[heap-data] use allocate-first pattern in UpdateBuffer()

[Oblivionsage]

UpdateBuffer() frees the old buffer before allocating a new one. If the allocation fails, mData still holds the old (now freed) pointer, leaving the object in an inconsistent state.

This changes UpdateBuffer() to use the same allocate-first pattern used by Heap::String::Set: allocate first, free only on success. On allocation failure the existing buffer is preserved.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a potential memory management issue in the Heap::Data::UpdateBuffer method. By reordering the allocation and deallocation logic, the change ensures that the object maintains a valid state even when memory allocation fails, aligning the implementation with established patterns used elsewhere in the codebase.

Highlights

• Memory Safety Improvement: Updated the UpdateBuffer method to adopt an allocate-first pattern, ensuring the existing buffer is only freed after a successful new allocation.
• State Consistency: Prevented potential inconsistent object states by ensuring the original buffer remains intact if a memory allocation fails.

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[gemini-code-assist]

Code Review

This pull request modifies UpdateBuffer in heap_data.cpp to adopt an allocate-first pattern, ensuring the old buffer is preserved if a new allocation fails. The review feedback suggests simplifying the logic to reduce duplication and improve clarity by separating the allocation step from the buffer initialization.

[github-actions]

Merging #12794 into main

name	branch	text	data	bss	total
ot-cli-ftd	dd855c3	482784	860	66540	550184
	f893ad7	482784	860	66540	550184
	+/-	+0	+0	+0	+0
ot-ncp-ftd	dd855c3	448692	764	61776	511232
	f893ad7	448692	764	61776	511232
	+/-	+0	+0	+0	+0
ot-cli-mtd	dd855c3	374944	764	50972	426680
	f893ad7	374944	764	50972	426680
	+/-	+0	+0	+0	+0
ot-ncp-mtd	dd855c3	356076	764	46240	403080
	f893ad7	356076	764	46240	403080
	+/-	+0	+0	+0	+0
ot-cli-ftd-br	dd855c3	599160	864	136612	736636
	f893ad7	599176	864	136612	736652
	+/-	+16	+0	+0	+16
ot-rcp	dd855c3	63328	568	20804	84700
	f893ad7	63328	568	20804	84700
	+/-	+0	+0	+0	+0

Library files

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libopenthread-ftd.a	dd855c3	250481	95	40319	290895
	f893ad7	250489	95	40319	290903
	+/-	+8	+0	+0	+8
libopenthread-cli-ftd.a	dd855c3	61750	0	8091	69841
	f893ad7	61750	0	8091	69841
	+/-	+0	+0	+0	+0
libopenthread-ncp-ftd.a	dd855c3	33583	0	5948	39531
	f893ad7	33583	0	5948	39531
	+/-	+0	+0	+0	+0
libopenthread-mtd.a	dd855c3	168856	0	24783	193639
	f893ad7	168864	0	24783	193647
	+/-	+8	+0	+0	+8
libopenthread-cli-mtd.a	dd855c3	41459	0	8059	49518
	f893ad7	41459	0	8059	49518
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libopenthread-ncp-mtd.a	dd855c3	25807	0	5948	31755
	f893ad7	25807	0	5948	31755
	+/-	+0	+0	+0	+0
libopenthread-ftd-br.a	dd855c3	367628	99	110351	478078
	f893ad7	367636	99	110351	478086
	+/-	+8	+0	+0	+8
libopenthread-cli-ftd-br.a	dd855c3	80957	0	8131	89088
	f893ad7	80957	0	8131	89088
	+/-	+0	+0	+0	+0
libopenthread-rcp.a	dd855c3	9946	0	5060	15006
	f893ad7	9946	0	5060	15006
	+/-	+0	+0	+0	+0
libopenthread-radio.a	dd855c3	19725	0	238	19963
	f893ad7	19725	0	238	19963
	+/-	+0	+0	+0	+0

[Oblivionsage]

I'll keep the current approach as it stays consistent with the existing pattern in Heap::String::Set and keeps the zero-length case explicit. Happy to adjust if a maintainer prefers the suggested refactor

[abtink]

@Oblivionsage, thanks for submitting this. It is a good find indeed.
LGTM. Regarding the Gemini suggestion, I think the way you have it is better (smaller). Thanks again.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.93%. Comparing base (dd855c3) to head (0bebfed).
⚠️ Report is 27 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12794      +/-   ##
==========================================
- Coverage   73.40%   70.93%   -2.48%     
==========================================
  Files         696      696              
  Lines       98509    93382    -5127     
==========================================
- Hits        72310    66237    -6073     
- Misses      26199    27145     +946     

Files with missing lines	Coverage Δ
src/core/common/heap_data.cpp	91.48% <100.00%> (+0.18%)	⬆️

... and 307 files with indirect coverage changes

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[jwhui]

Thanks! 👍🏼