async-imap does not do its own buffering, but calls flush() after
sending each command. Using BufWriter reduces the number of write()
system calls used to send a single command.
Note that BufWriter is set up on top of TLS streams, because
we can't guarantee that TLS libraries flush the stream before
waiting for response.
This makes it possible to fuzz test the functions
without exposing the module interface in the deltachat core
interface.
Also ensure that format_flowed will not grow a dependency
on deltachat core types.
If we move the detached signatures validation code out of try_decrypt(), we don't need to convert an
already parsed signed message part to Vec and then parse it back. Also this simplifies the
try_decrypt() semantics and return type. It can't make a good coffee anyway.
Services like Lacre [1] on Disroot and Inbound Encryption on Posteo [2]
offer to encrypt all incoming messages with the provided OpenPGP
public key. Resulting messages are encrypted, but not end-to-end encrypted
and not signed by the sender, therefore should not have a padlock displayed.
However, such encrypted and unsigned message is also not an indication
of an error on ongoing attack, so we shoud not report this as a problem
to the user.
[1] https://lacre.io/
[2] https://posteo.de/en/help/how-do-i-activate-inbound-encryption-with-my-public-pgp-key
This way we don't need a separate code path for signatures validation for unencrypted
messages. Also, now we degrade encryption only if there are no valid signatures, so the code for
upgrading encryption back isn't needed.
Note that if the message is encrypted, we don't check whether it's signed with an attached key
currently, otherwise a massive refactoring of the code is needed because for encrypted messages a
signature is checked and discarded first now.
* do not `SELECT *` on old tables to fill new ones
the old table may contain deprecrated columns for whatever reason;
as a result the query fails as the statement tries to insert eg.
16 columns into 12 colums
(concrete error for acpeerstate that have several deprecated columns)
* update CHANGELOG
IMAP capabilities and selected folder are IMAP session,
not IMAP client property.
Moving most operations into IMAP session structure
removes the need to constantly check whether IMAP session exists
and reduces number of invalid states, e.g. when a folder is selected but
there is no connection.
Capabilities are determined immediately after logging in,
so there is no need for `capabilities_determined` flag anymore.
Capabilities of the server are always known if there is a session.
`should_reconnect` flag and `disconnect()` function are removed: we
drop the session on error. Even though RFC 3501 says that a client
SHOULD NOT close the connection without a LOGOUT, it is more reliable
to always just drop the connection, especially after an error.
