In Python 2.7, encode strings in add_header() as ASCII (#72)

* In Python 2, encode other strings in add_header() calls into ASCII so getting this filename does not cause Unicode errors
* Fix test compatibility in Python3

marrow/mailer/message.py

@@ -322,11 +322,18 @@ def attach(self, name, data=None, maintype=None, subtype=None,
 				filename=(filename_charset, filename_language, filename)
 
 		if inline:
-			part.add_header('Content-Disposition', 'inline', filename=filename)
-			part.add_header('Content-ID', '<%s>' % filename)
+			if sys.version_info < (3, 0):
+				part.add_header('Content-Disposition'.encode('utf-8'), 'inline'.encode('utf-8'), filename=filename)
+				part.add_header('Content-ID'.encode('utf-8'), '<%s>'.encode('utf-8') % filename)
+			else:	
+				part.add_header('Content-Disposition', 'inline', filename=filename)
+				part.add_header('Content-ID', '<%s>' % filename)
 			self.embedded.append(part)
 		else:
-			part.add_header('Content-Disposition', 'attachment', filename=filename)
+			if sys.version_info < (3, 0):
+				part.add_header('Content-Disposition'.encode('utf-8'), 'attachment'.encode('utf-8'), filename=filename)
+			else:
+				part.add_header('Content-Disposition', 'attachment', filename=filename)
 			self.attachments.append(part)
 
 	def embed(self, name, data=None):

test/test_message.py

@@ -281,6 +281,29 @@ def test_mime_embed_failures(self):
 
 		with pytest.raises(TypeError):
 			message.embed('test.gif', object())
+
+	def test_that_add_header_and_collapse_header_are_inverses_ascii_filename(self):
+		message = self.build_message()
+		message.plain = "Hello world."
+		message.rich = "Farewell cruel world."
+		message.attach("wat.txt", b"not a unicode snowman") # calls add_header() under the covers
+		attachment = message.attachments[0]
+		filename = attachment.get_filename() # calls email.utils.collapse_rfc2231_value() under the covers
+		assert filename == "wat.txt"
+
+	def test_that_add_header_and_collapse_header_are_inverses_non_ascii_filename(self):
+		message = self.build_message()
+		message.plain = "Hello world."
+		message.rich = "Farewell cruel world."
+		message.attach("☃.txt", b"unicode snowman", filename_language='en-us')
+		attachment = message.attachments[0]
+		filename = attachment.get_param('filename', object(), 'content-disposition') # get_filename() calls this under the covers
+		assert isinstance(filename, tuple)  # Since attachment encoded according to RFC2231, should be represented as a tuple		
+		filename = attachment.get_filename()  # Calls email.utils.collapse_rfc2231_value() under the covers, currently fails
+		if sys.version_info < (3, 0):
+			assert isinstance(filename, basestring)  # Successfully converts tuple to a string
+		else:
+			assert isinstance(filename, str)
 
 	def test_recipients_collection(self):
 		message = self.build_message()