Push notification extension

This change adds XDELTAPUSH capability.

Delta Chat clients detecting this capability
can set /private/devicetoken IMAP metadata
on the inbox to subscribe for Apple (APNS)
notifications.

Notifications are implemented in a new
`chatmail-metadata` service
which handles requests to set /private/devicetoken
IMAP metadata from Delta Chat clients
and /private/messagenew requests from
push_notification_lua script.

To avoid sending notifications for
MDNs, webxdc updates and Delta Chat sync messages,
messages with Auto-Submitted header are ignored
by setting $Auto keyword (flag) on them in Sieve script
and skipping such messages in push_notification_lua script.
Outgoing messages are also ignored.

cmdeploy/src/cmdeploy/__init__.py

@@ -102,6 +102,7 @@ def _install_remote_venv_with_chatmaild(config) -> None:
         "doveauth",
         "filtermail",
         "echobot",
+        "chatmail-metadata",
     ):
         params = dict(
             execpath=f"{remote_venv_dir}/bin/{fn}",
@@ -337,6 +338,27 @@ def _configure_dovecot(config: Config, debug: bool = False) -> bool:
         mode="644",
     )
     need_restart |= auth_config.changed
+    lua_push_notification_script = files.put(
+        src=importlib.resources.files(__package__).joinpath(
+            "dovecot/push_notification.lua"
+        ),
+        dest="/etc/dovecot/push_notification.lua",
+        user="root",
+        group="root",
+        mode="644",
+    )
+    need_restart |= lua_push_notification_script.changed
+
+    sieve_script = files.put(
+        src=importlib.resources.files(__package__).joinpath(
+            "dovecot/default.sieve"
+        ),
+        dest="/etc/dovecot/default.sieve",
+        user="root",
+        group="root",
+        mode="644",
+    )
+    need_restart |= sieve_script.changed
 
     files.template(
         src=importlib.resources.files(__package__).joinpath("dovecot/expunge.cron.j2"),
@@ -484,7 +506,7 @@ def deploy_chatmail(config_path: Path) -> None:
 
     apt.packages(
         name="Install Dovecot",
-        packages=["dovecot-imapd", "dovecot-lmtpd"],
+        packages=["dovecot-imapd", "dovecot-lmtpd", "dovecot-sieve"],
     )
 
     apt.packages(

cmdeploy/src/cmdeploy/dovecot/default.sieve

@@ -0,0 +1,5 @@
+require ["imap4flags"];
+
+if header :is ["Auto-Submitted"] ["auto-replied", "auto-generated"] {
+	addflag "$Auto";
+}

cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2

@@ -21,7 +21,7 @@ mail_plugins = quota
 # these are the capabilities Delta Chat cares about actually 
 # so let's keep the network overhead per login small
 # https://github.com/deltachat/deltachat-core-rust/blob/master/src/imap/capabilities.rs
-imap_capability = IMAP4rev1 IDLE MOVE QUOTA CONDSTORE NOTIFY METADATA
+imap_capability = IMAP4rev1 IDLE MOVE QUOTA CONDSTORE NOTIFY METADATA XDELTAPUSH
 
 
 # Authentication for system users.
@@ -71,6 +71,9 @@ mail_privileged_group = vmail
 ## Mail processes
 ##
 
+# Pass all IMAP METADATA requests to the server implementing Dovecot's dict protocol.
+mail_attribute_dict = proxy:/run/dovecot/metadata.socket:metadata
+
 # Enable IMAP COMPRESS (RFC 4978).
 # <https://datatracker.ietf.org/doc/html/rfc4978.html>
 protocol imap {
@@ -79,7 +82,21 @@ protocol imap {
 }
 
 protocol lmtp {
-  mail_plugins = $mail_plugins quota
+  # quota plugin documentation:
+  # <https://doc.dovecot.org/configuration_manual/quota_plugin/>
+  #
+  # notify plugin is a dependency of push_notification plugin:
+  # <https://doc.dovecot.org/settings/plugin/notify-plugin/>
+  #
+  # push_notification plugin documentation:
+  # <https://doc.dovecot.org/configuration_manual/push_notification/>
+  #
+  # mail_lua and push_notification_lua are needed for Lua push notification handler.
+  # <https://doc.dovecot.org/configuration_manual/push_notification/#configuration>
+  #
+  # Sieve to mark messages that should not be notified as \Seen
+  # <https://doc.dovecot.org/configuration_manual/sieve/configuration/>
+  mail_plugins = $mail_plugins quota mail_lua notify push_notification push_notification_lua sieve
 }
 
 plugin {
@@ -95,7 +112,15 @@ plugin {
   # quota_over_flag_value = TRUE
 }
 
+# push_notification configuration
+plugin {
+  # <https://doc.dovecot.org/configuration_manual/push_notification/#lua-lua>
+  push_notification_driver = lua:file=/etc/dovecot/push_notification.lua
+}
 
+plugin {
+  sieve_default = file:/etc/dovecot/default.sieve
+}
 
 service lmtp {
   user=vmail

cmdeploy/src/cmdeploy/dovecot/push_notification.lua

@@ -0,0 +1,32 @@
+function dovecot_lua_notify_begin_txn(user)
+  return user
+end
+
+function contains(v, needle)
+  for _, keyword in ipairs(v) do
+    if keyword == needle then
+      return true
+    end
+  end
+  return false
+end
+
+function dovecot_lua_notify_event_message_new(user, event)
+  local mbox = user:mailbox(event.mailbox)
+  mbox:sync()
+
+  if user.username ~= event.from_address then
+    -- Incoming message
+    if not contains(event.keywords, "$Auto") then
+      -- Not an Auto-Submitted message, notifying.
+
+      -- Notify METADATA server about new message.
+      mbox:metadata_set("/private/messagenew", "")
+    end
+  end
+
+  mbox:free()
+end
+
+function dovecot_lua_notify_end_txn(ctx, success)
+end