From 64b8e014444982c3091340d989d5d9bf92c314cb Mon Sep 17 00:00:00 2001
From: Sorunome <mail@sorunome.de>
Date: Thu, 10 Sep 2020 11:24:37 +0200
Subject: [PATCH] fix: Handle duplicate indexes properly

---
 lib/encryption/encryption.dart | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/encryption/encryption.dart b/lib/encryption/encryption.dart
index f6f3a3c..b56dd1e 100644
--- a/lib/encryption/encryption.dart
+++ b/lib/encryption/encryption.dart
@@ -148,6 +148,13 @@ class Encryption {
         // TODO: maybe clear outbound session, if it is ours
         throw (DecryptError.CHANNEL_CORRUPTED);
       }
+      final existingIndex = inboundGroupSession.indexes.entries.firstWhere(
+          (e) => e.value == decryptResult.message_index,
+          orElse: () => null);
+      if (existingIndex != null && existingIndex.key != messageIndexKey) {
+        // TODO: maybe clear outbound session, if it is ours
+        throw (DecryptError.CHANNEL_CORRUPTED);
+      }
       inboundGroupSession.indexes[messageIndexKey] =
           decryptResult.message_index;
       if (!haveIndex) {