BLE: `BLECharacteristic::setValue()` cleanup and optimization #11751

Kolcha · 2025-08-21T09:49:08Z

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Description of Change

The change is just a code cleanup following common practices, no behavior change introduced.

Pass primitive types to BLECharacteristic::setValue() by value instead of by non-const reference.
There is no technical need to passing values by non-const reference there, non-const reference makes usage inconvenient (function return can't be passed directly as argument, temporary variable required), passing by value eliminates this inconvenience.
Don't create temporary variables in setValue() implementations for primitive types.
There is no technical need to create all those temporary variables, the address of the argument can be used directly. Such "integer to array" conversion is not required, because it basically does nothing, as ESP32 is little-endian architecture.
Pass pointer to const data to setValue()
There is no technical need to pass non-const data there. This allows to pass the data from read-only sources without removing the constness what is not always safe.
Avoid unnecessary String copies
Pass String by const reference to many setValue() functions to avoid copying it.

Test Scenarios

I have tested my Pull Request on Arduino-esp32 core v3.3.0 with ESP32 Board with this scenario:

Successful build of the project which uses BLE.
Created BLE service with 8 characteristics, 4 of them are uint16_t and 4 are float

Related links

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CLAassistant · 2025-08-21T09:49:15Z

All committers have signed the CLA.

github-actions · 2025-08-21T09:49:46Z

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There is no need to pass primitive types by reference, especially by non-const reference as it was in BLECharacteristic. Pass primitive types by value instead, as it should be, and used everywhere else except this one odd class. This allows allows to pass function result as `setValue()` argument without creating temporary variable.

SuGlider · 2025-08-21T13:11:50Z

It may be worth to test and verify it using other MCU SoCs, such as ESP32-S3 and ESP32-C3.
The proposed change has to do with making sure that the correct endianness (little and big endian) is used.

Based on BLE specification, it shall be little-endian, therefore if you try sending an int value, you will see that the hex values are arranged in little-endian format. The "human readable" value 0xAABBCCDD will for instance be transmitted and received as 0xDDCCBBAA.

The change takes into consideration the MCU endianless when compiling the code.

ESP32 is little-endian, therefore the PR proposed change works fine.
RISC-V is designed to be little-endian as default as well (C3/C6/C5/P4)
ESP32-S3 shall be also little-endian, therefore it shall work fine.

github-actions · 2025-08-21T13:25:12Z

Test Results

76 files 76 suites 13m 9s ⏱️
38 tests 38 ✅ 0 💤 0 ❌
241 runs 241 ✅ 0 💤 0 ❌

Results for commit f801bdd.

♻️ This comment has been updated with latest results.

github-actions · 2025-08-21T13:41:15Z

Memory usage test (comparing PR against master branch)

The table below shows the summary of memory usage change (decrease - increase) in bytes and percentage for each target.

Memory	FLASH [bytes]		FLASH [%]		RAM [bytes]		RAM [%]
Target	DEC	INC	DEC	INC	DEC	INC	DEC	INC
ESP32C5	0	0	0.00	0.00	0	0	0.00	0.00
ESP32S3	0	0	0.00	0.00	0	0	0.00	0.00
ESP32C3	0	0	0.00	0.00	0	0	0.00	0.00
ESP32C6	0	0	0.00	0.00	0	0	0.00	0.00
ESP32H2	0	0	0.00	0.00	0	0	0.00	0.00
ESP32	0	0	0.00	0.00	0	0	0.00	0.00

Click to expand the detailed deltas report [usage change in BYTES]

Target	ESP32C5		ESP32S3		ESP32C3		ESP32C6		ESP32H2		ESP32
Example	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM
libraries/BLE/examples/Beacon_Scanner	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/Client	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/EddystoneTLM_Beacon	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/EddystoneURL_Beacon	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/Notify	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/Scan	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/Server	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/Server_multiconnect	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/UART	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/Write	-	-	-	-	-	-	-	-	-	-	-	-
libraries/BLE/examples/iBeacon	-	-	-	-	-	-	-	-	-	-	-	-

SuGlider

Using C++ reinterpret_cast<uint8_t*> instead.

libraries/BLE/src/BLECharacteristic.cpp

SuGlider · 2025-08-21T14:02:00Z

Another suggestion of change here (using reinterpret_cast<uint8_t*>):

void BLECharacteristic::setValue(String value) {
  setValue(reinterpret_cast<uint8_t*>(value.c_str()), value.length());
}  // setValue

ESP32 is little-endian architecture, so the code that filled temporary arrays created from integers basically did nothing. Pass primitives as 'buffers' to generic `setValue()` instead. Also use sizeof() instead of hardcoded sizes as the argument.

