feat: for exponential backoff

src/client/util_backoff.ml

@@ -0,0 +1,13 @@
+type t = {
+  mutable delay_s: float;
+  min_delay_s: float;
+  max_delay_s: float;
+}
+
+let create () = { delay_s = 0.001; min_delay_s = 0.001; max_delay_s = 20. }
+
+let on_success self = self.delay_s <- max self.min_delay_s (self.delay_s /. 10.)
+
+let on_error self = self.delay_s <- min self.max_delay_s (self.delay_s *. 2.)
+
+let[@inline] cur_duration_s self = self.delay_s

src/client/util_backoff.mli

@@ -0,0 +1,12 @@
+(** Backoff behavior in case of errors *)
+
+type t
+(** Backoff state. Not thread safe *)
+
+val create : unit -> t
+
+val on_success : t -> unit
+
+val on_error : t -> unit
+
+val cur_duration_s : t -> float