Detect encoding of uploaded files and convert to UTF-8. Finally.

Gemfile

@@ -5,6 +5,7 @@ source 'https://rubygems.org'
 gem 'bcrypt'
 gem 'bootstrap-will_paginate'
 gem 'carrierwave'
+gem 'charlock_holmes', require: 'charlock_holmes/string'
 gem 'docker-api', require: 'docker'
 gem 'eventmachine'
 gem 'factory_bot_rails'

Gemfile.lock

@@ -133,6 +133,7 @@ GEM
       marcel (~> 1.0.0)
       mini_mime (>= 0.1.3)
       ssrf_filter (~> 1.0)
+    charlock_holmes (0.7.7)
     childprocess (3.0.0)
     chronic (0.10.2)
     coderay (1.1.3)
@@ -393,7 +394,7 @@ GEM
       rspec-mocks (~> 3.10)
       rspec-support (~> 3.10)
     rspec-support (3.10.2)
-    rubocop (1.14.0)
+    rubocop (1.15.0)
       parallel (~> 1.10)
       parser (>= 3.0.0.0)
       rainbow (>= 2.2.2, < 4.0)
@@ -525,6 +526,7 @@ DEPENDENCIES
   bootstrap-will_paginate
   capybara
   carrierwave
+  charlock_holmes
   concurrent-ruby
   database_cleaner
   docker-api

app/controllers/exercises_controller.rb

@@ -218,7 +218,7 @@ user_id: current_user.id, user_type: current_user.class.name
             file_params[:content] = nil
             file_params[:native_file] = file_attributes[:content]
           else
-            file_params[:content] = file_attributes[:content].read.encode.delete("\x00")
+            file_params[:content] = file_attributes[:content].read.detect_encoding!.encode.delete("\x00")
           end
         end
       end