fix(oracle): guard SUBSTRB end boundary

[yyqdbngt]

Summary - stop SUBSTRB from calling pg_mblen after reaching the end of a multibyte varlena payload - cover a substring ending exactly at the UTF-8 source boundary ## Testing - git diff --check Closes #1844 ## Summary by CodeRabbit * Bug Fixes * Corrected byte-based substring handling for multibyte text. * SUBSTRB now returns the complete string when the requested byte length ends exactly at a multibyte character boundary. * Tests * Added regression coverage for SUBSTRB('你好', 1, 6), confirming the expected result.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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Run ID: 73b46818-f48e-41dd-8b07-d47e27d97ad2

📥 Commits

Reviewing files that changed from the base of the PR and between 42ed378 and 1a43518.

📒 Files selected for processing (3)

• contrib/ivorysql_ora/expected/ora_character_datatype_functions.out
• contrib/ivorysql_ora/sql/ora_character_datatype_functions.sql
• contrib/ivorysql_ora/src/builtin_functions/character_datatype_functions.c

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📝 Walkthrough

Walkthrough

The multibyte SUBSTRB loop now prevents boundary overrun during character traversal. Regression coverage verifies that a six-byte limit returns the complete UTF-8 string 你好.

Changes

SUBSTRB multibyte boundary handling

Layer / File(s)	Summary
Guard multibyte boundary traversal contrib/ivorysql_ora/src/builtin_functions/character_datatype_functions.c	The text_substring_byte loop now checks subStrEnd before advancing past the requested end position.
Add exact-boundary regression coverage contrib/ivorysql_ora/sql/ora_character_datatype_functions.sql, contrib/ivorysql_ora/expected/ora_character_datatype_functions.out	The regression test verifies that SUBSTRB('你好', 1, 6) = '你好' evaluates to t.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 1a435

This change prevents SUBSTRB from inspecting beyond a multibyte input boundary and adds coverage for an exact UTF-8 byte boundary. The implementation and regression expectation align, with no remaining merge-blocking risk.

Suggested reviewers: ai-yang, hs-liuxh

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The implementation guards the multibyte SUBSTRB boundary before advancing and inspecting the next character. The SQL and expected-output changes add regression coverage for a UTF-8 substring that ends…
Out of Scope Changes check	✅ Passed	All changes are directly related to issue #1844. The implementation change and regression test cover the SUBSTRB multibyte boundary defect. No unrelated code changes are present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files. (2 skipped: 2 …
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing the Oracle SUBSTRB end-boundary handling.

Full details: Linked Issues check

Explanation

The implementation guards the multibyte SUBSTRB boundary before advancing and inspecting the next character. The SQL and expected-output changes add regression coverage for a UTF-8 substring that ends at the source boundary. These changes satisfy issue #1844.

Full details: Docstring Coverage

Explanation

Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files. (2 skipped: 2 unsupported.)

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[hanjianqiao]

Thank you for this patch! We'll review it shortly.