Add indefinite lenght support to cbor read functions.

[werwurm]

Add synthetic cbor type variant to the enum n20_cbor_types_e that indicate indefinite length encoding. And adds support for indefinite length encoding to the read and write header functions as well as to the cbor skip item function.

[github-actions]

LCOV of commit c9cfdfa during lcov-test-coverage-report #258

Summary coverage rate:
  lines......: 95.7% (3105 of 3245 lines)
  functions..: 99.2% (235 of 237 functions)
  branches...: 87.3% (1697 of 1943 branches)

Files changed coverage rate: n/a

[Copilot]

Pull request overview

This PR extends the library’s CBOR support to handle RFC 8949 indefinite-length encodings by introducing synthetic CBOR “types” (via the 0x100 bit) and updating header read/write plus skip-item behavior accordingly.

Changes:

• Add synthetic n20_cbor_type_*indefinite*_e variants and document their meaning (0x100 bit).
• Extend n20_cbor_write_header, n20_cbor_read_header, and n20_cbor_read_skip_item to support indefinite-length items and break (0xFF).
• Expand CBOR unit tests and adjust message tests to avoid using 0xFF as an “invalid item” now that it’s recognized as a break code.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/service/test/messages.cpp	Updates malformed message tests to use a reserved/invalid simple value (0xFE) instead of 0xFF (break).
src/core/test/cbor.cpp	Adds extensive coverage for indefinite-length header read/write and skip_item behavior; updates invalid-header parameterization.
src/core/cbor.c	Implements indefinite-length handling in header read/write and adds an internal-result-based skipper that can process break-terminated structures.
include/nat20/cbor.h	Introduces synthetic indefinite-length type variants and documents new behavior/contracts for read/write/skip.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

[mjain02]

I think you can mention that it's possible to have nested indefinite length arrays/maps, and if they're there, they also need to have the break stop codes.

[werwurm]

I added tests accordingly.

[mjain02]

Should this call the internal function like other cases?

Suggested change

	return n20_cbor_read_skip_item(s) ? n20_cbor_read_skip_item_ok_e
	return n20_cbor_read_skip_item_internal(s) ? n20_cbor_read_skip_item_ok_e

[werwurm]

No this is correct. If this returns ..._break_e it needs to be an error because we cannot have a tagged break symbol. So in terms of the internal semantic it would be _internal(s) == _ok_e ? _ok_e : _error_e which is exactly what n20_cbor_read_skip_item does.

[mjain02]

If we have a malformed indef length array, wouldn't it be possible for the recursion to overflow?

[werwurm]

The read functions make sure not to read past the end of the buffer. Even a definite length byte string can be larger than the buffer. In this case the read functions return false and the internal skip function returns ..._error_e.