Merge branch 'add-pagination-headers-to-api' into 'master'

Add pagination headers to already paginated API resources

Following #3045, I've added pagination headers using already available Kaminari methods.

## Pagination headers in action

![Screen_Shot_2016-01-14_at_12.14.53](/uploads/88807f754dd9aafbb24da85f6bdf9521/Screen_Shot_2016-01-14_at_12.14.53.png)

---

I've also added a shared example to test paginated API resources.

A possible next step would be to paginate all the API resources that return an array.

See merge request !2426

CHANGELOG

@@ -4,6 +4,7 @@ v 8.5.0 (unreleased)
   - Remove gray background from layout in UI
 
 v 8.4.0 (unreleased)
+  - Add pagination headers to already paginated API resources
   - Improve the consistency of commit titles, branch names, tag names, issue/MR titles, on their respective project pages
   - Autocomplete data is now always loaded, instead of when focusing a comment text area (Yorick Peterse)
   - Improved performance of finding issues for an entire group (Yorick Peterse)

lib/api/helpers.rb

@@ -97,11 +97,9 @@ module API
     end
 
     def paginate(relation)
-      per_page  = params[:per_page].to_i
+      relation.page(params[:page]).per(params[:per_page].to_i).tap do |data|
-      paginated = relation.page(params[:page]).per(per_page)
+        add_pagination_headers(data)
-      add_pagination_headers(paginated, per_page)
+      end
-
-      paginated
     end
 
     def authenticate!
@@ -329,16 +327,26 @@ module API
 
     private
 
-    def add_pagination_headers(paginated, per_page)
+    def add_pagination_headers(paginated_data)
+      header 'X-Total',       paginated_data.total_count.to_s
+      header 'X-Total-Pages', paginated_data.total_pages.to_s
+      header 'X-Per-Page',    paginated_data.limit_value.to_s
+      header 'X-Page',        paginated_data.current_page.to_s
+      header 'X-Next-Page',   paginated_data.next_page.to_s
+      header 'X-Prev-Page',   paginated_data.prev_page.to_s
+      header 'Link',          pagination_links(paginated_data)
+    end
+
+    def pagination_links(paginated_data)
       request_url = request.url.split('?').first
 
       links = []
-      links << %(<#{request_url}?page=#{paginated.current_page - 1}&per_page=#{per_page}>; rel="prev") unless paginated.first_page?
+      links << %(<#{request_url}?page=#{paginated_data.current_page - 1}&per_page=#{paginated_data.limit_value}>; rel="prev") unless paginated_data.first_page?
-      links << %(<#{request_url}?page=#{paginated.current_page + 1}&per_page=#{per_page}>; rel="next") unless paginated.last_page?
+      links << %(<#{request_url}?page=#{paginated_data.current_page + 1}&per_page=#{paginated_data.limit_value}>; rel="next") unless paginated_data.last_page?
-      links << %(<#{request_url}?page=1&per_page=#{per_page}>; rel="first")
+      links << %(<#{request_url}?page=1&per_page=#{paginated_data.limit_value}>; rel="first")
-      links << %(<#{request_url}?page=#{paginated.total_pages}&per_page=#{per_page}>; rel="last")
+      links << %(<#{request_url}?page=#{paginated_data.total_pages}&per_page=#{paginated_data.limit_value}>; rel="last")
 
-      header 'Link', links.join(', ')
+      links.join(', ')
     end
 
     def abilities

spec/requests/api/commit_status_spec.rb

@@ -1,6 +1,6 @@
 require 'spec_helper'
 
-describe API::API, api: true do
+describe API::CommitStatus, api: true do
   include ApiHelpers
   let(:user) { create(:user) }
   let(:user2) { create(:user) }
@@ -12,6 +12,10 @@ describe API::API, api: true do
   let(:commit_status) { create(:commit_status, commit: ci_commit) }
 
   describe "GET /projects/:id/repository/commits/:sha/statuses" do
+    it_behaves_like 'a paginated resources' do
+      let(:request) { get api("/projects/#{project.id}/repository/commits/#{commit.id}/statuses", user) }
+    end
+
     context "reporter user" do
       let(:statuses_id) { json_response.map { |status| status['id'] } }
 

spec/requests/api/notes_spec.rb

@@ -32,6 +32,10 @@ describe API::API, api: true  do
   before { project.team << [user, :reporter] }
 
   describe "GET /projects/:id/noteable/:noteable_id/notes" do
+    it_behaves_like 'a paginated resources' do
+      let(:request) { get api("/projects/#{project.id}/issues/#{issue.id}/notes", user) }
+    end
+
     context "when noteable is an Issue" do
       it "should return an array of issue notes" do
         get api("/projects/#{project.id}/issues/#{issue.id}/notes", user)

spec/support/api/pagination_shared_examples.rb

@@ -0,0 +1,20 @@
+# Specs for paginated resources.
+#
+# Requires an API request:
+#   let(:request) { get api("/projects/#{project.id}/repository/branches", user) }
+shared_examples 'a paginated resources' do
+  before do
+    # Fires the request
+    request
+  end
+
+  it 'has pagination headers' do
+    expect(response.headers).to include('X-Total')
+    expect(response.headers).to include('X-Total-Pages')
+    expect(response.headers).to include('X-Per-Page')
+    expect(response.headers).to include('X-Page')
+    expect(response.headers).to include('X-Next-Page')
+    expect(response.headers).to include('X-Prev-Page')
+    expect(response.headers).to include('Link')
+  end
+end