Live updates

Open pages don't poll for new mail. Each tab holds one stream from the server, /api/events (server-sent events), and the server says on it when something changed. (The one exception is a mailbox signed in for the first time: until its first folder is indexed, the page asks every 2 s.) That's why a reverse proxy must not buffer responses, and should speak HTTP/2: over HTTP/1.1 a browser allows six connections per site, and each tab's stream holds one. See Reverse proxy.

What the stream carries

Event	Means	The page
change	A mailbox's folders changed; lists any new Inbox messages	Refetches that mailbox's lists and counts
settings	A setting for everyone changed	Refetches everything shown from settings
account-settings	One mailbox's own settings changed (name, signature, page size…)	Refetches that mailbox's settings and lists
contacts	A contacts sync started or ended	Refetches the contact list
calendar	A mailbox's calendars or events changed (in another tab, browser or device); says when only the calendars did (a name, a colour, shown or hidden)	Refetches its calendars, and its events unless only the calendars changed
reauth	A mailbox's saved password stopped working	Asks you to sign in again
ready	The stream is set up	After a reconnect, refetches everything shown from settings
ping	Every 25 s, to keep the connection open	Nothing

Timings

• The server gathers changes for 150 ms and sends them as one change. The page waits 250 ms more, then refetches. If actions you made are still on their way to the server, it waits until they finish, so it never shows the server half-way (a star back for a moment after unstarring).
• Ticking a calendar on or off shows at once, and stays so: a list of calendars the server sent before it had the change is shown with the tick on top. Each calendar has one change on its way at a time, so clicking fast sends two at most, the last click last.
• New Inbox mail reaches an open page within about a second; mail in other folders within a minute. See Mail sync.
• If the stream drops, the page opens it again after 5 s.
• Apart from the stream, a page refetches anything older than 30 s when its window gets the focus again.
• Desktop notifications are for new, unread Inbox messages while the tab is in the background: at most three per change.

Signing out ends the stream

With every event, and every 25 s, the server checks that the session is still signed in to each mailbox on the stream and unexpired. One that isn't gets nothing more, so the subjects of new mail stop reaching a signed-out page. When no mailbox is left, the stream ends.

Settings changes

A setting changed on the admin page or with the viauna command applies without a restart or a reload, because the change is announced rather than polled for.

1. The change is written to the state store, with a row in the record of changes, in one transaction.
2. The server reads the settings again: at once for a change on its own admin page, or when the viauna command tells it, through the socket viauna.sock in the data directory. The announcement only says "changed": the server reads the store again, which stays the one source of truth, so a lost or repeated announcement can't leave a wrong value.
3. If any value differs, the server sends settings to every open page, the admin's own included. They refetch the configuration, the session, each mailbox's settings, filters, contacts and the admin page.

Every server also reads the settings again once a minute, as a safety net. That covers a socket that couldn't be made (some network filesystems can't hold one; Viauna then logs "no settings socket"). Servers sharing a PostgreSQL database would also tell each other with LISTEN/NOTIFY, and on MySQL or MariaDB within the minute, but running several instances against one database isn't supported yet.

A mailbox's own settings (name, signature, send-as addresses, images, page size) are sent as account-settings to every page on the server signed in to that mailbox, in other tabs and other browsers.

When each change takes effect

Most changes apply to the next request. Some only to what happens next:

Setting	Takes effect
ADMIN_ADDRESSES	At once: someone removed loses the admin page on their next request.
ALLOWED_DOMAINS, ALLOW_CUSTOM_SERVERS	At the next sign-in. Nobody already signed in is signed out: their sessions run until they expire or they sign out.
MAX_ACCOUNTS	When someone next adds an account. Nobody is signed out.
SESSION_DAYS	For new sessions at once; for each existing one the next time it's extended (on use, at most hourly). See Sessions.
MAX_UPLOAD_MB	At the next upload.
CACHE_MB	At the next trim of the message cache, after 50 more messages are downloaded.
CONTACTS, CONTACTS_SYNC	At once. A sync already running finishes.
CALENDAR	At once.
FILTERS, VACATION	Hidden in Viauna at once. Rules already on the mail server keep running until they're changed.
FILTER_FORWARDING	On: at once. Off: filters that forward keep forwarding until the mailbox's filters are next saved.
APP_NAME	Pages at once. The mail server sees the new name (in the IMAP ID Viauna sends) on new connections.
PASSWORD_CHANGE	At once.
Anything set in the environment	At the next restart.

There's no button yet to sign everyone out after narrowing who can sign in. Changing SECRET_KEY does it, for everyone: see Sessions.