(PUP-8243) Ignore leading BOM when reading templates

Specify the 'bom' flag to `read`. On Windows, we continue trying UTF-8, then the
default external encoding. On POSIX, we continue using the default external
encoding, which is what ruby defaults to.

Author: joshcooper

lib/puppet/file_system/file_impl.rb

@@ -84,7 +84,7 @@ def read(path, opts = {})
   end
 
   def read_preserve_line_endings(path)
-    read(path)
+    read(path, encoding: "bom|#{Encoding.default_external.name}")
   end
 
   def binread(path)

lib/puppet/file_system/windows.rb

@@ -109,8 +109,8 @@ def chmod(mode, path)
   end
 
   def read_preserve_line_endings(path)
-    contents = path.read( :mode => 'rb', :encoding => Encoding::UTF_8)
-    contents = path.read( :mode => 'rb', :encoding => Encoding::default_external) unless contents.valid_encoding?
+    contents = path.read( :mode => 'rb', :encoding => 'bom|utf-8')
+    contents = path.read( :mode => 'rb', :encoding => "bom|#{Encoding::default_external.name}") unless contents.valid_encoding?
     contents = path.read unless contents.valid_encoding?
 
     contents

spec/unit/file_system_spec.rb

@@ -290,6 +290,12 @@ def increment_counter_in_multiple_processes(file, num_procs, options)
         expect(Puppet::FileSystem.read_preserve_line_endings(file)).to eq("file content \r\nsecond line \n")
       end
     end
+
+    it "should ignore leading BOM" do
+      with_file_content("\uFEFFfile content \n") do |file|
+        expect(Puppet::FileSystem.read_preserve_line_endings(file)).to eq("file content \n")
+      end
+    end
   end
 
   context "read without an encoding specified" do

spec/unit/parser/templatewrapper_spec.rb

@@ -43,6 +43,13 @@
     expect(tw.result).to eq(full_file_name)
   end
 
+  it "ignores a leading BOM" do
+    full_file_name = given_a_template_file("bom_template", "\uFEFF<%= file %>")
+
+    tw.file = "bom_template"
+    expect(tw.result).to eq(full_file_name)
+  end
+
   it "evaluates a given string as a template" do
     expect(tw.result("template contents")).to eql("template contents")
   end