Make sure we always read PSL data as UTF-8

lib/twingly/public_suffix_list.rb

@@ -1,3 +1,4 @@
+require "addressable/idna"
 require "public_suffix"
 
 module Twingly
@@ -7,8 +8,9 @@ class PublicSuffixList
     private_constant :ACE_PREFIX
 
     # Extend the PSL with ASCII form of all internationalized domain names
-    def self.with_punycoded_names
-      list_data = File.read(PublicSuffix::List::DEFAULT_LIST_PATH)
+    def self.with_punycoded_names(encoding: Encoding::UTF_8)
+      list_path = PublicSuffix::List::DEFAULT_LIST_PATH
+      list_data = File.read(list_path, encoding: encoding)
       list = PublicSuffix::List.parse(list_data, private_domains: false)
 
       punycoded_names(list).each do |punycoded_name|

spec/lib/twingly/public_suffix_list_spec.rb

@@ -0,0 +1,30 @@
+require "spec_helper"
+
+require "twingly/public_suffix_list"
+
+describe Twingly::PublicSuffixList do
+  describe ".with_punycoded_names" do
+    subject { described_class.with_punycoded_names(encoding: encoding) }
+
+    context "when the list is data is read with the default encoding" do
+      subject { described_class.with_punycoded_names }
+
+      it { is_expected.to be_a(PublicSuffix::List) }
+    end
+
+    context "when the list data is read as UTF-8" do
+      let(:encoding) { Encoding::UTF_8 }
+
+      it { is_expected.to be_a(PublicSuffix::List) }
+    end
+
+    context "when the list data is read as US-ASCII" do
+      let(:encoding) { Encoding::US_ASCII }
+
+      it "parsing the data will fail" do
+        expect { subject }.
+          to raise_error(ArgumentError, "invalid byte sequence in US-ASCII")
+      end
+    end
+  end
+end