Viewable PDFs in browser

If a user tries to view a PDF, the file will be sent to the browser, and
the browser should display it (tested in FF and Chrome).

app/controllers/submissions_controller.rb

@@ -1,4 +1,5 @@
 require 'archive.rb'
+require 'pdf.rb'
 
 class SubmissionsController < ApplicationController
 
@@ -240,6 +241,11 @@ def view
     end
     return unless file
 
+    filename = @submission.handin_file_path
+    if PDF.is_pdf?(file) then
+      send_data(file, type: "application/pdf", disposition: "inline", filename: File.basename(filename)) and return
+    end
+
     begin
       @data = @submission.annotated_file(file, @filename, params[:header_position])
     rescue

lib/pdf.rb

@@ -0,0 +1,10 @@
+module PDF
+  def self.is_pdf?(file)
+    return false unless file
+    # all PDFs have '%PDF-<major-version>.<minor-version>' in them somewhere.
+    # this is used instead of MIME type detection because it should work
+    # for PDFs inside of Archives as well.
+    # the scrub call prevents invalid byte sequence errors.
+    return (file.scrub("*") =~ /\%PDF-\d+\.?\d+/)
+  end
+end