- asynchronous sockets using an event loop
- connect & starttls have completion callback parameters
- callbacks for notification about filled input buffer and emptied
output buffer
- unsent imap command queue
- used when
- socket output buffer is non-empty
- number of commands in flight exceeds limit
- last sent command requires round-trip
- command has a dependency on completion of previous command
- trashnc is tri-state so only a single "scout" trash APPEND/COPY is
sent at first. a possibly resulting CREATE is injected in front of
the remaining trash commands, so they can succeed (or be cancel()d
if it fails).
- queue's presence necessitates imap_cancel implementation
this prepares the code for being called from a callback.
notably, this makes the imap list parser have a "soft stack", so the
recursion can be suspended at any time.
instead of returning a write()-like result, return only a binary status
code - write errors are handled internally anyway, so user code doesn't
have to check the write length.
this makes the IMAP command submission interface asynchronous.
the functions still have synchronous return codes as well - this enables
clean error return paths. only when we invoke callbacks we resort to
refcounting.
as a "side effect", properly sequence commands after CREATE resulting
from [TRYCREATE].
synchronous error codes which are passed through callbacks aren't a
particularly good idea, after all: latest when the callback does stuff
which does not concern the caller, the return code becomes ambiguous.
instead, protect the sync_vars object with a refcount when invoking
driver functions from loops, as the callbacks they call could invalidate
the object and we would have no way of knowing that the loop should be
aborted prematurely. the upcoming async imap driver will also need a
refcount to protect the cancelation marker of the imap socket dispatcher
loop.
that way we don't have to piggy-back (possibly asynchronous) fatal
errors to particular commands.
internally, the drivers still use synchronous return values as well,
so they don't try to access the invalidated store after calling back.
just use the presence of an SSL object as an indicator. if something
goes wrong during the ssl handshake or certificate validation, the
socket must be immediately closed anyway.
don't pretend that the server has no literal+ for the time of the
first relevant command's synchronous execution. instead, enable the
lower layer to do the processing by telling it for which commands
trashnc ("trash's existence not confirmed") is relevant.
we always actually open the mailbox before appending to it, so we
obviously know that it exists - that's why the code was already
commented out. changing this assumption would significantly complicate
matters for little gain, so let's just assume it won't happen.
consequently, also don't set param.create when appending to regular
mailboxes.
- don't silently fail in release mode (expression with side effects
inside assert())
- save some redundand strlen()s by not throwing away known lengths
- reorganize the code for legibility
