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fix(unhead): escape control characters in JSON template parameters - #1039
📖 Documentation (updates to the documentation or readme)
🐞 Bug fix (a non-breaking change that fixes an issue)
👌 Enhancement (improving an existing functionality)
✨ New feature (a non-breaking change that adds functionality)
🧹 Chore (updates to the build process or auxiliary tools and libraries)
⚠️ Breaking change (fix or feature that would cause existing functionality to change)
📚 Description
An opted-in JSON or JSON-LD script becomes invalid JSON when a template parameter contains a newline, tab, or another U+0000–U+001F character. The current replacement only escapes quotes, backslashes, and <.
Use JSON.stringify to escape the replacement string, strip its enclosing quotes, and retain the existing < escape. This preserves string contents when parsed and keeps a parameter containing </script> from closing the script element. Non-JSON replacements retain their current behavior.
The regression tests render both script MIME types, covering all 32 control characters together with quotes, a backslash, and a closing-script sequence. All 64 cases fail with the original implementation and pass with this change. A plain-text control checks that newlines remain literal outside JSON.
Validation on macOS arm64, Node 24.19.0 and pnpm 12.4.1:
Focused template parameter suite: 71 passed.
pnpm lint: passed, with 12 warnings in existing files; changed-file ESLint check also passed.
CI=true TZ=UTC pnpm exec vitest run --maxWorkers=1: 2,563 passed, 8 skipped; includes export snapshots and the Nuxt Cloudflare fixture build.
pnpm test:import-inert: all 49 entries passed.
All four bundle-size scripts passed. The five tracked core bundles have identical raw/gzip sizes against a clean build of the base commit.
Built utils entry: all 32 control characters round-trip with the fix; all 32 produce invalid JSON on the base commit.
Earlier parallel test runs encountered missing build artifacts and temporary-file ENOENT errors; the final sequential run above passed after the build and fixture dependencies were complete. The initial local timezone also affected existing date snapshots; the final run uses UTC as in CI.
AI assistance: Codex helped implement the change and run the checks described above.
Summary by CodeRabbit
Bug Fixes
Improved JSON template-value escaping in server-rendered scripts, preserving special characters while preventing embedded </script> text from breaking the script.
Preserved newline characters in plain-text template substitutions.
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Walkthrough
JSON template substitutions now use JSON string escaping and escape less-than characters. Tests check SSR output for JSON script types and confirm that plain-text substitutions preserve newlines.
Changes: Template parameter escaping
Layer / File(s)
Summary
JSON escaping and regression tests packages/unhead/src/utils/templateParams.ts, packages/unhead/test/unit/server/templateParams.test.ts
JSON substitutions use JSON.stringify and replace < with \u003C. SSR tests check control-character round trips and ensure rendered script bodies contain no literal </script>. A plain-text test checks that newline characters remain unchanged.
JSON substitutions escape control characters while plain-text behavior remains unchanged. No merge-blocking issue was identified.
Pre-merge checks: 5
Check name
Status
Explanation
Title check
The title clearly identifies the JSON template parameter escaping fix.
Description check
The description completes the required sections and explains the issue, fix, and regression tests.
Linked Issues check
[#1038] The helper uses JSON string escaping and retains the < escape. SSR tests cover both JSON script MIME types, all 32 control characters, quotes, backslashes, and </script>. A plain-text test…
Out of Scope Changes check
[#1038] The helper change and regression tests address the linked JSON escaping issue. The plain-text test checks that unrelated substitution behavior remains unchanged.
Docstring Coverage
Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Full details: Linked Issues check
Explanation
[#1038] The helper uses JSON string escaping and retains the < escape. SSR tests cover both JSON script MIME types, all 32 control characters, quotes, backslashes, and </script>. A plain-text test checks that newlines remain unchanged.
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 with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 1 functions across 2 files.
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🤖 MERGED
Harlan Agent Kit posted this automated review. It is not Harlan's personal review or approval. AI open source policy. Last updated: 2026-11-07 10:42 UTC.
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🔗 Linked issue
Resolves #1038
❓ Type of change
📚 Description
An opted-in JSON or JSON-LD script becomes invalid JSON when a template parameter contains a newline, tab, or another U+0000–U+001F character. The current replacement only escapes quotes, backslashes, and
<.Use
JSON.stringifyto escape the replacement string, strip its enclosing quotes, and retain the existing<escape. This preserves string contents when parsed and keeps a parameter containing</script>from closing the script element. Non-JSON replacements retain their current behavior.The regression tests render both script MIME types, covering all 32 control characters together with quotes, a backslash, and a closing-script sequence. All 64 cases fail with the original implementation and pass with this change. A plain-text control checks that newlines remain literal outside JSON.
Validation on macOS arm64, Node 24.19.0 and pnpm 12.4.1:
pnpm lint: passed, with 12 warnings in existing files; changed-file ESLint check also passed.pnpm build,pnpm typecheck(CI heap setting), andpnpm test:attw: passed.CI=true TZ=UTC pnpm exec vitest run --maxWorkers=1: 2,563 passed, 8 skipped; includes export snapshots and the Nuxt Cloudflare fixture build.pnpm test:import-inert: all 49 entries passed.utilsentry: all 32 control characters round-trip with the fix; all 32 produce invalid JSON on the base commit.Earlier parallel test runs encountered missing build artifacts and temporary-file
ENOENTerrors; the final sequential run above passed after the build and fixture dependencies were complete. The initial local timezone also affected existing date snapshots; the final run uses UTC as in CI.AI assistance: Codex helped implement the change and run the checks described above.
Summary by CodeRabbit
</script>text from breaking the script.