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[kuntze] Use stack buffer for hex formatting in verbose logging - #12775

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bdraco merged 4 commits into
devfrom
kuntze
Jan 3, 2026
Merged

[kuntze] Use stack buffer for hex formatting in verbose logging#12775
bdraco merged 4 commits into
devfrom
kuntze

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@bdraco
@bdraco bdraco commented Jan 1, 2026
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What does this implement/fix?

Replace heap-allocating format_hex_pretty(...).c_str() with stack-based format_hex_pretty_to() in the kuntze component's verbose logging.

This eliminates a std::string heap allocation in the LOGV path. The buffer is wrapped in a compile guard to avoid stack allocation when verbose logging is disabled.

Buffer size is 24 bytes (format_hex_pretty_size(8)) based on typical Modbus response size (2 registers = 4 bytes data, plus overhead).

Types of changes

  • Bugfix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to not work as expected)
  • Developer breaking change (an API change that could break external components)
  • Code quality improvements to existing code or addition of tests
  • Other

Related issue or feature (if applicable):

  • n/a

Pull request in esphome-docs with documentation (if applicable):

  • n/a

Test Environment

  • ESP32
  • ESP32 IDF
  • ESP8266
  • RP2040
  • BK72xx
  • RTL87xx
  • nRF52840

Example entry for config.yaml:

# Standard kuntze configuration - no changes needed
uart:
  tx_pin: GPIO17
  rx_pin: GPIO16
  baud_rate: 19200

modbus:
  uart_id: modbus_uart

sensor:
  - platform: kuntze
    ph:
      name: "pH"

Checklist:

  • The code change is tested and works locally.
  • Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

@github-actions
github-actions Bot commented Jan 1, 2026
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To use the changes from this PR as an external component, add the following to your ESPHome configuration YAML file:

external_components:
  - source: github://pr#12775
    components: [kuntze]
    refresh: 1h

(Added by the PR bot)

@codecov-commenter
codecov-commenter commented Jan 1, 2026 •
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.31%. Comparing base (4e8c02b) to head (0393c31).

Additional details and impacted files 
@@            Coverage Diff             @@
##              dev   #12775      +/-   ##
==========================================
- Coverage   73.34%   73.31%   -0.03%     
==========================================
  Files          53       53              
  Lines       11284    11284              
  Branches     1531     1531              
==========================================
- Hits         8276     8273       -3     
- Misses       2608     2610       +2     
- Partials      400      401       +1

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:
  • ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

@github-actions
github-actions Bot commented Jan 1, 2026 •
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Memory Impact Analysis

Components: kuntze
Platform: esp8266-ard

Metric Target Branch This PR Change
RAM 29,488 bytes 29,216 bytes 📉 ✅ -272 bytes (-0.92%)
Flash 285,995 bytes 284,035 bytes 📉 ✅ -1,960 bytes (-0.69%)
📊 Component Memory Breakdown
Component Target Flash PR Flash Change
cpp_runtime 1,705 bytes 383 bytes 📉 -1,322 bytes (-77.54%)
[esphome]core 8,871 bytes 8,591 bytes 📉 🎉 -280 bytes (-3.16%)
cpp_stdlib 266 bytes 65 bytes 📉 -201 bytes (-75.56%)
[esphome]kuntze 1,005 bytes 997 bytes 📉 ✅ -8 bytes (-0.80%)
🔍 Symbol-Level Changes (click to expand)

Changed Symbols

Symbol Target Size PR Size Change
esphome::kuntze::Kuntze::on_modbus_data(std::vector<unsigned char, std::allocator ...esphome::kuntze::Kuntze::on_modbus_data(std::vector<unsigned char, std::allocator > const&)
 443 bytes 435 bytes 📉 -8 bytes (-1.81%)

Removed Symbols (top 15)

