xftp-server: add control port (#951)

Co-authored-by: Evgeny Poberezkin <2769109+epoberezkin@users.noreply.github.com>

src/Simplex/FileTransfer/Server/Control.hs

@@ -0,0 +1,31 @@
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Simplex.FileTransfer.Server.Control where
+
+import qualified Data.Attoparsec.ByteString.Char8 as A
+import Data.ByteString (ByteString)
+import Simplex.Messaging.Encoding.String
+
+data ControlProtocol
+  = CPStatsRTS
+  | CPDelete ByteString
+  | CPHelp
+  | CPQuit
+  | CPSkip
+
+instance StrEncoding ControlProtocol where
+  strEncode = \case
+    CPStatsRTS -> "stats-rts"
+    CPDelete bs -> "delete " <> strEncode bs
+    CPHelp -> "help"
+    CPQuit -> "quit"
+    CPSkip -> ""
+  strP =
+    A.takeTill (== ' ') >>= \case
+      "stats-rts" -> pure CPStatsRTS
+      "delete" -> CPDelete <$> (A.space *> strP)
+      "help" -> pure CPHelp
+      "quit" -> pure CPQuit
+      "" -> pure CPSkip
+      _ -> fail "bad ControlProtocol command"