Add validations before parsing actual source.

lib/ogp/open_graph.rb

@@ -3,13 +3,18 @@
 REQUIRED_ATTRIBUTES = %w(title type image url)
 
 module OGP
-  class MissingAttributeError < StandardError
-  end
-
   class OpenGraph
     attr_accessor :title, :type, :image, :url
 
     def initialize(source)
+      if source.nil? || source.empty?
+        raise ArgumentError.new('`source` cannot be nil or empty.')
+      end
+
+      if !source.include?('</html>')
+        raise MalformedSourceError
+      end
+
       document = Oga.parse_html(source)
       check_required_attributes(document)
       parse_required_attributes(document)
@@ -39,4 +44,10 @@ def attribute_exists(document, name)
       document.at_xpath("boolean(//head/meta[@property='og:#{name}'])")
     end
   end
+
+  class MissingAttributeError < StandardError
+  end
+
+  class MalformedSourceError < StandardError
+  end
 end

spec/lib/open_graph_spec.rb

@@ -21,5 +21,23 @@
         expect{OGP::OpenGraph.new(content)}.to raise_error(OGP::MissingAttributeError)
       end
     end
+
+    context 'with nil source' do
+      it 'should raise an error' do
+        expect{OGP::OpenGraph.new(nil)}.to raise_error(ArgumentError)
+      end
+    end
+
+    context 'with empty source' do
+      it 'should raise an error' do
+        expect{OGP::OpenGraph.new('')}.to raise_error(ArgumentError)
+      end
+    end
+
+    context 'with malformed source' do
+      it 'should raise an error' do
+        expect{OGP::OpenGraph.new('Lorem ipsum dolor sit amet, consectetur adipiscing elit.')}.to raise_error(OGP::MalformedSourceError)
+      end
+    end
   end
 end