New ObjectID#legal_oid_string. Use that in ObjectID#from_string.

lib/mongo/collection.rb

@@ -121,6 +121,11 @@ module XGen
           @db.drop_index(@name, '*')
         end
 
+        # Drop the entire collection. USE WITH CAUTION.
+        def drop
+          @db.drop_collection(@name)
+        end
+
         # Return an array of hashes, one for each index. Each hash contains:
         #
         # :name :: Index name

lib/mongo/types/objectid.rb

@@ -64,6 +64,7 @@ module XGen
         # Given a string representation of an ObjectID, return a new ObjectID
         # with that value.
         def self.from_string(str)
+          raise "illegal ObjectID format" unless legal_oid_string(str)
           data = []
           BYTE_ORDER.each_with_index { |string_position, data_index|
             data[data_index] = str[string_position * 2, 2].to_i(16)
@@ -71,6 +72,13 @@ module XGen
           self.new(data)
         end
 
+        def self.legal_oid_string(str)
+          len = BYTE_ORDER.length * 2
+          str =~ /([0-9a-f]+)/i
+          match = $1
+          str && str.length == len && match == str
+        end
+
         # +data+ is an array of bytes. If nil, a new id will be generated.
         # The time +t+ is only used for testing; leave it nil.
         def initialize(data=nil, t=nil)

tests/test_objectid.rb

@@ -73,6 +73,16 @@ class ObjectIDTest < Test::Unit::TestCase
     assert_equal @o.to_s, o2.to_s
   end
 
+  def test_legal_oid_string
+    assert !ObjectID.legal_oid_string(nil)
+    assert !ObjectID.legal_oid_string("fred")
+    assert !ObjectID.legal_oid_string("0000")
+    assert !ObjectID.legal_oid_string('000102030405060708090A0')
+    assert ObjectID.legal_oid_string('000102030405060708090A0B')
+    assert ObjectID.legal_oid_string('abcdefABCDEF123456789012')
+    assert !ObjectID.legal_oid_string('abcdefABCDEF12345678901x')
+  end
+
   def test_from_string_leading_zeroes
     hex_str = '000000000000000000abcdef'
     o = ObjectID.from_string(hex_str)