Add setting that says how much time to keep retrying activity delivery

config/settings-default.yaml

@@ -131,7 +131,6 @@ max-accounts: 3
 # Federation
 ###############################################################################
 
-
 # Whether to support federation. This includes:
 #
 # * Accept activities from other servers in the inbox
@@ -148,3 +147,11 @@ hashids-salt-file:      config/hashids_salt
 # Whether to reject an HTTP signature when we want to insert a new key or usage
 # record but reached the limit setting
 reject-on-max-keys:     true
+
+# The duration of time during which a remote actor is unreachable and we
+# periodically retry to deliver them activities. After that period of time, we
+# stop trying to deliver and we remove them from follower lists of local
+# actors.
+drop-delivery-after:
+  amount:               25
+  unit:                 weeks

src/Vervis/Settings.hs

@@ -31,8 +31,10 @@ import Control.Exception           (throw)
 import Data.Aeson                  (Result (..), fromJSON, withObject, (.!=),
                                     (.:?))
 import Data.FileEmbed              (embedFile)
-import Data.Time.Interval (TimeInterval)
-import Data.Time.Interval.Aeson (interval)
+import Data.Time.Clock
+import Data.Time.Interval
+import Data.Time.Interval.Aeson
+import Data.Time.Units
 import Data.Yaml                   (decodeEither')
 import Database.Persist.Postgresql (PostgresConf)
 import Language.Haskell.TH.Syntax  (Exp, Name, Q)
@@ -139,6 +141,11 @@ data AppSettings = AppSettings
       -- over HTTP, which possibly means we have to do more HTTP key fetching,
       -- and the target server gets a higher load of key fetch GET requests.
     , appRejectOnMaxKeys          :: Bool
+      -- | The duration of time during which a remote actor is unreachable and
+      -- we periodically retry to deliver them activities. After that period of
+      -- time, we stop trying to deliver and we remove them from follower lists
+      -- of local actors.
+    , appDropDeliveryAfter        :: NominalDiffTime
     }
 
 instance FromJSON AppSettings where
@@ -185,8 +192,13 @@ instance FromJSON AppSettings where
         appCapabilitySigningKeyFile <- o .: "capability-signing-key"
         appHashidsSaltFile          <- o .: "hashids-salt-file"
         appRejectOnMaxKeys          <- o .: "reject-on-max-keys"
+        appDropDeliveryAfter        <- ndt <$> o .: "drop-delivery-after"
 
         return AppSettings {..}
+        where
+        toSeconds :: TimeInterval -> Second
+        toSeconds = toTimeUnit
+        ndt = fromIntegral . toSeconds . interval
 
 -- | Settings for 'widgetFile', such as which template languages to support and
 -- default Hamlet settings.