fileserver: Improve 404 error detail and context

[Jualhosting]

🚀 Improve error handling in file server middleware

Overview

This PR improves the error handling inside the fileserver middleware, specifically addressing the ambiguity of 404 Not Found errors.

Previously, when a file was not found, a directory lacked an index file, or a file was hidden, the notFound method would return a generic caddyhttp.Error(http.StatusNotFound, nil) without any context. This made debugging difficult for users trying to figure out exactly why a resource was returning a 404.

🛠️ What’s been fixed?

• Updated notFound signature: The internal notFound function now accepts an err error argument.
• Contextual error propagation: All calls to notFound in staticfiles.go and browse.go now pass specific errors to the response instead of nil.
• Clearer Error Messages:
  • fmt.Errorf("directory without index file or browse enabled") when an index is missing.
  • fmt.Errorf("file is hidden") when a file matches the Hide paths configuration.
  • Passes through the underlying fs.ErrNotExist for missing files.

💡 Impact

These changes ensure that logs and error responses now contain actionable context when a 404 is triggered, significantly improving the debuggability of the file server without breaking the PassThru logic.

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🤖 AI Disclosure: The logic updates, context propagation, and documentation in this Pull Request were developed with the assistance of AI, carefully reviewed and tested to ensure Caddy's high standards are met.