notifications server rfc/schema (#332)

* notifications server rfc/schema

* update schema/protocol

protocol/simplex-uri-request.txt

@@ -13,6 +13,6 @@ Change controller: Evgeny Poberezkin <ep@simplex.chat>
 
 References:
 The syntax for connection requests in the latest version of SimpleX Agent Protocol:
-https://github.com/simplex-chat/simplexmq/blob/v5/protocol/agent-protocol.md#connection-request
+https://github.com/simplex-chat/simplexmq/blob/master/protocol/agent-protocol.md#connection-request
 SimpleX Messaging Protocol:
-https://github.com/simplex-chat/simplexmq/blob/v5/protocol/simplex-messaging.md
+https://github.com/simplex-chat/simplexmq/blob/master/protocol/simplex-messaging.md

protocol/smp-uri-request.txt

@@ -13,4 +13,4 @@ Change controller: Evgeny Poberezkin <ep@simplex.chat>
 
 References:
 The syntax for message queue URIs in the latest version of SimpleX Messaging Protocol:
-https://github.com/simplex-chat/simplexmq/blob/v5/protocol/simplex-messaging.md#smp-queue-uri
+https://github.com/simplex-chat/simplexmq/blob/master/protocol/simplex-messaging.md#smp-queue-uri

rfcs/2022-03-22-nofication-server.md

@@ -0,0 +1,91 @@
+# Notification server
+
+## Background and motivation
+
+SimpleX Chat clients should receive message notifications when not being online and/or subscribed to SMP servers.
+
+To avoid revealing identities of clients directly to SMP servers via any kind of push notification tokens, a new party called SimpleX Notification Server is introduced to act as a service for subscribing to SMP server queue notifications on behalf of clients and sending push notifications to them.
+
+## Proposal
+
+TCP service using the same TLS transport as SMP server, with the fixed size blocks (256 bytes?) and the following set of commands:
+
+### Protocol
+
+#### Create subscription
+
+Command:
+
+`%s"CREATE " ntfSmpQueueURI ntfPrivateKey token subPublicKey`
+
+Response:
+
+`s%"OK"`
+
+#### Check subscription status
+
+Command:
+
+`%s"CHECK " ntfSmpQueueURI`
+
+Response:
+
+```abnf
+statusResp = %s"STAT " status
+status = %s"ERR AUTH" / "ERR SMP AUTH" / %s"ERR SMP TIMEOUT" / %s"ACTIVE" / %s"PENDING"
+```
+
+#### Update subscription device token
+
+Command:
+
+`%s"TOKEN " ntfSmpQueueURI token`
+
+Response:
+
+`s%"OK" / %s"ERR"`
+
+#### Delete subscription (e.g. when deleting the queue or moving to another notification server)
+
+Command:
+
+`%s"DELETE " SP ntfSmpQueueURI`
+
+Response:
+
+`s%"OK" / %s"ERR"`
+
+### Agent schema changes
+
+See [migration](../src/Simplex/Messaging/Agent/Store/SQLite/Migrations/M20220322_notifications.hs)
+
+### Agent code
+
+```haskell
+data NtfOptions = NtfOptions
+  { ntfServer :: Server, -- same type as for SMP servers, probably will be renamed
+    ntfToken :: ByteString,
+    ntfInitialCheckDelay :: Int, -- initial check delay after subscription is created, seconds
+    ntfPeriodicCheckInterval :: Int -- subscription check interval, seconds
+  }
+
+data AgentConfig = AgentConfig {
+  -- ...
+  initialNtfOpts :: Maybe NtfOptions
+  -- ...
+  }
+
+data AgentClient = AgentClient {
+  -- ...
+  ntfOpts :: TVar (Maybe NtfOptions)
+  -- ...
+  }
+```
+
+A configuration parameter `initialNtfOpts :: Maybe NtfOptions` - if it is set or changes the agent would automatically manage subscriptions as SMP queues are subscribed/created/deleted and as the token or server changes.
+
+There will be a method to update notifications configuration in case token or server changes.
+
+All subscriptions will be managed in a separate subscription management loop, that would always take the earliest un-updated subscription that requires some action (ntf_sub_action column) and perform this action - the table of subscription would serve both as the table of existing subscriptions and required actions.
+
+E.g. if the queue is subscribed and there is no notification subscription, it will be created in the table with "create" action, and the loop would create it and schedule "check" action on it.

