fix(deps): update content-type to v3 and read the header string directly

[netlify-coding]

Opened by Netliloop run #392 (security-scan), asked in Slack

Why

• Renovate's #8472 (content-type v1 → v3) fails every build job: v3 is ESM-only, has no default export, and parse() takes a header string instead of a request object, so src/utils/proxy.ts and src/lib/functions/form-submissions-handler.ts no longer compile. Its sibling #8377 (@types/content-type v2) fails lint on its own because v2 is a stub pointing at the package's bundled types.
• Both PRs have re-run and failed on every weekly rebase since July; together they account for 64 + 40 failed integration jobs in the last four weeks.

What changed

• content-type goes to ^3.1.1 and @types/content-type is removed (v3 ships its own types).
• The three call sites import parse by name and pass req.headers['content-type']. The proxy already guarded on the header being present; the form handler now defaults a missing header to '', which parses to an empty type and falls through to neither form branch, matching the proxy's guard.
• Behaviour change to know about: v3 parse() never throws on a string, where v1 threw TypeError on a missing or malformed header. In src/utils/proxy.ts that TypeError was an unhandled rejection that crashed netlify dev on any POST with a malformed Content-Type; now such a request proxies normally and gets the static server's 405 (the new test covers this). The proxy only forwards form content types to the form handler, so the handler's own ?? '' is reached only when the functions server is called directly; there a missing header now takes the existing Invalid Content-Type warn-and-continue branch instead of throwing.
• A charset parameter is passed through to raw-body exactly as before: v1 also accepted any token value there, so charset=bogus still ends in raw-body's 415.
• All three call sites use the same req.headers['content-type'] ?? '' idiom.
• Root node_modules/content-type is now the ESM-only v3; npm ls content-type shows express, body-parser, type-is and verdaccio each keep a nested v1/v2 copy, so no CommonJS require('content-type') resolves to v3.
• Supersedes fix(deps): update dependency content-type to v3 #8472 and chore(deps): update dependency @types/content-type to v2 #8377, which can be closed when this merges.

How we verified

• npm run build, npm run typecheck, npm run lint: all exit 0 (on fix(deps): update dependency content-type to v3 #8472 the build fails with TS1192 and TS2345).
• CI=true npm run test:unit: 80 files passed.
• New integration test should keep serving when a form submission carries a malformed content type: a POST with Content-Type: not/a valid; ;; and a POST with no Content-Type at all (sent as a Buffer body, since node-fetch adds text/plain to a string body) must each get a 405 and the next GET a 200. On main it fails with request to http://localhost:33773/ failed, reason: socket hang up because the unhandled TypeError from content-type@1 kills the dev server; on this branch it passes (5.5 s).
• CI=true npx vitest run --retry=3 tests/integration/commands/dev/dev-forms-and-redirects.test.ts with the new test included: 14 passed (14).
• End to end with the built CLI (node bin/run.js dev --offline) against a fixture with a submission-created function, commands and output here: a urlencoded POST and a multipart POST with a file attachment both reached the function with the parsed fields (200, function log shows the fields); POSTs with no Content-Type, a malformed one, and application/json were not treated as forms (405) and a GET afterwards returned 200; application/x-www-form-urlencoded; charset=UTF-8 still matched.

What is left to test

• Nothing. CI ran the full matrix on the final commit: 35 checks, all green (unit on ubuntu/macOS/Windows, 8 integration shards, e2e, lint, format, typecheck, verify-docs, package-size).

Risk

low: one narrow code path in netlify dev (form-submission routing), covered by the integration test and the end-to-end check above; a wrong result shows immediately as a form POST not reaching the handler. No Linear issue: a self-contained dependency fix the CLI team can merge from this description.

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📝 Summary

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of requests with missing or malformed content-type headers, including form submissions and proxied requests.

Walkthrough

The content-type dependency and parsing call sites are updated. The form submission handler and proxy pass the content-type header value, or an empty string when the header is missing, to the parser. An integration test checks that malformed and missing content-type POST requests return 405 and that a subsequent GET returns 200.

Priority: ➖ Normal

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

Change: Bug fix

Suggested reviewers: ndhoule

Merge Risk: ⚪ Minimal · up to 7003e

This change updates content-type parsing so malformed or missing Content-Type headers no longer crash the dev server. No actionable merge-blocking risk was found.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the dependency update and the related change to read the content-type header directly.
Description check	✅ Passed	The description explains the dependency update, code changes, behavior, and reported verification. It is relevant to the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 3…
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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📊 Benchmark results

Comparing with 40d389e

• Dependency count: 1,017 ⬆️ 0.10% increase vs. 40d389e
• Package size: 379 MB ⬆️ 0.01% increase vs. 40d389e
• Number of ts-expect-error directives: 331 (no change)

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commit: 7003e35

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at
@tests/integration/commands/dev/dev-forms-and-redirects.test.ts:
- Around line 249-250: Update the `withoutHeader` request in the missing-header
test to use a Buffer body instead of a string, so `node-fetch` does not
automatically add a Content-Type header. Keep the assertion checking the 405
response.

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⛔ Files ignored due to path filters (1)

• package-lock.json is excluded by !**/package-lock.json

📒 Files selected for processing (4)

• package.json
• src/lib/functions/form-submissions-handler.ts
• src/utils/proxy.ts
• tests/integration/commands/dev/dev-forms-and-redirects.test.ts

🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• netlify/blueprints (manual)

Included review availability: This review used your included allowance. 3 included reviews remain after this review. Your included PR review attempts over the past 7 days set your current allowance at 4 reviews per hour. Your free on-demand review promotion remains active until October 9, 2026 at 6:00 PM UTC.