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

1 files changed, 19 insertions, 11 deletions

diff --git a/lib/api/helpers.rb b/lib/api/helpers.rb
index d46b5c42967..6d2380cf47d 100644
--- a/lib/api/helpers.rb
+++ b/lib/api/helpers.rb
@@ -97,11 +97,9 @@ module API
     end
 
     def paginate(relation)
-      per_page  = params[:per_page].to_i
-      paginated = relation.page(params[:page]).per(per_page)
-      add_pagination_headers(paginated, per_page)
-
-      paginated
+      relation.page(params[:page]).per(params[:per_page].to_i).tap do |data|
+        add_pagination_headers(data)
+      end
     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.current_page + 1}&per_page=#{per_page}>; rel="next") unless paginated.last_page?
-      links << %(<#{request_url}?page=1&per_page=#{per_page}>; rel="first")
-      links << %(<#{request_url}?page=#{paginated.total_pages}&per_page=#{per_page}>; rel="last")
+      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_data.current_page + 1}&per_page=#{paginated_data.limit_value}>; rel="next") unless paginated_data.last_page?
+      links << %(<#{request_url}?page=1&per_page=#{paginated_data.limit_value}>; rel="first")
+      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