fix: message cache removal crash (#2682)

tests/test_message_cache.nim

@@ -1,8 +1,10 @@
 {.used.}
 
-import std/sets, stew/[results, byteutils], testutils/unittests
+import std/[sets, random], stew/[results, byteutils], testutils/unittests
 import ../../waku/waku_core, ../../waku/waku_api/message_cache, ./testlib/wakucore
 
+randomize()
+
 suite "MessageCache":
   setup:
     ## Given
@@ -209,3 +211,39 @@ suite "MessageCache":
 
     check:
       cache.messagesCount() == 2
+
+  test "fuzzing":
+    let testContentTopic1 = "contentTopic1"
+    let testContentTopic2 = "contentTopic2"
+
+    let cache = MessageCache.init(50)
+
+    cache.contentSubscribe(testContentTopic1)
+    cache.contentSubscribe(testContentTopic2)
+
+    for _ in 0 .. 10000:
+      let numb = rand(1.0)
+
+      if numb > 0.4:
+        let topic = if rand(1.0) > 0.5: testContentTopic1 else: testContentTopic2
+
+        let testMessage = fakeWakuMessage(contentTopic = topic)
+
+        cache.addMessage(DefaultPubsubTopic, testMessage)
+      elif numb > 0.1:
+        let topic = if rand(1.0) > 0.5: testContentTopic1 else: testContentTopic2
+
+        let clear = rand(1.0) > 0.5
+        discard cache.getAutoMessages(topic, clear)
+      elif numb > 0.05:
+        if rand(1.0) > 0.5:
+          cache.pubsubUnsubscribe(DefaultPubsubTopic)
+        else:
+          cache.pubsubSubscribe(DefaultPubsubTopic)
+      else:
+        let topic = if rand(1.0) > 0.5: testContentTopic1 else: testContentTopic2
+
+        if rand(1.0) > 0.5:
+          cache.contentUnsubscribe(topic)
+        else:
+          cache.contentSubscribe(topic)

waku/waku_api/message_cache.nim

@@ -134,7 +134,7 @@ proc pubsubUnsubscribe*(self: MessageCache, pubsubTopic: PubsubTopic) =
     dec(j)
 
   # check if messages on this pubsub topic are indexed by any content topic, if not remove them.
-  for mId in msgIndices:
+  for mId in msgIndices.sorted(SortOrder.Descending):
     if not self.contentIndex.anyIt(it.msgIdx == mId):
       self.removeMessage(mId)
 
@@ -167,7 +167,7 @@ proc contentUnsubscribe*(self: MessageCache, contentTopic: ContentTopic) =
     dec(j)
 
   # check if messages on this content topic are indexed by any pubsub topic, if not remove them.
-  for mId in msgIndices:
+  for mId in msgIndices.sorted(SortOrder.Descending):
     if not self.pubsubIndex.anyIt(it.msgIdx == mId):
       self.removeMessage(mId)
 
@@ -275,7 +275,7 @@ proc getAutoMessages*(
   let messages = msgIndices.mapIt(self.messages[it])
 
   if clear:
-    for idx in msgIndices.reversed:
+    for idx in msgIndices.sorted(SortOrder.Descending):
       self.removeMessage(idx)
 
   return ok(messages)