Merge branch 'svg-render-size-limit' into 'master'

Limit the size of SVGs when viewing them as blobs

## What does this MR do?

This MR prevents rendering of SVG blobs larger than 2 MB.

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

I couldn't figure out how to properly test the view for this as this requires a large SVG (inflating the repository size) _or_ stubbing, the latter doesn't really seem possible using Spinach and all the stuff potentially involved.

## Why was this MR needed?

When rendering large SVG blobs (e.g. 20 MB files) a request may time out and consume a lot of memory.

## What are the relevant issue numbers?

#1435

## Screenshots (if relevant)

![svg_notice](/uploads/c8de32522eda95a41a24555c3f85bfc1/svg_notice.jpg)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [x] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] 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)

cc @jschatz1 @annabeldunstone (there are some UI changes, see the above screenshot).

See merge request !5794

1 files changed, 7 insertions, 0 deletions

diff --git a/app/models/blob.rb b/app/models/blob.rb
index 0df2805e448..12cc5aaafba 100644
--- a/app/models/blob.rb
+++ b/app/models/blob.rb
@@ -3,6 +3,9 @@ class Blob < SimpleDelegator
   CACHE_TIME = 60 # Cache raw blobs referred to by a (mutable) ref for 1 minute
   CACHE_TIME_IMMUTABLE = 3600 # Cache blobs referred to by an immutable reference for 1 hour
 
+  # The maximum size of an SVG that can be displayed.
+  MAXIMUM_SVG_SIZE = 2.megabytes
+
   # Wrap a Gitlab::Git::Blob object, or return nil when given nil
   #
   # This method prevents the decorated object from evaluating to "truthy" when
@@ -31,6 +34,10 @@ class Blob < SimpleDelegator
     text? && language && language.name == 'SVG'
   end
 
+  def size_within_svg_limits?
+    size <= MAXIMUM_SVG_SIZE
+  end
+
   def video?
     UploaderHelper::VIDEO_EXT.include?(extname.downcase.delete('.'))
   end