From 00cd66b16956a75a1c8dfb1f267b9a26603c09c7 Mon Sep 17 00:00:00 2001
From: Alban Gruin
Date: Mon, 20 Sep 2021 10:08:54 +0200
Subject: ics, ucs: generate event IDs with a random number

Until now, ucs generated unique IDs with the datetime and the number of
an event, starting by 0.  Unfortunately, if two calendars were generated
at the same second, they could have collisions.  To avoid that, the ICS
generator now uses a base ID generated randomly, which should be enough
to avoid collisions.  The RNG is self-initialised in the main function.

Signed-off-by: Alban Gruin <alban@pa1ch.fr>
---
 src/ics.ml | 4 +++-
 src/ucs.ml | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/ics.ml b/src/ics.ml
index 732cbd5..4de1897 100644
--- a/src/ics.ml
+++ b/src/ics.ml
@@ -19,6 +19,8 @@ open CalendarLib
 
 module StringSet = Set.Make (String)
 
+let rng_bound = int_of_float (2. ** 30.) - 1
+
 let to_date = Printer.Calendar.sprint "%Y%m%dT%H%M%S"
 let current_date () = to_date @@ Calendar.now ()
 
@@ -101,5 +103,5 @@ let to_string tz events =
    VERSION:2.0\r\n\
    PRODID:-//ucs//\r\n"
   ^ vtimezone
-  ^ gen_events 0 "" events
+  ^ gen_events (Random.int rng_bound) "" events
   ^ "END:VCALENDAR\r\n"
diff --git a/src/ucs.ml b/src/ucs.ml
index 9950d8c..74849e7 100644
--- a/src/ucs.ml
+++ b/src/ucs.ml
@@ -1,5 +1,5 @@
 (*
- *    Copyright (C) 2020  Alban Gruin
+ *    Copyright (C) 2020, 2021  Alban Gruin
  *
  *    ucs is free software: you can redistribute it and/or modify
  *    it under the terms of the GNU Affero General Public License as published
@@ -67,4 +67,5 @@ let () =
     Term.(const run $ base_url $ celcat_url $ port $ socket),
     Term.info "ucs" ~version:(Version.version ()) ~doc ~exits in
   CalendarLib.Time_Zone.(change Local);
+  Random.self_init ();
   Term.(exit @@ eval cmd)
-- 
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