Added DB#master method.

lib/mongo/db.rb

@@ -49,6 +49,8 @@ module XGen
         # The name of the database.
         attr_reader :name
 
+        attr_reader :host, :port
+
         # The database's socket. For internal use only.
         attr_reader :socket
 
@@ -151,6 +153,20 @@ module XGen
           ok?(doc) && is_master.kind_of?(Numeric) && is_master.to_i == 1
         end
 
+        # Returns a string of the form "host:port" that points to the master
+        # database. Works even if this is the master database.
+        def master
+          doc = db_command(:ismaster => 1)
+          is_master = doc['ismaster']
+          raise "Error retrieving master database" unless ok?(doc) && is_master.kind_of?(Numeric)
+          case is_master.to_i
+          when 1
+            "#@host:#@port"
+          else
+            doc['remote']
+          end
+        end
+
         # Close the connection to the database.
         def close
           @socket.close

tests/test_db_api.rb

@@ -354,4 +354,8 @@ class DBAPITest < Test::Unit::TestCase
     assert @db.master?
   end
 
+  def test_master
+    assert_equal "#{@db.host}:#{@db.port}", @db.master
+  end
+
 end