There is no technical need to pass non-const data there. Also it is a common practice to pass const data to the functions with write semantics, as they not supposed to modify the data. This allows to pass the data from read-only sources without removing the constness what is not always safe.

Pass String by const reference to many `setValue()` functions to avoid copying it. Even there are not so much data inside these strings, it just looks too odd to copy them every time. Also this change decreases binary size (~200 bytes in my case).

Co-authored-by: Copilot <[email protected]>

libraries/BLE/src/BLECharacteristic.cpp

SuGlider · 2025-08-27T14:42:57Z

@Kolcha - Thanks for the contribution.

I have tested it using u16 and u32 characteristics and it is working correctly with ESP32. ESP32-S3, ESP32-C3 and ESP32-C6.
All good. Ready for merging.

SuGlider

LGTM. Tested with ESP32, ESP32-S3, ESP32-C3 and ESP32-C6 using u16/u32 characteristics.

SuGlider · 2025-08-27T14:49:45Z

@lucasssvaz - PTAL. All seems fine.
As described it solves an existent limitation related to passing const values such as, pCharacteristic->setValue(0x1234);

Copilot

Pull Request Overview

This PR optimizes the BLE library's setValue() methods by improving parameter passing and eliminating unnecessary temporary variables. The changes focus on making the API more efficient and user-friendly without altering behavior.

Pass primitive types by value instead of non-const reference to allow direct function return usage
Replace manual byte array construction with direct memory access using reinterpret_cast
Change string and data parameters to const references/pointers to avoid unnecessary copies

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
libraries/BLE/src/BLEValue.h	Updates method signatures to use const references for String and const pointers for data
libraries/BLE/src/BLEValue.cpp	Implements const reference parameters for addPart and setValue methods
libraries/BLE/src/BLEDescriptor.h	Changes setValue signatures to use const parameters
libraries/BLE/src/BLEDescriptor.cpp	Implements const parameters and uses reinterpret_cast for type conversion
libraries/BLE/src/BLECharacteristic.h	Updates setValue overloads to pass primitives by value and use const references
libraries/BLE/src/BLECharacteristic.cpp	Replaces manual byte manipulation with reinterpret_cast and direct memory access
libraries/BLE/src/BLE2901.h	Changes setDescription to use const String reference
libraries/BLE/src/BLE2901.cpp	Implements const String reference parameter

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libraries/BLE/src/BLECharacteristic.cpp

Kolcha requested review from lucasssvaz and SuGlider as code owners August 21, 2025 09:49

Kolcha force-pushed the ble-cleanup branch 2 times, most recently from 05c13c0 to 3fa7ff5 Compare August 21, 2025 10:02

Kolcha force-pushed the ble-cleanup branch from 3fa7ff5 to af59210 Compare August 21, 2025 10:06

lucasssvaz requested a review from Copilot August 21, 2025 11:59

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Kolcha force-pushed the ble-cleanup branch from af59210 to c6517e4 Compare August 21, 2025 14:17

Kolcha added 2 commits August 22, 2025 05:54

Kolcha force-pushed the ble-cleanup branch from c23050a to 5edf464 Compare August 22, 2025 04:09

Merge branch 'master' into ble-cleanup

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fix(ble): matches the function signature with const u8*

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Co-authored-by: Copilot <[email protected]>

SuGlider reviewed Aug 27, 2025

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fix(ble): matches the function signature with const u8*

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SuGlider added 2 commits August 27, 2025 10:04

fix(ble): matches the function signature with const u8*

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Merge branch 'master' into ble-cleanup

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SuGlider self-requested a review August 27, 2025 14:43

SuGlider approved these changes Aug 27, 2025

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SuGlider self-assigned this Aug 27, 2025

SuGlider requested review from Copilot, me-no-dev and P-R-O-C-H-Y August 27, 2025 14:50

SuGlider added the Area: BLE Issues related to BLE label Aug 27, 2025

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github-project-automation bot moved this to Todo in Arduino ESP32 Core Project Roadmap Aug 27, 2025

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Merge branch 'master' into ble-cleanup

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me-no-dev merged commit 098d4f3 into espressif:master Aug 29, 2025
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BLE: BLECharacteristic::setValue() cleanup and optimization #11751

BLE: BLECharacteristic::setValue() cleanup and optimization #11751

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Checklist

Description of Change

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Memory usage test (comparing PR against master branch)

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Pull Request Overview

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BLE: `BLECharacteristic::setValue()` cleanup and optimization #11751

BLE: `BLECharacteristic::setValue()` cleanup and optimization #11751

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