   end
+
+  test 'tracer global tags can be changed by the user' do
+    update_config(:tags, { 'component' => 'api', 'section' => 'users' })
+
+    tracer = Rails.configuration.datadog_trace[:tracer]
+
+    assert_equal(tracer.tags['component'], 'api')
+    assert_equal(tracer.tags['section'], 'users')
+  end
 end