Add GemFile to read .gem files

lib/rubygems_fp.rb

@@ -1,3 +1,6 @@
+require "rubygems"
+require "rubygems/package"
+
 class RubyGemsFP
   VERSION = '1.0.0'
 
@@ -18,4 +21,27 @@ def file_exists?(path)
       File.exists? File.join(gem_dir, path)
     end
   end
+
+  class GemFile
+    def initialize(io)
+      @io = io
+    end
+
+    def self.from_path(path)
+      new File.open(path)
+    end
+
+    def read_file(path)
+      Gem::Package.open(@io) do |pkg|
+        pkg.each do |e|
+          if e.full_name == path
+            return e.read
+          end
+        end
+      end
+
+      nil
+    end
+
+  end
 end

test/test_gemfile.rb

@@ -0,0 +1,19 @@
+require "rubygems"
+require "rubygems_fp"
+require "test/unit"
+
+class TestRubyGemsFPGemFile < Test::Unit::TestCase
+  def setup
+    @path = File.expand_path("../test-1.0.gem", __FILE__)
+  end
+
+  def test_read_file
+    gf = RubyGemsFP::GemFile.from_path @path
+    assert_equal "This is a file in the test gem\n", gf.read_file("test-file")
+  end
+
+  def test_read_file_nonexistant
+    gf = RubyGemsFP::GemFile.from_path @path
+    assert_equal nil, gf.read_file("not_there")
+  end
+end

test/test_rubygems_fp.rb

@@ -73,7 +73,7 @@ def quick_gem(name, version='2')
     return spec
   end
 
-  def test_sanity
+  def test_gem_dir
     a = quick_gem "a", "2"
 
     s = RubyGemsFP::Specification.new(a)