Fixed bug of ESP32 crashing when using DMX out

[Nuet0815]

Fixed bug of ESP32 crashing when using DMX out:
-When exceeding the DMX channel limit, the SparkFunDMX.cpp tried to write to static chanSize (line 132) because the variables where swapped.
-When exceeding the channel upper & lower limit now, the value is ignored, previous implementation "idea" was to set as channel 512 value, which is not correct.
-There are still some non-optimal parts in the lib, but it at least works for now.

Summary by CodeRabbit

• Bug Fixes

  • Improved DMX channel bounds validation to consistently return 0 for out-of-range channel values instead of silently adjusting them.

• Refactor

  • Simplified DMX channel read/write logic with explicit maximum channel constraints.
  • Removed legacy defaultMax fallback behavior for more predictable channel handling.

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[coderabbitai]

Walkthrough

Modifies DMX channel handling in SparkFunDMX.cpp by replacing defaultMax fallback with explicit dmxMaxChannel cap in initialization functions, strengthening read() bounds checking to return 0 for out-of-range channels, and simplifying write() function logic with direct dmxData array access.

Changes

Cohort / File(s)	Summary
DMX Channel Bounds Checking wled00/src/dependencies/dmx/SparkFunDMX.cpp	Modified initRead and initWrite to use dmxMaxChannel instead of defaultMax fallback; updated read() to return 0 for out-of-range channels (< 1 or > chanSize) instead of clamping; simplified write() with early return for invalid channels and direct dmxData indexing; removed defaultMax macro usage

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~15 minutes

Suggested reviewers

• softhack007
• willmmiles

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: fixing an ESP32 crash bug related to DMX output. It aligns with the PR objectives and the code changes that strengthen channel bounds checks and eliminate unsafe fallback behavior.

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✨ Finishing touches

• 📝 Generate docstrings

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@wled00/src/dependencies/dmx/SparkFunDMX.cpp`:
- Around line 129-132: The write method in SparkFunDMX::write has an off-by-one
bounds check allowing Channel == chanSize which writes past the end of dmxData;
update the condition to reject Channel values >= chanSize (i.e., ensure valid
Channel is 1..chanSize-1) so accesses to dmxData[Channel] cannot overflow;
modify the check that currently uses (Channel > chanSize) to use (Channel >=
chanSize) (referencing SparkFunDMX::write, Channel, chanSize, chanQuant and
dmxData).

[coderabbitai]

⚠️ Potential issue | 🟠 Major

Off-by-one error in bounds check allows potential buffer overflow.

In write mode, chanSize = chanQuant + 1. When chanQuant = 512 (max), chanSize = 513. The check Channel > chanSize evaluates Channel > 513, which allows Channel = 513 to pass, resulting in dmxData[513] — an out-of-bounds write (array indices are 0–512).

Proposed fix

 void SparkFunDMX::write(int Channel, uint8_t value) {
-  if ((Channel < 1) || (Channel > chanSize)) return;
+  if ((Channel < 1) || (Channel >= chanSize)) return;
   dmxData[Channel] = value; //start byte at dmxData[0]
 }

Based on learnings, in WLED the priority is to prevent out-of-bounds memory access.

🤖 Prompt for AI Agents

In `@wled00/src/dependencies/dmx/SparkFunDMX.cpp` around lines 129 - 132, The
write method in SparkFunDMX::write has an off-by-one bounds check allowing
Channel == chanSize which writes past the end of dmxData; update the condition
to reject Channel values >= chanSize (i.e., ensure valid Channel is
1..chanSize-1) so accesses to dmxData[Channel] cannot overflow; modify the check
that currently uses (Channel > chanSize) to use (Channel >= chanSize)
(referencing SparkFunDMX::write, Channel, chanSize, chanQuant and dmxData).