use header for test track visitor id (#29)

app/models/test_track/session.rb

@@ -12,6 +12,7 @@ def manage
     yield
   ensure
     manage_cookies!
+    manage_response_headers!
     notify_unsynced_assignments! if sync_assignments?
     create_alias! if signed_up?
   end
@@ -48,7 +49,11 @@ def sign_up!(identifier_type, identifier_value)
   alias signed_up? signed_up
 
   def visitor
-    @visitor ||= TestTrack::Visitor.new(id: cookies[visitor_cookie_name])
+    @visitor ||= TestTrack::Visitor.new(id: visitor_id)
+  end
+
+  def visitor_id
+    cookies[visitor_cookie_name] || request_headers[visitor_request_header_name]
   end
 
   def set_cookie(name, value)
@@ -100,10 +105,26 @@ def request
     controller.request
   end
 
+  def response
+    controller.response
+  end
+
   def cookies
     controller.send(:cookies)
   end
 
+  def request_headers
+    request.headers
+  end
+
+  def response_headers
+    response.headers
+  end
+
+  def manage_response_headers!
+    response_headers[visitor_response_header_name] = visitor.id if visitor.id_overridden_by_existing_visitor?
+  end
+
   def notify_unsynced_assignments!
     payload = {
       mixpanel_distinct_id: mixpanel_distinct_id,
@@ -170,6 +191,14 @@ def visitor_cookie_name
     ENV['TEST_TRACK_VISITOR_COOKIE_NAME'] || 'tt_visitor_id'
   end
 
+  def visitor_request_header_name
+    ENV['TEST_TRACK_VISITOR_REQUEST_HEADER_NAME'] || 'X-TT-Visitor-ID'
+  end
+
+  def visitor_response_header_name
+    ENV['TEST_TRACK_VISITOR_RESPONSE_HEADER_NAME'] || 'X-Set-TT-Visitor-ID'
+  end
+
   def fully_qualified_cookie_domain_enabled?
     ENV['TEST_TRACK_FULLY_QUALIFIED_COOKIE_DOMAIN_ENABLED'] == '1'
   end

app/models/test_track/visitor.rb

@@ -98,6 +98,10 @@ def loaded?
     !offline? && @remote_visitor.present?
   end
 
+  def id_overridden_by_existing_visitor?
+    @id_overridden_by_existing_visitor || false
+  end
+
   private
 
   def assignments
@@ -113,6 +117,7 @@ def remote_visitor
   end
 
   def merge!(other)
+    @id_overridden_by_existing_visitor = id != other.id
     @id = other.id
     @assignment_registry = assignment_registry.merge(other.assignment_registry)
     @unsynced_assignments = nil

spec/models/test_track/session_spec.rb

@@ -1,10 +1,12 @@
 require 'rails_helper'
 
 RSpec.describe TestTrack::Session do
-  let(:controller) { instance_double(ApplicationController, cookies: cookies, request: request) }
+  let(:controller) { instance_double(ApplicationController, cookies: cookies, request: request, response: response) }
   let(:cookies) { { tt_visitor_id: "fake_visitor_id", mp_fakefakefake_mixpanel: mixpanel_cookie }.with_indifferent_access }
+  let(:headers) { {} }
   let(:mixpanel_cookie) { { distinct_id: "fake_distinct_id", OtherProperty: "bar" }.to_json }
-  let(:request) { double(:request, host: "www.foo.com", ssl?: true) }
+  let(:request) { double(:request, host: "www.foo.com", ssl?: true, headers: headers) }
+  let(:response) { double(:response, headers: {}) }
   let(:unsynced_assignments_notifier) { instance_double(TestTrack::UnsyncedAssignmentsNotifier, notify: true) }
 
   subject { described_class.new(controller) }
@@ -59,6 +61,38 @@
         expect(cookies['tt_visitor_id'][:value]).to eq "real_visitor_id"
       end
 
+      context 'test track visitor id is the same as existing visitor id' do
+        before do
+          real_visitor = instance_double(TestTrack::Visitor, id: "fake_visitor_id", assignment_registry: {})
+          identifier = instance_double(TestTrack::Remote::Identifier, visitor: real_visitor)
+          allow(TestTrack::Remote::Identifier).to receive(:create!).and_return(identifier)
+        end
+
+        it "does not return the visitor id in the reponse header" do
+          subject.manage do
+            subject.log_in!("identifier_type", "value")
+          end
+
+          expect(controller.response.headers).not_to have_key('X-Set-TT-Visitor-ID')
+        end
+      end
+
+      context 'test track visitor id differs from existing visitor id' do
+        before do
+          real_visitor = instance_double(TestTrack::Visitor, id: "real_visitor_id", assignment_registry: {})
+          identifier = instance_double(TestTrack::Remote::Identifier, visitor: real_visitor)
+          allow(TestTrack::Remote::Identifier).to receive(:create!).and_return(identifier)
+        end
+
+        it "returns the existing visitor id in the reponse header" do
+          subject.manage do
+            subject.log_in!("identifier_type", "value")
+          end
+
+          expect(controller.response.headers['X-Set-TT-Visitor-ID']).to eq('real_visitor_id')
+        end
+      end
+
       it "changes the distinct_id in the mixpanel cookie" do
         subject.manage do
           subject.log_in!("identifier_type", "value")
@@ -81,6 +115,45 @@
       end
     end
 
+    context "current visitor id is passed via the header" do
+      let(:cookies) { {} }
+      let(:headers) { { 'X-TT-Visitor-ID' => 'fake_visitor_id' } }
+
+      before do
+        real_visitor = instance_double(TestTrack::Visitor, id: "real_visitor_id", assignment_registry: {})
+        identifier = instance_double(TestTrack::Remote::Identifier, visitor: real_visitor)
+        allow(TestTrack::Remote::Identifier).to receive(:create!).and_return(identifier)
+      end
+
+      describe '#sign_up!' do
+        it "provides the current visitor id when requesting an identifier" do
+          subject.manage do
+            subject.sign_up!("identifier_type", "value")
+
+            expect(TestTrack::Remote::Identifier).to have_received(:create!).with(
+              identifier_type: "identifier_type",
+              visitor_id: "fake_visitor_id",
+              value: "value"
+            )
+          end
+        end
+      end
+
+      describe '#log_in!' do
+        it "provides the current visitor id when requesting an identifier" do
+          subject.manage do
+            subject.log_in!("identifier_type", "value")
+
+            expect(TestTrack::Remote::Identifier).to have_received(:create!).with(
+              identifier_type: "identifier_type",
+              visitor_id: "fake_visitor_id",
+              value: "value"
+            )
+          end
+        end
+      end
+    end
+
     context "mixpanel" do
       it "resets the mixpanel cookie to the same value if already there" do
         subject.manage {}