[coap] encapsulate Request state and hide its Metadata

[abtink]

This commit updates the CoapBase::Request class to encapsulate its internal state. The mMessage pointer and mMetadata struct are now private, and their properties are accessed and modified through explicit getter and setter methods (e.g., GetMessage(), IsConfirmable(), MarkAsAcknowledged()).

By doing so, the code that manages pending requests no longer directly manipulates the internal metadata fields, improving code structure and maintainability.

[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 significantly refactors the CoapBase::Request class to enhance its object-oriented design by encapsulating its internal state. By making the mMessage and mMetadata members private and providing controlled access through public methods, the changes improve code maintainability, reduce direct manipulation of internal data, and promote a cleaner interface for managing CoAP requests.

Highlights

• Encapsulation of Request State: The internal state of CoapBase::Request, specifically the mMessage pointer and mMetadata struct, was made private to enforce encapsulation.
• New Accessor Methods: Introduced explicit public getter and setter methods (e.g., GetMessage(), IsConfirmable(), MarkAsAcknowledged()) within CoapBase::Request to control access to its internal properties.
• Refactored Metadata Logic: Methods previously part of CoapBase::Request::Metadata (like HasSamePeerAddrAndPort, ShouldRetransmit, UpdateRetxCounterAndTimeout, IsObserveSubscription) were moved and promoted to public methods of the CoapBase::Request class.
• Relocated ProcessObserveSend: The ProcessObserveSend method was moved from the CoapBase class to the CoapBase::PendingRequests nested class, improving logical grouping.

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[gemini-code-assist]

Code Review

This pull request effectively encapsulates the CoapBase::Request state by making its internal members private and introducing getter/setter methods. The changes improve code structure and maintainability as intended. I found one critical issue in src/core/coap/coap.hpp where a method was renamed incorrectly, which will cause a compilation error. Other than that, the refactoring looks good.

[abtink]

/gemini review

[github-actions]

Merging #12675 into main

name	branch	text	data	bss	total
ot-cli-ftd	7696e38	482192	860	66540	549592
	cda4f2d	482208	860	66540	549608
	+/-	+16	+0	+0	+16
ot-ncp-ftd	7696e38	448124	764	61776	510664
	cda4f2d	448124	764	61776	510664
	+/-	+0	+0	+0	+0
ot-cli-mtd	7696e38	374888	764	50972	426624
	cda4f2d	374888	764	50972	426624
	+/-	+0	+0	+0	+0
ot-ncp-mtd	7696e38	356036	764	46240	403040
	cda4f2d	356036	764	46240	403040
	+/-	+0	+0	+0	+0
ot-cli-ftd-br	7696e38	598344	868	136596	735808
	cda4f2d	598344	868	136596	735808
	+/-	+0	+0	+0	+0
ot-rcp	7696e38	63328	568	20804	84700
	cda4f2d	63328	568	20804	84700
	+/-	+0	+0	+0	+0

Library files

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	cda4f2d	249838	95	40319	290252
	+/-	+8	+0	+0	+8
libopenthread-cli-ftd.a	7696e38	61727	0	8091	69818
	cda4f2d	61727	0	8091	69818
	+/-	+0	+0	+0	+0
libopenthread-ncp-ftd.a	7696e38	33581	0	5948	39529
	cda4f2d	33581	0	5948	39529
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libopenthread-mtd.a	7696e38	168562	0	24783	193345
	cda4f2d	168570	0	24783	193353
	+/-	+8	+0	+0	+8
libopenthread-cli-mtd.a	7696e38	41436	0	8059	49495
	cda4f2d	41436	0	8059	49495
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libopenthread-ncp-mtd.a	7696e38	25805	0	5948	31753
	cda4f2d	25805	0	5948	31753
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libopenthread-ftd-br.a	7696e38	366645	100	110335	477080
	cda4f2d	366653	100	110335	477088
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libopenthread-cli-ftd-br.a	7696e38	80934	0	8131	89065
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libopenthread-rcp.a	7696e38	9944	0	5060	15004
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libopenthread-radio.a	7696e38	19715	0	238	19953
	cda4f2d	19715	0	238	19953
	+/-	+0	+0	+0	+0

[gemini-code-assist]

Code Review

This pull request refactors the CoapBase::Request class to improve encapsulation by making its internal state private. The direct access to mMessage and mMetadata is replaced by a set of getter and setter methods. This is a good improvement to the code structure and maintainability. The changes are consistent and correctly implemented across the codebase. The ProcessObserveSend method has also been logically moved to the PendingRequests class. The implementation looks solid and I have no specific comments.

[codecov]

Codecov Report

❌ Patch coverage is 93.67089% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.80%. Comparing base (7696e38) to head (5ec45de).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/core/coap/coap.cpp	91.37%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12675      +/-   ##
==========================================
- Coverage   74.58%   73.80%   -0.78%     
==========================================
  Files         695      694       -1     
  Lines       95626    96562     +936     
==========================================
- Hits        71318    71270      -48     
- Misses      24308    25292     +984     

Files with missing lines	Coverage Δ
src/core/coap/coap.hpp	96.15% <100.00%> (+2.40%)	⬆️
src/core/coap/coap.cpp	86.95% <91.37%> (+0.17%)	⬆️

... and 125 files with indirect coverage changes

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