Add helper for MimeMagic.by_path

lib/mimemagic.rb

@@ -78,6 +78,11 @@ class MimeMagic
     mime ? new(mime) : nil
   end
 
+  # Lookup mime type by filename
+  def self.by_path(path)
+    by_extension(File.extname(path))
+  end
+
   # Lookup mime type by magic content analysis.
   # This is a slow operation.
   def self.by_magic(io)

test/mimemagic_test.rb

@@ -34,6 +34,14 @@ describe 'MimeMagic' do
     MimeMagic.by_extension('').should.equal nil
   end
 
+  it 'should recognize by a path' do
+    MimeMagic.by_path('/adsjkfa/kajsdfkadsf/kajsdfjasdf.html').should.equal 'text/html'
+    MimeMagic.by_path('something.html').should.equal 'text/html'
+    MimeMagic.by_path('wtf.rb').should.equal 'application/x-ruby'
+    MimeMagic.by_path('where/am.html/crazy').should.equal nil
+    MimeMagic.by_path('').should.equal nil
+  end
+
   it 'should recognize by magic' do
     Dir['test/files/*'].each do |file|
       mime = file[11..-1].gsub('.', '/')