extension: ccache-remote: fix Docker host-gateway for hostnames resolving to loopback

[iav]

Summary

• When avahi-browse discovers a ccache service on the local machine, it returns 127.0.0.1 as the address. The code used this IP directly in --add-host, making the hostname resolve to the container's own loopback inside Docker instead of the host machine, causing all remote cache lookups to fail (err=N in ccache stats).
• Fix: after resolving the hostname, check if the resulting IP is a loopback address and use host-gateway instead, consistent with the existing handling for literal localhost/127.0.0.1 in the storage URL.

Test plan

• Build with ccache-remote extension when avahi discovers local ccache service
• Verify Docker container resolves the hostname to host machine, not container loopback
• Verify remote ccache hits work (no err=N in ccache stats)

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

Summary by CodeRabbit

• Bug Fixes
  • Docker host resolution: loopback addresses (127.* / ::1) are now handled via host-gateway to avoid connectivity issues.
  • Clearer debug logging for loopback cases to aid diagnostics.
  • Non-loopback and unresolved host behaviors remain unchanged.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: c8242a2f-2525-43ea-b335-24ca6c016328

📥 Commits

Reviewing files that changed from the base of the PR and between 4b7620d and 49fb658.

📒 Files selected for processing (1)

• extensions/ccache-remote/ccache-remote.sh

🚧 Files skipped from review as they are similar to previous changes (1)

• extensions/ccache-remote/ccache-remote.sh

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📝 Walkthrough

Walkthrough

The shell script now detects when a Docker host resolution yields a loopback address (127.* or ::1) and adds the host using host-gateway instead of the resolved IP, with a dedicated debug log; non-loopback and unresolved-resolution paths are unchanged.

Changes

Cohort / File(s)	Summary
Docker Host Resolution Logic extensions/ccache-remote/ccache-remote.sh	Detect loopback resolutions (127.* or ::1); when detected, use --add-host with host-gateway and emit a loopback-specific debug message. Retains existing behavior for non-loopback resolutions and unresolved hosts.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 I sniffed a loopback on the run,
Replaced the IP with host-gateway fun,
A tiny hop, a tidy fix,
Docker paths now play their tricks,
This rabbit nods — the script is done! 🥕

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: fixing Docker host-gateway handling for hostnames that resolve to loopback addresses in the ccache-remote extension.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/ccache-remote-loopback-host-gateway

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@extensions/ccache-remote/ccache-remote.sh`:
- Around line 400-402: The current block appends
"--add-host=${_host}:host-gateway" to DOCKER_EXTRA_ARGS when _resolved_ip is
loopback, which will break on Docker <20.10.0; add a Docker-version gate before
modifying DOCKER_EXTRA_ARGS (use the same logic in both places where
DOCKER_EXTRA_ARGS is appended around _host/_resolved_ip), e.g., detect Docker
Engine version via `docker version --format '{{.Server.Version}}'` and only use
"host-gateway" when the semantic version is >=20.10.0; if the version is older,
either skip adding the host-gateway entry or fall back to resolving and
injecting the actual host IP, and call display_alert with an appropriate message
mentioning _host and _resolved_ip to indicate the fallback.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 504b6119-7003-4648-a2be-b687bc5a78ed

📥 Commits

Reviewing files that changed from the base of the PR and between 532aaff and 4b7620d.

📒 Files selected for processing (1)

• extensions/ccache-remote/ccache-remote.sh