Symbol Size
std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_M_replace(unsig...std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_M_replace(unsigned int, unsigned int, char const*, unsigned int)
 280 bytes
std::__cxx11::to_string(unsigned int) 279 bytes
esphome::format_hex_pretty_uint8(unsigned char const*, unsigned int, char, bool) 237 bytes
std::__detail::__to_chars_10_impl<unsigned int>(char*, unsigned int, unsigned int)::__digits 201 bytes
std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_M_mutate(unsign...std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_M_mutate(unsigned int, unsigned int, char const*, unsigned int)
 139 bytes
std::__cxx11::basic_string<char, std::char_traits, std::allocator >::resize(unsigned ...std::__cxx11::basic_string<char, std::char_traits, std::allocator >::resize(unsigned int)
 117 bytes
std::__cxx11::basic_string<char, std::char_traits, std::allocator >::basic_string(std...std::__cxx11::basic_string<char, std::char_traits, std::allocator >::basic_string(std::__cxx11::basic_string<char, std::char_traits, std::allocator > const&)
 98 bytes
std::__cxx11::basic_string<char, std::char_traits, std::allocator > std::operator+<ch...std::__cxx11::basic_string<char, std::char_traits, std::allocator > std::operator+<char, std::char_traits, std::allocator >(std::__cxx11::basic_string<char, std::char_traits, std::allocator >&&, std::__cxx11::basic_string<char, std::char_traits, std::allocator >&&)
 87 bytes
std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_M_append(char c...std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_M_append(char const*, unsigned int)
 84 bytes
std::__cxx11::basic_string<char, std::char_traits, std::allocator >::basic_string(std...std::__cxx11::basic_string<char, std::char_traits, std::allocator >::basic_string(std::__cxx11::basic_string<char, std::char_traits, std::allocator >&&)
 72 bytes
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::append(char const*) 57 bytes
esphome::format_hex_pretty[abi:cxx11](std::vector<unsigned char, std::allocator > ...esphome::format_hex_pretty[abi:cxx11](std::vector<unsigned char, std::allocator > const&, char, bool)
 43 bytes
std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_S_assign(char*,...std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_S_assign(char*, unsigned int, char)
 26 bytes
std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_S_move(char*, c...std::__cxx11::basic_string<char, std::char_traits, std::allocator >::_S_move(char*, char const*, unsigned int)
 22 bytes

Note: This analysis measures static RAM and Flash usage only (compile-time allocation).
Dynamic memory (heap) cannot be measured automatically.
⚠️ You must test this PR on a real device to measure free heap and ensure no runtime memory issues.

This analysis runs automatically when components change. Memory usage is measured from a representative test configuration.

bdraco
bdraco commented Jan 1, 2026
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Comment thread esphome/components/kuntze/kuntze.cpp Outdated
@bdraco
bdraco marked this pull request as ready for review January 1, 2026 02:20
@bdraco
bdraco requested a review from ssieb as a code owner January 1, 2026 02:20
Copilot AI review requested due to automatic review settings January 1, 2026 02:20
@github-actions
github-actions Bot commented Jan 1, 2026
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👋 Hi there! I've automatically requested reviews from codeowners based on the files changed in this PR.

@ssieb - You've been requested to review this PR as codeowner(s) of 1 file(s) that were modified. Thanks for your time! 🙏

bdraco
bdraco commented Jan 1, 2026
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Comment thread esphome/components/kuntze/kuntze.cpp Outdated
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Pull request overview

This PR optimizes the kuntze component's verbose logging by replacing heap-allocating format_hex_pretty(...).c_str() with stack-based format_hex_pretty_to(). This eliminates a std::string heap allocation in the logging path.

Key Changes:

  • Added include for esphome/core/helpers.h to access the stack-based formatting function
  • Introduced KUNTZE_MAX_LOG_BYTES constant (8 bytes) and allocated a 24-byte stack buffer for hex formatting
  • Replaced format_hex_pretty(data).c_str() with format_hex_pretty_to(hex_buf, data.data(), data.size())

Comment thread esphome/components/kuntze/kuntze.cpp
Comment thread esphome/components/kuntze/kuntze.cpp
@bdraco
bdraco commented Jan 3, 2026
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Thanks

@bdraco
bdraco merged commit a57011b into dev Jan 3, 2026
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@bdraco
bdraco deleted the kuntze branch January 3, 2026 02:36
@github-actions github-actions Bot locked and limited conversation to collaborators Jan 5, 2026
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@swoboda1337 swoboda1337 swoboda1337 approved these changes
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