From 312f2efc81c843ebf1ba048594196241c8810988 Mon Sep 17 00:00:00 2001
From: DohanKim <hodoli2776@kaist.ac.kr>
Date: Wed, 10 Jun 2026 17:31:40 +0900
Subject: [PATCH] fix: tolerate transport send errors when relaying TURN client
 messages

handle_ex_turn_msg matches the transport send result with a bare
':ok =' in both the gathering-transaction and relay-candidate branches.
When the underlying socket has already been closed (e.g. a late ex_turn
timer/refresh message arriving for a relay candidate whose socket went
away), the send returns {:error, :closed} and the whole ICEAgent crashes
with a MatchError, taking the PeerConnection down with it:

    ** (MatchError) no match of right hand side value: {:error, :closed}
        lib/ex_ice/priv/ice_agent.ex:950: ExICE.Priv.ICEAgent.handle_ex_turn_msg/3

Observed in production (ex_ice 0.13.0 relaying via Cloudflare TURN, in an
ex_webrtc/Membrane SFU where the agent crash cascaded into the media
pipeline).

Handle the error the way nearby send paths already do: log, then drop
the gathering transaction / close the relay candidate gracefully.
---
 lib/ex_ice/priv/ice_agent.ex | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/lib/ex_ice/priv/ice_agent.ex b/lib/ex_ice/priv/ice_agent.ex
index b4d0844..612e47e 100644
--- a/lib/ex_ice/priv/ice_agent.ex
+++ b/lib/ex_ice/priv/ice_agent.ex
@@ -954,8 +954,20 @@ defmodule ExICE.Priv.ICEAgent do
 
           {:send, dst, data, client} ->
             tr = %{tr | client: client}
-            :ok = ice_agent.transport_module.send(tr.socket, dst, data)
-            put_in(ice_agent.gathering_transactions[tr_id], tr)
+
+            case ice_agent.transport_module.send(tr.socket, dst, data) do
+              :ok ->
+                put_in(ice_agent.gathering_transactions[tr_id], tr)
+
+              {:error, reason} ->
+                Logger.debug("""
+                Couldn't send TURN message for gathering transaction, reason: #{inspect(reason)}. \
+                Dropping the transaction.\
+                """)
+
+                {_, ice_agent} = pop_in(ice_agent.gathering_transactions[tr_id])
+                update_gathering_state(ice_agent)
+            end
 
           {:error, _reason, _client} ->
             {_, ice_agent} = pop_in(ice_agent.gathering_transactions[tr_id])
@@ -971,9 +983,20 @@ defmodule ExICE.Priv.ICEAgent do
           {:send, dst, data, client} ->
             cand = %{cand | client: client}
             ice_agent = put_in(ice_agent.local_cands[cand.base.id], cand)
+
             # we can't use do_send here as it will try to create permission for the turn address
-            :ok = ice_agent.transport_module.send(cand.base.socket, dst, data)
-            ice_agent
+            case ice_agent.transport_module.send(cand.base.socket, dst, data) do
+              :ok ->
+                ice_agent
+
+              {:error, reason} ->
+                Logger.debug("""
+                Couldn't send TURN message on candidate: #{inspect(cand)}, reason: #{inspect(reason)}. \
+                Closing candidate.\
+                """)
+
+                close_candidate(ice_agent, cand)
+            end
 
           {:permission_expired, _ip, client} ->
             cand = %{cand | client: client}