add X-FakeSMTPd-Receiver headers

Author: srittau

README.md

@@ -6,7 +6,8 @@ FakeSMTPd is an SMTP server for testing mail functionality. Any mail sent via
 this server will be saved, but will not be forwarded any further.
 
 Mail is printed to stdout by default in default mbox format, as defined in
-[RFC 4155](https://www.ietf.org/rfc/rfc4155.txt).
+[RFC 4155](https://www.ietf.org/rfc/rfc4155.txt). The SMTP mail receivers
+are added in X-FakeSMTPd-Receiver headers.
 
 Usage
 -----

fakesmtpd/mbox.py

@@ -4,6 +4,8 @@
 def print_mbox_mail(stream, state: State) -> None:
     """Print a mail in RFC 4155 default mbox format."""
     stream.write(f"From {state.reverse_path} {state.date.ctime()}\n")
+    for receiver in state.forward_path:
+        stream.write(f"X-FakeSMTPd-Receiver: {receiver}\n")
     stream.write(state.mail_data.replace("\r\n", "\n"))
     stream.write("\n")
     stream.flush()

fakesmtpd_test/mbox.py

@@ -19,6 +19,8 @@ def test_print(self):
         state.mail_data = "Subject: Foo\r\n\r\nText\r\n"
         print_mbox_mail(out, state)
         assert_equal("From sender@example.com Sun Jun  4 14:34:15 2017\n"
+                     "X-FakeSMTPd-Receiver: receiver1@example.com\n"
+                     "X-FakeSMTPd-Receiver: receiver2@example.com\n"
                      "Subject: Foo\n"
                      "\n"
                      "Text\n"