Add support for maven package download via API [ci skip]

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/uploaders/packages/package_file_uploader.rb

@@ -4,5 +4,18 @@ class Packages::PackageFileUploader < GitlabUploader
 
   storage_options Gitlab.config.packages
 
-  # TODO: Implement me
+  def store_dir
+    dynamic_segment
+  end
+
+  private
+
+  def dynamic_segment
+    File.join(disk_hash[0..1], disk_hash[2..3], disk_hash,
+              'packages', model.package.id.to_s, 'files', model.id.to_s)
+  end
+
+  def disk_hash
+    @disk_hash ||= Digest::SHA2.hexdigest(model.package.project_id.to_s)
+  end
 end

lib/api/api.rb

@@ -172,6 +172,7 @@ module API
     mount ::API::License
     mount ::API::ProjectMirror
     mount ::API::ProjectPushRule
+    mount ::API::Packages
     ## EE-specific API V4 endpoints END
 
     route :any, '*path' do

lib/api/packages.rb

+module API
+  class Packages < Grape::API
+    content_type :md5, 'text/plain'
+    content_type :sha1, 'text/plain'
+
+    params do
+      requires :id, type: String, desc: 'The ID of a project'
+    end
+    resource :projects, requirements: API::PROJECT_ENDPOINT_REQUIREMENTS do
+      desc 'Download the maven package file' do
+        detail 'This feature was introduced in GitLab 11.3'
+      end
+      get ':id/maven/*file_path' do
+        checksum = %w(md5 sha1).include?(params[:format])
+
+        file_path, _, file_name = params[:file_path].rpartition('/')
+        file_name = file_name + '.' + params[:format] unless checksum
+
+        app_path, _, version = file_path.rpartition('/')
+        app_group, _, app_name = app_path.rpartition('/')
+
+        metadata = ::Packages::MavenMetadatum.find_by(app_group: app_group,
+                                                    app_name: app_name,
+                                                    app_version: version)
+
+        package_file = metadata.package.package_files.find_by(file: file_name)
+
+        if checksum
+          case params[:format]
+          when 'md5'
+            package_file.file_md5
+          when 'sha1'
+            package_file.file_sha1
+          end
+        else
+          present_carrierwave_file!(package_file.file)
+        end
+      end
+
+      desc 'Upload the maven package file' do
+        detail 'This feature was introduced in GitLab 11.3'
+      end
+      post ':id/maven/*file_path' do
+        # parse file path, create an upload, save record in database
+      end
+    end
+  end
+end