[#48] Expose request id within parent app when using middleware

* Update TravisCI testing matrix
* Update CHANGELOG
* Update README
* Update `ApplicationInsights::Rack::TrackRequest#call` to implement the above
* Add associated tests

.travis.yml

@@ -6,6 +6,7 @@ rvm:
   - 2.2.0
   - 2.3.3
   - 2.4.0
+  - 2.5.0
   - ruby-head
 
 cache: bundler

CHANGELOG.md

@@ -3,7 +3,7 @@
 This file needs to be updated with every significant pull request. It is used to write down release notes.
 
 ## Version 0.5.6
-
+* Expose request id to parent Rack application when using `ApplicationInsights::Rack::TrackRequest` middleware through `env['ApplicationInsights.request.id']`
 
 ## Version 0.5.5
 * Add some basic logging when failed to send telemetry to the server

README.md

@@ -145,3 +145,17 @@ use ApplicationInsights::Rack::TrackRequest, '<YOUR INSTRUMENTATION KEY GOES HER
 # For rails, suggest to set up this middleware in application.rb so that unhandled exceptions from controllers are also collected
 config.middleware.use 'ApplicationInsights::Rack::TrackRequest', '<YOUR INSTRUMENTATION KEY GOES HERE>', <buffer size>
 ```
+
+#### Retrieving a request's AppInsight ID  ####
+```ruby
+# from time to time you may need to access a request's AppInsight id from within your app
+application_insights_request_id = env['ApplicationInsights.request.id']
+
+# this can be used for a number of different purposes, including telemetry correlation
+uri = URI('http://api.example.com/search/?q=test')
+
+req = Net::HTTP::Get.new(uri)
+req['Request-Id'] = "|#{application_insights_request_id}." if application_insights_request_id
+
+Net::HTTP.start(uri.hostname, uri.port) { |http| http.request(req) }
+```

lib/application_insights/rack/track_request.rb

@@ -24,6 +24,9 @@ def initialize(app, instrumentation_key, buffer_size = 500, send_interval = 60)
       # Track requests and send data to Application Insights asynchronously.
       # @param [Hash] env the rack environment.
       def call(env)
+        id = rand(16**32).to_s(16)
+        env['ApplicationInsights.request.id'] = id
+
         start = Time.now
         begin
           status, headers, response = @app.call(env)
@@ -44,7 +47,6 @@ def call(env)
         end
 
         request = ::Rack::Request.new env
-        id = rand(16**32).to_s(16)
         start_time = start.iso8601(7)
         duration = format_request_duration(stop - start)
         success = status.to_i < 400

lib/application_insights/version.rb

@@ -1,3 +1,3 @@
 module ApplicationInsights
-  VERSION = '0.5.6'
+  VERSION = '0.5.6'.freeze
 end

test/application_insights/rack/test_track_request.rb

@@ -36,6 +36,8 @@ def test_call_works_as_expected
     assert_equal url, request_data.url
     assert_equal true, request_data.duration.start_with?("00.00:00:02")
     assert Time.parse(request_data.start_time) - start_time < 0.01
+
+    assert env['ApplicationInsights.request.id']  =~ (/^\h{1,32}$/)
   end
 
   def test_call_with_failed_request
@@ -54,6 +56,8 @@ def test_call_with_failed_request
     payload = sender.buffer[0]
     request_data = payload[0].data.base_data
     assert_equal false, request_data.success
+
+    assert env['ApplicationInsights.request.id']  =~ (/^\h{1,32}$/)
   end
 
   def test_call_with_unhandled_exception
@@ -80,6 +84,8 @@ def test_call_with_unhandled_exception
     exception_data = payload[1].data.base_data
     assert_equal instrumentation_key, payload[1].i_key
     assert_equal 'Unhandled', exception_data.handled_at
+
+    assert env['ApplicationInsights.request.id']  =~ (/^\h{1,32}$/)
   end
 
   def test_internal_client