Closes#13484.
These options tell zulip whether to prefer the plaintext or html version
of the email message. prefer-text is the default behavior, so including
the option doesn't change anything as of now, but we're adding it to
prepare to potentially change the default behavior in the future.
As we add more address options, which will have different behavior than
simply setting option_name=True, we need to migrate this subsystem to
something that better supports more complex logic and will allow
encapsulating it, instead of needing to be put all over the
decode_email_address function.
In addition to the "+show-sender" option, we now add "+include-footers"
which disables stripping of the footer from the email body if this token
is included in the email address.
To enable a comfortable way of adding more optional tokens in the
address (like current '+show-sender') we change decode_email_address to
return a general dictionary containing options specified through adding
these optional tokens in the To: address. For now, we only have
"+show-sender", but more can be easily added using this change.
With the previous commit, fixes#1836.
As specified in the issue above, we make
get_email_gateway_message_string_from_address raise an exception if
it doesn't recognise the email gateway address pattern. Then, we make
appropriate adjustments in the codepaths which call this function.
These functions don't really belong in actions.py, so we move them out,
into email_mirror_helpers.py. They can't go directly into
email_mirror.py or we'd get circular imports resulting in ImportError.
Mateusz Mandera