Merge branch 'download_snippets' into 'master'

Added 'Download' button to snippet view

## What does this MR do?

Adds a `Download` button above a snippet.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

Requested in #22811 

## Screenshots (if relevant)

![image](/uploads/59b67aa02cc601c08a18fd60c37797ed/image.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #22811

See merge request !6720

1 files changed, 11 insertions, 3 deletions

diff --git a/app/controllers/snippets_controller.rb b/app/controllers/snippets_controller.rb
index d198782138a..dee57e4a388 100644
--- a/app/controllers/snippets_controller.rb
+++ b/app/controllers/snippets_controller.rb
@@ -1,10 +1,10 @@
 class SnippetsController < ApplicationController
   include ToggleAwardEmoji
 
-  before_action :snippet, only: [:show, :edit, :destroy, :update, :raw]
+  before_action :snippet, only: [:show, :edit, :destroy, :update, :raw, :download]
 
   # Allow read snippet
-  before_action :authorize_read_snippet!, only: [:show, :raw]
+  before_action :authorize_read_snippet!, only: [:show, :raw, :download]
 
   # Allow modify snippet
   before_action :authorize_update_snippet!, only: [:edit, :update]
@@ -12,7 +12,7 @@ class SnippetsController < ApplicationController
   # Allow destroy snippet
   before_action :authorize_admin_snippet!, only: [:destroy]
 
-  skip_before_action :authenticate_user!, only: [:index, :show, :raw]
+  skip_before_action :authenticate_user!, only: [:index, :show, :raw, :download]
 
   layout 'snippets'
   respond_to :html
@@ -75,6 +75,14 @@ class SnippetsController < ApplicationController
     )
   end
 
+  def download
+    send_data(
+      @snippet.content,
+      type: 'text/plain; charset=utf-8',
+      filename: @snippet.sanitized_file_name
+    )
+  end
+
   protected
 
   def snippet