Add optional flag for quoting fields

RFC stanard requires all fields to be US-ASCII. Additional `quote`
may provide extra security (RFC-1806 p. 2.3), but does not allow
for interoperability with API that requires ASCII characters outside
`quote` set e.g. emails[] becomes emails%5B%5D

fixes aio-libs#903

aiohttp/helpers.py

@@ -85,11 +85,12 @@ class FormData:
     """Helper class for multipart/form-data and
     application/x-www-form-urlencoded body generation."""
 
-    def __init__(self, fields=()):
+    def __init__(self, fields=(), quote_fields=True):
         from . import multipart
         self._writer = multipart.MultipartWriter('form-data')
         self._fields = []
         self._is_multipart = False
+        self._quote_fields = quote_fields
 
         if isinstance(fields, dict):
             fields = list(fields.items())
@@ -181,7 +182,9 @@ def _gen_form_data(self, *args, **kwargs):
         for dispparams, headers, value in self._fields:
             part = self._writer.append(value, headers)
             if dispparams:
-                part.set_content_disposition('form-data', **dispparams)
+                part.set_content_disposition(
+                    'form-data', quote_fields=self._quote_fields, **dispparams
+                )
                 # FIXME cgi.FieldStorage doesn't likes body parts with
                 # Content-Length which were sent via chunked transfer encoding
                 part.headers.pop(hdrs.CONTENT_LENGTH, None)

aiohttp/multipart.py

@@ -851,7 +851,7 @@ def _apply_content_transfer_encoding(self, stream):
             raise RuntimeError('unknown content transfer encoding: {}'
                                ''.format(encoding))
 
-    def set_content_disposition(self, disptype, **params):
+    def set_content_disposition(self, disptype, quote_fields=True, **params):
         """Sets ``Content-Disposition`` header.
 
         :param str disptype: Disposition type: inline, attachment, form-data.
@@ -868,7 +868,7 @@ def set_content_disposition(self, disptype, **params):
                 if not key or not (TOKEN > set(key)):
                     raise ValueError('bad content disposition parameter'
                                      ' {!r}={!r}'.format(key, val))
-                qval = quote(val, '')
+                qval = quote(val, '') if quote_fields else val
                 lparams.append((key, '"%s"' % qval))
                 if key == 'filename':
                     lparams.append(('filename*', "utf-8''" + qval))

tests/test_helpers.py

@@ -131,6 +131,20 @@ def test_invalid_formdata_content_transfer_encoding():
                            content_transfer_encoding=invalid_val)
 
 
+def test_formdata_field_name_is_quoted():
+    form = helpers.FormData()
+    form.add_field("emails[]", "[email protected]", content_type="multipart/form-data")
+    res = b"".join(form("ascii"))
+    assert b'name="emails%5B%5D"' in res
+
+
+def test_formdata_field_name_is_not_quoted():
+    form = helpers.FormData(quote_fields=False)
+    form.add_field("emails[]", "[email protected]", content_type="multipart/form-data")
+    res = b"".join(form("ascii"))
+    assert b'name="emails[]"' in res
+
+
 def test_access_logger_format():
     log_format = '%T {%{SPAM}e} "%{ETag}o" %X {X} %%P'
     mock_logger = mock.Mock()