This function should only return temporary errors, e.g. database errors,
as precheck_imf() and dc_receive_imf::add_parts() treat them as such,
retrying the fetch on failure. When permanent errors, like missing
Message-ID, are bubbled up, they cause infinite fetch loop.
* First try making get_recipients use MailHeader (nice and functional)
* Get it to compile by using not-so-functional style
* Add "empty-from" test, drop unnecessary check for error; continue using addrparse_header() instead of addrparse()
* Try to use functional style, unfortunately, I can't get the compiler to accept it
* Do it imperative-style: Do not overwrite To with Cc and vice versa
* Use addrparse_header() once more
* Still addrparse_header()
* Clippy
* Fix compile errors in tests
* Fix typo
* Fix tests again ;-)
* Code style
* Code style; try a HashMap<addr: String, display_name: String> as an address list but I am not convinced
* Code style; Use Vec<SingleInfo> as address list
* Clippy
* Add tests
* Add another test
* Remove stale comments
If error is ignored, the message will never be fetched again, even if
there was a database write error.
dc_receive_imf itself is modified to ignore unrecoverable errors, to
prevent endless refetching of incorrect messages.
these events take the message-id as parameter and might be used
to update an existing list (although to recommended)
if the event is issued for hidden messages,
this might led to "empty" messages flashing up -
the ui tries to get the message from the event,
after a moment, on the next update, the message disappears again
as hidden messages are of course not returned eg. by dc_get_chat_msgs().
the effect was probably always visible for secure-join-messages on ios,
however, become much more visible recently when read-receipts are added
as hidden messages as well (to make them auto-deletable).
the footer mark normally used in email-conversations is `-- `,
note the trailing space, see RFC 3676, §4.3
unfortunately, the final space is removed by some providers,
which lead to footers showing up on delta-to-delta-conversations
(on nondc-to-delta, this is not an issue as we cannot be sure anyway
and show a [...] therefore)
this change accepts lines with only `--` as a footer separator
if there is no other footer separator
and if the line before is empty and the line after is not.
as there is still some chance to remove text accidentally,
see tests, some protection against that is needed in another commit.
