From e9f25a55b01fd019849cd0667c908d285b8197f7 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Tue, 8 Sep 2026 15:39:00 +0200
Subject: [PATCH] [esphome][core] Give a lost OTA chunk ack time to be
 retransmitted

---
 esphome/components/esphome/ota/ota_esphome.cpp | 5 ++++-
 esphome/espota2.py                             | 8 +++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/esphome/components/esphome/ota/ota_esphome.cpp b/esphome/components/esphome/ota/ota_esphome.cpp
index 1005ed214b..1e751de869 100644
--- a/esphome/components/esphome/ota/ota_esphome.cpp
+++ b/esphome/components/esphome/ota/ota_esphome.cpp
@@ -41,7 +41,10 @@ const noise::NoiseContext &ESPHomeOTAComponent::noise_context_() const {
 #endif
 static constexpr uint16_t OTA_BLOCK_SIZE = 8192;
 static constexpr uint32_t OTA_SOCKET_TIMEOUT_HANDSHAKE = 20000;  // milliseconds for initial handshake
-static constexpr uint32_t OTA_SOCKET_TIMEOUT_DATA = 90000;       // milliseconds for data transfer
+// Milliseconds for data transfer. Outlasts lwIP retransmitting a lost chunk ack
+// six times (1.5 + 3 + 6 + 12 + 24 + 48 s); the CLI waits longer (160 s) so the
+// device is always free again before the CLI retries
+static constexpr uint32_t OTA_SOCKET_TIMEOUT_DATA = 105000;
 
 // Single-instance pointer — multi-port configs are rejected in final_validate.
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
diff --git a/esphome/espota2.py b/esphome/espota2.py
index ce403c398d..e72d07d810 100644
--- a/esphome/espota2.py
+++ b/esphome/espota2.py
@@ -694,8 +694,10 @@ def perform_ota(
 
     _LOGGER.info("Handshake complete")
 
-    # Timeout must match device-side OTA_SOCKET_TIMEOUT_DATA to prevent premature failures
-    sock.settimeout(90.0)
+    # Longer than the device's OTA_SOCKET_TIMEOUT_DATA (105 s) so a stalled
+    # session is gone before a retry, and long enough for lwIP to get a lost
+    # chunk ack through after six retransmissions
+    sock.settimeout(160.0)
 
     if extended_proto:
         send_check(sock, ota_type, "ota type")
@@ -854,7 +856,7 @@ def run_ota_impl_(
     # clean up a half-open connection (its handshake watchdog runs at 20s);
     # moving on to the next address family stays immediate. Known limitation:
     # a silent mid-transfer drop with no reset can wedge the device until its
-    # 90s data timeout, which outlasts this budget; the retries target the
+    # 105s data timeout, which outlasts this budget; the retries target the
     # common failures where the device resets or closes the link promptly.
     total_attempts = len(res) + EXTRA_UPLOAD_ATTEMPTS
     last_error = ""