simplexmq.cabal

@@ -41,6 +41,7 @@ library
       Simplex.Messaging.Agent.Store.SQLite.Migrations
       Simplex.Messaging.Agent.Store.SQLite.Migrations.M20220101_initial
       Simplex.Messaging.Agent.Store.SQLite.Migrations.M20220301_snd_queue_keys
+      Simplex.Messaging.Agent.Store.SQLite.Migrations.M20220322_notifications
       Simplex.Messaging.Client
       Simplex.Messaging.Crypto
       Simplex.Messaging.Crypto.Ratchet

src/Simplex/Messaging/Agent/Store/SQLite/Migrations.hs

@@ -26,6 +26,7 @@ import Database.SQLite.Simple.QQ (sql)
 import qualified Database.SQLite3 as SQLite3
 import Simplex.Messaging.Agent.Store.SQLite.Migrations.M20220101_initial
 import Simplex.Messaging.Agent.Store.SQLite.Migrations.M20220301_snd_queue_keys
+import Simplex.Messaging.Agent.Store.SQLite.Migrations.M20220322_notifications
 
 data Migration = Migration {name :: String, up :: Text}
   deriving (Show)
@@ -33,7 +34,8 @@ data Migration = Migration {name :: String, up :: Text}
 schemaMigrations :: [(String, Query)]
 schemaMigrations =
   [ ("20220101_initial", m20220101_initial),
-    ("20220301_snd_queue_keys", m20220301_snd_queue_keys)
+    ("20220301_snd_queue_keys", m20220301_snd_queue_keys),
+    ("20220322_notifications", m20220322_notifications)
   ]
 
 -- | The list of migrations in ascending order by date

src/Simplex/Messaging/Agent/Store/SQLite/Migrations/M20220322_notifications.hs

@@ -0,0 +1,46 @@
+{-# LANGUAGE QuasiQuotes #-}
+
+module Simplex.Messaging.Agent.Store.SQLite.Migrations.M20220322_notifications where
+
+import Database.SQLite.Simple (Query)
+import Database.SQLite.Simple.QQ (sql)
+
+m20220322_notifications :: Query
+m20220322_notifications =
+  [sql|
+ALTER TABLE rcv_queues ADD COLUMN ntf_id BLOB;
+
+ALTER TABLE rcv_queues ADD COLUMN ntf_public_key BLOB;
+
+ALTER TABLE rcv_queues ADD COLUMN ntf_private_key BLOB;
+
+CREATE UNIQUE INDEX idx_rcv_queues_ntf ON rcv_queues (host, port, ntf_id);
+
+CREATE TABLE ntf_servers (
+  ntf_host TEXT NOT NULL,
+  ntf_port TEXT NOT NULL,
+  ntf_key_hash BLOB NOT NULL,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  PRIMARY KEY (ntf_host, ntf_port)
+) WITHOUT ROWID;
+
+CREATE TABLE ntf_subscriptions (
+  ntf_host TEXT NOT NULL,
+  ntf_port TEXT NOT NULL,
+  ntf_sub_status TEXT NOT NULL, -- new, created, active, pending, error_auth
+  ntf_sub_action TEXT, -- if there is an action required on this subscription: create / check / token / delete
+  ntf_sub_action_ts TEXT, -- the earliest time for the action, e.g. checks can be scheduled every X hours
+  ntf_token TEXT NOT NULL, -- or BLOB?
+  smp_host TEXT NOT NULL,
+  smp_port TEXT NOT NULL,
+  smp_ntf_id BLOB NOT NULL,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL, -- this is to check subscription status periodically to know when it was last checked
+  PRIMARY KEY (ntf_host, ntf_port, smp_host, smp_port, smp_ntf_id),
+  FOREIGN KEY (ntf_host, ntf_port) REFERENCES ntf_servers
+    ON DELETE RESTRICT ON UPDATE CASCADE,
+  FOREIGN KEY (smp_host, smp_port, smp_ntf_id) REFERENCES rcv_queues (host, port, ntf_id)
+    ON DELETE RESTRICT ON UPDATE CASCADE
+) WITHOUT ROWID;
+|]