From 34f7ff58ee2afc197751019305abdc8c83d80a6b Mon Sep 17 00:00:00 2001
From: Jackson Xu <jacksong_github@163.com>
Date: Fri, 3 Jul 2026 11:30:37 +0800
Subject: [PATCH] modbus: limit link error-recovery sleep+flush to
 confirmations

ETIMEDOUT triggers _sleep_response_timeout() + modbus_flush()
regardless of msg_type. On the indication path this stalls a
non-blocking server for response_timeout and can flush a client
request that arrives during the sleep window, dropping it silently.
Scope the recovery to MSG_CONFIRMATION, matching the client-side
retry intent it was written for.
---
 src/modbus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/modbus.c b/src/modbus.c
index abdd718c..d371d6da 100644
--- a/src/modbus.c
+++ b/src/modbus.c
@@ -444,7 +444,7 @@ int _modbus_receive_msg(modbus_t *ctx, uint8_t *msg, msg_type_t msg_type)
 #else
                 int saved_errno = errno;
 
-                if (errno == ETIMEDOUT) {
+                if (errno == ETIMEDOUT && msg_type == MSG_CONFIRMATION) {
                     _sleep_response_timeout(ctx);
                     modbus_flush(ctx);
                 } else if (errno == EBADF) {