allow passing custom headers in FormRequest.from_response()

scrapy/http/request/form.py

@@ -56,10 +56,12 @@ class FormRequest(Request):
             for k, v in formdata.iteritems():
                 for v2 in v if hasattr(v, '__iter__') else [v]:
                     form.new_control('text', k, {'value': v2})
-        
+
         if dont_click:
             url, body, headers = form._switch_click('request_data')
         else:
             url, body, headers = form.click_request_data(**(clickdata or {}))
 
-        return cls(url, method=form.method, body=body, headers=headers, **kwargs)
+        kwargs.setdefault('headers', {}).update(headers)
+
+        return cls(url, method=form.method, body=body, **kwargs)

scrapy/tests/test_http_request.py

@@ -231,6 +231,21 @@ class FormRequestTest(RequestTest):
         self.assertEqual(fs['test2'].value, 'xxx')
         self.assertEqual(fs['six'].value, 'seven')
 
+    def test_from_response_extra_headers(self):
+        respbody = """
+<form action="post.php" method="POST">
+<input type="hidden" name="test" value="val1">
+<input type="hidden" name="test" value="val2">
+<input type="hidden" name="test2" value="xxx">
+</form>
+        """
+        headers = {"Accept-Encoding": "gzip,deflate"}
+        response = Response("http://www.example.com/this/list.html", body=respbody)
+        r1 = self.request_class.from_response(response, formdata={'one': ['two', 'three'], 'six': 'seven'}, headers=headers, callback=lambda x: x)
+        self.assertEqual(r1.method, 'POST')
+        self.assertEqual(r1.headers['Content-type'], 'application/x-www-form-urlencoded')
+        self.assertEqual(r1.headers['Accept-Encoding'], 'gzip,deflate')
+
     def test_from_response_get(self):
         respbody = """
 <form action="get.php" method="GET">