add collection name validation

lib/mongo/collection.rb

@@ -26,6 +26,24 @@ module XGen
         attr_reader :db, :name, :hint
 
         def initialize(db, name)
+          case name
+          when Symbol, String
+          else
+            raise RuntimeError, "new_name must be a string or symbol"
+          end
+
+          name = name.to_s
+
+          if name.empty? or name.include? ".."
+            raise RuntimeError, "collection names cannot be empty"
+          end
+          if name.include? "$" and not name.match(/^\$cmd/)
+            raise RuntimeError, "collection names must not contain '$'"
+          end
+          if name.match(/^\./) or name.match(/\.$/)
+            raise RuntimeError, "collection names must not start or end with '.'"
+          end
+
           @db, @name = db, name
           @hint = nil
         end

tests/test_db_api.rb

@@ -713,6 +713,27 @@ class DBAPITest < Test::Unit::TestCase
     @@coll.modify({"hello" => "world"}, {"$inc" => "hello"})
   end
 
+  def test_collection_names
+    assert_raise RuntimeError do
+      @@db.collection(5)
+    end
+    assert_raise RuntimeError do
+      @@db.collection("")
+    end
+    assert_raise RuntimeError do
+      @@db.collection("te$t")
+    end
+    assert_raise RuntimeError do
+      @@db.collection(".test")
+    end
+    assert_raise RuntimeError do
+      @@db.collection("test.")
+    end
+    assert_raise RuntimeError do
+      @@db.collection("tes..t")
+    end
+  end
+
   def test_rename_collection
     @@db.drop_collection("foo")
     @@db.drop_collection("bar")