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Reduce SerializationBuffer stack size from 768 to 512 bytes

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768 bytes on the httpd task stack contributes to stack overflow when
combined with other stack-allocated buffers (query string parsing, etc.).
512 bytes still covers all typical JSON payloads (sensors ~200B, lights
~170B, climate ~500-700B). Only extreme edge cases with 40+ options
trigger heap fallback.
This commit is contained in:
J. Nick Koston
2026-02-11 18:57:53 -06:00
parent 840ad30880
commit aa870483f1
2 changed files with 5 additions and 5 deletions
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4
esphome/components/json/json_util.cpp
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@@ -70,7 +70,7 @@ SerializationBuffer<> JsonBuilder::serialize() {
// directly in the caller's stack frame, eliminating the move constructor call entirely.
//
// WITHOUT NRVO: Each return would trigger SerializationBuffer's move constructor, which
// must memcpy up to 768 bytes of stack buffer content. This happens on EVERY JSON
// must memcpy up to 512 bytes of stack buffer content. This happens on EVERY JSON
// serialization (sensor updates, web server responses, MQTT publishes, etc.).
//
// WITH NRVO: Zero memcpy, zero move constructor overhead. The buffer lives directly
@@ -89,7 +89,7 @@ SerializationBuffer<> JsonBuilder::serialize() {
// Should show only destructor, NOT move constructor
//
// Why we avoid measureJson(): It instantiates DummyWriter templates adding ~1KB flash.
// Instead, try stack buffer first. 768 bytes covers 99.9% of JSON payloads (sensors ~200B,
// Instead, try stack buffer first. 512 bytes covers 99.9% of JSON payloads (sensors ~200B,
// lights ~170B, climate ~700B). Only entities with 40+ options exceed this.
//
// ===========================================================================================