From c81eb7079f53996b2b677ca9ba82b96bd10df4ef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marcin=20W=C3=B3jtowicz?= <marcin.wojtowicz@iohk.io>
Date: Mon, 20 Oct 2025 19:31:55 +0200
Subject: [PATCH] driver: bugfix

Using maybeToList will cause the accumulator to hold the trailing
bytes twice. This will result in the annotator grabbing the wrong
fragments in raw format. The messages will decode properly; however
if these raw fragments are forwarded to other peers, they will be
rejected and the remote will close the connection.
---
 ...ocodile-dentist_bugfix_runannotateddecoder.md | 16 ++++++++++++++++
 .../lib/Ouroboros/Network/Driver/Simple.hs       |  3 +--
 2 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 ouroboros-network/changelog.d/20251020_193107_crocodile-dentist_bugfix_runannotateddecoder.md

diff --git a/ouroboros-network/changelog.d/20251020_193107_crocodile-dentist_bugfix_runannotateddecoder.md b/ouroboros-network/changelog.d/20251020_193107_crocodile-dentist_bugfix_runannotateddecoder.md
new file mode 100644
index 00000000000..f57ce99a183
--- /dev/null
+++ b/ouroboros-network/changelog.d/20251020_193107_crocodile-dentist_bugfix_runannotateddecoder.md
@@ -0,0 +1,16 @@
+<!--
+A new scriv changelog fragment.
+
+Uncomment the section that is right (remove the HTML comment wrapper).
+For top level release notes, leave all the headers commented out.
+-->
+
+<!--
+### Breaking
+
+- A bullet item for the Breaking category.
+
+
+### Non-Breaking
+
+- bugfix `runAnnotatedDecoderWithChannel`
diff --git a/ouroboros-network/framework/lib/Ouroboros/Network/Driver/Simple.hs b/ouroboros-network/framework/lib/Ouroboros/Network/Driver/Simple.hs
index baf6c256576..6bd17eee2bd 100644
--- a/ouroboros-network/framework/lib/Ouroboros/Network/Driver/Simple.hs
+++ b/ouroboros-network/framework/lib/Ouroboros/Network/Driver/Simple.hs
@@ -50,7 +50,6 @@ import Control.Monad.Class.MonadFork
 import Control.Monad.Class.MonadThrow
 import Control.Tracer (Tracer (..), contramap, traceWith)
 import Data.Functor.Identity (Identity (..))
-import Data.Maybe (maybeToList)
 
 
 -- $intro
@@ -327,7 +326,7 @@ runAnnotatedDecoderWithChannel
   -> DecodeStep bytes failure m (bytes -> a)
   -> m (Either failure (a, Maybe bytes))
 
-runAnnotatedDecoderWithChannel Channel{recv} bs0 = go (maybeToList bs0) bs0
+runAnnotatedDecoderWithChannel Channel{recv} = go []
   where
     go :: [bytes]
        -> Maybe bytes