Improve handling of large diffs

Diffs with a large number of changed lines time out (504 HTTP error) or
generate a HTML page that's so heavy web browsers struggle with it.

https://github.com/gitlabhq/gitlabhq/pull/5014 introduced limits on
commit line count so that only a safe portion is rendered. This was
later undone by code refactoring in be5b6db8, e0eb4803 and c741fcab.
This patch re-introduces a safe limit on number of lines.

1 files changed, 14 insertions, 5 deletions

diff --git a/app/helpers/diff_helper.rb b/app/helpers/diff_helper.rb
index 162778ade58..1b10795bb7b 100644
--- a/app/helpers/diff_helper.rb
+++ b/app/helpers/diff_helper.rb
@@ -7,14 +7,23 @@ module DiffHelper
     end
   end
 
-  def safe_diff_files(diffs)
-    diffs.first(allowed_diff_size).map do |diff|
-      Gitlab::Diff::File.new(diff)
+  def allowed_diff_lines
+    if diff_hard_limit_enabled?
+      Commit::DIFF_HARD_LIMIT_LINES
+    else
+      Commit::DIFF_SAFE_LINES
     end
   end
 
-  def show_diff_size_warning?(diffs)
-    diffs.size > allowed_diff_size
+  def safe_diff_files(diffs)
+    lines = 0
+    safe_files = []
+    diffs.first(allowed_diff_size).each do |diff|
+      lines += diff.diff.lines.count
+      break if lines > allowed_diff_lines
+      safe_files << Gitlab::Diff::File.new(diff)
+    end
+    safe_files
   end
 
   def diff_hard_limit_enabled?