Guard antimeridian boundary vertex appends

[Komzpa]

Motivation

• Prevent stack-buffer-overflow when splitting polar/antimeridian-crossing H3 cell boundaries by ensuring we never append past the fixed CellBoundary.verts capacity.

Description

• Add a capacity-checked helper boundary_add_vert(CellBoundary *, const LatLng *) that asserts the CellBoundary has room before appending a vertex in h3_postgis/src/wkb_indexing.c.
• Replace all direct part->verts[part->numVerts++] and res->verts[res->numVerts++] writes in boundary_split_180 and boundary_split_180_polar with calls to boundary_add_vert to enforce the bound.
• Preserve existing behavior by raising the existing split assertion (SPLIT_ASSERT) when a split would exceed the vertex array instead of allowing silent overflow.

Testing

• Performed a syntax-only compile check using cc -fsyntax-only with temporary PostgreSQL/H3/WKB stubs, which succeeded.
• Ran git diff --check to validate no whitespace/git-diff issues, which passed.
• Attempted full CMake configuration with cmake -S . -B build -DBUILD_TESTING=OFF, which failed due to an external FetchContent download of H3 v4.5.0 returning HTTP 403 from the environment proxy, so full integration build/tests could not complete in this environment.

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use a larger split buffer for seam vertices

When a valid H3 boundary already uses more than six of CellBoundary's fixed vertex slots, the polar splitter appends the original vertices plus four synthetic antimeridian/pole vertices; this new guard turns those cases into Cell boundary split exceeds CellBoundary vertex capacity errors for h3_cell_to_boundary_wkb/geometry instead of producing the boundary. The bounds check needs to be paired with a split representation sized for the extra seam vertices, otherwise high-resolution polar or distorted antimeridian cells remain unusable.

Useful? React with 👍 / 👎.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 331e0a81-50e5-47e1-86f4-55e681edf6d1

📥 Commits

Reviewing files that changed from the base of the PR and between 9d70e9c and 78277ae.

📒 Files selected for processing (1)

• h3_postgis/src/wkb_indexing.c

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📝 Walkthrough

Walkthrough

This PR adds a new boundary_add_vert helper function to centralize bounds checking when appending vertices to a CellBoundary. All direct vertex buffer writes in boundary_split_180 and boundary_split_180_polar are replaced with calls to this helper, which asserts the fixed vertex capacity constraint.

Changes

Boundary Vertex Capacity Enforcement

Layer / File(s)	Summary
Boundary vertex helper definition h3_postgis/src/wkb_indexing.c	Introduces boundary_add_vert, a static helper that appends a LatLng vertex to a CellBoundary while asserting the vertex buffer capacity via SPLIT_ASSERT.
Standard antimeridian splitting integration h3_postgis/src/wkb_indexing.c	boundary_split_180 routes current vertex and split/intersection vertex additions through boundary_add_vert, replacing direct boundary->verts[...++] writes while preserving vertex construction.
Polar antimeridian splitting integration h3_postgis/src/wkb_indexing.c	boundary_split_180_polar updates current vertex and final intersection point insertions to use boundary_add_vert, centralizing capacity enforcement in polar boundary expansion.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A boundary grows, one vertex blessed,
Each point now checked before it rests,
Split and polar paths align—
One helper guards the sacred line! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Guard antimeridian boundary vertex appends' directly and clearly summarizes the main change: adding guard/bounds-checking to vertex append operations in antimeridian boundary processing.
Description check	✅ Passed	The description is comprehensive and directly related to the changeset, detailing the motivation for preventing buffer overflows, the specific helper function added, and the affected functions.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/propose-fix-for-cellboundary-overflow-vulnerability

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