feat: derive host from hostname for plain object targets and bracket IPv6 literals

[bjohansebas]

When a proxy target is passed as a plain ProxyTargetDetailed object containing only hostname / port / protocol (no host), setupOutgoing leaves outgoing.host as undefined. The subsequent changeOrigin branch then constructs a malformed Host header:

Host: undefined:<port>

For IPv6 literals (e.g. hostname: "::1"), the problem is if a consumer tries to derive host manually, RFC 3986 §3.2.2 requires brackets in URI host syntax that aren't present in the bare hostname.

Unblock: webpack/webpack-dev-server#5663

Summary by CodeRabbit

• Bug Fixes

  • Host headers are now derived reliably from hostname and port, with correct RFC 3986-compliant bracketed formatting for IPv6 to prevent malformed Host values.

• Tests

  • Added coverage verifying Host header derivation, IPv6 formatting/bracketing behavior, default port handling, and preservation of incoming Host when changeOrigin is disabled.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 126178ee-cbac-443d-a975-bf358e42a2d4

📥 Commits

Reviewing files that changed from the base of the PR and between 06165ac and 489d4ec.

📒 Files selected for processing (1)

• test/_utils.test.ts

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📝 Walkthrough

Walkthrough

setupOutgoing now builds outgoing.host from outgoing.hostname and outgoing.port when host is missing, adding RFC 3986 brackets for IPv6 literals; tests cover IPv4, IPv6, default-port behavior, and changeOrigin=false preservation.

Changes

Host Header Derivation from Hostname and Port

Layer / File(s)	Summary
setupOutgoing Host Derivation src/_utils.ts	setupOutgoing sets outgoing.host by combining outgoing.hostname and outgoing.port when outgoing.host is undefined, detecting IPv6 literals and wrapping them in brackets per RFC 3986.
Tests for Host Header Derivation test/_utils.test.ts	Added tests validating Host header composition from hostname:port, IPv6 bracketing and non-double-bracketing, use of protocol default port when port is omitted, and that changeOrigin: false preserves the incoming Host.

🎯 3 (Moderate) | ⏱️ ~20 minutes

"I hopped through headers, small and fleet,
Bracketed IPv6 so hosts look neat,
From hostname and port I weave the line,
No malformed Host — the request's fine! 🐇"

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the main changes: deriving host from hostname for plain object targets and bracketing IPv6 literals per RFC 3986.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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 unit tests (beta)

• Create PR with unit tests

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[bjohansebas]

hi @pio

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.93%. Comparing base (6e251d9) to head (7a36d89).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #136      +/-   ##
==========================================
+ Coverage   94.91%   94.93%   +0.02%     
==========================================
  Files           8        8              
  Lines         786      790       +4     
  Branches      320      324       +4     
==========================================
+ Hits          746      750       +4     
  Misses         35       35              
  Partials        5        5              

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[pi0]

Thnx and sorry for delay on this!