Let a site name its public address so writes from any other address are refused

[SirLouen]

Closes #241

What

A new optional setting, GOPHENBERG_PUBLIC_URL, names the address people reach the site at. When it is set, a write counts as the site's own only when it was sent to that address, and a browser's write only when its page stands there too. An older browser that sends only Origin is judged against that address, so it can save behind any proxy. Every refused write is now logged with its reason: host, origin, fetch-site or scheme. Leaving the setting unset keeps today's behaviour, apart from the new log line.

Why

Behind a proxy that hides the scheme, an older browser was refused on the site's own pages. Another domain pointed at the server's address could make a visitor's browser post to the public plugin paths. And a refused write left nothing in the server log, so a misconfigured proxy was hard to find.

Testing Instructions

1. Start Gophenberg with GOPHENBERG_PUBLIC_URL=https://example.com and post to /api/auth/login at the server's own address, for example http://localhost:8081. The answer is 403 with the code request_cross_origin, and the server logs write refused with reason=host.
2. Leave the setting unset and repeat. The sign in reaches the login handler as before.
3. Start it with GOPHENBERG_PUBLIC_URL=https://example.com/blog. The server refuses to start and names the setting.
4. Run make cover and make lint.

Summary by CodeRabbit

• New Features
  • Added optional GOPHENBERG_PUBLIC_URL configuration to identify the site’s public address. When set, writes sent to a different address are refused; reads remain available.
  • Refused writes are logged with a reason, and users receive a request_cross_origin response.
• Documentation
  • Added public-address configuration guidance and updated the Docker Compose example with a sample domain.
  • Clarified that invalid public-address settings prevent startup and documented cross-origin protection for plugin writes and webhooks.

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Reviewing files that changed from the base of the PR and between 5a4f464 and 2803b76.

📒 Files selected for processing (3)

• docs/src/content/docs/self-hosting/install.md
• internal/server/publicurl.go
• internal/server/publicurl_test.go

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

• docs/src/content/docs/self-hosting/install.md

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📝 Walkthrough

Walkthrough

The server now accepts an optional GOPHENBERG_PUBLIC_URL. When configured, it checks unsafe requests against that address, refuses mismatches with a 403 response, and logs refusal details. Reads remain allowed. Tests and documentation cover configuration and request behavior.

Changes

Public address write protection

Layer / File(s)	Summary
Public URL configuration .env.example, internal/server/publicurl.go, internal/server/server.go, cmd/gophenberg/run.go, cmd/gophenberg/publicurl_test.go, internal/server/publicurl_test.go, docs/src/content/docs/self-hosting/configuration.md, docs/src/content/docs/self-hosting/install.md	The server parses and validates GOPHENBERG_PUBLIC_URL, passes it into server configuration, and documents the setting. Tests cover accepted, unset, and invalid values.
Unsafe request checks and refusal logging internal/server/crossorigin.go, internal/server/server.go, internal/server/publicurl_test.go, test/features/features/cross-origin-writes.feature, docs/src/content/docs/extending/write-a-plugin.md	The guard checks unsafe requests against the configured public address and logs refusal details. It retains the 403 error response. Tests cover host, origin, proxy, port, and read behavior.
Application and feature validation cmd/gophenberg/publicurl_test.go, test/features/features/public-address.feature, test/features/features_test.go, test/features/steps_cross_origin_test.go, test/features/world_test.go	Command and feature tests configure the public address and verify request outcomes, plugin submissions, and refusal logs.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant Browser
  participant crossOriginProtection
  participant originGuard
  participant Plugin
  participant Logger
  Browser->>crossOriginProtection: Send unsafe request
  crossOriginProtection->>originGuard: Judge request
  alt Request refused
    originGuard->>Logger: Log refusal reason and request details
    originGuard-->>Browser: Return uncached 403
  else Request accepted
    originGuard-->>crossOriginProtection: Allow request
    crossOriginProtection->>Plugin: Forward accepted request
  end

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Merge Risk: ⚪ Minimal · up to 2803b

The public-address checks add the documented write protection, while leaving the setting unset preserves existing behavior. No material merge risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 58.97% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 39 functions across 9 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: configuring a site's public address and refusing writes sent to other addresses.
Linked Issues check	✅ Passed	Issue #241 requires optional GOPHENBERG_PUBLIC_URL support, refusal of writes sent to another address, refusal logs, and unchanged behavior when unset. ParsePublicURL validates the setting and rej…
Out of Scope Changes check	✅ Passed	The changed source, tests, and documentation directly support Issue #241. The environment example, startup validation, public-address documentation, integration scenarios, and logging test helpers doc…

Full details: Docstring Coverage

Explanation

Docstring coverage is 58.97% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 39 functions across 9 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 1

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Inline comments:
In `@docs/src/content/docs/self-hosting/install.md`:
- Around line 74-76: Update the install guide’s “Three values to change” lead-in
to say “Four values to change,” matching the four configuration values listed
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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository: gopherium/gophenberg/.coderabbit.yaml

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Run ID: 3f5362f0-1da5-4f62-a32d-1dde55e5c834

📥 Commits

Reviewing files that changed from the base of the PR and between adfb8a4 and 5a4f464.

📒 Files selected for processing (15)

• .env.example
• cmd/gophenberg/publicurl_test.go
• cmd/gophenberg/run.go
• docs/src/content/docs/extending/write-a-plugin.md
• docs/src/content/docs/self-hosting/configuration.md
• docs/src/content/docs/self-hosting/install.md
• internal/server/crossorigin.go
• internal/server/publicurl.go
• internal/server/publicurl_test.go
• internal/server/server.go
• test/features/features/cross-origin-writes.feature
• test/features/features/public-address.feature
• test/features/features_test.go
• test/features/steps_cross_origin_test.go
• test/features/world_test.go

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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[greptile-apps]

Confidence Score: 5/5

Safe to merge.

Summary

Adds optional canonical public URL handling for write-request validation, including startup validation and coverage for direct, proxied, browser, server-to-server, and read-request flows. The hostname validation now rejects port-only public URL values.

_{Reviews (2) · Last reviewed commit: "docs(self-hosting): count the four value..."}