mirror/esphome
1
0
Fork 0
mirror of https://github.com/esphome/esphome.git synced 2026-02-28 18:04:19 -07:00
Code Issues Packages Projects Releases Wiki Activity

Reduce SerializationBuffer stack size from 768 to 512 bytes

Browse Source 
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 9ef0ad3f9d
commit 181fb4f8ac
2 changed files with 5 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
esphome/components/json/json_util.cpp
View File

@@ -75,7 +75,7 @@ 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
@@ -94,7 +94,7 @@ 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.
//
// ===========================================================================================

6
esphome/components/json/json_util.h
View File

@@ -17,9 +17,9 @@ namespace esphome {
namespace json {
/// Buffer for JSON serialization that uses stack allocation for small payloads.
/// Template parameter STACK_SIZE specifies the stack buffer size (default 768 bytes).
/// Template parameter STACK_SIZE specifies the stack buffer size (default 512 bytes).
/// Supports move semantics for efficient return-by-value.
template<size_t STACK_SIZE = 768> class SerializationBuffer {
template<size_t STACK_SIZE = 512> class SerializationBuffer {
public:
static constexpr size_t BUFFER_SIZE = STACK_SIZE; ///< Stack buffer size for this instantiation
@@ -177,7 +177,7 @@ class JsonBuilder {
}
/// Serialize the JSON document to a SerializationBuffer (stack-first allocation)
/// Uses 768-byte stack buffer by default, falls back to heap for larger JSON
/// Uses 512-byte stack buffer by default, falls back to heap for larger JSON
SerializationBuffer<> serialize();
private: