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

  • Fixed an issue where Host headers could become malformed in certain proxy configurations. The system now properly derives Host headers from hostname and port values, with correct RFC 3986-compliant formatting for IPv6 addresses.

• Tests

  • Added test cases to validate correct Host header derivation and IPv6 address formatting in proxy configurations.

[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: cf5e36d8-afbc-4bf0-bd30-cb4d4e4d1d69

📥 Commits

Reviewing files that changed from the base of the PR and between 9dc2425 and 06165ac.

📒 Files selected for processing (2)

• src/_utils.ts
• test/_utils.test.ts

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📝 Walkthrough

Walkthrough

setupOutgoing now derives outgoing.host from outgoing.hostname and outgoing.port when outgoing.host is undefined. The implementation includes RFC 3986-compliant bracketing for IPv6 literal hostnames to prevent malformed Host headers in changeOrigin scenarios. Two test cases validate the new behavior for both standard and IPv6 hostnames.

Changes

Host Header Derivation from Hostname and Port

Layer / File(s)	Summary
setupOutgoing Host Derivation src/_utils.ts	setupOutgoing now sets outgoing.host by combining outgoing.hostname and outgoing.port when outgoing.host is undefined. Detects IPv6 literals and wraps them in brackets per RFC 3986 to prevent malformed Host headers.
Tests for Host Header Derivation test/_utils.test.ts	Added two test cases: one validates that Host header is composed from hostname:port (e.g., example.com:8080), and another validates that IPv6 hostnames are bracketed per RFC 3986 (e.g., [::1]:8080).

🎯 2 (Simple) | ⏱️ ~8 minutes

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🐰 Hops of joy through IPv6 brackets,
No more malformed Host headers in packets,
hostname and port now compile so bright,
RFC 3986 formats them right! ✨

🚥 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 specifically describes the main change: deriving host from hostname for plain object targets and bracketing IPv6 literals, which directly matches the changeset modifications.
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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