[wasphin]

What problem does this PR solve?

Problem Summary:

Couchbase manifest parsing currently accepts arbitrarily nested JSON and ignores bytes after an embedded NUL.

What is changed and the side effects?

Changed:

• Validate manifest JSON with an iterative reader and a nesting limit of 100 before constructing the DOM.
• Require the reader to consume the complete input and build the DOM iteratively.
• Cover boundary depths, deeply nested arrays, quoted brackets, and embedded NULs.

Side effects:

• Performance effects: Adds one linear validation pass over each manifest.
• Breaking backward compatibility: Manifests deeper than 100 levels or containing embedded NULs are rejected. No API signature changes.

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Check List:

• Changes compile locally.
• Added focused regression coverage.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

🟢 Approval recommended

Source review found no blocking issues, and focused regression cases cover the intended behavior; tests were not executed during this review.

No open issues 🎉

What changed in this PR

This PR hardens Couchbase manifest parsing by limiting JSON nesting to 100 levels and rejecting input truncated by embedded NUL bytes.

Changes:

• Adds iterative validation with depth and complete-input checks before constructing the DOM iteratively.
• Adds regression coverage for boundary depths, deeply nested arrays, quoted brackets, and embedded NULs.

File	Description
test/​brpc_couchbase_unittest.cpp	Tests nesting limits and input-validation edge cases.
src/​brpc/​couchbase.cpp	Enforces bounded nesting and complete-input validation before DOM construction.

_{Review effort: Balanced}