[Fixes: #11520] Rotate mailservers on error conditions

If a mailserver request is failing we disconnect at the 3rd attempt.

Though once we are disconnected, we connect again to the same mailserver
based on ping time.

This commit changes the behavior so that mailservers are penalized if
they are returning errors.

Signed-off-by: Andrea Maria Piana <andrea.maria.piana@gmail.com>

src/status_im/mailserver/constants.cljs

@@ -11,6 +11,9 @@
 (def max-limit 1000)
 (def backoff-interval-ms 3000)
 (def default-limit max-limit)
+;; If a mailserver fails, how long before we should consider them again
+;; for selection, in ms
+(def cooloff-period 120000)
 (def connection-timeout
   "Time after which mailserver connection is considered to have failed"
   10000)

src/status_im/mailserver/core.cljs

@@ -100,10 +100,11 @@
                  :method  "admin_removePeer"
                  :params  [enode]}
         payload (.stringify js/JSON (clj->js args))]
-    (status/call-private-rpc payload
-                             (handlers/response-handler
-                              #(log/info "mailserver: remove-peer success" %)
-                              #(log/error "mailserver: remove-peer error" %)))))
+    (when enode
+      (status/call-private-rpc payload
+                               (handlers/response-handler
+                                #(log/info "mailserver: remove-peer success" %)
+                                #(log/error "mailserver: remove-peer error" %))))))
 
 (re-frame/reg-fx
  :mailserver/add-peer
@@ -272,6 +273,31 @@
                        :on-success
                        #(re-frame/dispatch [::get-latency-callback %])}]}))
 
+(fx/defn log-mailserver-failure [{:keys [db now]}]
+  (when-let [mailserver (fetch-current db)]
+    {:db (assoc-in db [:mailserver/failures (:address mailserver)] now)}))
+
+(defn sort-mailservers
+  "Sort mailservers sorts the mailservers by recent failures, and by rtt
+  for breaking ties"
+  [{:keys [now db]} mailservers]
+  (let [mailserver-failures (:mailserver/failures db)
+        sort-fn (fn [a b]
+                  (let [failures-a (get mailserver-failures (:address a))
+                        failures-b (get mailserver-failures (:address b))
+                        has-a-failed? (boolean
+                                       (and failures-a (<= (- now failures-a) constants/cooloff-period)))
+                        has-b-failed? (boolean
+                                       (and failures-b (<= (- now failures-b) constants/cooloff-period)))]
+                    ;; If both have failed, or none of them, then compare rtt
+                    (cond
+                      (= has-a-failed? has-b-failed?)
+                      (compare (:rttMs a) (:rttMs b))
+                     ;; Otherwise prefer the one that has not failed recently
+                      has-a-failed? 1
+                      has-b-failed? -1)))]
+    (sort sort-fn mailservers)))
+
 (fx/defn set-current-mailserver-with-lowest-latency
   "Picks a random mailserver amongs the ones with the lowest latency
    The results with error are ignored
@@ -281,7 +307,7 @@
   (let [successful-pings (remove :error latency-results)]
     (when (seq successful-pings)
       (let [address (-> (take (pool-size (count successful-pings))
-                              (sort-by :rttMs successful-pings))
+                              (sort-mailservers cofx successful-pings))
                         rand-nth
                         :address)
             mailserver-id (mailserver-address->id db address)]
@@ -575,10 +601,14 @@
   (when (contains? db :multiaccount)
     (let [last-connection-attempt (:mailserver/last-connection-attempt db)]
       (when (and (fetch-use-mailservers? cofx)
-                 (<= (- now last-connection-attempt)))
-        (fx/merge cofx
-                  (when (not= :connected (:mailserver/state db))
-                    (change-mailserver)))))))
+                 ;; We are not connected
+                 (not= :connected (:mailserver/state db))
+                 ;; We either never tried to connect to this peer
+                 (or (nil? last-connection-attempt)
+                     ;; Or 30 seconds have passed and no luck
+                     (<= (- now last-connection-attempt) (* constants/connection-timeout 3))))
+        ;; Then we change mailserver
+        (change-mailserver cofx)))))
 
 (fx/defn reset-request-to
   [{:keys [db]}]
@@ -974,6 +1004,7 @@
                          (:attempts current-request))
         (fx/merge cofx
                   {:db (update db :mailserver/current-request dissoc :attempts)}
+                  (log-mailserver-failure)
                   (change-mailserver))
         (let [mailserver (get-mailserver-when-ready cofx)
               offline?   (= :offline (:network-status db))]

src/status_im/mailserver/core_test.cljs

@@ -879,3 +879,20 @@
               {:from 2
                :to   8}
               #{"chat1"}))))))
+
+(deftest sort-mailserver-test
+  (testing "it orders them by whether they have failed first and by rtts"
+    (let [now                 (inc constants/cooloff-period)
+          mailserver-failures {:a 1
+                               :b 0}
+          cofx {:now now
+                :db {:mailserver/failures mailserver-failures}}
+          mailserver-pings [{:address :a :rttMs 2}
+                            {:address :b :rttMs 3}
+                            {:address :d :rttMs 1}
+                            {:address :e :rttMs 4}]
+          expected-order  [{:address :d :rttMs 1}
+                           {:address :b :rttMs 3}
+                           {:address :e :rttMs 4}
+                           {:address :a :rttMs 2}]]
+      (is (= expected-order (mailserver/sort-mailservers cofx mailserver-pings))))))