test an ordered hash and encode them specially in c

ext/cbson/cbson.c

@@ -289,7 +289,18 @@ static void write_doc(bson_buffer* buffer, VALUE hash) {
     int start_position = buffer->position;
     int length_location = buffer_save_bytes(buffer, 4);
 
-    rb_hash_foreach(hash, write_element, (VALUE)buffer);
+    // we have to check for an OrderedHash and handle that specially
+    if (strcmp(rb_class2name(RBASIC(hash)->klass), "OrderedHash") == 0) {
+        VALUE keys = rb_funcall(hash, rb_intern("keys"), 0);
+        int i;
+        for(i = 0; i < RARRAY(keys)->len; i++) {
+            VALUE key = RARRAY(keys)->ptr[i];
+            VALUE value = rb_hash_aref(hash, key);
+            write_element(key, value, (VALUE)buffer);
+        }
+    } else {
+        rb_hash_foreach(hash, write_element, (VALUE)buffer);
+    }
 
     // write null byte and fill in length
     buffer_write_bytes(buffer, &zero, 1);

tests/test_bson.rb

@@ -1,5 +1,6 @@
 $LOAD_PATH[0,0] = File.join(File.dirname(__FILE__), '..', 'lib')
 require 'mongo'
+require 'mongo/util/ordered_hash'
 require 'test/unit'
 
 class BSONTest < Test::Unit::TestCase
@@ -37,6 +38,16 @@ class BSONTest < Test::Unit::TestCase
     assert_equal doc, @b.deserialize
   end
 
+  def test_ordered_hash
+    doc = OrderedHash.new
+    doc["b"] = 1
+    doc["a"] = 2
+    doc["c"] = 3
+    doc["d"] = 4
+    @b.serialize(doc)
+    assert_equal doc, @b.deserialize
+  end
+
   def test_object
     doc = {'doc' => {'age' => 42, 'name' => 'Spongebob', 'shoe_size' => 9.5}}
     @b.serialize(doc)