From 5aa9c18dfc67ed7030fd2375a624258cadc5194f Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Mon, 9 Mar 2026 21:49:06 -1000
Subject: [PATCH] [ota,socket] Add SO_SNDTIMEO and use delay(0) in readall_

- Add SO_SNDTIMEO to OTA socket to prevent blocking writes from
  stalling the WDT when the TCP send buffer is full
- Add SO_SNDTIMEO as no-op in raw TCP (writes never block)
- Use delay(0) instead of delay(1) in readall_() since SO_RCVTIMEO
  already handles the wait
- Keep delay(1) in writeall_() since raw TCP writes are non-blocking
  and would spin on EWOULDBLOCK without it
---
 esphome/components/esphome/ota/ota_esphome.cpp  | 7 ++++++-
 esphome/components/socket/headers.h             | 1 +
 esphome/components/socket/lwip_raw_tcp_impl.cpp | 4 ++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/esphome/components/esphome/ota/ota_esphome.cpp b/esphome/components/esphome/ota/ota_esphome.cpp
index b84bfe67917..e955dbf1b1c 100644
--- a/esphome/components/esphome/ota/ota_esphome.cpp
+++ b/esphome/components/esphome/ota/ota_esphome.cpp
@@ -258,6 +258,9 @@ void ESPHomeOTAComponent::handle_data_() {
   tv.tv_sec = 2;
   tv.tv_usec = 0;
   this->client_->setsockopt(SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+  // Also set send timeout to prevent blocking writes from stalling the WDT
+  // when the TCP send buffer is full (e.g., network congestion).
+  this->client_->setsockopt(SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));
   this->client_->setblocking(true);
 
   // Acknowledge auth OK - 1 byte
@@ -413,7 +416,9 @@ bool ESPHomeOTAComponent::readall_(uint8_t *buf, size_t len) {
     } else {
       at += read;
     }
-    this->yield_and_feed_watchdog_();
+    // read() already waited via SO_RCVTIMEO, just yield without 1ms stall
+    App.feed_wdt();
+    delay(0);
   }
 
   return true;
diff --git a/esphome/components/socket/headers.h b/esphome/components/socket/headers.h
index c3f7e1e0467..0eece6480f6 100644
--- a/esphome/components/socket/headers.h
+++ b/esphome/components/socket/headers.h
@@ -52,6 +52,7 @@
 #define SO_KEEPALIVE 0x0008 /* keep connections alive */
 #define SO_BROADCAST 0x0020 /* permit to send and to receive broadcast messages (see IP_SOF_BROADCAST option) */
 #define SO_RCVTIMEO 0x1006  /* receive timeout */
+#define SO_SNDTIMEO 0x1005  /* send timeout */
 
 #define SOL_SOCKET 0xfff /* options for socket level */
 
diff --git a/esphome/components/socket/lwip_raw_tcp_impl.cpp b/esphome/components/socket/lwip_raw_tcp_impl.cpp
index 7995e83d245..8fb11c6c78b 100644
--- a/esphome/components/socket/lwip_raw_tcp_impl.cpp
+++ b/esphome/components/socket/lwip_raw_tcp_impl.cpp
@@ -355,6 +355,10 @@ int LWIPRawCommon::setsockopt(int level, int optname, const void *optval, sockle
     this->recv_timeout_cs_ = cs > 255 ? 255 : static_cast<uint8_t>(cs);
     return 0;
   }
+  if (level == SOL_SOCKET && optname == SO_SNDTIMEO) {
+    // Raw TCP writes are non-blocking (tcp_write), so send timeout is a no-op.
+    return 0;
+  }
   if (level == IPPROTO_TCP && optname == TCP_NODELAY) {
     if (optlen != 4) {
       errno = EINVAL;